Eugene A. Krejsa and James R. Stone

Diversitech, Inc., Cincinnati, Ohio

Enhanced Fan Noise Modeling for Turbofan Engines

NASA/CR—2014-218421

December 2014
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Eugene A. Krejsa and James R. Stone

Diversitech, Inc., Cincinnati, Ohio

Enhanced Fan Noise Modeling for Turbofan Engines

NASA/CR—2014-218421

December 2014

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

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NASA/CR—2014-218421 1 

Enhanced Fan Noise Modeling for Turbofan Engines 

Eugene A. Krejsa and James R. Stone 

Diversitech, Inc. 

Cincinnati, Ohio 45246 

Abstract 

This report describes work by consultants to Diversitech Inc. for the NASA Glenn Research Center 

(GRC) to revise the fan noise prediction procedure based on fan noise data obtained in the 9- by 15 Foot 

Low-Speed Wind Tunnel at GRC. 

The purpose of this task is to begin development of an enhanced, analytical, more physics-based, fan 

noise prediction method applicable to commercial turbofan propulsion systems. The method is to be 

suitable for programming into a computational model for eventual incorporation into NASA’s current 

aircraft system noise prediction computer codes. The scope of this task is in alignment with the mission of 

the Propulsion 21 research effort conducted by the coalition of NASA, state government, industry, and 

academia to develop aeropropulsion technologies. 

A model for fan noise prediction was developed based on measured noise levels for the R4 rotor with 

several outlet guide vane variations and three fan exhaust areas. The model predicts the complete fan 

noise spectrum, including broadband noise, tones, and for supersonic tip speeds, combination tones. Both 

spectra and directivity are predicted. Good agreement with data was achieved for all fan geometries. 

Comparisons with data from a second fan, the ADP fan, also showed good agreement. 

Introduction 

An important aspect of aircraft system noise studies is the prediction of the noise from the aircraft 

propulsion system. The major sources of noise associated with the propulsion system are the jet exhaust, 

the fan, the combustor and the turbine. Depending on the engine cycle, the noise signature is usually 

dominated by either fan or jet noise. Noise from the combustor and the turbine can also contribute and 

often limit the overall benefit resulting from reductions in fan and jet noise. Within NASA, the 

methodologies used to predict aircraft noise rely on the routines developed in the 1970s (and their 

updates) in the support of the ANOPP noise prediction program (Ref. 1). These routines are also 

incorporated in the FOOTPR noise prediction program (Ref. 2). 

While much work has been done recently to update the jet noise prediction methods, References 3 to 

7, only limited updates have been done for the other components. The updates to the jet noise model have 

emphasized developing the prediction capability for newer jet noise reduction concepts such as 

mixer/ejectors and conventional nozzles with tabs and/or chevrons. These advances to the jet noise 

prediction capabilities will allow systems studies to properly assess the impact of these jet noise reduction 

concepts. Similar to the progress in reducing jet noise, much progress has been made in the reduction of 

fan noise. Vane sweep and lean have resulted in several decibel (dB) of fan noise reduction, Reference 8. 

More modern test facilities, which allow for fan noise measurement under simulated flight conditions, 

have generated a significant amount of high quality fan noise data. The original fan noise prediction 

procedure, developed by Heidmann, Reference 9, was based primarily on data from static fan tests. It is 

now known that such data are often contaminated by noise resulting from the ingestion of vortices or 

other turbulence from the test stand or other nearby structures. Even data from well designed static test 

facilities can be influenced by noise resulting from the ingestion of ground vortices, although the use of 

inlet flow control devices minimizes this effect. Likewise, fan noise levels inferred from engine tests are 

often tainted by the difficulty in separating the various engine noise sources from each other. 
NASA/CR—2014-218421 2 

As a result of the use of improved experimental diagnostics techniques and theoretical advances, a 

much improved understanding of the nature of fan noise generation currently exists. This improved 

understanding of the physics of fan noise generation can easily be incorporated into empirical models by 

properly dividing the total fan noise into its appropriate sources and by modeling each of these sources 

with the proper physical parameters. The purpose of the current effort is to develop an improved fan noise 

prediction procedure based on recent fan noise data and an improved understanding of fan noise 

generation. 

Fan Noise Generation 

Fan noise is characterized by both tones and broadband noise. At subsonic fan tip speeds, the tones 

occur at harmonics of the blade passage frequency, whereas for supersonic fan tip speeds the tones are at 

multiples of 1/rev. (Envia, Ref. 10, using time domain averaging, did observe the existence of tones at 

multiples of 1/rev. in the analysis of vane unsteady pressure signals for a subsonic operating condition.) 

A description of fan noise generation can be found in Reference 11. 

At subsonic tip speeds, fan tones for modern turbofan engines, without inlet guide vanes, can be 

generated by inlet flow distortions and by blade/exit guide vane interaction. Groeneweg, Reference 12, 

Huff, Reference 13, and Envia et al., Reference 14, all agree that blade/vane interaction is the principal 

source of fan tones for fans with subsonic tip speeds. Blade/vane interaction noise is due to the unsteady 

response of the stator vanes to the periodic wakes from the fan blades, resulting in spinning pressure 

modes within the duct. Tyler and Sofrin, Reference 15, show that only those modes with a sonic or 

supersonic circumferential Mach number at the duct outer wall will propagate. These modes are referred 

to as “cut-on” modes. Modes with a subsonic circumferential Mach are “cut-off” and decay exponentially 

within the duct. 

At supersonic tip speeds, an additional noise source exists. This source is referred to as combination 

tone noise, or multiple pure tones, or “buzz-saw” noise. It is generally thought that this noise results from 

shock waves that form on the rotor blade leading edges. Ideally, tones resulting from these shock waves 

would be at multiples of the blade passage frequency. However, due to blade-to-blade differences, tones 

are generated at multiples of once per rev. Combination tones propagate only out of the engine inlet. 

The nature of fan broadband noise is less understood than that of tone noise, although significant 

progress is being made in the modeling of fan broadband noise. It is generally agreed that one source of 

fan broadband noise is the interaction of the turbulence in the fan wakes with the stator vanes. Physics 

based models of this mechanism require the prediction of the turbulence intensity, spectra, and scales. 

Another potential source of fan broadband noise is the interaction of inlet turbulence with the fan blades. 

The modeling of this source also requires detailed prediction of the turbulence characteristics. 

Current Prediction Procedures 

While significant progress is being made in the prediction of fan noise from basic principles, more 

effort in this area is still needed. In addition, this approach does not lend itself easily to system studies 

where it may be required to evaluate many different engine cycles and designs at various operating 

conditions. For this type of study, simpler empirical models are more appropriate. However the results 

from the physics based models can be very valuable in developing these empirical approaches. 

Several empirical procedures currently exist for the prediction of fan noise. The original ANOPP 

method was developed by Heidmann, Reference 9, in 1979. This method is based on a methodology 

developed by the Boeing Company under contract with the NASA Ames Research Center, Reference 16. 

Since then several updates and modifications have been reported. In Reference 17, Kontos compared the 

Heidmann methodology against data from GE engines and recommended several modifications to the 

method to better predict the fan noise from the GE engines. Likewise in Reference 18, Hough and Weir of 

Allied Signal modified the Heidmann methodology to better predict the fan noise from three smaller 

Allied Signal engines. An earlier modification to the Heidmann method was also developed by Allied 
NASA/CR—2014-218421 3 

Signal as part of the General Aviation Synthesis Program (GASP) program. Boeing, Reference 19, has 

also developed a fan noise correlation based on data from The Boeing Company, GE Aircraft Engines, 

Pratt and Whitney, and NASA. The methodology is described in Reference 20. 

All of the empirical methods consider five sources: inlet fan tones, inlet fan broadband noise, inlet 

combination tones, aft tones, and aft broadband noise. Relations, either in the form of equations, tables or 

plots, are provided for the source strength, directivity, and spectra. The effect of flight is also usually 

included in the methodologies. 

Current Task 

The objective of the current task is to update the empirical fan noise prediction methodology based on 

more recent fan noise data obtained in the NASA Glenn 9- by 15-Foot Low-Speed Wind Tunnel. The 

tunnel test section walls, floor, and ceiling are acoustically treated to produce an anechoic test 

environment. Acoustic data is obtained on a 93 in. (measured from fan centerline) sideline using a 

translating microphone probe. Data is obtained at geometric angles ranging from 27.2 to 134.6 degrees 

relative to the fan rotor plane. 

In recent years a series of fan noise tests were conducted to study the effect of stator vane sweep and 

fan nozzle area variation on fan noise. Data from the tests with the R4 rotor are used for this task. This 

rotor has 22 blades with a design tip speed of 1,215 ft/sec. and a design pressure ratio of 1.47. Three stator 

sets were used. The baseline stator was designed for cut-off of the fundamental tone with 54 vanes. Two 

other stators with 26 vanes were also used. For one of these two sets, the vanes were swept 30 degrees. In 

addition to the variation in stator design, the R4 rotor and baseline, 54 vane, stator were tested with three 

fan nozzle areas and two tip clearances. Also as part of these tests, diagnostic measurements were made 

including laser Doppler velocimetry measurements taken between the rotor and stator and barriers were 

used to separate inlet and aft fan noise. Tests were also conducted with no stator, i.e., rotor alone tests, to 

determine the significance of noise sources other than rotor/stator interaction noise. Table 1 lists the test 

configurations. 

Comparison of Current Prediction Methods 

In Figures 1 to 4, the normalized predicted peak levels for the R4 fan with the baseline outlet guide 

vane set are shown comparing the five prediction methodologies. In Figure 1, levels for inlet broadband 

noise are plotted. Predicted levels using the method developed by Allied Signal are 3 dB lower than the 

Heidmann prediction at all fan speeds. Predicted levels using the method developed by Kontos at GE are 

lower due to the lack of the rotor-stator spacing effect used in the Heidmann method and a steeper slope 

with tip relative Mach number at relative Mach numbers greater than 0.9. The levels predicted using the 

Boeing method are slightly lower then those predicted by Kontos at low speeds but are significantly lower 

than all other methods at high speeds. Levels predicted by the Dunn and Peart method are higher than all 

other methods at low speeds, agree with Heidmann at intermediate speeds and are lower than Heidmann, 

with a more rapid decrease, at high speeds. 

Predicted inlet tone levels are shown in Figure 2. Here, more variation in predicted levels exists than 

existed for inlet broadband levels, with the difference exceeding 15 dB at low speeds and about 20 dB at 

high speeds. The levels predicted by the Allied Signal method are the lowest at all speeds, being 7.5 dB 

lower at all speeds. The jump in level at about 1200 rpm in the Heidmann, Kontos, and Allied Signal 

methods results from the lack of the cut-off effect as the tip speed goes supersonic. No such effect is 

included in either the Dunn and Peart or the Boeing method. 

In Figures 3 and 4 predicted aft noise levels are shown. Again, significant difference exist with levels 

predicted by the Dunn and Peart method being the highest for both broadband and tone noises. The trend 

with fan speed is similar for aft broadband noise for the five methodologies. 
NASA/CR—2014-218421 4 

Directivities are compared in Figures 5 and 6 for inlet and aft broadband noise and in Figures 7 and 8 

for inlet and aft tone noise. The methods of Heidmann and Kontos agree on the directivity for all four 

sources. The methodology developed in the GASP program agrees with the Heidmann directivity for both 

inlet and aft broadband sources, while the Allied Signal methodology agrees with the Heidmann inlet 

broadband directivity. For all other cases, the methods agree on the location of the peak levels within 

10 degrees although differences in excess of 5 dB quickly exist aft of the peak for inlet broadband and 

tone noise and forward of the aft noise peaks. 

Broadband spectra are compared in Figures 9 and 10. The Heidmann, Kontos, and GASP 

methodologies all agree on both the inlet and aft broadband spectra shapes. The newer Allied Signal 

methodology lowers the peak frequency from 2.5 times the BPF to 2 times BPF and lowers the fall off 

rate below the peak and increases it above the peak. In the methodology developed by Boeing, the peak 

frequencies for inlet and aft broadband noise are both higher than that of the Heidmann methodology. 

In Figures 11 and 12, predictions made using five prediction methods are compared with measured 

data for the R4 rotor with the baseline outlet guide vanes, baseline nozzle, and 0.02 in. tip clearance, 

approach fan speed at 60 and 120 degrees from the inlet. At low frequencies there is obviously another 

noise source that is dominating the measured levels. At 60 degrees, the method of Heidmann, Kontos and 

Boeing all do a reasonable job of prediction the fan broadband noise, while the method of Dunn and Peart 

over predicts it. The spectra derived by Allied Signal, based on the engine data, do not agree well with the 

R4 data. All methods over-predict the importance of the fan tone. Similar results are seen at 120 degrees, 

with the method proposed by Kontos tending to be a few dB above the data. 

Assuming that the prediction methodologies compared in Figures 1 to 10 each represent the data base 

from which they were derived, it is obvious that no one methodology is a universal fan noise prediction 

methodology, or that there are significant difference in fan noise measurement technology. One might 

assume that the reason that the method of Dunn and Peart differs significantly from the other 

methodologies is that it is based on static engine data obtained prior to the use of inlet flow control 

devices used more recently to minimize ingestion of vortices. Other differences could result from 

difference in assessment of fan noise from engine test data. Differing assumptions regarding other engine 

sources can impact the value assigned to fan noise, although this should not be an issue for fan tones. 

Initial Calculations for Current Task 

The noise source extraction methodology developed by Stone requires that initial predictions of the 

noise sources be made. These initial assessments are then used along with the experimental data to 

provide “extracted” levels for the various noise sources. These “extracted” levels are then used to modify 

the prediction procedures. The process can then be repeated using the modified prediction procedures for 

further updates. For the current task the method of Heidmann was chosen to make the initial fan noise 

calculation. This was based on the initial comparison of the existing prediction methods with the data. 

While predictions using the Boeing methodology were in reasonable agreement with the data, it was felt 

that the complexity of the Boeing method was not justified for the limited data set used in this task. 

However, this did not mean that the approach used by Boeing would not be considered to guide the 

updates. 

An analysis technique that we use in analyzing the experimental data in comparison with the 

predictive model is termed component noise extraction, as mentioned in the previous paragraph. By this 

we mean that we use the predictive model to estimate the relative contributions of the various noise 

generation mechanisms. We then subtract from the measured SPL at each angle and frequency the 

predicted difference between each component of interest and the total noise. We term this the 

“experimental/extracted” noise component. Where the component of interest is the dominant component, 

the correction is very small, and where the correction is 10 dB or more we do not rely on the data to use in 

improving the predictive model. We then adjust the component noise coefficients to improve the 

agreement in the range where each component is important, leading after a number of such comparisons 

to an improved predictive model. We will show specific examples in this report. 
NASA/CR—2014-218421 5 

In addition to fan noise prediction, a methodology for jet noise prediction was also needed. The 

method chosen was that of Stone et al., Reference 21. As a check on this methodology, comparisons were 

made with data recently obtained by Brown and Bridges at NASA GRC, Reference 22. The data used for 

these comparisons were for subsonic ambient jet conditions since these were the closest to the exhaust 

conditions of the fan rig. The nozzle used to obtain the data in Reference 21 was a simple conical nozzle, 

while the exhaust of the fan rig was a convergent nozzle with an extended centerbody. For this task, this 

centerbody was modeled as an extended plug. Data for nozzles with plugs were part of the database used 

to develop the correlation presented in Reference 21. The model developed in Reference 21 describes the 

jet noise in terms of three sources. The highest frequency source originates from the shear layer just 

downstream of the nozzle exit and is referred to as the small scale source. The lowest frequency source is 

considered to originate from the fully developed flow several diameters downstream of the nozzle and is 

referred to as the merged source. The third source at intermediate frequencies, referred as the transitional 

source, is thought of as resulting from the flow field between the initial and fully developed regions. Plug 

separation noise is also predicted for configurations featuring a plug. Each noise source is described in 

terms of spectra, directivity, source location, and level correlations. A complete description of the model 

is presented in Reference 21. 

This model was developed primarily for coannular nozzles, as nearly all modern turbofan engines 

feature dual-stream nozzles. But, an attempt was made to assure that these relations limited properly to 

the case of the single-stream conic nozzle. The comparisons with the recent data of Brown and Bridges at 

NASA GRC, Reference 22, indicate that significantly better agreement could be obtained by adjusting 

component noise coefficients, particularly for the small scale mixing noise. 

Initial comparisons of the predicted fan and jet noise with experimental data clearly indicated that an 

additional low frequency noise source was contributing to the data. Speculation was that this noise was 

due to scrubbing of the fan exhaust jet on the extended fan rig centerbody. While this source did not 

appear to have a significant effect on the data above 1000 Hz. where the fan noise dominated for most 

conditions, it could interfere with the interpretation of the data at high fan speeds where multiple pure 

tones were present below 1000 Hz. Also for completeness, it was felt that this source should be modeled. 

Model for Scrubbing Noise Source 

Procedurally, the plug separation noise model of Reference 21 was used as a starting point, and 

modifications were developed to fit the experimental data. First the fan noise was estimated using the 

Heidmann model, and this was used in the “extraction” technique mentioned earlier to separate the 

“jet/background” noise component. This is illustrated in Figure 13. The experimental data are indicated 

by the open black circle symbols, and the predicted fan noise is shown by the dashed blue line. As 

mentioned earlier, there is clearly non-fan noise at the low frequencies. The prediction for this jet/ 

background noise is shown by the dotted red line, with the coefficient adjusted to roughly match the low 

frequency data. The resulting total noise prediction is shown by the solid black line. The red square 

symbols are the experimental/extracted jet/background noise calculated by subtracting the predicted total 

minus jet/background noise from the experimental total. The analogously calculated experimental/ 

extracted fan noise is shown by the blue diamonds. Even though the predictions at this point are crude, the 

experimental/extracted levels, except where they are near equal, are considered reliable. To emphasize 

this fact the experimental/extracted data are only plotted when within 10 dB of the total noise. The results 

are shown at T = 60 and 120 deg in Figures 13(a) and (b). As we will describe later, as the predictive 

models are refined the total prediction approaches the experimental data. Note that the experimental data 

drop off very steeply at low frequency and are not thought to be reliable. 

Once the jet/background noise has been extracted from the total noise level, it can be further broken 

down into its components. This is illustrated for T = 30, 60, 90, 120, and 150 deg in Figures 14(a) to (e). 

The experimental/extracted jet/background noise is shown by the X symbols; it is further broken down 

into large-scale (red circle), transitional/intermediate-scale (green diamonds), and small-scale mixing 

(blue squares) noise as well as plug/interaction noise (violet triangles). Also noted on the figures are the 
NASA/CR—2014-218421 6 

effective directivity angles for each component (Ref. 21), which indicate the very near geometric field of 

these sources. Here the iteration process has progressed and the “predicted” values are based on the final 

jet/background and fan noise models, so the differences seen are with respect to the finalized models. 

Since the plug/interaction noise is so far above the other components, comparisons of the other 

constituents with their predicted values are meaningless. Note that at T = 150 deg (Fig. 14(e)), the smallscale mixing noise is predicted to come close to the plug noise, so it is important to note that the 

coefficient for small-scale mixing noise has been reduced by 4 dB from Reference 21, based on the 

comparisons with the data of Reference 22. As the jet velocity increases, this noise component increases 

with the fifth power of jet velocity; so at higher fan speed, and consequently jet velocity, the large-scale 

mixing noise can also become important at aft angles, as will be shown later herein. 

The spectral directivity relations developed for this plug/interaction noise are purely empirical, with 

the peak frequency at each angle not changing as a function of jet velocity, as would generally be 

expected. 

Comparison of Initial Predictions With Data 

Comparison of Low Frequency Noise Source With Fan Rig Data 

Predicted jet mixing plus scrubbing noise are compared with data from the fan rig for a range of jet 

exhaust velocities in Figures 15 to 18. At the lowest jet velocity, Figure 15, the scrubbing noise dominates 

the jet mixing noise at all angles and frequencies. As the jet velocity increases, the jet mixing noise 

becomes more important especially at aft angles near 1000 Hz. At 150 degrees at the highest jet velocity, 

corresponding to 100 percent fan speed, the jet mixing noise is higher then the scrubbing noise. In all 

cases the predicted jet mixing plus scrubbing noise agrees reasonably well with the data where fan noise 

is not expected. At the highest speed, combination tones are the likely cause of the difference between the 

data and predictions at frequencies above 500 Hz. 

Comparison of Initial Total Noise Predictions With Fan Data 

As mentioned above initial predictions are made with existing methodologies. This is true with the 

exception that the new model for the scrubbing noise was included in the initial prediction. Thus for this 

step, the low frequency noise scrubbing source and jet noise models described above are used along with 

the current Heidmann fan noise prediction methodology. The only adjustment made to the existing 

Heidmann prediction method, Reference 9, was to lower the level of the combination tones by 12 dB. It 

has been commonly accepted that Fan C on which Heidmann’s combination tone correlation was based, 

had unusually high levels of combination tones. Comparisons with data are shown in Figures 19 to 21 for 

the baseline fan with the nominal exhaust nozzle, baseline outlet guide vanes, and 0.02 in. tip clearance 

for fan speeds of 61.7, 87.5, and 100 percent. These speeds correspond to approach, cutback, and takeoff 

respectively. At the approach speed, Figure 19, the first and second harmonic are both over-predicted. 

The broadband levels appear to be about right, but the inlet spectrum needs to be shifted higher by one or 

two one-third octave bands. At the cutback fan speed, Figure 20, the over-prediction of the fan tones is 

even greater. The value of the fan tip relative Mach number at this speed is in the range where the 

Heidmann methodology predicts a sharp increase in inlet fan tone level with tip relative Mach number. 

Although the aft tone prediction does not include a sharp rise in level, the aft tones are still overpredicted. The inlet broadband noise is also over-predicted as are the broadband levels in the aft below the 

second harmonic. At takeoff condition, Figure 21, the aft tone and the inlet broadband noises are overpredicted. It also appears that combination tone noise is increasing the levels at the aft angle above that 

which is predicted. 

Among the objectives of the current task was to ensure that the fan noise prediction procedure is 

capable of predicting noise changes due to changes in fan geometry such as vane count, vane sweep and 

lean, and fan exhaust area. Figure 22 compares results from the current Heidmann prediction procedure 
NASA/CR—2014-218421 7 

with data from two tests with differing vane counts at the approach fan speed condition. The data show a 

decrease in broadband level at the aft angle. No such decrease is predicted by the Heidmann method. 

Examination of the other existing prediction procedures indicated that they would likewise not predict the 

measured difference in aft broadband level. 

Figure 23 shows measured and predicted levels for three exhaust nozzle areas at 50 percent fan speed. 

The predictions are made using the Heidmann methodology and only fan noise predictions are shown. 

The data clearly show a decrease in levels with increasing exhaust areas. The predictions show very little 

change in level. 

Figure 24 shows the effect of vane sweep on measured and predicted levels. The predictions for the 

swept vanes were made assuming the 30 degrees of sweep added one rotor chord to the rotor stator 

spacing. While the prediction show a reduction at all frequencies the same is not true for the data. In fact 

at the range of the fan noise spectrum the data actually shows a slight increase in level with vane sweep. 

Extracted Fan Noise Levels, Spectra, and Directivities 

Just as we broke down the jet/background noise into its constituent terms by the extraction process, 

we can break down the experimental/extracted fan noise into inlet broadband, aft broadband, inlet tone, 

aft tone and combination tone constituents. This is illustrated in Figure 25. At T = 30 deg (Fig. 25(a)) the 

extraction process has established that fan noise is significant at above 1000 Hz. Below the blade passage 

frequency, combination tones are evident. The first harmonic tone is predicted accurately, but the higher 

harmonics are over-predicted. (In adjusting the various component levels it is attempted to find the 

combination of coefficients that minimizes average errors at all angles for each component at all 

frequencies where it is important, so exact agreement with the first harmonic is coincidental.) Because of 

the strong pure and multiple tone contributions, it is difficult to judge the agreement of the broadband 

noise here. At T = 60 deg (Fig. 25(b)) the combination tones are predicted to become stronger, and while 

this is observed the quantitative agreement is not good. Here, the second and higher harmonics are in 

reasonably good agreement with prediction, while the fundamental is significantly under-predicted. The 

agreement at frequencies beyond the band containing the fundamental is rather good with the predicted 

mix of tones and broadband contributions. At T = 90q (Fig. 25(c)) essentially the same observations can 

be made as at T = 60 deg. At T = 120 deg (Fig. 25(d)) the overall agreement is fairly good, but the first 

three harmonic tones are somewhat over-predicted. At T = 150 deg (Fig. 25(e)) there is reasonable 

agreement except at the fundamental tone, which is significantly over-predicted and at 200 Hz there is a 

significant under-prediction of a sharp combination tone. 

As can be judged from this discussion, it would be very difficult to develop improved predictive 

models by looking at a number of isolated cases. Instead we bring together the component data for a 

number of test conditions in normalized form, after having gone through the extraction and adjustment 

process. 

First we addressed the directivities of the fan noise components. For broadband noise we averaged the 

highest 3 experimental/extracted SPLs at each angle as an approximation to the peak of the spectrum. We 

then plotted these values normalized to the value at T = 60 deg for inlet noise and T = 120 deg for aft 

noise against angle, using only data for cases where tip speed is subsonic to avoid possible interference 

from combination tones. The results are shown in Figure 26(a) for inlet broadband noise and in 

Figure 26(b) for aft broadband noise. In both cases it can be seen that the experimental results differ from 

the Heidmann model. We therefore developed new empirical relations for use in our subsequent modeling 

that agree more closely with the experimental/extracted data. 
NASA/CR—2014-218421 8 

For the harmonic tones a similar approach was tried, plotting the experimental/extracted SPL, 

normalized to its value at T = 60 deg for inlet noise and T = 120 deg for aft noise against angle, using only 

data for cases where tip speed is subsonic to avoid possible interference from combination tones. The 

results for the inlet tones are shown in Figure 27(a) to (c) for the first, second and third harmonics, in 

comparison with the Heidmann prediction. There is a lot of scatter, and the results change from one 

harmonic to another; because of the lack of any definitive trends, we retained the Heidmann directivity 

relations. For the aft tones, the situation is more promising, as can be seen in Figures 28(a) to (c) for the 

first, second and third harmonics. Although the first harmonic shows some scatter, the second and third 

behave in a more regular manner. All three harmonics agree better with the new relation than with that of 

Heidmann, although the difference is not as great as it was for broadband noise. 

For combination tones, our directivity plots were made by averaging the highest five experimental/ 

extracted SPLs at each angle. These values, normalized to the value at T = 60 deg, are plotted against 

angle in Figure 29. The trends exhibited by the experimental/extracted data differ significantly from the 

Heidmann prediction, so we developed a new relation, as shown in the figure. 

Using these new directivity relations, we next evaluated the spectra. First, the normalized spectra at 

several angles for inlet broadband noise were considered. The experimental/ extracted SPL is normalized 

to the predicted peak SPL at T = 60 deg is plotted against the non-dimensional logarithmic frequency 

parameter, log (f/BPF), at T = 30, 40, 50, 60, 70 and 80 deg Figures 30(a) to (f). At higher angles the aft 

broadband noise is dominant; it even contributes significantly at 50 to 60 deg in some cases. Generally, 

although there is scatter the experimental/extracted spectra have the predicted shape, but the peak 

frequency was shifted higher by two 1/3 octave bands, and the directivity effects (angle to angle) are 

adequately modeled. On some charts there are points at near log (f/BPF) = 0.0 that deviate significantly 

due to under or over prediction of the fundamental tone. 

The analogous plots for the aft broadband noise are shown in Figure 31. Here the experimental/ 

extracted SPL is normalized to the predicted peak at T = 120 deg. Particularly at the more aft angles, it 

appears that a linear low frequency roll-off might be more appropriate, but we did not make such a 

change at present. No adjustment was made to the peak frequency for the aft broadband noise. There are 

also significant problems with tones not adequately predicted at the aft angles. 

Similar plots for combination tones are shown in Figures 32(a) to (l). For this component the spectral 

shape varies with conditions due differing relative levels of the 1/2, 1/4 and 1/8 BPF peaks, so for each set 

of experimental extracted data there is a corresponding prediction. These relative contributions were 

adjusted from Heidmann to better agree with the data. Even with the increased predicted contribution of 

the 1/4 and 1/8 BPF peaks, it appears within the scatter that these sub-peaks are under-predicted, and the 

peaks do not always fall at the predicted 1/2, 1/4, and 1/8 BPF. However, the trends predicted with 

operating conditions are predicted roughly. 

Having modified the spectral directivity relations for the fan noise components, the final step to 

developing the new predictive model is to determine the coefficients (actually logarithmic intercepts) for 

the level relations. The numerical values are dependent on changes made to the correlating equations. The 

results shown in Figure 33 for each component are consistent with the final relations. The coefficient, 

obtained by minimizing the error over the range this component is important, is plotted against tip relative 

Mach number, and the final correlating expressions are obtained by a an “eye-ball” simplified relation 

that agrees reasonably with the experimental results. The inlet broadband coefficients are plotted against 

tip relative Mach number in Figure 33(a); the correlating expression starts from a constant value at low 

MTR changing to a linear decrease with increasing MTR at higher speed. For inlet tones (Fig. 33(b)) a 

linear decrease across the full range is seen. For combination tones (Fig. 33(c)) there does not appear to 

be any systematic variation, so a constant is used. For the aft broadband (Fig. 33(d)) and tones 

(Fig. 33(e)), linearly decreasing relations are found. 
NASA/CR—2014-218421 9 

Revised Fan Noise Prediction 

The revised predictive relations evolved in the preceding section, along with changes to the basic 

relations found to be appropriate, led to the new predictive procedure. Like the other prediction 

procedures, predictions are made for each of the fan noise components, i.e., inlet broadband, inlet tones, 

aft broadband, aft tones, and combination tones for supersonic fan tip speeds. For each component 

relations are derived for level, spectra and directivity. The 1/3 octave spectra at 1 Meter radius are given 

as a function of angle by the following equation where F1, F2, F3, F4, and F5 are defined for each 

component. 

SPL(f, T) @1 M. = 10 log10(m/mo) + 40 log10('T/'To) 

 + F1(MTR) + F2(RSS) + F3(T) + F4(f/fb) 

Where: 

 f = 1/3 octave center frequency, Hz. 

 fb = blade passage frequency, Hz. 

m = mass flow rate lb/sec (kg/sec) 

 mo = reference flow rate. 1 lb/sec (.453 kg/sec) 

 MTR = tip relative Mach number 

 RSS = rotor stator spacing divided by fan blade chord, % 

 SPL = 1/3 octave sound pressure level, re. 20 PPa 

'T = total temperature rise across the fan, qR, K 

'To = reference fan total temperature rise, 1 qR (.555 K) 

T = angle from inlet axis, degrees. 

Inlet Broadband Noise: 

 F1 = 34; MTR < .72 

 F1 = 34 -43(MTR - .72); MTR >= .72 

 F2 = - 5 log10RSS/300); For no inlet distortion present, 

F2 = - 5 log10(RSS/300); For RSS < 100 and inlet distortion present, 

F2 = - 5 log10(100/300); For RSS >= 100 and inlet distortion present 

 F3 = Directivity (See Table 2) 

 F4 = 10 log10[e-F5] 

F5 = -1/2{ln(f/4fb)/ln(2.2)}2 

Inlet Tone Noise: 

 F1 = 42 -20MTR 

 F2 = - 10 log10(RSS/300); For no inlet distortion present, 

 F2 = - 10 log10(RSS/300); For RSS < 100 and inlet distortion present, 

 F2 = - 10 log10(100/300); For RSS >= 100 and inlet distortion present 

 F3 = Directivity (See Table 2) 

 F4 = 0; k = 1, cut-on MTip /(1- VNumber/BNumber) > 1.05 or MTip > 1.05 

 = -8; k = 1, cut-off MTip /(1- VNumber/BNumber) < 1.05 and MTip < 1.05 

 = 3- 3k; k > 1 

Where k is harmonic number 

Combination Tones: The combination tone model consists of three spectra, one peaking at 1/2 BPF, one 

at 1/4 BPF, and one at 1/8 BPF. 
NASA/CR—2014-218421 10 

For 1/2 BPF 

 F1 = -18 + 46.5 (MTR -1)/.146; MTR < 1.146 

 F1 = 28.5 - 12 (MTR -1.146)/.854; MTR >= 1.146 

F2 = 0 

 F3 = Directivity (See Table 2) 

 F4 = 20log10(f/.5fb) f < .5fb 

 F4 = -20log10(f/.5fb) f >= .5fb 

For 1/4 BPF 

 F1 = -15 + 47.5(MTR -1)/.322; MTR < 1.322 

 F1 = 32.5 - 9(MTR -1.322)/.678; MTR >= 1.322 

F2 = 0 

 F3 = Directivity (See Table 2) 

 F4 = 30 log10 (f/.25fb) f < .25fb 

 F4 = -30 log10 (f/.25fb) f >= .25fb 

For 1/8 BPF 

 F1 = -12 + 41.2(MTR -1)/.61; MTR < 1.61 

 F1 = 29.2 - 4.7(MTR -1.61)/.39; MTR >= 1.61 

F2 = 0 

 F3 = Directivity (See Table 2) 

 F4 = 30 log10 (f/.125fb) f < .125fb 

 F4 = -20 log10 (f/.125fb) f >= .125fb 

Aft Broadband Noise: 

 F1 = 34 -17(MTR - .65) 

 F2 = - 5 log10 (RSS/300); For no inlet distortion present, 

 F2 = - 5 log10 (RSS/300); For RSS < 100 and inlet distortion present, 

 F2 = - 5 log10 (100/300); For RSS >= 100 and inlet distortion present 

 F3 = Directivity (See Table 2) 

 F4 = 10 log10 [e-F5] 

F5 = -1/2{ln(f/2.5fb)/ln(2.2)}2 

Aft Tone Noise: 

 F1 = 46 -20MTR 

 F2 = - 10 log10 (RSS/300); For no inlet distortion present, 

 F2 = - 10 log10 (RSS/300); For RSS < 100 and inlet distortion present, 

 F2 = - 10 log10 (100/300); For RSS >= 100 and inlet distortion present 

 F3 = Directivity (See Table 2) 

F4 = 0; k = 1, cut-on MTip /(1- VNumber/BNumber) > 1.05 or MTip > 1.05 

 = -8; k = 1, cut-off MTip /(1- VNumber/BNumber) < 1.05 and MTip < 1.05 

 = 3- 3k; k > 1 

Where k is harmonic number 
NASA/CR—2014-218421 11 

While the measured aft broadband levels for the low vane count (26 vane) stator appear to be lower 

then those measured for the baseline (54 vane) stator at some frequencies, including a reduction based on 

vane count increases the average difference between the data and the predictions. Obviously the effect of 

vane count is more complex then a simple level adjustment. Thus no adjustment for vane count is 

included in the model. This prediction procedure is based on data from fans without inlet guide vanes and 

the data is assumed to be free of contributions due to inlet distortion. For fans with inlet guide vanes 

and/or distortions, Heidmann’s equations for rotor-stator spacing and the effect of distortion on tones 

should be used. 

Comparison of Revised Model With Data 

Comparison With R4 Rotor Data 

Comparisons were made with five different configurations of the R4 rotor, all with 0.02-in. tip clearance: 

(1) The baseline OGV (54 vanes) with the nominal nozzle (labeled R4BOGVNOM02) 

(2) The baseline OGV (54 vanes) with the design point nozzle (area increased 5 percent over the nominal 

nozzle (labeled R4BOGV+5-02)) 

(3) The baseline OGV (54 vanes) with the high flow nozzle (area increased 7.5 percent over the nominal 

nozzle (labeled R4BOGV+75-02)) 

(4) The low vane count OGV (26 vanes) with the nominal nozzle (labeled R4LVCGVNOM02) 

(5) The low noise OGV (26 swept vanes) with the nominal nozzle (labeled R4LNGVNOM02) 

One sample is shown for each configuration, but more comparisons were made, as summarized 

statistically in Table 3. In these comparisons the experimental spectra are compared with total predicted 

from the jet/background noise model plus the revised model or the Heidmann model. For the revised 

models, the predicted contributions of all the fan noise constituents are also shown. 

The first comparison shown is for R4BOGVNOM02 at 91 percent speed, a high enough tip speed for 

combination tones to be present, in Figures 34(a) to (e) at angles T of 30, 60, 90, 120 and 150 deg. At 

T = 30 deg (Fig. 34(a)) the 100 and 125 Hz experimental SPLs appear quite low, as will be seen in all 

comparisons, so they will not be further considered. At about 1000 Hz and below the jet/background 

noise is clearly dominant. The revised model agrees very well with the data except that the fundamental 

tone at 4000 Hz. is under-predicted by about 4 dB, whereas the Heidmann model over-predicts across the 

spectrum. At T = 60 deg (Fig. 34(b)) the agreement is not as good. The first and second harmonic are on 

the order of 10 dB higher than predicted. The combination tone noise is somewhat over-predicted, and the 

broadband plus tone noise is under-predicted. The Heidmann model agrees better with the high frequency 

data, but greatly over-predicts combination tones. Similar observations, though not quite so pronounced, 

can be made at T = 90 deg (Fig. 34(c)). In the aft quadrant, T = 120 deg and 150q (Figs. 34(d) and (e)) the 

agreement is better, although not as good as desired, and the sharp tone at T = 150q and 2000 Hz is well 

above either the revised or Heidmann predictions. Overall, in comparison with the revised model the 

SPLs at all angles and frequencies of 400 Hz and higher, the experimental data are 1.0 dB above predicted 

with an RMS error of 3.1 dB. This is the worst agreement seen in these comparisons. The Heidmann 

model over-predicts the experimental data by an average of 3.0 dB with an RMS error of 5.9 dB, so even 

in this worst case, the errors are about half those seen with the Heidmann model. 

For R4BOGV+5-02, comparison is made at the very low speed of 50 percent in Figure 35 at the same 

angles as the previous figure. At T = 30 deg (Fig. 35(a)) the agreement is excellent up to 10,000 Hz, with 

the higher frequency broadband noise slightly under-predicted. The Heidmann model significantly overpredicts for around 10,000 Hz and below. At T = 60 deg (Fig. 35(b)) the revised model slightly overpredicts below 8,000 Hz and agrees almost perfectly at higher frequencies. The Heidmann model again 

under-predicts over most of the spectrum, but under-predicts somewhat at the highest frequencies. 
NASA/CR—2014-218421 12 

At T = 90 deg (Fig. 35(c)) similar comments can be made regarding the revised model, but he Heidmann 

model over-predicts at all frequencies. At T = 120 deg (Fig. 35(d)) the agreement is not as good, with as 

much as a 5 dB over-prediction in the vicinity of 2,000 Hz, whereas the Heidmann model over-predicts 

except at the highest frequencies. At T = 150 deg (Fig. 35(e)) the two predictive models give similar 

results and only rough agreement with the experimental data. For the revised model the average overprediction is 0.3 dB and the RMS error is 1.9 dB, while for the Heidmann model the over-prediction is 

3.0 dB and the RMS error is 4.3 dB. 

For R4BOGV+7.5-02, comparison is made at the intermediate 75 percent speed in Figure 36. At 

T = 30 deg (Fig. 36(a)) the agreement with the revised model is rather good, except for modest overprediction of the first and second harmonics, while the Heidmann model significantly over-predicts both 

tone and broad-band levels. Very similar observations can be made at T = 60 deg (Fig. 36(b)). At 

T = 90 deg (Fig. 36(c)) the revised model over-predicts the broadband noise at lower frequencies and 

under-predicts it at high frequency with reasonable agreement in the middle range, while again the 

Heidmann model over-predicts across the spectrum. At T = 120 deg (Fig. 36(d)) the same qualitative 

comments can be made for the revised model, but the magnitude of the disagreement is greater, especially 

in the lower frequency range. The Heidmann model continues to over-predict more than the revised 

model at low to middle frequencies, but at high frequencies it agrees better. At T = 150 deg (Fig. 36(e)) 

the agreement with both models is fair, with the Heidmann model agreeing better in the lower frequency 

range and the revised model doing better at higher frequencies. For the revised model the average overprediction is 0.8 dB and The RMS error is 1.8 dB, while for the Heidmann model the corresponding 

measures are 3.9 and 4.9 dB. 

For R4LVCGVNOM02, comparison is made at 100 percent speed, where combination tones are 

dominant over much the spectral directivity range. At T = 30 deg (Fig. 37(a)) the agreement with the 

revised model is very good, but with a slight over-prediction of the tones, while the Heidmann model 

over-predicts across the spectrum. At T = 60 deg (Fig. 37(b)) the agreement with the revised model is 

fairly good considering difficulty in dealing with the combination tones, and again the Heidmann model 

over-predicts across the spectrum. At T = 90 deg (Fig. 37(c)) there is rough agreement with both models, 

probably slightly better for the revised model. At T = 120 deg (Fig. 37(d)) there is rather good agreement 

with the revised model and slightly less-good agreement with the Heidmann model. At T = 150 deg 

(Fig. 37(e)) there is very good agreement with the revised model and, again, slightly less-good agreement 

with the Heidmann model. For the revised model the average over-prediction is 0.8 dB and the RMS error 

is 2.1 dB, while for the Heidmann model the corresponding measures are 5.0 and 6.6 dB. 

For R4LNGVNOM02, the comparison is made at 80 percent speed in Figure 38. At T = 30 deg 

(Fig. 38(a)) the agreement with the revised model is very good, while the Heidmann model over-predicts 

across the spectrum. At T = 60 deg (Fig. 38(b)) the agreement, while still good with the revised model, is 

not quite so good, and again the Heidmann model over-predicts except at the highest frequency. At 

T = 90 deg (Fig. 38(c)) the agreement with the revised model is excellent, while the Heidmann model 

over-predicts across the spectrum. At T = 120 deg (Fig. 38(d)) there is a slight over-prediction for the 

revised model, but not as great as for the Heidmann model. At T = 150 deg (Fig. 38(e)) falls mainly 

between the two predictive models, except for the fundamental tone which is about 6 dB above both 

predictions. For the revised model the average over/under-prediction is 0.0 dB and the RMS error is 

2.4 dB, while for the Heidmann model the corresponding measures are 2.7 dB (over-prediction) and 

3.7 dB. 

The statistical results are summarized in Table 3. For each comparison the mean and RMS errors are 

given for both the revised model and the Heidmann model. Comparisons with ADP fan data are also 

included. It is clear that the revised model offers a significant advancement in statistical accuracy, which 

is not surprising in view of the many problems influencing the experimental data available to Heidmann. 
NASA/CR—2014-218421 13 

Comparison With ADP Data 

To check on the generality of the revised fan noise prediction model, comparisons were made with 

data from a different fan. This fan, referred to as ADP or Advanced Ducted Propeller, was designed by 

Pratt and Whitney with a fan pressure ratio of 1.285 at takeoff and a design tip relative Mach number of 

0.91. This compares with the R4 fan which was designed by General Electric with a fan pressure ratio of 

1.51 at takeoff and a design tip relative Mach number 1.26. 

Comparison of measured and predicted levels are shown in Figure 39 at approach conditions. 

Predicted total levels with both the current method and the Heidmann method are shown. The jet and 

scrubbing noise models are the same for both fan noise models, thus the identical results at low 

frequencies. The curve labeled pred. fan is the predicted fan noise using the current model. At 30 degrees 

the current model is in better agreement with the data at frequencies at and below the 2nd fan harmonic. 

At mid frequencies, the Heidmann method provides a better prediction but the current model is better at 

high frequencies. 

At 60 degrees the current model does a better job over most of the frequency range. At 90 degrees the 

current model is better below the second harmonic and the Heidmann model ids better above the third 

harmonic. At 120 degrees the Heidmann model is slightly better over most of the frequency range. At 

150 degrees both models under-predict the measured levels with the current model being slightly better. 

In Figure 40 comparisons with ADP data at takeoff are shown. At 30 degrees, both models overpredict the broadband fan noise levels At 60 degrees both models predict levels reasonably close to the 

data with the current model doing better at frequencies below the second harmonic and the Heidmann 

model doing better above the third harmonic. At 90 degrees, again both models agree reasonably well 

with the data, with the Heidmann model being slightly better. At 120 degrees the two models predict 

nearly identical levels with both under-predicting the higher frequency levels. At 150 degrees, the current 

predictions are closer to the data but are several dB low at intermediate frequencies. 

Comparison of Model With Heidmann 

While the plots comparing the predictions using the current model also show predicted levels using 

the Heidmann model, differences in the models are not obvious since the apparent difference in prediction 

can result from differences in level correlations, differences in directivity, and differences in spectra. In 

this section plots comparing these three elements of the prediction procedures will be discussed. In 

Figure 41, normalized component levels for the two models are compared. The inlet broadband levels, 

Figure 41(a), start out nearly equal, but the new model shows a much steeper decrease with tip relative 

Mach number. Kontos et al., Reference in there revision of the Heidmann model also increased the 

decrease for the in inlet broadband coefficient but not as severely as the current model. This steeper 

decrease of the current resembles that of the Boeing prediction, Reference 20. 

The inlet and aft tone levels, Figures 41(b) and (d), are reduced significantly relative to the Heidmann 

model. Both the Kontos et al. and Allied Signal models reduced the inlet tone levels and the Boeing and 

Allied Signal models reduced the aft tone levels. 

Aft broadband levels, Figure 41(c), in the current model are relatively close to those of the Heidmann 

model as were those of the Boeing model. 

Directivities used in the two models are compared in Figures 25 to 28. Except for the combination 

tone directivity, only modest changes were made with no change made in the inlet tone directivity. The 

inlet broadband spectrum was shifted to peak at four times the blade passage frequency rather then 

2.5 times as in the Heidmann model. No change in the peak frequency was made for the aft broadband 

noise and no change in the shape of the spectra was made for either inlet or aft broadband noise. The 

cut-off effect on the tones was unchanged as was the harmonic fall off rate. 
NASA/CR—2014-218421 14 

Summary and Concluding Remarks 

A model for fan noise prediction was developed based on measured noise levels for the R4 rotor with 

several outlet guide vane variations and three fan exhaust areas. The fan test was part of a Source 

Diagnostic Test series conducted in the NASA Glenn Research Center 9- by 15-Foot Low-Speed Wind 

Tunnel. The fan was a 22 in. diameter fan with 22 blades with a design tip speed of 1215 ft/sec. Data from 

three stator sets were used in the development of the model. These are: the baseline 54 radial vane OGV 

designed to “cut-off” the blade passage frequency tone; the 26 radial vanes OGV which did not cut off the 

blade passage tone; and the 26 swept vane OGV which also did not cut off the blade passage tone but had 

the potential to reduce the fan tones. Data for these three OGV’s were obtained withy the nominal exhaust 

nozzle. For the baseline OGV data were obtained with two exhaust nozzles with increased area. 

The model predicts the complete fan noise spectrum, including broadband noise, tones, and for 

supersonic tip speeds, combination tones. Both spectra and directivity are predicted. Comparison with 

data shows the model is capable of predicting the effect of outlet guide vane number, exhaust area 

change, and vane sweep. Comparisons with data from a second fan, the ADP fan, also showed good 

agreement. 

Although reasonable agreement with data was obtained, the model was developed primarily based on 

data from one fan. Even though extensive data for that fan, including the above mentioned geometry 

variations, was used, the model needs to be tested over a much wider range of fan designs. Examination 

of data obtained without exit guide vanes present (Results not included in this report.) showed that the 

rotor alone noise levels were usually with 10 dB, and occasionally within 3 dB, of the results with the 

stator present. Future models should include the rotor alone noise as a separate source, even though 

limited data is available to generalize such a model. 
NASA/CR—2014-218421 15 

TABLE 1.—SDT2 ACOUSTIC DATA CONFIGURATIONS 

[Bold Configurations are with acoustic barrier wall in place, * denotes time domain data.] 

R4 Rotor—Acoustic Operating Line Nozzle (flight nominal nozzle) 

Baseline OGV Low Noise OGV Low Vane Count OGV 

Nom. .020 .030 Nom. .020 .030 Nom. .020 .030 

*03Oct02 

*02Oct02 

03Oct02a 

*10Sep02 *26Sep02 

R4 Rotor—Design Point Nozzle (+5 percent flow) 

Baseline OGV Low Noise OGV Low Vane Count OGV 

Nom. .020 .030 Nom. .020 .030 Nom. .020 .030 

 07Oct02a 

07Oct02 

R4 Rotor—Standard Flight Nozzle (+7.5 percent flow)

Baseline OGV Low Noise OGV Low Vane Count OGV 

Nom. .020 .030 Nom. .020 .030 Nom. .020 .030 

 08Oct02 

08Oct02a 

R4 Rotor Alone—Rotor Alone Nacelle Configuration 

No Barrier Wall Barrier Wall in Place 

*21May03 – .020 rub, nom. noz. 

29May03 – .020 rub, nom. noz., strut plates 

29May03a – .020 rub, nom. noz., partial plates 

02Jun03 – nom. rub, nom. noz. 

02Jun03a – .030 rub, nom. noz. 

10Jun03 – .020 rub, +7.5 percent noz. 

13Jun03 – .020 rub, +5 percent noz. 

04Jun03 – .020 rub, nom. noz. 

04Jun03a – .030 run, nom. noz. 

05Jun03 – nom. rub, nom. noz. 

10Jun03a – .020 rub, +7.5 percent noz. 

12Jun03 – .020 rub, +5 percent noz. 
NASA/CR—2014-218421 16 

TABLE 2.—DIRECTIVITIES FOR FAN NOISE COMPONENTS 

DIRECTIVITY FUNCTION F3

ANGLE

INLET 

BROADBAND

INLET 

TONES

COMBINATION 

TONES

AFT 

BROADBAND

AFT 

TONES

0 -0.5 -3 -28 -30 -50

10 -1 -1.5 -23 -25 -41

20 -1.25 0 -18 -20.8 -33

30 -1.41 0 -13 -19.5 -26

40 -1.4 0 -8 -18.4 -20.6

50 -2.2 -1.2 -3 -16.7 -17.9

60 -4.5 -3.5 0 -14.5 -14.7

70 -8.5 -6.8 -1.3 -12 -11.2

80 -13 -10.5 -2.6 -9.6 -9.3

90 -18.5 -15.5 -3.9 -6.9 -7.1

100 -24 -19 -5.2 -4.5 -4.7

110 -30 -25 -6.5 -1.8 -2

120 -36 -32 -7.9 -0.3 0

130 -42 -40 -9.4 0.5 0.8

140 -48 -49 -11 0.7 1

150 -54 -59 -12.7 -1.9 -1.6

160 -60 -70 -14.5 -4.5 -4.2

170 -66 -80 -16.4 -9 -9

180 -73 -90 -18.4 -15 -15
NASA/CR—2014-218421 17 

TABLE 3.—STATISTICAL SUMMARY 

Errors (Expeimental - Predicted, 400-8000 Hz)

 Revised Prediction Heidmann 

Fan Configuration % Speed Mean RMS Mean RMS

R4BOGV+5-02 50 -0.3 1.9 -3.0 4.3

R4BOGV+5-02 75 -1.0 1.5 -3.7 4.4

R4BOGV+5-02 95 0.9 2.2 -5.2 7.1

R4BOGV+5-02 Average -0.1 1.9 -4.0 5.3

R4BOGV+7.5-02 50 -0.8 2.8 -3.9 5.2

R4BOGV+7.5-02 75 -0.8 1.8 -3.9 4.9

R4BOGV+7.5-02 87.5 0.8 2.2 -3.5 5.3

R4BOGV+7.5-02 Average -0.3 2.3 -3.8 5.1

R4LVCGVNOM02 55 -0.6 1.8 -2.3 3.8

R4LVCGVNOM02 75 -0.9 1.9 -3.3 4.2

R4LVCGVNOM02 100 -0.8 2.1 -5.0 6.6

R4LVCGVNOM02 Average -0.8 1.9 -3.5 4.9

R4LNGVNOM02 65 0.4 1.5 -1.1 2.6

R4LNGVNOM02 80 0.0 2.4 -2.7 3.7

R4LNGVNOM02 90 -0.4 2.2 -3.9 5.5

R4LNGVNOM02 Average 0.0 2.0 -2.6 3.9

R4BOGVNOM02 55 0.3 1.5 -1.3 3.0

R4BOGVNOM02 70 1.5 2.0 -0.3 2.1

R4BOGVNOM02 91 1.0 3.1 -3.0 5.9

R4BOGVNOM02 Average 0.9 2.2 -1.5 3.7

R4 Overall Average 0.0 2.1 -3.1 4.6

ADP Approach 1.3 3.0 0.8 3.7

ADP Takeoff -0.7 2.7 -4.6 5.0

ADP Average 0.3 2.9 -1.9 4.4

R4 and ADP Average 0.0 2.2 -2.9 4.5
NASA/CR—2014-218421 18 

NORMALIZED PEAK INLET BROADBAND NOISE LEVEL

40

45

50

55

60

65

70

6400 7400 8400 9400 10400 11400 12400 13400

FAN SPEED, RPM

PEAK 1/3 OCTAVE SPL-20LOG(DELTA T)-10LOG( FLOW),

dB

HEIDMAN

ALLIED SIGNAL

KONTOS (GE)

BOEING

DUNN and PEART

Figure 1 - Comparison of predicted normalized inlet broadband noise levels.

NORMALIZED PEAK INLET FUNDAMENTAL TONE LEVEL

40

45

50

55

60

65

70

6000 7000 8000 9000 10000 11000 12000 13000 14000

FAN SPEED, RPM

PEAK 1/3 OCTAVE SPL-20LOG(DELTA T)-10LOG(FLOW), dB

HEIDMANN

ALLIED SIGNAL

KONTOS (GE)

BOEING

DUNN and PEART

Figure 2 - Comparison of predicted normalized inlet fundamental tone levels. 
NASA/CR—2014-218421 19 

NORMALIZED PEAK AFT BROADBAND LEVEL

55

60

65

70

75

6000 7000 8000 9000 10000 11000 12000 13000 14000

FAN SPEED, RPM

PEAK 1/3 OCTAVE SPL-20LOG(DELTA T)-10LOG(FLOW), dB

HEIDMANN

ALLIED SIGNAL

KONTOS (GE)

BOEING

DUNN and PEART

Figure 3 - Comparison of predicted normalized aft broadband levels. 

NORMALIZED PEAK AFT FUNDAMENTAL TONE LEVEL

55

60

65

70

75

6000 7000 8000 9000 10000 11000 12000 13000 14000

FAN SPEED, RPM

PEAK 1/3 OCTAVE SPL-20LOG(DELTA T)-10LOG(FLOW), dB

HEIDMANN

ALLIED SIGNAL

KONTOS (GE)

BOEING

DUNN and PEART

Figure 4 - Comparison of predicted normalized aft broadband levels. 
NASA/CR—2014-218421 20 

INLET BROADBAND NOISE DIRECTIVITY

-40

-35

-30

-25

-20

-15

-10

-5

0

0 20 40 60 80 100 120 140 160 180

ANGLE FROM INLET, DEGREES

SPL - SPLpeak, dB

HEIDMANN, KONTOS,

ALLIED SIGNAL and GASP

BOEING

DUNN and PEART

Figure 5 - Comparison of inlet broadband directivities.

AFT BROADBAND DIRECTIVITY

-40

-35

-30

-25

-20

-15

-10

-5

0

0 20 40 60 80 100 120 140 160 180

ANGLE FROM INLET, DEGREES

SPL - SPLpeak, dB

HEIDMANN, KONTOS and GASP

ALLIED SIGNAL

BOEING

DUNN and PEART

Figure 6 - Comparison of aft broadband directivities. 
NASA/CR—2014-218421 21 

INLET TONE DIRECTIVITY

-40

-35

-30

-25

-20

-15

-10

-5

0

0 20 40 60 80 100 120 140 160 180

ANGLE FROM INLET, DEGREES

SPL - SPLpeak, dB

HEIDMANN and KONTOS

ALLIED SIGNAL

GASP

BOEING

DUNN and PEART

Figure 7 - Comparison of inlet tone directivities. 

AFT TONE DIRECTIVITY

-40

-35

-30

-25

-20

-15

-10

-5

0

0 20 40 60 80 100 120 140 160 180

ANGLE FROM INLET, DEGREES

SPL - SPLpeak, dB

HEIDMANN and KONTOS

ALLIED SIGNAL

GASP

BOEING

DUNN and PEART

Figure 8 - Comparison of aft tone directivities. 
NASA/CR—2014-218421 22 

INLET BROADBAND NOISE SPECTRA

-20

-15

-10

-5

0

5

0.1 1 10

NORMALIZED FREQUENCY, F/Fbpf

SPL - SPLpeak, dB

HEIDMAN, KONTOS, and GASP

ALLIED SIGNAL

BOEING

DUNN and PEART

Figure 9 - Comparison of inlet broadband noise spectra. 

AFT BROADBAND NOISE SPECTRA

-20

-15

-10

-5

0

5

0.1 1 10

NORMALIZED FREQUENCY, F/Fbpf

SPL - SPLpeak

HEIDMANN, KONTOS, and

GASP

ALLIED SIGNAL

BOEING

DUNN and PEART

Figure 10 - Comparison of inlet broadband noise spectra. 
NASA/CR—2014-218421 23 

APPROACH, 60 DEGREES

40

50

60

70

80

90

100

110

120

100 1000 10000 100000

FREQUENCY, HZ.

SPL, dB

DATA

HEIDMANN

ALLIED SIGNAL

KONTOS (GE)

BOEING

DUNN and PEART

Figure 11 - Comparison of predictions with measured data. R4 rotor with baseline outlet guide vanes, 

baseline nozzle, and 0.02 in. tip clearance, approach fan speed at 60 degrees from the inlet. 

APPROACH 120 DEGREES

40

50

60

70

80

90

100

110

120

100 1000 10000 100000

FREQUENCY, HZ.

SPL, dB

DATA

HEIDMANN

ALLIED SIGNAL

KONTOS (GE)

BOEING

DUNN and PEART

Figure 12 - Comparison of predictions with measured data. R4 rotor with baseline outlet guide vanes, 

baseline nozzle, and 0.02 in. tip clearance, approach fan speed at 120 degrees from the inlet. 
NASA/CR—2014-218421 24 

(a) Directivity Angle T = 60 deg

Figure 13 - First Level Extraction of Fan and Jet/Background Noise for R4 Rotor with Baseline 

BOGVs, 0.02-in. gap and Design Point Nozzle.

45

50

55

60

65

70

75

80

85

90

95

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Pred. Total

Extr. Jet/BG

Pred. J/BG

Heid. Pred. Fan

Extrct. Fan

(b) Directivity Angle T = 120 deg

Figure 13 - First Level Extraction of Fan and Jet/Background Noise for R4 Rotor with Baseline 

BOGVs, 0.02-in. gap and Design Point Nozzle.

50

55

60

65

70

75

80

85

90

95

100

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Pred. Total

Extr. Jet/BG

Pred. J/BG

Heid. Pred. Fan

Extrct. Fan
NASA/CR—2014-218421 25 

Figure 14 - Component Spectral Extraction and Correaltion for Vmix/camb = 0.35, Mf = 0.1 

(Fan R4BOGV+7.5-02, 50% Speed)

50

55

60

65

70

75

80

85

90

100 1000 10000

1/3-Octave-Band Center Frequency, f, Hz

Free-Field

Lossless

Sound

Pressure

Level

on 7.44-ft

Sidelinet,

SPL, dB

SPLJ/BG,EE

SPLL,EE

SPLS,EE

SPLT,EE

SPLP,EE

SPLJ/BG,Pred

SPLL,Pred

SPLS,Pred

SPLT,Pred

SPLP,Pred

Effective Directivity Angles: thet'M = 18.2, 

thet'O = 25, thet'I = 25.7, thet'P = 19.3

(a) Directivity Angle = 30 deg

Figure 14 - Component Spectral Extraction and Correaltion for Vmix/camb = 0.35, Mf = 0.1 

(Fan R4BOGV+7.5-02, 50% Speed)

55

60

65

70

75

80

85

90

95

100 1000 10000

1/3-Octave-Band Center Frequency, f, Hz

Free-Field

Lossless

Sound

Pressure

Level

on 7.44-ft

Sideline,

SPL, dB

SPLJ/BG,EE

SPLL,EE

SPLS,EE

SPLT,EE

SPLP,EE

SPLJ/BG,Pred

SPLL,Pred

SPLS,Pred

SPLT,Pred

SPLP,Pred

Effective Directivity Angles: thet'M = 46.6, 

thet'O = 43, thet'I = 48.5, thet'P = 31

(b) Directivity Angle = 60 deg
NASA/CR—2014-218421 26 

Figure 14 - Component Spectral Extraction and Correaltion for Vmix/camb = 0.35, Mf = 0.1 

(Fan R4BOGV+7.5-02, 50% Speed)

55

60

65

70

75

80

85

90

95

100 1000 10000

1/3-Octave-Band Center Frequency, f, Hz

Free-Field

Lossless

Sound

Pressure

Level

on 7.44-ft

Sideline,

SPL, dB

SPLJ/BG,EE

SPLL,EE

SPLS,EE

SPLT,EE

SPLP,EE

SPLJ/BG,Pred

SPLL,Pred

SPLS,Pred

SPLT,Pred

SPLP,Pred

Effective Directivity Angles: thet'M = 70.4, 

thet'O = 57.4, thet'I = 70, thet'P = 42

(c) Directivity Angle = 90 deg

Component Coefficients, CM = 140, CO = 

132, CI = 135, and CP = 130.3

Figure 14 - Component Spectral Extraction and Correaltion for Vmix/camb = 0.35, Mf = 0.1 

(Fan R4BOGV+7.5-02, 50% Speed)

60

65

70

75

80

85

90

95

100

100 1000 10000

1/3-Octave-Band Center Frequency, f, Hz

Free-Field

Lossless

Sound

Pressure

Level

on 7.44-ft

Sideline,

SPL, dB

SPLJ/BG,EE

SPLL,EE

SPLS,EE

SPLT,EE

SPLP,EE

SPLJ/BG,Pred

SPLL,Pred

SPLS,Pred

SPLT,Pred

SPLP,Pred

Effective Directivity Angles: thet'M = 95.9, 

thet'O = 76.9, thet'I = 95.3, thet'P = 60.1

(d) Directivity Angle = 120 deg
NASA/CR—2014-218421 27 

Figure 14 - Component Spectral Extraction and Correaltion for Vmix/camb = 0.35, Mf = 0.1 

(Fan R4BOGV+7.5-02, 50% Speed)

60

65

70

75

80

85

90

95

100

100 1000 10000

1/3-Octave-Band Center Frequency, f, Hz

Free-Field

Lossless

Sound

Pressure

Level

on 7.44-ft

Sideline,

SPL, dB

SPLJ/BG,EE

SPLL,EE

SPLS,EE

SPLT,EE

SPLP,EE

SPLJ/BG,Pred

SPLL,Pred

SPLS,Pred

SPLT,Pred

SPLP,Pred

Effective Directivity Angles: thet'M = 126, 

thet'O = 119.1, thet'I = 128, thet'P = 111.2

(e) Directivity Angle = 150 deg
NASA/CR—2014-218421 28 

Figure 15. Comparison of Predicted Jet and Scrubbing Noise with Measured Low Frequency 

Fan Rig Data, Vmix/camb = 0.36

60

65

70

75

80

85

90

95

100

100 1000 10000

1/3-Octave-Band Center Frequency, f, Hz

Free-Field

Lossless

Sound

Pressure

Level

on 7.44-ft

Sideline,

SPL, dB MEASURED

PREDICTED JET +

SCRUBBING NOISE

JET NOISE

SCRUBBING NOISE

(a) Directivity Angle = 60 deg

Figure 15. Comparison of Predicted Jet and Scrubbing Noise with Measured Low Frequency 

Fan Rig Data, Vmix/camb = 0.36

60

65

70

75

80

85

90

95

100

100 1000 10000

1/3-Octave-Band Center Frequency, f, Hz

Free-Field

Lossless

Sound

Pressure

Level

on 7.44-ft

Sideline,

SPL, dB

MEASURED

PREDICTED JET +

SCRUBBING NOISE

JET NOISE

SCRUBBING NOISE

(b) Directivity Angle = 90 deg
NASA/CR—2014-218421 29 

Figure 15. Comparison of Predicted Jet and Scrubbing Noise with Measured Low Frequency 

Fan Rig Data, Vmix/camb = 0.36

60

65

70

75

80

85

90

95

100

100 1000 10000

1/3-Octave-Band Center Frequency, f, Hz

Free-Field

Lossless

Sound

Pressure

Level

on 7.44-ft

Sideline,

SPL, dB

MEASURED

PREDICTED JET +

SCRUBBING NOISE

JET NOISE

SCRUBBING NOISE

(c) Directivity Angle = 120 deg

Figure 15. Comparison of Predicted Jet and Scrubbing Noise with Measured Low Frequency 

Fan Rig Data, Vmix/camb = 0.36

60

65

70

75

80

85

90

95

100

100 1000 10000

1/3-Octave-Band Center Frequency, f, Hz

Free-Field

Lossless

Sound

Pressure

Level

on 7.44-ft

Sideline,

SPL, dB

MEASURED

PREDICTED JET +

SCRUBBING NOISE

JET NOISE

SCRUBBING NOISE

(d) Directivity Angle = 150 deg
NASA/CR—2014-218421 30 

Figure 16. Comparison of Predicted Jet and Scrubbing Noise with Measured Low Frequency 

Fan Rig Data, Vmix/camb = 0.499

60

65

70

75

80

85

90

95

100

100 1000 10000

1/3-Octave-Band Center Frequency, f, Hz

Free-Field

Lossless

Sound

Pressure

Level

on 7.44-ft

Sideline,

SPL, dB MEASURED

PREDICTED JET +

SCRUBBING NOISE

JET NOISE

SCRUBBING NOISE

(a) Directivity Angle = 60 deg

Figure 16. Comparison of Predicted Jet and Scrubbing Noise with Measured Low Frequency 

Fan Rig Data, Vmix/camb = 0.499

65

70

75

80

85

90

95

100

105

100 1000 10000

1/3-Octave-Band Center Frequency, f, Hz

Free-Field

Lossless

Sound

Pressure

Level

on 7.44-ft

Sideline,

SPL, dB MEASURED

PREDICTED JET +

SCRUBBING NOISE

JET NOISE

SCRUBBING NOISE

(b) Directivity Angle = 90 deg
NASA/CR—2014-218421 31 

Figure 16. Comparison of Predicted Jet and Scrubbing Noise with Measured Low Frequency 

Fan Rig Data, Vmix/camb = 0.499

70

75

80

85

90

95

100

105

110

100 1000 10000

1/3-Octave-Band Center Frequency, f, Hz

Free-Field

Lossless

Sound

Pressure

Level

on 7.44-ft

Sideline,

SPL, dB

MEASURED

PREDICTED JET +

SCRUBBING NOISE

JET NOISE

SCRUBBING NOISE

(c) Directivity Angle = 120 deg

Figure 16. Comparison of Predicted Jet and Scrubbing Noise with Measured Low Frequency 

Fan Rig Data, Vmix/camb = 0.499

70

75

80

85

90

95

100

105

110

100 1000 10000

1/3-Octave-Band Center Frequency, f, Hz

Free-Field

Lossless

Sound

Pressure

Level

on 7.44-ft

Sideline,

SPL, dB

MEASURED

PREDICTED JET +

SCRUBBING NOISE

JET NOISE

SCRUBBING NOISE

(d) Directivity Angle = 150 deg
NASA/CR—2014-218421 32 

Figure 17. Comparison of Predicted Jet and Scrubbing Noise with Measured Low Frequency 

Fan Rig Data, Vmix/camb = 0.634

70

75

80

85

90

95

100

105

110

100 1000 10000

1/3-Octave-Band Center Frequency, f, Hz

Free-Field

Lossless

Sound

Pressure

Level

on 7.44-ft

Sideline,

SPL, dB MEASURED

PREDICTED JET +

SCRUBBING NOISE

JET NOISE

SCRUBBING NOISE

(a) Directivity Angle = 60 deg

Figure 17. Comparison of Predicted Jet and Scrubbing Noise with Measured Low Frequency 

Fan Rig Data, Vmix/camb = 0.634

75

80

85

90

95

100

105

110

115

100 1000 10000

1/3-Octave-Band Center Frequency, f, Hz

Free-Field

Lossless

Sound

Pressure

Level

on 7.44-ft

Sideline,

SPL, dB MEASURED

PREDICTED JET +

SCRUBBING NOISE

JET NOISE

SCRUBBING NOISE

(b) Directivity Angle = 90 deg
NASA/CR—2014-218421 33 

Figure 17. Comparison of Predicted Jet and Scrubbing Noise with Measured Low Frequency 

Fan Rig Data, Vmix/camb = 0.634

80

85

90

95

100

105

110

115

120

100 1000 10000

1/3-Octave-Band Center Frequency, f, Hz

Free-Field

Lossless

Sound

Pressure

Level

on 7.44-ft

Sideline,

SPL, dB

MEASURED

PREDICTED JET +

SCRUBBING NOISE

JET NOISE

SCRUBBING NOISE

(c) Directivity Angle = 120 deg

Figure 17. Comparison of Predicted Jet and Scrubbing Noise with Measured Low Frequency 

Fan Rig Data, Vmix/camb = 0.634

80

85

90

95

100

105

110

115

120

100 1000 10000

1/3-Octave-Band Center Frequency, f, Hz

Free-Field

Lossless

Sound

Pressure

Level

on 7.44-ft

Sideline,

SPL, dB

MEASURED

PREDICTED JET +

SCRUBBING NOISE

JET NOISE

SCRUBBING NOISE

(d) Directivity Angle = 150 deg
NASA/CR—2014-218421 34 

Figure 18. Comparison of Predicted Jet and Scrubbing Noise with Measured Low Frequency 

Fan Rig Data, Vmix/camb = 0.689

80

85

90

95

100

105

110

115

120

100 1000 10000

1/3-Octave-Band Center Frequency, f, Hz

Free-Field

Lossless

Sound

Pressure

Level

on 7.44-ft

Sideline,

SPL, dB

MEASURED

PREDICTED JET +

SCRUBBING NOISE

JET NOISE

SCRUBBING NOISE

(a) Directivity Angle = 60 deg

Figure 18. Comparison of Predicted Jet and Scrubbing Noise with Measured Low Frequency 

Fan Rig Data, Vmix/camb = 0.689

80

85

90

95

100

105

110

115

120

100 1000 10000

1/3-Octave-Band Center Frequency, f, Hz

Free-Field

Lossless

Sound

Pressure

Level

on 7.44-ft

Sideline,

SPL, dB

MEASURED

PREDICTED JET +

SCRUBBING NOISE

JET NOISE

SCRUBBING NOISE

(b) Directivity Angle = 90 deg
NASA/CR—2014-218421 35 

Figure 18. Comparison of Predicted Jet and Scrubbing Noise with Measured Low Frequency 

Fan Rig Data, Vmix/camb = 0.689

80

85

90

95

100

105

110

115

120

100 1000 10000

1/3-Octave-Band Center Frequency, f, Hz

Free-Field

Lossless

Sound

Pressure

Level

on 7.44-ft

Sideline,

SPL, dB MEASURED

PREDICTED JET +

SCRUBBING NOISE

JET NOISE

SCRUBBING NOISE

(c) Directivity Angle = 120 deg

Figure 18. Comparison of Predicted Jet and Scrubbing Noise with Measured Low Frequency 

Fan Rig Data, Vmix/camb = 0.689

80

85

90

95

100

105

110

115

120

100 1000 10000

1/3-Octave-Band Center Frequency, f, Hz

Free-Field

Lossless

Sound

Pressure

Level

on 7.44-ft

Sideline,

SPL, dB MEASURED

PREDICTED JET +

SCRUBBING NOISE

JET NOISE

SCRUBBING NOISE

(d) Directivity Angle = 150 deg
NASA/CR—2014-218421 36 

a. 60 Degrees

65

70

75

80

85

90

95

100

105

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Pred. Tot.

Pred. Jet

Pred. Fan

b) 120 Degrees

65

70

75

80

85

90

95

100

105

110

115

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Pred. Tot.

Pred. Jet

Pred. Fan

Figure 19 - Comparison of initial predictions with data at approach fan speed, for R4 rotor with nominal area 

nozzle, baseline OGV and 0.02 in. tip clearance. 
NASA/CR—2014-218421 37 

a) 60 Degrees

70

75

80

85

90

95

100

105

110

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Pred. Tot.

Pred. Jet

Pred. Fan

b) 120 Degrees

75

80

85

90

95

100

105

110

115

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Pred. Tot.

Pred. Jet

Pred. Fan

Figure 20 - Comparison of initial predictions with data at cutback fan speed, for R4 rotor with nominal area nozzle, 

baseline OGV, and 0.02 in. tip clearance. 
NASA/CR—2014-218421 38 

a) 60 Degrees

80

85

90

95

100

105

110

115

120

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Pred. Tot.

Pred. Jet

Pred. Fan

b) 120 Degrees

80

85

90

95

100

105

110

115

120

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Pred. Tot.

Pred. Jet

Pred. Fan

Figure 21 - Comparison of initial predictions with data at takeoff fan speed, for R4 rotor with nominal area nozzle, 

baseline OGV, and 0.02 in. tip clearance. 
NASA/CR—2014-218421 39 

a) 60 DEGREES

70

75

80

85

90

95

100

105

100 1000 10000 100000

FREQUENCY, HZ.

SPL, dB

DATA - 54 VANES

DATA 26 VANES

PREDICTED - 54 VANES

PREDICTED 26 VANES

b) 120 DEGREES

70

75

80

85

90

95

100

105

110

100 1000 10000 100000

FREQUENCY, HZ.

SPL, dB

DATA - 54 VANES

DATA - 26 VANES

PREDICTED - 54 VANES

DATA - 26 VANES

Figure 22 - Comparison of predictions and data for the baseline OGV with 54 stators and the low 

vane count OGV with 26 stators for rotor R4, with the nominal exhaust nozzle, 0.02 tip clearance 

at approach fan speed. 
NASA/CR—2014-218421 40 

a) 60 DEGREES

60

65

70

75

80

85

90

95

100

100 1000 10000 100000

FREQUENCY, HZ.

SPL, dB

MEASURED, NOMINAL NOZZLE

MEASURED, +5% NOZZLE

MEASURED, +7.5% NOZZLE

PREDICTED, NOMINAL NOZZLE

PREDICTED +5% NOZZLE

PREDICTED, +7.5% NOZZLE

b) 120 DEGREES

65

70

75

80

85

90

95

100

105

100 1000 10000 100000

FREQUENCY, HZ.

SPL, dB

MEASURED NOMINAL NOZZLE

MEASURED +5% NOZZLE

MEASURED + 7.5% NOZZLE

PREDICTED NOMINAL NOZZLE

PREDICTED +5% NOZZLE

PREDICTED +7.5% NOZZLE

Figure 23 - Comparison of predictions and data for the R4 rotor with the baseline 54 stator OGV and 

0.02 tip clearance with varying exhaust nozzle areas at 50% fan speed. 
NASA/CR—2014-218421 41 

a) 60 DEGREES

75

80

85

90

95

100

105

100 1000 10000 100000

FREQUENCY, HZ.

SPL, dB

MEASURED STRAIGHT VANES

MEASURED SWEPT VANES

PREDICTED STRAIGHT VANES

PREDICTED SWEPT VANES

b) 120 DEGREES

80

85

90

95

100

105

110

100 1000 10000 100000

FREQUENCY, HZ.

SPL, dB

MEASURED STRAIGHT VANES

MEASURED SWEPT VANES

PREDICTED STRAIGHT VANES

PREDICTED SWEPT VANES

Figure 24 - Comparison of predictions and data for the low vane count OGV with 26 straight 

vanes and the low noise OGV with 26 swept vanes for rotor R4, with the nominal exhaust 

nozzle, 0.02 tip clearance at approach fan speed. 
NASA/CR—2014-218421 42 

(a) Directivity Angle T = 30 deg 

Figure 25 - Second Level Component Spectral Extraction for Rotor R4; Baseline OGV; .02 Tip 

Clearance; Nominal Nozzle; 93% Speed; Coefficients Adjusted to Minimize Errors.

70

75

80

85

90

95

100

105

110

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Extrct. Fan

Pred. Fan

Extrct. Inlet BB

Pred. Inlet BB

Extrct. Combi. Tones

Pred. Combi. Tones

Extrct. Inlet Tones

Pred. Inlet Tones

Extrct. Aft BB

Pred. Aft BB

(b) Directivity Angle T = 60 deg 

Figure 25 - Second Level Component Spectral Extraction for Rotor R4; Baseline OGV; .02 Tip 

Clearance; Nominal Nozzle; 93% Speed; Coefficients Adjusted to Minimize Errors.

45

50

55

60

65

70

75

80

85

90

95

100

105

110

115

120

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Extrct. Fan

Pred. Fan

Extrct. Inlet BB

Pred. Inlet BB

Extrct. Aft BB

Pred. Aft BB

Extrct. Combi. Tones

Extrct. Inlet Tones

Pred. Combi. Tones

Pred. Inlet Tones

Extrct. Aft Tones

Pred. Aft Tones
NASA/CR—2014-218421 43 

(c) Directivity Angle T = 90 deg

Figure 25 - Second Level Component Spectral Extraction for Rotor R4; Baseline OGV; .02 Tip 

Clearance; Nominal Nozzle; 93% Speed; Coefficients Adjusted to Minimize Errors.

50

55

60

65

70

75

80

85

90

95

100

105

110

115

120

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Extrct. Fan

Pred. Fan

Extrct. Aft BB

Pred. Aft BB

Extrct. Combi. Tones

Pred. Combi. Tones

Extrct. Aft Tones

Pred. Aft Tones

(d) Directivity Angle T = 120 deg

Figure 25 - Second Level Component Spectral Extraction for Rotor R4; Baseline OGV; .02 Tip 

Clearance; Nominal Nozzle; 93% Speed; Coefficients Adjusted to Minimize Errors.

80

85

90

95

100

105

110

115

120

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Extrct. Fan

Pred. Fan

Extrct. Aft BB

Pred. Aft BB

Extrct. Combi. Tones

Pred. Combi. Tones

Extrct. Aft Tones

Pred. Aft Tones
NASA/CR—2014-218421 44 

(e) Directivity Angle T = 150 deg 

Figure 25 - Second Level Component Spectral Extraction for Rotor R4; Baseline OGV; .02 Tip 

Clearance; Nominal Nozzle; 93% Speed; Coefficients Adjusted to Minimize Errors.

75

80

85

90

95

100

105

110

115

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Extrct. Fan

Pred. Fan

Pred. Combi. Tones

Extrct. Aft BB

Pred. Aft BB

Extrct. Aft Tones

Pred. Aft Tones

Extrct. Combi. Tones

 (a) Inlet (Normalized to T = 60 deg)

Figure 26 - Broadband Directivity Correlation (Average of Highest 3 SPLs) Vs. Directivity 

Angle

-16

-15

-14

-13

-12

-11

-10

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

1

2

3

4

20 30 40 50 60 70 80 90 100

Directivity Angle, T, deg

Normalized Peak Broadband SPL relative to T = 60 deg, 

dB

Heidmann

R4BOGVNOMNOM-55

R4BOGVNOMNOM-65

R4LVCGVNOM02-80

R4LVCGVNOM02-50

R4LVCGVNOM02-65

New Prediction
NASA/CR—2014-218421 45 

(b) Aft (Normalized to T =120 deg)

Figure 26 - Broadband Directivity Correlation (Average of Highest 3 SPLs) Vs. Directivity 

Angle

-16

-15

-14

-13

-12

-11

-10

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

1

2

3

4

40 60 80 100 120 140 160

Directivity Angle, T, deg

Normalized Peak Broadband SPL relative to T = 120 deg, dB

Heidmann

R4BOGVNOMNOM-55

R4BOGVNOMNOM-65

R4BOGVNOM02-80

R4LVCGVNOM02-50

R4LVCGVNOM02-65

New Prediction

(a) 1st Harmonic

Figure 27 - Inlet Tone Directivity Correlation (Normalized to T = 60 deg) Vs. Directivity Angle

-12

-11

-10

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

1

2

3

4

5

6

20 30 40 50 60 70 80 90

Directivity Angle, T, deg

Normalized 1st Inlet Harmonic SPL relative to T = 60 deg, dB

Heidmann

R4BOGVNOMNOM-55

R4BOGVNOMNOM-65

R4LVCGVNOM02-80

R4LVCGVNOM02-50

R4LVCGVNOM02-65
NASA/CR—2014-218421 46 

(b) 2nd Harmonic

Figure 27 - Inlet Tone Directivity Correlation (Normalized to T = 60 deg) Vs. Directivity Angle

-12

-11

-10

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

1

2

3

4

20 30 40 50 60 70 80 90

Directivity Angle, T, deg

Normalized 2nd Inlet Harmonic SPL relative to T = 60 deg, dB

Heidmann

R4BOGVNOMNOM-55

R4BOGVNOMNOM-65

R4BOGVNOMNOM-80

R4LVCGVNOM02-50

R4LVCGVNOM02-65

(c) 3rd Harmonic Tone

Figure 27- Inlet Directivity Correlation (Normalized to T = 60 deg) Vs. Directivity Angle

-12

-11

-10

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

1

2

3

4

20 30 40 50 60 70 80 90

Directivity Angle, T, deg

Normalized 3rd Inlet Harmonic SPL relative to T = 60 deg, dB

Heidmann

R4BOGVNOMNOM-65

R4LVCGVNOM02-80

R4LVCGVNOM02-50

R4LVCGVNOM02-65
NASA/CR—2014-218421 47 

(a) 1st Harmonic Tone

Figure 28 - Aft Directivity Correlation (Normalized to T = 120 deg) Vs. Directivity 

Angle

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

2

4

6

8

10

40 60 80 100 120 140 160

Directivity Angle, T, deg

Normalized 1st Aft Harmonic SPL relative to T = 

120 deg, dB

Heidmann

R4BOGVNOMNOM-55

R4BOGVNOMN02-65

R4LVCGVNOM02-80

R4LVCGVNOM02-50

R4LVCGVNOM02-65

New Prediction

(b) 2nd Harmonic Tone

Figure 28 - Aft Directivity Correlation (Normalized to T = 120 deg) Vs. Directivity 

Angle

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

2

4

6

8

10

40 60 80 100 120 140 160

Directivity Angle, T, deg

Normalized 2nd Aft Harmonic SPL relative to T = 

120 deg, dB

Heidmann

R4BOGVNOMNOM-55

R4BOGVNOMN02-65

R4LVCGVNOM02-80

R4LVCGVNOM02-50

R4LVCGVNOM02-65

New Prediction
NASA/CR—2014-218421 48 

(c) 3rd Harmonic

Figure 28 - Aft Tone Directivity Correlation (Normalized to T = 120 deg) Vs. 

Directivity Angle

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

2

4

6

8

10

40 60 80 100 120 140 160

Directivity Angle, T, deg

Normalized 3rd Aft Harmonic SPL relative to T = 

120 deg, dB

Heidmann

R4BOGVNOMNOM-55

R4BOGVNOMN02-65

R4LVCGVNOM02-80

R4LVCGVNOM02-50

R4LVCGVNOM02-65

New Prediction

Figure 29 - Combination Tone Directivity Correlation (Normalized to T = 60 deg) 

Vs. Directivity Angle (Based on 5 highest SPLs)

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

2

20 40 60 80 100 120 140 160

Directivity Angle, T, deg

Normalized Combination Tone High-5 Average SPL 

relative to T = 60 deg, dB

Heidmann

R4BOGVNOM02-93

R4BOGVNOM02-100

R4LVCGVNOM02-100

New Correlation
NASA/CR—2014-218421 49 

(a) Directivity Angle T = 30 deg

Figure 30 - Normalized Inlet Broadband SPL Spectra 

-30

-25

-20

-15

-10

-5

0

5

-0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Logarithmic Normalized Frequency, log (f/BPF)

Normalized Sound Pressure Level, SPLexp - 

SPLpk,pred,60, dB

Predicted

R4BOGVNOM02-65

R4BOGVNOM02-70

R4BOGVNOM02-80

R4LVCGVNOM02-50

R4LVCGVNOM02-65

R4BOGVNOMNOM-55

R4BOGVNOMNOM-70

R4BOGVNOMNOM-87.5

R4BOGV+5-02-50

R4BOGV+5-02-70

R4BOGV+7.5-02-61.7

R4BOGV+7.5-02-70

R4BOGV+7.5-02-80

R4LVCGNOM02-70

R4LNGVNOM02-70

R4LNGVNOM02-80

(b) Directivity Angle T = 40 deg

Figure 30 - Normalized Inlet Broadband SPL Spectra

-30

-25

-20

-15

-10

-5

0

5

-0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Logarithmic Normalized Frequency, log (f/BPF)

Normalized Sound Pressure Level, SPLexp - 

SPLpk,pred,60, dB

Predicted

R4BOGVNOM02-65

R4BOGVNOM02-70

R4BOGVNOM02-80

R4LVCGVNOM02-50

R4LVCGVNOM02-65

R4BOGVNOMNOM-55

R4BOGVNOMNOM-70

R4BOGVNOMNOM-87.5

R4BOGV+5-02-50

R4BOGV+5-02-70

R4BOGV+7.5-02-61.7

R4BOGV+7.5-02-70

R4BOGV+7.5-02-80

R4LVCGNOM02-70

R4LNGVNOM02-70

R4LNGVNOM02-80
NASA/CR—2014-218421 50 

(c) Directivity Angle T = 50 deg

Figure 30 - Normalized Inlet Broadband SPL Spectra 

-30

-25

-20

-15

-10

-5

0

5

-0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Logarithmic Normalized Frequency, log (f/BPF)

Normalized Sound Pressure Level, SPLexp - SPLpk,pred,60,

dB

Predicted

R4BOGVNOM02-65

R4BOGVNOM02-70

R4BOGVNOM02-80

R4LVCGVNOM02-50

R4LVCGVNOM02-65

R4BOGVNOMNOM-55

R4BOGVNOMNOM-70

R4BOGVNOMNOM-87.5

R4BOGV+5-02-50

R4BOGV+5-02-70

R4BOGV+7.5-02-61.7

R4BOGV+7.5-02-70

R4BOGV+7.5-02-80

R4LVCGNOM02-70

R4LNGVNOM02-70

R4LNGVNOM02-80

(d) Directivity Angle T = 60 deg

Figure 30 - Normalized Inlet Broadband SPL Spectra

-30

-25

-20

-15

-10

-5

0

5

-0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Logarithmic Normalized Frequency, log (f/BPF)

Normalized Sound Pressure Level, SPLexp - 

SPLpk,pred,60, dB

Predicted

R4BOGVNOM02-65

R4BOGVNOM02-70

R4BOGVNOM02-80

R4LVCGVNOM02-50

R4LVCGVNOM02-65

R4BOGVNOMNOM-55

R4BOGVNOMNOM-70

R4BOGVNOMNOM-87.5

R4BOGV+5-02-50

R4BOGV+5-02-70

R4BOGV+7.5-02-61.7

R4BOGV+7.5-02-70

R4BOGV+7.5-02-80

R4LVCGNOM02-70

R4LNGVNOM02-70

R4LNGVNOM02-80
NASA/CR—2014-218421 51 

(e) Directivity Angle T = 70 deg

Figure 30 - Normalized Inlet Broadband SPL Spectra 

-30

-25

-20

-15

-10

-5

0

5

-0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Logarithmic Normalized Frequency, log (f/BPF)

Normalized Sound Pressure Level, SPLexp - 

SPLpk,pred,60, dB

Predicted

R4BOGVNOM02-65

R4BOGVNOM02-70

R4BOGVNOM02-80

R4LVCGVNOM02-50

R4LVCGVNOM02-65

R4BOGVNOMNOM-55

R4BOGVNOMNOM-70

R4BOGVNOMNOM-87.5

R4BOGV+5-02-50

R4BOGV+5-02-70

R4BOGV+7.5-02-61.7

R4BOGV+7.5-02-70

R4BOGV+7.5-02-80

R4LVCGNOM02-70

R4LNGVNOM02-70

R4LNGVNOM02-80

(f) Directivity Angle T = 80 deg

Figure 30 - Normalized Inlet Broadband SPL Spectra

-30

-25

-20

-15

-10

-5

0

5

-0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Logarithmic Normalized Frequency, log (f/BPF)

Normalized Sound Pressure Level, SPLexp - 

SPLpk,pred,60, dB

Predicted

R4BOGVNOM02-65

R4BOGVNOM02-70

R4BOGVNOM02-80

R4LVCGVNOM02-50

R4LVCGVNOM02-65

R4BOGVNOMNOM-55

R4BOGVNOMNOM-70

R4BOGVNOMNOM-87.5

R4BOGV+5-02-50

R4BOGV+5-02-70

R4BOGV+7.5-02-61.7

R4BOGV+7.5-02-70

R4BOGV+7.5-02-80

R4LVCGNOM02-70

R4LNGVNOM02-70

R4LNGVNOM02-80
NASA/CR—2014-218421 52 

(a) Directivity Angle T = 60 deg

Figure 31 - Normalized Aft Broadband SPL Spectra 

-35

-30

-25

-20

-15

-10

-5

0

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Logarithmic Normalized Frequency, log (f/BPF)

Normalized Sound Pressure Level, SPLexp - 

SPLpk,pred,120, dB

Predicted

R4BOGVNOM02-65

R4BOGVNOM02-70

R4BOGVNOM02-80

R4LVCGVNOM02-50

R4LVCGVNOM02-65

R4BOGVNOMNOM-55

R4BOGVNOMNOM-70

R4BOGVNOMNOM-87.5

R4BOGV+5-02-50

R4BOGV+5-02-70

R4BOGV+7.5-02-61.7

R4BOGV+7.5-02-70

R4BOGV+7.5-02-80

R4LVCGNOM02-70

R4LNGVNOM02-70

R4LNGVNOM02-80

 (b) Directivity Angle T = 70 deg

Figure 31 - Normalized Aft Broadband SPL Spectra

-35

-30

-25

-20

-15

-10

-5

0

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Logarithmic Normalized Frequency, log (f/BPF)

Normalized Sound Pressure Level, SPLexp - 

SPLpk,pred,120, dB

Predicted

R4BOGVNOM02-65

R4BOGVNOM02-70

R4BOGVNOM02-80

R4LVCGVNOM02-50

R4LVCGVNOM02-65

R4BOGVNOMNOM-55

R4BOGVNOMNOM-70

R4BOGVNOMNOM-87.5

R4BOGV+5-02-50

R4BOGV+5-02-70

R4BOGV+7.5-02-61.7

R4BOGV+7.5-02-70

R4BOGV+7.5-02-80

R4LVCGNOM02-70

R4LNGVNOM02-70

R4LNGVNOM02-80
NASA/CR—2014-218421 53 

 (c) Directivity Angle T = 80 deg

Figure 31 - Normalized Aft Broadband SPL Spectra

-35

-30

-25

-20

-15

-10

-5

0

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Logarithmic Normalized Frequency, log (f/BPF)

Normalized Sound Pressure Level, SPLexp - 

SPLpk,pred,120, dB

Predicted

R4BOGVNOM02-65

R4BOGVNOM02-70

R4BOGVNOM02-80

R4LVCGVNOM02-50

R4LVCGVNOM02-65

R4BOGVNOMNOM-55

R4BOGVNOMNOM-70

R4BOGVNOMNOM-87.5

R4BOGV+5-02-50

R4BOGV+5-02-70

R4BOGV+7.5-02-61.7

R4BOGV+7.5-02-70

R4BOGV+7.5-02-80

R4LVCGNOM02-70

R4LNGVNOM02-70

R4LNGVNOM02-80

 (d) Directivity Angle T = 90 deg

Figure 31 - Normalized Aft Broadband SPL Spectra

-30

-25

-20

-15

-10

-5

0

5

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Logarithmic Normalized Frequency, log (f/BPF)

Normalized Sound Pressure Level, SPLexp - 

SPLpk,pred,120, dB

Predicted

R4BOGVNOM02-65

R4BOGVNOM02-70

R4BOGVNOM02-80

R4LVCGVNOM02-50

R4LVCGVNOM02-65

R4BOGVNOMNOM-55

R4BOGVNOMNOM-70

R4BOGVNOMNOM-87.5

R4BOGV+5-02-50

R4BOGV+5-02-70

R4BOGV+7.5-02-61.7

R4BOGV+7.5-02-70

R4BOGV+7.5-02-80

R4LVCGNOM02-70

R4LNGVNOM02-70

R4LNGVNOM02-80
NASA/CR—2014-218421 54 

 (e) Directivity Angle T = 100 deg

Figure 31 - Normalized Aft Broadband SPL Spectra

-30

-25

-20

-15

-10

-5

0

5

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Logarithmic Normalized Frequency, log (f/BPF)

Normalized Sound Pressure Level, SPLexp - 

SPLpk,pred,120, dB

Predicted

R4BOGVNOM02-65

R4BOGVNOM02-70

R4BOGVNOM02-80

R4LVCGVNOM02-50

R4LVCGVNOM02-65

R4BOGVNOMNOM-55

R4BOGVNOMNOM-70

R4BOGVNOMNOM-87.5

R4BOGV+5-02-50

R4BOGV+5-02-70

R4BOGV+7.5-02-61.7

R4BOGV+7.5-02-70

R4BOGV+7.5-02-80

R4LVCGNOM02-70

R4LNGVNOM02-70

R4LNGVNOM02-80

 (f) Directivity Angle T = 110 deg

Figure 31 - Normalized Aft Broadband SPL Spectra

-30

-25

-20

-15

-10

-5

0

5

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Logarithmic Normalized Frequency, log (f/BPF)

Normalized Sound Pressure Level, SPLexp - 

SPLpk,pred,120, dB

Predicted

R4BOGVNOM02-65

R4BOGVNOM02-70

R4BOGVNOM02-80

R4LVCGVNOM02-50

R4LVCGVNOM02-65

R4BOGVNOMNOM-55

R4BOGVNOMNOM-70

R4BOGVNOMNOM-87.5

R4BOGV+5-02-50

R4BOGV+5-02-70

R4BOGV+7.5-02-61.7

R4BOGV+7.5-02-70

R4BOGV+7.5-02-80

R4LVCGNOM02-70

R4LNGVNOM02-70

R4LNGVNOM02-80
NASA/CR—2014-218421 55 

 (g) Directivity Angle T = 120 deg

Figure 31 Normalized Aft Broadband SPL Spectra

-25

-20

-15

-10

-5

0

5

10

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Logarithmic Normalized Frequency, log (f/BPF)

Normalized Sound Pressure Level, SPLexp - 

SPLpk,pred,120, dB

Predicted

R4BOGVNOM02-65

R4BOGVNOM02-70

R4BOGVNOM02-80

R4LVCGVNOM02-50

R4LVCGVNOM02-65

R4BOGVNOMNOM-55

R4BOGVNOMNOM-70

R4BOGVNOMNOM-87.5

R4BOGV+5-02-50

R4BOGV+5-02-70

R4BOGV+7.5-02-61.7

R4BOGV+7.5-02-70

R4BOGV+7.5-02-80

R4LVCGNOM02-70

R4LNGVNOM02-70

R4LNGVNOM02-80

 (h) Directivity Angle T = 130 deg

Figure 31 - Normalized Aft Broadband SPL Spectra

-25

-20

-15

-10

-5

0

5

10

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Logarithmic Normalized Frequency, log (f/BPF)

Normalized Sound Pressure Level, SPLexp - 

SPLpk,pred,120, dB

Predicted

R4BOGVNOM02-65

R4BOGVNOM02-70

R4BOGVNOM02-80

R4LVCGVNOM02-50

R4LVCGVNOM02-65

R4BOGVNOMNOM-55

R4BOGVNOMNOM-70

R4BOGVNOMNOM-87.5

R4BOGV+5-02-50

R4BOGV+5-02-70

R4BOGV+7.5-02-61.7

R4BOGV+7.5-02-70

R4BOGV+7.5-02-80

R4LVCGNOM02-70

R4LNGVNOM02-70

R4LNGVNOM02-80
NASA/CR—2014-218421 56 

 (i) Directivity Angle T = 140 deg

Figure 31 - Normalized Aft Broadband SPL Spectra

-25

-20

-15

-10

-5

0

5

10

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Logarithmic Normalized Frequency, log (f/BPF)

Normalized Sound Pressure Level, SPLexp - 

SPLpk,pred,120, dB

Predicted

R4BOGVNOM02-65

R4BOGVNOM02-70

R4BOGVNOM02-80

R4LVCGVNOM02-50

R4LVCGVNOM02-65

R4BOGVNOMNOM-55

R4BOGVNOMNOM-70

R4BOGVNOMNOM-87.5

R4BOGV+5-02-50

R4BOGV+5-02-70

R4BOGV+7.5-02-61.7

R4BOGV+7.5-02-70

R4BOGV+7.5-02-80

R4LVCGNOM02-70

R4LNGVNOM02-70

R4LNGVNOM02-80

 (j) Directivtity Angle T = 150 deg

Figure 31 - Normalized Aft Broadband SPL Spectra

-40

-35

-30

-25

-20

-15

-10

-5

0

5

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Logarithmic Normalized Frequency, log (f/BPF)

Normalized Sound Pressure Level, SPLexp - 

SPLpk,pred,120, dB

Predicted

R4BOGVNOM02-65

R4BOGVNOM02-70

R4BOGVNOM02-80

R4LVCGVNOM02-50

R4LVCGVNOM02-65

R4BOGVNOMNOM-55

R4BOGVNOMNOM-70

R4BOGVNOMNOM-87.5

R4BOGV+5-02-50

R4BOGV+5-02-70

R4BOGV+7.5-02-61.7

R4BOGV+7.5-02-70

R4BOGV+7.5-02-80

R4LVCGNOM02-70

R4LNGVNOM02-70

R4LNGVNOM02-80
NASA/CR—2014-218421 57 

 (a) Directivity Angle T = 30 deg

Figure 32 - Normalized Inlet Combination Tone SPL Spectra

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

-1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

Logarithmic Normalized Frequency, log (f/BPF)

Normalized Sound Pressure Level, SPLexp - 

SPLpk,pred,60, dB

Pred-R4BOGVNOM02-100

Exp-R4BOGVNOM02-100

Pred-R4BOGVNOM02-93

Exp-R4BOGVNOM02-93

Pred-R4LVCGVNOM02-100

Exp-R4LVCGVNOM02-100

Pred-R4BOGV+5-02-100

Exp-R4BOGV+5-02-100

Pred-R4LNGVNOM02-100

R4LNGVNOM02-100

 (b) Directivity Angle T = 40 deg

Figure 32 - Normalized Inlet Combination Tone SPL Spectra

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

-1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

Logarithmic Normalized Frequency, log (f/BPF)

Normalized Sound Pressure Level, SPLexp - 

SPLpk,pred,60, dB

Pred-R4BOGVNOM02-100

Exp-R4BOGVNOM02-100

Pred-R4BOGVNOM02-93

Exp-R4BOGVNOM02-93

Pred-R4LVCGVNOM02-100

Exp-R4LVCGVNOM02-100

Pred-R4BOGVNOMNOM-87.5

Exp-R4BOGVNOMNOM-87.5

Pred-R4BOGV+5-02-100

Exp-R4BOGV+5-02-100

Pred-R4LNGVNOM02-100

R4LNGVNOM02-100
NASA/CR—2014-218421 58 

 (c) Directivity Angle T = 50 deg

Figure 32 - Normalized Inlet Combination Tone SPL Spectra

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

-1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

Logarithmic Normalized Frequency, log (f/BPF)

Normalized Sound Pressure Level, SPLexp - 

SPLpk,pred,60, dB

Pred-R4BOGVNOM02-100

Exp-R4BOGVNOM02-100

Pred-R4BOGVNOM02-93

Exp-R4BOGVNOM02-93

Pred-R4LVCGVNOM02-100

Exp-R4LVCGVNOM02-100

Pred-R4BOGVNOMNOM-87.5

Exp-R4BOGVNOMNOM-87.5

Pred-R4BOGV+5-02-100

Exp-R4BOGV+5-02-100

Pred-R4LNGVNOM02-100

R4LNGVNOM02-100

 (d) Directivity Angle T = 60 deg

Figure 32 - Normalized Inlet Combination Tone SPL Spectra

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

-1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

Logarithmic Normalized Frequency, log (f/BPF)

Normalized Sound Pressure Level, SPLexp - 

SPLpk,pred,60, dB

Pred-R4BOGVNOM02-100

Exp-R4BOGVNOM02-100

Pred-R4BOGVNOM02-93

Exp-R4BOGVNOM02-93

Pred-R4LVCGVNOM02-100

Exp-R4LVCGVNOM02-100

Pred-R4BOGVNOMNOM-87.5

Exp-R4BOGVNOMNOM-87.5

Pred-R4BOGV+5-02-100

Exp-R4BOGV+5-02-100

Pred-R4LNGVNOM02-100

R4LNGVNOM02-100
NASA/CR—2014-218421 59 

 (e) Directivity Angle T = 70 deg

Figure 32 - Normalized Inlet Combination Tone SPL Spectra

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

-1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

Logarithmic Normalized Frequency, log (f/BPF)

Normalized Sound Pressure Level, SPLexp - 

SPLpk,pred,60, dB

Pred-R4BOGVNOM02-100

Exp-R4BOGVNOM02-100

Pred-R4BOGVNOM02-93

Exp-R4BOGVNOM02-93

Pred-R4LVCGVNOM02-100

Exp-R4LVCGVNOM02-100

Pred-R4BOGVNOMNOM-87.5

Exp-R4BOGVNOMNOM-87.5

Pred-R4BOGV+5-02-100

Exp-R4BOGV+5-02-100

Pred-R4LNGVNOM02-100

R4LNGVNOM02-100

 (f) Directivity Angle T = 80 deg

Figure 32 - Normalized Inlet Combination Tone SPL Spectra

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

-1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

Logarithmic Normalized Frequency, log (f/BPF)

Normalized Sound Pressure Level, SPLexp - 

SPLpk,pred,60, dB

Pred-R4BOGVNOM02-100

Exp-R4BOGVNOM02-100

Pred-R4BOGVNOM02-93

Exp-R4BOGVNOM02-93

Pred-R4LVCGVNOM02-100

Exp-R4LVCGVNOM02-100

Pred-R4BOGVNOMNOM-87.5

Exp-R4BOGVNOMNOM-87.5

Pred-R4BOGV+5-02-100

Exp-R4BOGV+5-02-100

Pred-R4LNGVNOM02-100

R4LNGVNOM02-100
NASA/CR—2014-218421 60 

 (g) Directivity Angle T = 90 deg

Figure 32 - Normalized Inlet Combination Tone SPL Spectra

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

-1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

Logarithmic Normalized Frequency, log (f/BPF)

Normalized Sound Pressure Level, SPLexp - 

SPLpk,pred,60, dB

Pred-R4BOGVNOM02-100

Exp-R4BOGVNOM02-100

Pred-R4BOGVNOM02-93

Exp-R4BOGVNOM02-93

Pred-R4LVCGVNOM02-100

Exp-R4LVCGVNOM02-100

Pred-R4BOGVNOMNOM-87.5

Exp-R4BOGVNOMNOM-87.5

Pred-R4BOGV+5-02-100

Exp-R4BOGV+5-02-100

Pred-R4LNGVNOM02-100

R4LNGVNOM02-100

 (h) Directivity Angle T = 100 deg

Figure 32 - Normalized Inlet Combination Tone SPL Spectra

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

-1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

Logarithmic Normalized Frequency, log (f/BPF)

Normalized Sound Pressure Level, SPLexp - 

SPLpk,pred,60, dB

Pred-R4BOGVNOM02-100

Exp-R4BOGVNOM02-100

Pred-R4BOGVNOM02-93

Exp-R4BOGVNOM02-93

Pred-R4LVCGVNOM02-100

Exp-R4LVCGVNOM02-100

Pred-R4BOGVNOMNOM-87.5

Exp-R4BOGVNOMNOM-87.5

Pred-R4BOGV+5-02-100

Exp-R4BOGV+5-02-100

Pred-R4LNGVNOM02-100

R4LNGVNOM02-100
NASA/CR—2014-218421 61 

 (i) Directivity Angle T = 110 deg

Figure 32 - Normalized Inlet Combination Tone SPL Spectra

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

-1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

Logarithmic Normalized Frequency, log (f/BPF)

Normalized Sound Pressure Level, SPLexp - 

SPLpk,pred,60, dB

Pred-R4BOGVNOM02-100

Exp-R4BOGVNOM02-100

Pred-R4BOGVNOM02-93

Exp-R4BOGVNOM02-93

Pred-R4LVCGVNOM02-100

Exp-R4LVCGVNOM02-100

Exp-R4BOGVNOMNOM-87.5

Pred-R4BOGV+5-02-100

Exp-R4BOGV+5-02-100

Pred-R4LNGVNOM02-100

R4LNGVNOM02-100

 (j) Directivity Angle T = 120 deg

Figure 32 - Normalized Inlet Combination Tone SPL Spectra

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5

-1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

Logarithmic Normalized Frequency, log (f/BPF)

Normalized Sound Pressure Level, SPLexp - 

SPLpk,pred,60, dB

Pred-R4BOGVNOM02-100

Exp-R4BOGVNOM02-100

Pred-R4BOGVNOM02-93

Exp-R4BOGVNOM02-93

Pred-R4LVCGVNOM02-100

Exp-R4LVCGVNOM02-100

Pred-R4BOGV+5-02-100

Exp-R4BOGV+5-02-100

Pred-R4LNGVNOM02-100

R4LNGVNOM02-100
NASA/CR—2014-218421 62 

(k) Directivity Angle T = 130 deg

Figure 32 - Normalized Inlet Combination Tone SPL Spectra

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

-1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

Logarithmic Normalized Frequency, log (f/BPF)

Normalized Sound Pressure Level, SPLexp - 

SPLpk,pred,60, dB

Pred-R4BOGVNOM02-100

Exp-R4BOGVNOM02-100

Pred-R4BOGVNOM02-93

Exp-R4BOGVNOM02-93

Pred-R4LVCGVNOM02-100

Exp-R4LVCGVNOM02-100

Pred-R4BOGV+5-02-100

Exp-R4BOGV+5-02-100

Pred-R4LNGVNOM02-100

R4LNGVNOM02-100

 (l) Directivity Angle T = 140 deg

Figure 32 - Normalized Inlet Combination Tone SPL Spectra

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

-1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

Logarithmic Normalized Frequency, log (f/BPF)

Normalized Sound Pressure Level, SPLexp - 

SPLpk,pred,60, dB

Pred-R4BOGVNOM02-100

Exp-R4BOGVNOM02-100

Pred-R4BOGVNOM02-93

Exp-R4BOGVNOM02-93

Pred-R4LVCGVNOM02-100

Exp-R4LVCGVNOM02-100

Pred-R4BOGV+5-02-100

Exp-R4BOGV+5-02-100

Pred-R4LNGVNOM02-100

R4LNGVNOM02-100
NASA/CR—2014-218421 63 

(a) Inlet Broadband

Figure 33 - Fan Noise Component Coefficient Correlation

5

10

15

20

25

30

35

40

0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3

Tip Relative Mach Number, MTR, dimensionless

Component Coefficient, C(B,I), dB

R4BOGVNOMN02

R4LVCGVNOM02

R4BOGV+5-02

R4BOGV+7.5-02

R4LNGVNOM02

CORRELATION

(b) Inlet Tones

Figure 33 - Fan Noise Component Coefficient Correlation

5

10

15

20

25

30

35

0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3

Tip Relative Mach Number, MTR, dimensionless

Component Coefficient, C(T,I), dB

R4BOGVNOMN02

R4LVCGVNOM02

R4BOGV+5-02

R4BOGV+7.5-02

R4LNGVNOM02

CORRELATION
NASA/CR—2014-218421 64 

-30

-25

-20

-15

-10

1 1.05 1.1 1.15 1.2 1.25 1.3

Tip Relative Mach Number, MTR, dimensionless

Component Coefficient, C(CT), dB

R4BOGVNOMN02

R4LVCGVNOM02

R4BOGV+5-02

R4LNGVNOM02

CORRELATION

(c) Combination Tones

Figure 33 - Fan Noise Component Coefficient Correlation

(d) Aft Broadband

Figure 33 - Fan Noise Component Coefficient Correlation

20

25

30

35

40

0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3

Tip Relative Mach Number, MTR, dimensionless

Component Coefficient, C(B,A), dB

R4BOGVNOMN02

R4LVCGVNOM02

R4BOGV+5-02

R4BOGV+7.5-02

R4LNGVNOM02

CORRELATION
NASA/CR—2014-218421 65 

(e) Aft Tone

Figure 33 - Fan Noise Component Coefficient Correlation

20

25

30

35

40

0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3

Tip Relative Mach Number, MTR, dimensionless

Component Coefficient, C(B,A), dB

R4BOGVNOMN02

R4LVCGVNOM02

R4BOGV+5-02

R4BOGV+7.5-02

R4LNGVNOM02

CORRELATION

(a) Directivity Angle T = 30 deg

Figure 34 - Comparison of Experimental and Modified Fan Component and Total Noise for 

R4BOGVNOM02-91.

45

50

55

60

65

70

75

80

85

90

95

100

105

110

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Inlet BB

Pred. Inlet Tones

Pred. Combi. Tones

Pred. Aft BB

Pred. Aft Tones
NASA/CR—2014-218421 66 

(b) Directivity Angle T = 60 deg

Figure 34 - Comparison of Experimental and Modified Fan Component and Total Noise for 

R4BOGVNOM02-91.

55

60

65

70

75

80

85

90

95

100

105

110

115

120

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Inlet BB

Pred. Inlet Tones

Pred. Combi. Tones

Pred. Aft BB

Pred. Aft Tones

(c) Directivity Angle T = 90 deg

Figure 34 - Comparison of Experimental and Modified Fan Component and Total Noise for 

R4BOGVNOM02-91.

55

60

65

70

75

80

85

90

95

100

105

110

115

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Inlet BB

Pred. Inlet Tones

Pred. Combi. Tones

Pred. Aft BB

Pred. Aft Tones
NASA/CR—2014-218421 67 

(d) Directivity Angle T = 120 deg

Figure 34 - Comparison of Experimental and Modified Fan Component and Total Noise for 

R4BOGVNOM02-91.

60

65

70

75

80

85

90

95

100

105

110

115

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Inlet BB

Pred. Inlet Tones

Pred. Combi. Tones

Pred. Aft BB

Pred. Aft Tones

(e) Directivity Angle T = 150 deg

Figure 34 - Comparison of Experimental and Modified Fan Component and Total Noise for 

R4BOGVNOM02-91.

70

75

80

85

90

95

100

105

110

115

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Pred. Tot.

Pred. BG

Pred. Combi. Tones

Pred. Aft BB

Pred. Aft Tones

Heidmann
NASA/CR—2014-218421 68 

(b) Directivity Angle T = 60 deg

Figure 35 - Comparison of Experimental and Modified Fan Component and Total Noise for 

R4BOGV+5-02-50.

45

50

55

60

65

70

75

80

85

90

95

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Inlet BB

Pred. Inlet Tones

Pred. Aft BB

Pred. Aft Tones

(a) Directivity Angle T = 30 deg

Figure 35 - Comparison of Experimental and Modified Fan Component and Total Noise for 

R4BOGV+5-02-50.

40

45

50

55

60

65

70

75

80

85

90

95

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Inlet BB

Pred. Inlet Tones

Pred. Aft BB

Pred. Aft Tones
NASA/CR—2014-218421 69 

(c) Directivity Angle T = 90 deg

Figure 35 - Comparison of Experimental and Modified Fan Component and Total Noise for 

R4BOGV+5-02-50.

45

50

55

60

65

70

75

80

85

90

95

100

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Inlet BB

Pred. Inlet Tones

Pred. Aft BB

Pred. Aft Tones

(d) Directivity Angle T = 120 deg

Figure 35 - Comparison of Experimental and Modified Fan Component and Total Noise for 

R4BOGV+5-02-50.

50

55

60

65

70

75

80

85

90

95

100

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Inlet BB

Pred. Inlet Tones

Pred. Aft BB

Pred. Aft Tones
NASA/CR—2014-218421 70 

(e) Directivity Angle T = 150 deg

Figure 35 - Comparison of Experimental and Modified Fan Component and Total Noise for 

R4BOGV+7.5-02-50.

55

60

65

70

75

80

85

90

95

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Aft BB

Pred. Aft Tones

(a) Directivity Angle T = 30 deg

Figure 36 - Comparison of Experimental and Modified Fan Component and Total Noise for 

R4BOGV+7.5-02-75.

45

50

55

60

65

70

75

80

85

90

95

100

105

110

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Inlet BB

Pred. Inlet Tones

Pred. Aft BB

Pred. Aft Tones
NASA/CR—2014-218421 71 

(b) Directivity Angle T = 60 deg

Figure 36 - Comparison of Experimental and Modified Fan Component and Total Noise for 

R4BOGV+7.5-02-75.

45

50

55

60

65

70

75

80

85

90

95

100

105

110

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Inlet BB

Pred. Inlet Tones

Pred. Aft BB

Pred. Aft Tones

(c) Directivity Angle T = 90 deg

Figure 36 - Comparison of Experimental and Modified Fan Component and Total Noise for 

R4BOGV+7.5-02-75.

45

50

55

60

65

70

75

80

85

90

95

100

105

110

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Inlet BB

Pred. Inlet Tones

Pred. Aft BB

Pred. Aft Tones
NASA/CR—2014-218421 72 

(d) Directivity Angle T = 120 deg

Figure 36 - Comparison of Experimental and Modified Fan Component and Total Noise for 

R4BOGV+7.5-02-75.

45

50

55

60

65

70

75

80

85

90

95

100

105

110

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Inlet BB

Pred. Inlet Tones

Pred. Aft BB

Pred. Aft Tones

(e) Directivity Angle T = 150 deg

Figure 36 - Comparison of Experimental and Modified Fan Component and Total Noise for 

R4BOGV+7.5-02-75.

45

50

55

60

65

70

75

80

85

90

95

100

105

110

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Aft BB

Pred. Aft Tones
NASA/CR—2014-218421 73 

(a) Directivity Angle T = 30 deg

Figure 37 - Comparison of Experimental and Modified Fan Component and Total Noise for 

R4LVCGVNOM02-100.

45

50

55

60

65

70

75

80

85

90

95

100

105

110

115

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Inlet BB

Pred. Inlet Tones

Pred. Combi. Tones

Pred. Aft BB

Pred. Aft Tones

(b) Directivity Angle T = 60 deg

Figure 37 - Comparison of Experimental and Modified Fan Component and Total Noise for 

R4LVCGVNOM02-100.

60

65

70

75

80

85

90

95

100

105

110

115

120

125

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Inlet BB

Pred. Inlet Tones

Pred. Combi. Tones

Pred. Aft BB

Pred. Aft Tones
NASA/CR—2014-218421 74 

(c) Directivity Angle T = 90 deg

Figure 37 - Comparison of Experimental and Modified Fan Component and Total Noise for 

R4LVCGVNOM02-100.

45

50

55

60

65

70

75

80

85

90

95

100

105

110

115

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Inlet BB

Pred. Inlet Tones

Pred. Combi. Tones

Pred. Aft BB

Pred. Aft Tones

(d) Directivity Angle T = 120 deg

Figure 37 - Comparison of Experimental and Modified Fan Component and Total Noise for 

R4LVCGVNOM02-100.

45

50

55

60

65

70

75

80

85

90

95

100

105

110

115

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Inlet BB

Pred. Inlet Tones

Pred. Combi. Tones

Pred. Aft BB

Pred. Aft Tones
NASA/CR—2014-218421 75 

(e) Directivity Angle T = 150 deg

Figure 37 - Comparison of Experimental and Modified Fan Component and Total Noise for 

R4LVCGVNOM02-1000.

45

50

55

60

65

70

75

80

85

90

95

100

105

110

115

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Pred. Tot.

Pred. BG

Pred. Combi. Tones

Pred. Aft BB

Pred. Aft Tones

Heidmann

(a) Directivity Angle T = 30 deg

Figure 38 - Comparison of Experimental and Modified Fan Component and Total Noise for 

R4LNGVNOM-02-80.

45

50

55

60

65

70

75

80

85

90

95

100

105

110

115

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Inlet BB

Pred. Inlet Tones

Pred. Aft BB

Pred. Aft Tones
NASA/CR—2014-218421 76 

(b) Directivity Angle T = 60 deg

Figure 38 - Comparison of Experimental and Modified Fan Component and Total Noise for 

R4LNGVNOM-02-80.

50

55

60

65

70

75

80

85

90

95

100

105

110

115

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Inlet BB

Pred. Inlet Tones

Pred. Aft BB

Pred. Aft Tones

(c) Directivity Angle T = 90 deg

Figure 38 - Comparison of Experimental and Modified Fan Component and Total Noise for 

R4LNGVNOM-02-80.

50

55

60

65

70

75

80

85

90

95

100

105

110

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Inlet BB

Pred. Inlet Tones

Pred. Aft BB

Pred. Aft Tones
NASA/CR—2014-218421 77 

(d) Directivity Angle T = 120 deg

Figure 38 - Comparison of Experimental and Modified Fan Component and Total Noise for 

R4LNGVNOM-02-80.

60

65

70

75

80

85

90

95

100

105

110

115

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Inlet BB

Pred. Inlet Tones

Pred. Aft BB

Pred. Aft Tones

(e) Directivity Angle T = 150 deg

Figure 38 - Comparison of Experimental and Modified Fan Component and Total Noise for 

R4LNGVNOM-02-80.

65

70

75

80

85

90

95

100

105

110

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Pred. Tot.

Pred. BG

Pred. Aft BB

Pred. Aft Tones

Heidmann
NASA/CR—2014-218421 78 

(a) Directivity Angle T = 30 deg

Figure 39 - Comparison of Experimental and Modified Fan Component and Total Noise for 

ADP at Approach Fan Speed

40

45

50

55

60

65

70

75

80

85

90

95

100

105

110

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Inlet BB

Pred. Inlet Tones

Pred. Combi. Tones

Pred. Aft BB

Pred. Aft Tones

(b) Directivity Angle T = 60 deg

Figure 39 - Comparison of Experimental and Modified Fan Component and Total Noise for

 ADP at Approach Fan Speed.

40

45

50

55

60

65

70

75

80

85

90

95

100

105

110

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Inlet BB

Pred. Inlet Tones

Pred. Combi. Tones

Pred. Aft BB

Pred. Aft Tones
NASA/CR—2014-218421 79 

(c) Directivity Angle T = 90 deg

Figure 39 - Comparison of Experimental and Modified Fan Component and Total Noise for

ADP at Approach Fan Speed.

45

50

55

60

65

70

75

80

85

90

95

100

105

110

115

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Inlet BB

Pred. Inlet Tones

Pred. Combi. Tones

Pred. Aft BB

Pred. Aft Tones

(d) Directivity Angle T = 120 deg

Figure 39 - Comparison of Experimental and Modified Fan Component and Total Noise for

ADP at Approach Fan Speed.

45

50

55

60

65

70

75

80

85

90

95

100

105

110

115

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Inlet BB

Pred. Inlet Tones

Pred. Combi. Tones

Pred. Aft BB

Pred. Aft Tones
NASA/CR—2014-218421 80 

(e) Directivity Angle T = 150 deg

Figure 39 - Comparison of Experimental and Modified Fan Component and Total Noise for 

ADP at Approach Fan Speed.

45

50

55

60

65

70

75

80

85

90

95

100

105

110

115

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Pred. Tot.

Pred. BG

Pred. Combi. Tones

Pred. Aft BB

Pred. Aft Tones

Heidmann

(a) Directivity Angle T = 30 deg

Figure 40 - Comparison of Experimental and Modified Fan Component and Total Noise for 

ADP at Takeoff Fan Speed

50

55

60

65

70

75

80

85

90

95

100

105

110

115

120

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Inlet BB

Pred. Inlet Tones

Pred. Combi. Tones

Pred. Aft BB

Pred. Aft Tones
NASA/CR—2014-218421 81 

(b) Directivity Angle T = 60 deg

Figure 40 - Comparison of Experimental and Modified Fan Component and Total Noise for 

ADP at Takeoff Fan Speed.

50

55

60

65

70

75

80

85

90

95

100

105

110

115

120

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Inlet BB

Pred. Inlet Tones

Pred. Combi. Tones

Pred. Aft BB

Pred. Aft Tones

(c) Directivity Angle T = 90 deg

Figure 40 - Comparison of Experimental and Modified Fan Component and Total Noise for 

ADP at Takeoff Fan Speed.

50

55

60

65

70

75

80

85

90

95

100

105

110

115

120

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Inlet BB

Pred. Inlet Tones

Pred. Combi. Tones

Pred. Aft BB

Pred. Aft Tones
NASA/CR—2014-218421 82 

(d) Directivity Angle T = 120 deg

Figure 40 - Comparison of Experimental and Modified Fan Component and Total Noise for 

ADP at Takeoff Fan Speed.

50

55

60

65

70

75

80

85

90

95

100

105

110

115

120

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Heidmann

Pred. Tot.

Pred. BG

Pred. Inlet BB

Pred. Inlet Tones

Pred. Combi. Tones

Pred. Aft BB

Pred. Aft Tones

(e) Directivity Angle T = 150 deg

Figure 40 - Comparison of Experimental and Modified Fan Component and Total Noise for

 ADP at Takeoff Fan Speed.

50

55

60

65

70

75

80

85

90

95

100

105

110

115

120

100 1000 10000 100000

1/3-Octave-Band Center Frequency, f, Hz

Sound Pressure level, SPL, dB re 20 PPa

Exp. Tot.

Pred. Tot.

Pred. BG

Pred. Combi. Tones

Pred. Aft BB

Pred. Aft Tones

Heidmann
NASA/CR—2014-218421 83 

a) INLET BROADBAND

40

45

50

55

60

65

70

0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4

TIP RELATIVE MACH NUMBER

NORMALIZED LEVEL

HEIDMANN

CURRENT MODEL

b) INLET TONE

40

45

50

55

60

65

70

75

0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4

TIP RELATIVE MACH NUMBER

NORMALIZED LEVEL

HEIDMANN

CURRENT MODEL

Figure 41 - Comparison of normalized component levels for the current model and 

Heidmann’s model. 
NASA/CR—2014-218421 84 

c) AFT BROADBAND

40

45

50

55

60

65

70

0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4

TIP RELATIVE MACH NUMBER

NORMALIZED LEVEL

HEIDMANN

CURRENT MODEL

d) AFT TONE

40

45

50

55

60

65

70

0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5

TIP RELATIVE MACH NUMBER

NORMALIZED LEVEL

HEIDMANN

CURRENT MODEL

Figure 41 - concluded. Comparison of normalized component levels for the current model and 

Heidmann’s model. 
NASA/CR—2014-218421 85 

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Parts 1 and 2, 1982. 

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