AIAA–2009–3140

David M. Elliott, Richard P. Woodward, and Gary G. Podboy

Glenn Research Center, Cleveland, Ohio

Acoustic Performance of Novel Fan Noise Reduction 

Technologies for a High Bypass Model Turbofan at 

Simulated Flight Conditions

NASA/TM—2010-215841

April 2010
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AIAA–2009–3140

David M. Elliott, Richard P. Woodward, and Gary G. Podboy

Glenn Research Center, Cleveland, Ohio

Acoustic Performance of Novel Fan Noise Reduction 

Technologies for a High Bypass Model Turbofan at 

Simulated Flight Conditions

NASA/TM—2010-215841

April 2010

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

15th Aeroacoustics Conference (30th Aeroacoustics Conference)

cosponsored by AIAA and CEAS

Miami, Florida, May 11–13, 2009
Available from

NASA Center for Aerospace Information

7115 Standard Drive

Hanover, MD 21076–1320

National Technical Information Service

5301 Shawnee Road

Alexandria, VA 22312

Available electronically at http://gltrs.grc.nasa.gov

This work was sponsored by the Fundamental Aeronautics Program 

at the NASA Glenn Research Center.

Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2010-215841 1 

Acoustic Performance of Novel Fan Noise Reduction Technologies 

for a High Bypass Model Turbofan at Simulated Flight Conditions 

David M. Elliott, Richard P. Woodward, and Gary G. Podboy 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Abstract 

Two novel fan noise reduction technologies, over the rotor acoustic treatment and soft stator vane 

technologies, were tested in an ultra-high bypass ratio turbofan model in the NASA Glenn Research 

Center’s 9- by 15-Foot Low-Speed Wind Tunnel. The performance of these technologies was compared 

to that of the baseline fan configuration, which did not have these technologies. Sideline acoustic data and 

hot film flow data were acquired and are used to determine the effectiveness of the various treatments. 

The material used for the over the rotor treatment was foam metal and two different types were used. The 

soft stator vanes had several internal cavities tuned to target certain frequencies. In order to accommodate 

the cavities it was necessary to use a cut-on stator to demonstrate the soft vane concept.

Nomenclature 

OTR over the rotor 

OAPWL overall acoustic power level 

ADP Advanced Ducted Propulsor 

FeCrAlY Iron-Chromium-Aluminum-Yttrium alloy 

CoNiCrW Cobalt-Nickel-Chromium-Tungsten alloy 

TEB Trailing edge blowing 

BPF Blade passage frequency 

rpm revolutions per minute 

OASPL overall sound pressure level 

SPL sound pressure level 

dB decibel 

Hz Hertz 

PSD Power spectral density 

rpmc corrected revolutions per minute

I. Introduction 

As part of the NASA Fundamental Aeronautics Program’s Subsonic Fixed Wing Project, two novel 

fan noise reduction techniques were investigated for noise attenuation in turbofan engines. These 

consisted of over the rotor (OTR) acoustic treatment and soft stator vane. Both concepts had been 

investigated in earlier test programs in a low-speed, very low-pressure ratio research fan at the NASA 

Glenn Research Center’s Aeroacoustic Propulsion Laboratory (Ref. 1). Both had demonstrated significant 

noise reduction potential, with OTR showing 4 dB reduction in the fan inlet overall noise power level, 

and the soft vane showing 2 dB reduction in aft acoustic power levels. As a follow on, it was decided to 

test both concepts in a higher bypass ratio model with a pressure ratio more indicative of actual turbofan 

engines. The motivation for the use of the OTR is that placing treatment over the rotor should allow for 

attenuation of rotor self noise. The OTR could also have an additional use as part of a fan blade 

containment system. While a Cobalt-Nickel-Chromium-Tungsten (CoNiCrW) alloy was used in earlier 

tests, it was decided to try an Iron-Chromium-Aluminum-Yttrium (FeCrAlY) alloy for this test as well. In 
NASA/TM—2010-215841 2 

all, three OTR configurations were tried. The motivation behind the use of soft vane is that by integrating 

tuned internal cavities in the design of the vane, the soft stators may attenuate rotor-stator interaction 

noise. To accommodate the cavities, it was necessary to use a larger vane than would have been possible 

with the baseline cut-off stator. Therefore, a cut-on stator with nearly half the vane count and twice the 

chord and thickness as the baseline stator was designed and used for this purpose. For the sake of 

comparison, a low-count solid stator vane pack was also tested, as was the baseline cut-off stator. Sideline 

microphones and hot film sensors were used to determine the effectiveness of the OTR and soft stator 

vane technologies. These results will be discussed in this paper. 

II. Test Hardware 

The Pratt & Whitney Advanced Ducted Propulsor (ADP) was chosen as the model fan testbed for this 

test. The ADP is representative of an ultra high bypass ratio, low tip speed turbofan engine. The fan used 

for the OTR portion of the test was the Trailing Edge Blowing (TEB) fan, which has internal passages 

inside the rotor blades to allow the blowing of air from its trailing edge (Ref. 2). The blowing capability 

of this fan was not used for this test. This fan was chosen due to its relatively thick blade outer edge, 

which in turn allows a non-concave rub strip to be used. It was thought that this would simplify the 

fabrication of the metal foam rotor treatments. The TEB fan is made of composite material as opposed to 

titanium. This fan is 55.9 cm (22 in.) in diameter and there are 18 rotor blades with a simulated core 

having 63 inlet vanes and 16 support struts downstream of the inlet vanes. The blade tip gap to the casing 

treatment was approximately 0.076 cm (0.030 in.). The fan used for the soft stator testing is the ADP 

Fan 1. This fan is similar in aerodynamic performance to the TEB fan but without the hollow passages for 

the blowing (Ref. 3). In the baseline configuration, the ADP has a hard casing treatment and 45 solid 

short chord vanes (i.e., a cut-off design). The blade tip gap to the casing treatment for Fan 1 was 

approximately 0.140 cm (0.055 in.). For this test, three different OTR treatments were tried, a double 

depth exposed FeCrAlY, a double depth FeCrAlY with perforate cover sheet, and a double-depth 

CoNiCrW with perforate cover sheet. The overall design intent for the OTR treatments was to give 

attenuation for as wide a frequency range as possible. For the stator vane portion of the test, a 25 hard 

long chord stator set and a 25 soft long chord stator set were tried. Note that both represent a cut-on stator 

design. The 25 hard stator set was used to investigate the change in acoustics from a cut-off to cut-on 

stator design. The soft stator set was hollow with tuned internal cavities. The tuned cavities were exposed 

to the exterior of the vane by a mesh perforate covering the suction side of the vane. The soft stator vanes 

were designed for 2xBPF (blade passage frequency). A picture of the model fan as installed in the NASA 

Glenn Research Center’s 9- by15-Foot Low-Speed Wind Tunnel is shown in Figure 1. The FeCrAlY 

treatment with no rubstrip is shown in Figure 2 and the perforate covering the metal foam rubstrips is 

shown in Figure 3. A photograph of the soft stator vanes as installed in the ADP model is shown in 

Figure 4. 

III. Data Acquisition 

This test was conducted in the NASA Glenn Research Center’s 9- by15-Foot Low-Speed Wind 

Tunnel (Refs. 4 to 6). All data was taken at a wind tunnel flow of 0.1 Mach in order to provide flight 

clean-up. Data was acquired at corrected model speeds of 62, 76.6, 86, 95.4, and 100 percent. The 62, 86, 

and 100 percent speeds correspond to the rating conditions of approach, cutback, and takeoff, 

respectively. This corresponds to 5425, 7525, and 8750 corrected rpm’s. 

A. Sideline Acoustics 

Sideline acoustic measurements were obtained using a traversing microphone probe at a 2.24 m 

(88-in.) distance on a track parallel to the fan axis. Data were taken at 48 positions on the traverse at 2.5°

intervals ranging from 27.2° to 134.6° relative to the inlet of the model along the flow axis. The emitted 
NASA/TM—2010-215841 3 

angles of the traversing probe at 0.1 Mach number correspond to the range 24.6° to 130.6°. To obtain 

more angular extent, three fixed microphone probes were placed in the rear of the test section that 

correspond to measured angles of 140°, 150°, and 160°. At 0.1 Mach these angles transform to 136.4°, 

147.2°, and 158.1° emission angles, respectively. The microphones used were 0.635 cm (1/4-in.) in 

diameter. Data were taken at a sampling rate of 200 kHz in order to get a frequency range of up to 50 kHz 

or greater. This would permit increasing later data to full scale values. Corrections to the data have been 

made for microphone response, bullet nose receptivity, atmospheric attenuation and spherical spreading. 

All far-field data shown will be corrected to 30.48 cm (1 ft) lossless. The accuracy of the data system is 

on the order of ±1 dB. 

B. Hot Film 

A hot-film probe was used to obtain detailed flow field measurements in order to determine to what 

extent a porous liner changes the flow downstream of the tip of the fan relative to a conventional, 

nonporous liner. Separate surveys were conducted with the perforate cover sheet double CoNiCrW and 

the baseline hardwall liners installed in the model. Figure 5 shows a photograph of the hot-film probe 

installed in the NASA Fan model upstream of the stator vanes. The measurements were obtained by 

translating the probe to 25 equally-spaced radial locations in an axial plane 5.66 cm (2.23 in.) downstream 

of the tip trailing edge. Each radial survey covered approximately the outer half of the fan bypass duct; 

the outer and innermost measurement locations were 0.15 cm (0.06 in.) and 6.63 cm (2.61 in.) from the 

outer case, respectively. The hot-film measurements were made using a dual-sensor, TSI model 1246-20, 

cross-film probe. The cross-film designation stems from the x-pattern formed by the two cylindrical hotfilm sensors when viewed from a direction above and perpendicular to the two parallel planes containing 

the sensors. Since these two planes are very close together (separated by only about 1 mm) the two 

sensors which form the x-pattern can be thought of as lying in one plane. A cross-film probe allows the 

flow angle in this plane and the flow speed to be measured. The hot-film data presented in this report 

were obtained using a probe which had the x-pattern oriented radially, therefore this probe was used to 

measure the radial flow angle and the flow speed. 

IV. Results 

When testing the OTR treatments with a perforate cover sheet, an interesting phenomenon occurred. 

In this instance damage was done to the composite blade tip and edge. The blade tip was worn away and 

the edge became serrated. The serrations in the blade edge seemed to match up with the holes in the 

perforate cover sheet. This damage is shown in Figure 6. At this time it is speculated that the cause of this 

is high pressure air being jettisoned from the treatment through the perforate cover sheet holes and thus 

eroding the blades. It was possible to repair the blades, although it could not be guaranteed that the blades 

were restored to the exact original condition. Another consequence of the damage was that later runs 

using the OTR and perforate cover sheet were done more cautiously. In some later runs with OTR and 

perforate cover sheet, only the lower fan speeds were obtained, primarily the CoNiCrW metal foam. It 

should also be noted that the blade tip gap was changed to also try and minimize the blade deterioration. 

The results discussed in this paper will have a 0.030 in.-tip gap for the OTR analysis and a 0.050in.-tip 

gap for the Soft Stator comparisons. 

A. Sideline Acoustic Results 

1. Over the Rotor Treatment Comparisons 

It is beneficial to examine actual sound pressure level (SPL) spectra results to get an idea of what the 

treatments are doing with respect to frequency. Figure 7 shows SPL in terms of power spectral density 

(PSD) versus frequency of the hardwall and three OTR treatments at 62 percent speed and 41° emission 
NASA/TM—2010-215841 4 

angle. The first thing to note for this plot is the increase in noise for the exposed FeCrAlY configuration, 

especially in the lower frequency range. There is no consistent result regarding BPF tones, but there does 

appear to be a lower noise signature for the OTR treatments in the high frequency broadband. Figure 8 

shows the 62 percent speed at the aft angle of 128°. There is no discernable difference in the hardwall 

versus perforate cover sheet OTR treatments, however once again the exposed OTR treatment shows a 

higher noise level at low frequency. Figures 9 and 10 show the spectral results at 86 percent speed for the 

inlet angle of 33° and the aft angle of 128°, respectively. The 33° emission angle was shown as opposed 

to the previous 41° angle data to get a wider perspective of what the inlet results are. The results are 

similar to the 62 percent speed with the exposed OTR treatments being noisier in the lower frequency 

range while the perforate cover sheet OTR treatments exhibit a slight advantage in broadband at higher 

frequencies for the inlet. 

To get a better idea of what the overall noise changes from configuration to configuration are, it is 

advantageous to look at the overall sound pressure level (OASPL) versus angle for the different speeds. 

These OASPL values are for the 1 to 50 kHz range in order to remove low frequencies where the 9- by 

15-Foot Low-Speed Wind Tunnel is non-anechoic. Figures 11 through 15 through show the OASPL 

directivities for different speeds. Once again it is seen that the exposed OTR treatment is noisier than the 

other configurations. For the 76.6 and 86 percent speeds, over an inlet angle range of 20° to 

approximately 50° there is reduction on the order of 2 dB on OASPL basis for the perforate cover sheet 

OTR treatments. The perforate cover sheet OTR treatments do not show a difference relative to the 

baseline in other angle ranges. 

Overall Power Levels can be used to get a good summary of how effective the OTR treatments are. 

Figure 16 shows OAPWL versus speed for the different configurations. Like the OASPL values, these 

power levels are for the 1 to 50 kHz range. This plot shows the small advantage on the order of 1 dB for 

the perforate cover sheet OTR treatments for the intermediate speeds of 76.6 and 86 percent. The higher 

noise level of the exposed OTR treatment at all speeds is shown to be on the order of 1 dB. 

2. Soft Stator Vane Comparisons 

During the testing of the 25 hard and soft stator vanes, it was discovered that an extraneous tone and 

its harmonics were present in the 9- by 15-Foot Low-Speed Wind Tunnel at 86 percent speed. This tone 

does not appear to be fan or model related. It has been speculated to be drive rig valve noise. The 

presence of the extraneous noise overwhelms the results for the 86 percent speed and thus they will not be 

used extensively. Figures 17 through 20 show example spectral results of the soft stator. One notable 

aspect of these results is the reduction in high frequency broadband above 6 kHz by going successively 

from the 45 vane hard stator to the 25 vane hard stator and finally to the 25 vane soft stator 

configurations. This result is on the order of 1 dB for the 45 hard vane (i.e., cut-off design) to 25 hard 

vane (i.e., cut-on design) change, and somewhat less from the 25 hard vane to 25 soft vane configuration. 

The 1 dB reduction is due entirely to the change from the cut-off stator to a cut-on stator. The smaller 

reduction shows what the benefit of the soft stator cavities entails. There is much tradeoff for the BPF 

tones and no configuration shows a decided advantage in this area, although the 100 percent speed 31°

emission angle data and to a lesser extent 100 percent speed 130° emission angle data show the 

disadvantage of abandoning the cut-off design since there is an increase in most of the lower BPF tones. 

As for the OTR results, integrating over all angles gives OAPSL directivity for each speed and these are 

shown in Figures 21 through 24. At 62 percent speed, an advantage of approximately 1 dB is seen for the 

change from 45 hard stators to 25 hard stators, and another approximately 1 dB going to the 25 soft 

stators for the inlet quadrant. This reduction is not as wide spread in the aft quadrant, in fact, in some 

angle regions no benefit is seen. At 76.6 percent speed the results are different in that the inlet shows no 

advantage for the 25 soft stators as compared to the 45 hard stators while there is a penalty for the 25 hard 

stators. There is a noise penalty for both of the 25 vane stators in the aft quadrant at the 76.6 percent 

speed. At 95.4 percent speed, there is conflicting results depending on what angle range is examined and 

no configuration shows an overall advantage. Lastly at 100 percent speed it appears the 25-stator 
NASA/TM—2010-215841 5 

configurations show a penalty on the order of 3 to 4 dB at the peak noise angle of 130°. Referring back to 

the inlet PSD spectra for 100 percent speed shows that there is much more tonal energy for the 25 hard 

stator configuration. These tones show up as non-BPF tones especially around the 4 to 6 kHz range. This 

phenomenon can sometimes be associated with blade-to-blade variation, but since the same rotor was 

used for all 3 stator packs, this tonal noise is probably excited by the different stator vane configuration. 

In general it appears that the 25 hard vane and 25 soft vane provide most of their advantage at the lower 

speed. Figure 25 shows OAPWL for the three configurations versus speed. The low speed advantage of 

the 25 vane configurations can be seen at the low speed. For the other speeds where useful data exists, it 

should be noted that while the 25 hard stator configuration has a small noise penalty relative to the 45 

hard stator, the soft vane technology brings the noise level back down to the 45 stator level. This fact 

could be useful for when cutoff needs to be abandoned for non-noise reasons. Then the soft stator 

technology could be utilized to lower the noise cutoff levels. 

B. Hot Film Results for Over the Rotor Treatment 

Hot-film results obtained with the fan operating at 62, 86, and 100 percent speed are provided in 

Figures 26 to 28, respectively. Each figure shows a comparison between the flow fields developed 

downstream of the fan tip with the hardwall and perforate cover sheet double CoNiCrW liners installed in 

the model. Color contour plots of mean flow speed (in. ft/s), mean radial flow angle (in degrees, with 

positive outward), the standard deviation of the flow speed (in. ft/s), and turbulence intensity (a 

percentage, determined by dividing the standard deviation of the flow speed by the mean flow speed) are 

provided for each of the six fan speed/liner combinations. The view depicted is from downstream looking 

upstream at the “average passage” flow occurring in the axial plane of the measurements; the rotor blades 

would rotate clockwise in this view. The approximate locations of the tip vortices are depicted by the 

black dots overlaid on top of the radial flow angle contour plots. As shown, the center location of the tip 

vortex was assumed to coincide with the circumferential location of the abrupt change in radial flow angle 

in the tip region of the blade passage. 

A comparison of the data obtained at the different fan speeds indicates that the changes in the tip flow 

which result from switching from the hardwall to the perforate cover sheet liner becomes more significant 

as the fan speed increases. At low fan speed (Fig. 26), the mean flow speed, the standard deviation of the 

flow speed, and the turbulence intensity changed very little when the hardwall liner was replaced by the 

perforate cover sheet liner. The primary effect of the perforate cover sheet liner was to cause a slight 

change in the circumferential location of the tip vortex. The tip vortex was found to be further away from 

the blade from which it was created when the perforate cover sheet liner was installed in the model. This 

may indicate that the tip vortex “releases” from the blade sooner (i.e., at an axial location closer to the 

leading edge of the blade) when a porous as opposed to a hardwall liner is installed outboard of the fan 

tip. A similar change in the circumferential location of the tip vortex is also seen in the 86 and 

100 percent fan speed data (see Figs. 27 and 28). At these higher speeds this change is also accompanied 

by a change in both the mean flow speed and the unsteadiness of the flow downstream of the fan tip; the 

mean flow speed decreases and both the unsteadiness (turbulence intensity) and the thickness of the 

turbulent region along the outer surface of the fan duct increase when the perforate cover sheet as 

opposed to the hardwall liner is installed in the model. These changes become more dramatic as the rotor 

speed increases from 86 to 100 percent speed. These changes are thought to result from the flow of air in 

and out of the holes in the perforate cover sheet liner. The increased turbulence along the outer wall of the 

fan duct is likely to lead to increased rotor/stator interaction broadband noise which would tend to 

counteract the noise attenuation effects of the perforate cover sheet liner. In order for the perforate cover 

sheet liner to result in a net decrease in broadband noise, it must attenuate more noise than would be 

created by this increase in turbulence. 
NASA/TM—2010-215841 6 

V. Conclusion 

While some implementation problems did arise during this test, the potential viability of OTR and 

soft stator technology was shown. The OTR configurations with perforate covering showed a slight 

attenuation in inlet broadband noise. They also showed some OASPL reduction on the order of 1 to 2 dB 

for two intermediate model speeds of 76.6 and 86 percent This translates to an OAPWL reduction of 1 dB 

at these two speeds. There was very little difference at the other three speeds tested. The OTR treatment 

with no perforate cover sheet was actually noisier at most conditions when compared to the hardwall 

baseline. This was generally on the order of 1 dB. While the perforate cover sheet OTR treatments did not 

give the noise reductions seen in earlier tests, this test showed the concept in a higher speed higherpressure ratio device. The phenomenon of blade erosion when the OTR with perforate cover sheets were 

used needs to be investigated more fully in the future to determine the exact mechanism causing this. It 

has been noted in other tests that the use of a metal blade or the incorporation of OTR treatment into the 

rubstrip in a different manner may alleviate this problem. 

The 25 count stator vane configurations did show high frequency broadband noise reduction as 

compared to the 45 count stator vanes over a wide frequency range. The 25 soft stator vane configuration 

had more of this broadband noise reduction than the 25 hard stator configuration. The reduction of the 25 

soft stator configuration relative to the 25 hard stator configuration was on the order of 1 dB. The 25 

stator vane hardware did show some inlet noise reduction at the lowest speed, but at the higher speeds the 

addition of tonal energy negated the inlet advantage seen at the lower speed. The low speed inlet noise 

reduction produced by the 25 stator vanes was on the order of 1dB. An important aspect of the soft stators 

is that the noise level was reduced to near the 45 stator vane configuration for the higher speeds. This is 

very useful if a cutoff stator design needs to be abandoned for non-noise reasons. In this situation the soft 

stator vanes can reduce the noise of a cut-on stator set closer to a cutoff stator set. 

The hot film data generally gave an explanation as to why the OTR treatments did not attenuate noise 

well at the higher speeds. The flow speed and turbulence intensity downstream of the fan change very 

little at low speeds when going from a hardwall to OTR treatment. At higher speeds, changes in mean 

flow speed and turbulence intensity along with an increase in the thickness of the turbulent region may be 

adding to rotor/stator interaction noise thereby offsetting any reduction from the OTR treatment. Flow in 

and out of the perforate cover sheet holes may be causing the changes at higher speeds. 

References 

1. Sutliff, D.L. and Jones, M.G., “Foam-Metal Liner Attenuation of Low-Speed Fan Noise,” AIAA 

Paper 2008–2897, Aug. 2008. 

2. Woodward, Richard P., Fite, E. Brian, and Podboy, Gary G., “Noise Benefits of Rotor Trailing Edge 

Blowing for a Model Turbofan,” AIAA–2007–1241, January, 2007. 

3. Jeracki, R.J., “Comprehensive Report of Fan Performance from Duct Rake Instrumentation on 1.294 

Pressure Ratio, 806 ft/sec Tip Speed Turbofan Simulator Models,” NASA/TM—2006-213863, Feb. 

2006. 

4. Dahl, M.D., and Woodward, R.P., “Comparison Between Design and Installed Acoustic 

Characteristics of the NASA Lewis 9-by 15-Foot Low-Speed Wind Tunnel Acoustic Treatment,” 

NASA TP–2996, Apr. 1990.

5. Dahl, M.D., and Woodward, R.P., “Background Noise Levels Measured In the NASA Lewis 9- by 

15-Foot Low-Speed Wind Tunnel,” NASA TP–3274, Nov. 1992.

6. Woodward, R.P., and Dittmar, J.H., “Background Noise Levels Measured in the NASA Lewis 9- by 

15- Foot Low-Speed Wind Tunnel,” NASA TM–106817/AIAA–95–0720, 1995. 
NASA/TM—2010-215841 7 

Figure 1.—The Advanced Ducted Propulsor model as installed in the NASA Glenn 

Research Center’s 9- by 15-Foot Low-Speed Wind Tunnel. Microphones are 

visible at left. 

Figure 2.—The FeCrAlY metal foam OTR treatment with no perforate cover sheet 

as installed in the ADP model. 
NASA/TM—2010-215841 8 

Figure 3.—A metal foam OTR treatment with perforate cover sheet installed in the 

ADP model. 

Figure 4.—The soft stator vanes behind the rotor in the ADP model. 
NASA/TM—2010-215841 9 

Figure 5.—Photograph of a hot-film probe installed in the NASA Fan model. 

Figure 6.—Damage on the composite blade which coincides with the holes in the 

perforate covering the metal foam OTR treatment. 
NASA/TM—2010-215841 10 

 Figure 7.—Hardwall and OTR treatments, PSD versus frequency at 62 percent 

model speed and 41° emission angle, 0.030 in. blade tip gap and 45 hard stator 

vanes. 

Figure 8.—Hardwall and OTR treatments, PSD versus frequency at 62 percent 

model speed and 128° emission angle, 0.030 in. blade tip gap and 45 hard 

stator vanes. 
NASA/TM—2010-215841 11 

Figure 9.—Hardwall and OTR treatments, PSD versus frequency at 86 percent 

model speed and 33° emission angle, 0.030 in. blade tip gap and 45 hard 

stator vanes. 

Figure 10.—Hardwall and OTR treatments, PSD versus frequency at 86 percent 

model speed and 128° emission angle, 0.030 in. blade tip gap and 45 hard 

stator vanes. 
NASA/TM—2010-215841 12 

Figure 11.—Hardwall and OTR treatments, OASPL versus emission angle at 62 percent 

model speed, 0.030 in. blade tip gap and 45 hard stator vanes. 

 Figure 12.—Hardwall and OTR treatments, OASPL versus emission angle at 76.6 percent 

model speed, 0.030 in. blade tip gap and 45 hard stator vanes. 
NASA/TM—2010-215841 13 

Figure 13.—Hardwall and OTR treatments, OASPL versus emission angle at 86 percent 

model speed, 0.030 in. blade tip gap and 45 hard stator vanes. 

Figure 14.—Hardwall and OTR treatments, OASPL versus emission angle at 95.4 percent 

model speed, 0.030 in. blade tip gap and 45 hard stator vanes. 
NASA/TM—2010-215841 14 

Figure 15.—Hardwall and OTR treatments, OASPL versus emission angle at 100 percent 

model speed, 0.030 in. blade tip gap and 45 hard stator vanes. 

Figure 16.—Hardwall and OTR treatments, OAPWL versus corrected rpm (rpmc), 

0.030 in. blade tip gap and 45 hard stator vanes. 
NASA/TM—2010-215841 15 

Figure 17.—Comparison of three stator configurations, PSD versus frequency at 

62 percent model speed and 31° emission angle, Fan 1, hardwall rubstrip. 

Figure 18.—Comparison of three stator configurations, PSD versus frequency at 

62 percent model speed and 130° emission angle, Fan 1, hardwall rubstrip. 
NASA/TM—2010-215841 16 

 Figure 19.—Comparison of three stator configurations, PSD versus frequency 

at 100 percent model speed and 31° emission angle, Fan 1, hardwall rubstrip. 

 Figure 20.—Comparison of three stator configurations, PSD versus frequency at 

100 percent model speed and 130° emission angle, Fan 1, hardwall rubstrip. 
NASA/TM—2010-215841 17 

 Figure 21.—Comparison of three stator configurations, OASPL versus emission angle at 

62 percent model speed, Fan1, hardwall rubstrip. 

 Figure 22.—Comparison of three stator configurations, OASPL versus emission angle at 

76.6 percent model speed, Fan1, hardwall rubstrip. 
NASA/TM—2010-215841 18 

 Figure 23.—Comparison of three stator configurations, OASPL versus emission angle at 

95.4 percent model speed, Fan1, hardwall rubstrip. 

 Figure 24.—Comparison of three stator configurations, OASPL versus emission angle at 

100 percent model speed, Fan1, hardwall rubstrip. 
NASA/TM—2010-215841 19 

Figure 25.—Comparison of three stator configurations, OAPWL versus corrected RPM, Fan1, 

hardwall rubstrip. 

Figure 26.—Comparison of tip wake flows measured at 62 percent speed with 

hardwall and perforate cover sheet double CoNiCrW liners. 
NASA/TM—2010-215841 20 

Figure 27.—Comparison of tip wake flows measured at 86 percent speed with 

hardwall and perforate cover sheet double CoNiCrW liners. 

Figure 28.—Comparison of tip wake flows measured at 100 percent speed with 

hardwall and perforate cover sheet double CoNiCrW liners. 
REPORT DOCUMENTATION PAGE Form Approved 

OMB No. 0704-0188 

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PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 

1. REPORT DATE (DD-MM-YYYY)

01-04-2010 

2. REPORT TYPE

Technical Memorandum 

3. DATES COVERED (From - To)

4. TITLE AND SUBTITLE

Acoustic Performance of Novel Fan Noise Reduction Technologies for a High Bypass Model 

Turbofan at Simulated Flight Conditions 

5a. CONTRACT NUMBER

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

Elliott, David, M.; Woodward, Richard, P.; Podboy, Gary, G. 

5d. PROJECT NUMBER

5e. TASK NUMBER

5f. WORK UNIT NUMBER

WBS 561581.02.08.03.18.02 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration 

John H. Glenn Research Center at Lewis Field 

Cleveland, Ohio 44135-3191 

8. PERFORMING ORGANIZATION

 REPORT NUMBER

E-17102 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration 

Washington, DC 20546-0001 

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 ACRONYM(S)

NASA 

11. SPONSORING/MONITORING

 REPORT NUMBER

NASA/TM-2010-215841 

12. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified-Unlimited 

Subject Category: 71 

Available electronically at http://gltrs.grc.nasa.gov 

This publication is available from the NASA Center for AeroSpace Information, 443-757-5802

13. SUPPLEMENTARY NOTES

14. ABSTRACT

Two novel fan noise reduction technologies, over the rotor acoustic treatment and soft stator vane technologies, were tested in an ultra-high 

bypass ratio turbofan model in the NASA Glenn Research Center’s 9- by 15-Foot Low-Speed Wind Tunnel. The performance of these 

technologies was compared to that of the baseline fan configuration, which did not have these technologies. Sideline acoustic data and hot 

film flow data were acquired and are used to determine the effectiveness of the various treatments. The material used for the over the rotor 

treatment was foam metal and two different types were used. The soft stator vanes had several internal cavities tuned to target certain 

frequencies. In order to accommodate the cavities it was necessary to use a cut-on stator to demonstrate the soft vane concept.

15. SUBJECT TERMS

Aeroacoustics; Acoustic attenuation; Acoustic measurement; Aircraft noise; Engine noise 

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF

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26 

19a. NAME OF RESPONSIBLE PERSON

STI Help Desk (email:help@sti.nasa.gov) 

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443-757-5802 

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