Richard P. Woodward and Christopher E. Hughes

Glenn Research Center, Cleveland, Ohio

Acoustic Performance of an Advanced Model

Turbofan in Three Aeroacoustic Test Facilities

NASA/TM—2012-217608

June 2012
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Richard P. Woodward and Christopher E. Hughes

Glenn Research Center, Cleveland, Ohio

Acoustic Performance of an Advanced Model

Turbofan in Three Aeroacoustic Test Facilities

NASA/TM—2012-217608

June 2012

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135
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Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2012-217608 1 

Acoustic Performance of an Advanced Model Turbofan 

in Three Aeroacoustic Test Facilities 

Richard P. Woodward and Christopher E. Hughes 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Abstract 

A model advanced turbofan was acoustically tested in the NASA Glenn 9- by 15-Foot-Low-Speed 

Wind Tunnel (LSWT), and in two other aeroacoustic facilities. The Universal Propulsion Simulator 

(UPS) fan was designed and manufactured by the General Electric Aircraft Engines (GEAE) Company, 

and featured active core, as well as bypass, flow paths. The reference test configurations were with the 

metal, M4, rotor with hardwall and treated bypass flow ducts. The UPS fan was tested within an airflow 

at a Mach number of 0.20 (limited flow data were also acquired at a Mach number of 0.25) which is 

representative of aircraft takeoff and approach conditions. Comparisons were made between data acquired 

within the airflow (9×15 LSWT and German-Dutch Wind Tunnel (DNW)) and outside of a free jet 

(Boeing Low Speed Aero acoustic Facility (LSAF) and DNW). Sideline data were acquired on an 89-in. 

(nominal 4 fan diameters) sideline using the same microphone assembly and holder in the 9×15 LSWT 

and DNW facilities. These data showed good agreement for similar UPS operating conditions and 

configurations. Distortion of fan spectra tonal content through a free jet shear layer was documented, 

suggesting that in-flow acoustic measurements are required for comprehensive fan noise diagnostics. 

However, there was good agreement for overall sound power level (PWL) fan noise measurements made 

both within and outside of the test facility airflow. 

Introduction 

The Universal Propulsion Simulator (UPS) fan was designed and built by General Electric Aircraft 

Engines (GEAE) to explore advanced fan stage concepts for future quiet turbofan engines. The fan stage 

was tested in the NASA Glenn 9- by 15-Foot-Low Speed Wind Tunnel (LSWT) using several rotor 

designs. These acoustic tests explored the fan performance with unswept, forward-swept, and aft-swept 

rotors of both metal and composite construction. The fan stage was tested with, and without acoustic 

treatment on the outer wall of the bypass flow duct. 

The UPS fan was also tested in the Boeing Low Speed Aero acoustic Facility (LSAF) free jet, and in 

the German-Dutch Wind Tunnel (DNW) free jet facility using the baseline “M4” rotor with and without 

bypass duct acoustic treatment. Tests in the DNW and 915 facilities were performed in air flowing at a 

Mach number of 0.20; while the LSAF tests were conducted with a free jet flow at Mach numbers of 0.20 

and 0.25. These airflows are representative of aircraft takeoff and approach conditions. 

Acoustic test results from these three facilities provided a unique opportunity to compare and quantify 

data quality and acquisition techniques for far field acoustic data acquired both within the flow field 

(NASA 915; DNW inflow acoustic surveys), and outside of a free jet shear layer (Boeing LSAF and 

DNW out of flow surveys). 

Reference 1 is a GEAE report comparing acoustic results for the UPS fan in these three facilities from 

the perspective of evaluating the 915 LSWT data quality relative to that obtained in the LSAF and DNW 

facilities. Toward that end, Reference 1 concludes that the 915 LSWT is a “viable test facility for quiet, 

high-bypass ratio, model-fan-rig, acoustic testing.” The current report, based on NASA evaluation of the 

data, confirms this conclusion and also explores aspects of the UPS acoustic data beyond what was 

presented in Reference 1. 
NASA/TM—2012-217608 2 

Description of Test 

Research Fan 

The UPS fan is representative of future, high bypass ratio turbofan engines. Figure 1 is a crosssectional sketch of the UPS fan. The bypass rotor diameter is 22.0 in. The bypass rotor-vane ratio is 

adequate to achieve cutoff of the fundamental interaction tone (Refs. 2 and 3). The UPS fan has an active 

core (or booster) stage which includes a powered rotor (same rotational speed as the bypass fan) with inlet 

and outlet stators. The core flow passage also has deswirl struts slightly downstream of the core outlet 

guide vanes, and aft load struts somewhat further downstream. The core passage also has a full passage 

screen to adjust flow rates, and subsequently stage bypass ratio. Table 1 is a listing of the fan design 

parameters. 

UPS fan stage results presented herein are for the M4 unswept metal rotor. Additional acoustic tests 

performed in the 915 LSWT allowed investigation of rotor forward and aft sweep effects, and relative 

performance of composite versus metal blade construction (Ref. 4). The rotor was powered by a high 

pressure air turbine drive (Ref. 5) with the drive air and instrumentation supplied through a support strut 

mounted on the test facility floor. 

The acoustic results reported herein are for the UPS bypass fan stage with either hard or acoustically 

treated walls. Figure 1 shows the presence of acoustic treatment in the inlet and bypass ducts. The 

acoustic treatment was always present on the inner wall of the bypass duct upstream and downstream of 

the bypass stator. The inlet and outer wall bypass duct treatment panels were removable and could be 

replaced with hard-wall panels. However for the tests reported here, the acoustic treatment was always 

present on the outer bypass duct wall between the rotor and the stator. Letter designations are used in this 

report to distinguish between different configurations of hard wall and treated wall panels in the inlet and 

the outlet section of the bypass duct. The letter “H” designates a hard-wall panel and the letter “T” 

designates a treated panel. Thus, the hard-wall configuration is designated “HTH” and the completely 

treated configuration is designated “TTT.” 

Test Facilities and Acoustic Instrumentation 

The UPS fan was tested in three “world class” aeroacoustic facilities. These facilities included the 

915 LSWT, the Boeing free-jet facility (LSAF), and the German-Dutch large free-jet facility, (DNW). 

Testing in these three facilities provided comparative acoustic results for the M4 unswept metal rotor with 

hard-wall (HTH) and two treated bypass duct configurations. These tests also afforded an opportunity to 

compare relative merits of taking fan acoustic data within an airflow (915 LSWT and DNW) and outside 

of a free jet (LSAF and DNW). 

NASA Glenn 915 LSWT 

The 915 LSWT is located in the low speed return leg of the 86 Supersonic Wind Tunnel (Fig. 2). 

The tunnel test section walls, floor and ceiling had acoustic treatment to produce an anechoic test 

environment (Refs. 6 to 8). Figure 3 is a sketch of the test fan installed in the 915 LSWT. Sideline 

acoustic data were acquired with a computer-controlled translating microphone probe (also seen in the 

photograph of Figure 4) and with an array of fixed microphones mounted on the tunnel wall. The 

translating microphone probe acquired data at 48 sideline geometric angles from 29 to 138 relative to 

the fan inlet highlight. The translating probe traverse was at 89 in. from the fan rotational axis 

(approximately four fan diameters). The acoustic data were acquired through a digital computer system 

and stored for post-run analysis. Acoustic data were acquired in a Mach number 0.20 flow, which is 

representative of takeoff and approach conditions and provides flight acoustic conditions (Ref. 9). 

 
NASA/TM—2012-217608 3 

Constant bandwidth spectra were acquired in the 915 LSWT at 6 and 118 Hz bandwidths at each 

translating probe position. These constant bandwidth spectra were electronically merged and used to 

generate 1/3rd octave spectra. The 915 LSWT results presented herein are in terms of both constant 

bandwidth and 1/3rd octave spectra. The survey data were instrument corrected and corrected for 

atmospheric attenuation using Doppler-shifted frequencies over the propagation path (lossless acoustic 

data). Geometric (observed) sideline angles were converted to emission angles according to the 

relationship: 

em = geom -sin-1(Mosin geom) 

where em and geom are, respectively, the emission and observed sideline angles, and Mo is the test 

section Mach number. 

There was initially some concern as to the validity of translating microphone probe survey data as 

opposed to data acquired with conventional fixed microphones. The fixed wall microphone array was 

vertically staggered to minimize wake interaction from upstream microphone holders. Acoustic data 

acquired during the 915 LSWT UPS test were used to compare fixed and translating microphone data 

quality (Ref. 8). Wakes from upstream microphone holders were seen to persist a significant distance 

downstream, thus possibly compromising data quality from downstream fixed microphones. Also, the 

vertical stagger used to minimize this wake interaction introduced a new, azimuthal variation in the 

acquired data—a problem not associated with a single traversing microphone. Otherwise, data quality 

from both fixed and translating microphones was shown to be equivalent. Acoustic data presented herein 

are for the translating microphone probe. 

Boeing LSAF 

The Boeing Low Speed Aeroacoustic Facility (Ref. 10) (LSAF) allows aeroacoustic testing in a free 

jet environment, rather than within the tunnel flow as provided by the NASA LSWT. Figure 5 is shows 

the mic placement relative to the UPS fan installed in the LSAF. Data were taken with free jet Mach 

numbers of 0.20 and 0.25. Acoustic data were only acquired outside of the free jet due to free jet size 

limitations. Data were acquired by Boeing and GEAE. These data were instrument corrected and adjusted 

for free jet shear layer effects and atmospheric attenuation, and are primarily presented as lossless 1/3rd

octave results at corresponding emission angles. Limited constant bandwidth spectra were also acquired; 

however these data were not provided with absolute noise levels. 

German-Dutch Wind Tunnel DNW 

The DNW is a large free-jet facility (Refs. 11 to 13) which permits acoustic data acquisition both 

within the free jet (as for the NASA LSWT) and outside the shear layer (LSAF). Figures 6 and 7 are 

sketches which show the UPS installation in the DNW facility. Acoustic data were acquired by DNW and 

GEAE personnel and as constant bandwidth (36 Hz) and 1/3rd octave spectra. Acoustic data were acquired 

at three sidelines distances: 

 Fixed microphones outside of the free jet on a 36 ft sideline. 

 Within the free jet on a 120-in. sideline using the DNW translating microphone assembly. 

 Within the free jet on an 88-in. sideline using the same holder and microphone as was used for the 

NASA 915 UPS tests. 

The acoustic data were likewise instrument corrected and adjusted for atmospheric attenuation. Data 

for the 36 ft sideline were also corrected for the free jet shear layer. The DNW data are presented in terms 

of sideline emission angles relative to the UPS inlet highlight. 
NASA/TM—2012-217608 4 

Results and Discussion 

Aerodynamic Performance 

NASA 915 LSWT Results 

Limited aerodynamic results are available for the UPS tests in the 915 LSWT. Data were taken at a 

tunnel Mach number of 0.20 over a range of fan speeds from 7400 to 14000 corrected revolutions per 

minute (rpm) (see Table 2). The fan design speed (Table 1) was 12647 rpm for the baseline (M4) rotor. 

The UPS fan was tested in the 915 LSWT with the baseline rotor with and without bypass duct 

acoustic treatment. Acoustic treatment was always present on the inner flow surface of the bypass duct 

(see Fig. 1). Data were taken with acoustic treatment on the outer surface of the bypass duct and without 

acoustic treatment on the outer surface. 

A representative aerodynamic fan map of pressure ratio versus bypass corrected weight flow is shown 

in Figure 8. These results are for the UPS tests in the 915 LSWT for the M4 rotor in the hardwall and 

acoustic duct treatment configurations. These results show little change in performance between these 

three configurations. 

Acoustic Performance 

NASA 915 LSWT Results 

Effective Perceived Noise 

The effective perceived noise level (EPNL) provides a subjective measure of the aircraft flyover noise 

levels. This value is derived from the flyover sound pressure level profiles and is a function of frequency, 

duration, and tone content. Effective perceived noise levels were calculated by GEAE for a 1000-ft. 

flyover using the 915 LSWT results. Assumptions were made in generating the noise profiles since the 

stipulated 10 dB sideline noise reduction from peak levels was typically not captured by the tunnel 

acoustic instrumentation for aft angles. A scale factor of 5.6 was used. EPNL values are calculated from 

“full-scale engine” sound pressure data up to 10 kHz. Thus model acoustic data up to about 60 kHz were 

utilized with this scale factor. Figure 9 compares EPNL levels for the baseline M4 rotor at 0 fan axis 

angle-of-attack. Results are shown for the hard-wall (HTH) and treated (TTT) bypass duct configurations. 

Sideline Acoustic Results 

Figure 10 shows the nominal core and bypass blade-vane interaction frequencies as a function of fan 

speed. This figure is included to assist in identifying tone orders in subsequent acoustic spectra. 

Figure 11 shows constant bandwidth (6 Hz) spectra for the M4 rotor at a 74 sideline emission angle at 

12 k corrected rpm (rpmc). There is significant multiple pure tone (MPT) content for the results for the 

hardwall (HTH) configuration in Figure 11. The spectrum with duct acoustic treatment (TTT) in place 

shows the treatment effectiveness in reducing these MPT levels at this upstream sideline location. 

Figure 12 presents selected sideline 1/3rd octave band directivities for the two test configurations. 

Results are shown for a subsonic rotor tip speed (8.2 k rpmc) and a transonic speed (12 k rpmc). The 

broadband noise results at 8 kHz and 8.2 k rpmc (Fig. 12(a)) show noise levels for the hard-wall 

configuration (HTH) to be highest at the downstream sideline angles. Duct acoustic treatment (TTT) 

reduced noise levels at all measured sideline angles. Similar results are seen for the bypass 3 BPF tone 

(Fig. 12(b)). There is considerable MPT content in the noise spectra at 12 k rpmc (Figs. 12(c) to (e)) at 

forward emission angles, showing the effectiveness of the acoustic treatment for reducing MPT levels. 
NASA/TM—2012-217608 5 

Boeing LSAF Results 

The UPS fan was tested in the Boeing LSAF free-jet facility. Far field microphones were located 

outside of the free jet as shown in Figure 5. Acoustic UPS data provided by GEAE to NASA were for the 

M4 metal rotor in the HTH, HTT, and TTT configurations. (The HTT configuration was with a hard-wall 

inlet duct, and acoustic treatment between the bypass rotor and stator as well as downstream of the fan 

stage.) Table 3 lists the LSAF data points available for this analysis. These data come from two separate 

LSAF entries. The first data set, designated “Entry 2” had the far field microphone array at a 6.1-m (20-ft) 

distance from the model centerline in the aft direction and on a 6.1-m (20-ft) radius in the upstream 

direction as illustrated in Figure 5. For this entry data were taken for the UPS model within the free jet at 

velocities with Mach numbers of 0.20 and 0.25. The second data entry, “Entry 3,” had a free jet velocity 

with Mach number 0.20 and microphones that were located in a similar pattern with radius and sideline 

distances of 4.6-m (15-ft). 

LSAF and 915 LSWT Directivities 

Figures 13 to 24 compare 1/3rd octave directivities from LSAF with comparable 915 LSWT results. 

In particular, these figures compare the relative effectiveness of the bypass duct acoustic treatment for the 

UPS fan as installed in these two facilities. A second objective is to validate the relatively close 

(4 fan diameter) sideline used in the NASA 915 LSWT to obtain far field data. The concern is that noise 

radiates from both the fan inlet and exhaust, and noise data taken too close to the model will not show 

true far field directivities. The LSAF data were adjusted to an 88-in. sideline for comparison with the 

915 LSWT data. 

Figure 13 shows 1/3rd octave directivities at 8.2 k rpmc and 5 kHz (spectral broadband region). Data 

are shown comparing the TTT and HTH results from the 915 LSWT with similar results from the two 

LSAF entries. A directivity curve at windmill condition is included in the 915 LSWT comparisons to 

show that fan noise data, even at this low fan speed, is above tunnel background noise levels. The general 

trend is that the acoustic liner was somewhat more effective in the LSAF tests than what was observed for 

the 915 LSWT tests. The reason for this difference is unknown, but may relate to slight differences in 

the fan build (segment alignment, seals, etc.) for the two tests. The data trends are similar between the 

915 LSWT and LSAF Entry 2 data—in both instances the liners were much more effective at aft 

sideline angles. The LSAF Entry 2 data also compares noise levels for the HTH configuration with both 

free jet flows with Mach numbers 0.20 and 0.25, showing that there is essentially no difference in 

measured fan noise levels for these two flows. The LSAF Entry 3 data shows a comparison between TTT 

and HTT configurations, with the expected result that aft sideline noise levels (aft treatment for both 

curves) are identical. 

Figure 14 presents directivity results for the same fan speed at 8 kHz (broadband). These results also 

show the acoustic liner to have better performance in the LSAF tests than for the 915 LSWT tests. 

Figures 15 and 16 show directivities at 10 k rpmc. Again, liner performance is somewhat better in the 

LSAF. Results for the 915 LSWT at 6300 Hz (broadband) and 8 kHz (bypass 2BPF/core BPF) suggest 

that the liner was effective in removing both tone and broadband noise. 

Liner performance in the 915 LSWT was quite good at fan speeds with significant MPT spectral 

content. Figures 17 and 18 show directivities at 11 k rpmc. MPT content begins to appear in the constant 

bandwidth spectra at this fan speed. At 4 kHz (Fig. 17, MPT and bypass BPF tones) the liner significantly 

reduced noise levels for sideline angles downstream greater than about 55. A second trend—evident in 

these directivity comparisons, is for higher noise levels associated with the liner at upstream angles from 

30 to 55. The reason for these high liner-associated levels is unclear, but may be due to inflow 

disturbances associated with the presence of the liner. Another unexplained result is the difference in aft 

noise levels for the LSAF Entry 3 results where both configurations (TTT and HTT) had aft duct 

treatment. 
NASA/TM—2012-217608 6 

Figure 18 compares directivities for 11 k rpmc at 8 kHz, which contain MPT, bypass 2BPF and core 

BPF tones. Again, inlet acoustic liner effectiveness was greater in LSAF than in the 915 LSWT. The 

high noise levels observed for the acoustic liner at 4 kHz (Fig. 17) near 45 sideline emission angle are 

not seen at this higher frequency. 

Figures 19 to 21 show directivity comparisons at 12 k rpmc, which is the speed region of maximum 

MPT content. Figure 19 shows broadband results at 4 kHz. (Only TTT data were available for the LSAF 

Entry 2.) MPT generation in both facilities is significant at this speed and the liner is apparently quite 

effective for removing these tones. The downstream noise level difference between the TTT and HTT 

configurations for the LSAF Entry 3 data is significant in Figure 19. This trend (which persists throughout 

the 12 k rpmc comparison between the 915 LSWT and the LSAF directivities) continually shows 

relatively higher aft noise levels for the HTT configurations. The reason for this difference in what should 

be comparable (same duct treatment) data is unknown. It is possible that something changed on the aft 

liner for the HTT configuration and that this suggested change degraded the acoustic environment of the 

UPS fan for subsequent higher fan speeds with this configuration. 

Figure 20 shows results for 5000 Hz, which contain the bypass BPF tone which is now cut-on. The 

liner effectiveness is especially good for the LSAF Entry 3 results (LSAF HTH results for Entry 2 were 

not available). The 915 LSWT results show a higher upstream noise level associated with the liner 

similar to what was observed at 11 k rpmc and 4000 Hz (Fig. 17). The directivity comparisons at 8 kHz 

(Bypass 2BPF, Fig. 21) again show somewhat better liner performance in the LSAF. 

Figures 22 to 24 show directivity results at 13 k rpmc, where all rotor-stator interaction tones are 

firmly cut-on. Multiple pure tones are also present in the spectra. Figure 22 shows results for the 

broadband at 4 kHz, while Figures 23 and 24 show, respectively, the bypass BPF tone at 5 kHz, and the 

bypass 2BPF and core BPF tones at 10 kHz. The comparisons at 4 kHz (broadband) again show the liner 

to be much more effective in the LSAF than in the 915 LSWT. However, there is still a significant 

difference in liner performance for the two LSAF entries, with Entry 3 results showing the high 

downstream noise levels associated with the HTT configuration. 

The 915 LSWT TTT and HTH comparisons in Figures 22 to 24 show the liner to only be effective 

in the downstream region, while the liner continues to be effective throughout the sideline survey for the 

two LSAF entries. 

Shear Layer Tone Distortion 

Fan tones originating from blade row interaction and MPTs are often distorted through a free jet shear 

layer, with this effect becoming more pronounced at higher frequencies. This effect is explored for the 

comparisons between the 915 LSWT and the LSAF data of selected constant bandwidth spectra in 

Figures 25 to 30. Spectra for both the 915 LSWT data and LSAF data have a 6 Hz bandwidth. A limited 

selection of constant bandwidth spectra for the UPS LSAF entries was available to NASA. The absolute 

calibration of these spectra was unavailable. 

Figure 25 compares UPS M4 HTH data acquired within an airflow with Mach number 0.20 

(915 LSWT) with data acquired outside a free jet with Mach number 0.25 (LSAF). The fan is operating 

at 8.2 k rpmc and the data are for a sideline emission angle of 130. Highly-defined pure tones which are 

present in the wind tunnel data are poorly defined in spectra acquired outside of the free jet due to shear 

layer diffraction. 

This effect is even more dramatic at 11 k rpmc and a 75 emission angle where the spectra have 

significant MPT content (Fig. 26). Figures 27 and 28 show the shear layer diffraction effects at 12 k rpmc

and sideline emission angles of 50 and 75, respectively. Tones occurring at frequencies below about 

4 kHz are fairly well represented outside of the free jet shear layer. 

The UPS fan showed reduced MPT generation with the rotor well into supersonic tip speed 

(13 k rpmc, Figs. 29 and 30). In these comparisons, the tones were only effectively transmitted through 

the free jet shear layer at frequencies below 2 kHz. 
NASA/TM—2012-217608 7 

It is important to note that this lack of tone resolution through a free jet shear layer does not seem to 

affect EPNL calculations, which are based on the acoustic energy along a “flyover” sideline. Thus, free 

jet data is valid for measurements such as EPNLs, but appears to have limited value for diagnostic fan 

source analysis. 

DNW Results 

The German-Dutch Wind Tunnel (DNW) tests of the UPS fan provided a unique opportunity to 

directly compare data acquired both within and outside of a free jet. Also, data acquired from the DNW 

tests could be directly compared to the inflow results from the 915 LSWT and far field data acquired 

outside of a shear layer (LSAF). Acoustic data were acquired for the two baseline UPS configurations 

utilizing the metal M4 rotor and hardwall (HTH) and treated (TTT) bypass flow passages. Acoustic data 

were acquired in the DNW along a 36-ft sideline outside of the free jet as well as with sideline traverses at 

120 and 88 in. within the free jet (Figs. 6 and 7). The closer, 88-in. sideline data were acquired using the 

exact same microphone holder and microphone assembly as was used to acquire the 915 LSWT data, 

making these comparisons especially valid. All of the DNW data were acquired with a free jet operating 

at a Mach number of 0.20. Table 4 shows the data points which were acquired for the UPS fan in the 

DNW facility and subsequently provided to NASA by GEAE. Data were provided as both 1/3rd octave 

and 36 Hz constant bandwidth spectra. 

Effect of Sideline Distance 

There continues to be some question as to the minimum acceptable sideline distance for 

representative fan acoustic data. Data taken in the 915 LSWT are physically limited to about a 

89-in. sideline. Figure 31 compares data taken in the DNW at two different sideline distances within the 

free jet. The data were processed by General Electric to a 20-ft sideline using their proprietary software. 

These data are for the M4 rotor hardwall condition with the fan operating at 10 k rpmc. Data were taken at 

a 88-in. sideline using the NASA Glenn streamlined microphone holder, and at a 120-in. sideline using 

DNW survey apparatus. These results offer a unique opportunity to simultaneously compare noise 

directivities at two sideline distances without source uncertainties such as fan rebuild and different 

atmospheric test conditions. 

Results for bypass BPF (4 kHz) through 3BPF (12.5 kHz) (Figs. 31(a) to (c)) show good agreement 

between the two sideline distances. There is a slight upstream directivity shift for the 120-in. sideline at 

downstream angles. This is a geometric error caused by using the inlet highlight as the 90 reference for 

noise which radiates from the fan exhaust. There is an upstream region of higher noise levels for the 

88-in. sideline which was observed at 16 and 25 kHz (Figs. 31(d) and (e)). The reason for this difference 

is unknown. There is a region of lower noise around 90 for the closer, 88-in. sideline at 40 kHz 

(Fig. 31(f)) which may relate to more separation of the forward and aft radiation patterns at this closer 

spacing. The results of Figure 31 show that data taken at the closer 89-in. sideline in the 915 LSWT are 

reasonably representative of fan far field results. 

Directivity Comparisons 

Figures 32 to 45 present 1/3rd octave directivity comparisons of corresponding 915 LSWT and DNW 

UPS data for the TTT and HTH configurations. The DNW data is for the NASA microphone at an 88-in. 

sideline. These comparisons tend to be quite good, giving further confidence that valid data may be 

acquired in either facility. 

Figures 32 to 34 compare directivities at 8.2 k rpmc (8100 rpmc for the DNW data) for, respectively, 

the bypass 2BPF and core BPF tone at 6300 Hz, broadband at 10 kHz, and broadband at 20 kHz. The 

UPS tone directivities (Fig. 32) were somewhat higher for the DNW data. There was close agreement 

between the 915 LSWT and DNW data for broadband at 10 and 20 kHz. The “dip” in the data seen 
NASA/TM—2012-217608 8 

around 90 is a consequence of the sideline traverse being relatively close (4 fan diameters) with resulting 

separation of fan forward and aft radiation patterns. 

Figures 35 to 38 show directivity comparisons at 10 k rpmc. UPS operation at 10 k rpmc provides data 

which does not contain MPTs, and is therefore not subject to the variable onset of these tones due to 

specific test flow conditions, etc. Results shown in Figures 35 to 38 are for, respectively, broadband at 

4 kHz, bypass 2BPF and core BPF at 8 kHz, bypass 4BPF and core 2BPF at 16 kHz, and bypass 6BPFand 

core 3BPF at 25 kHz. The agreement between corresponding UPS and DNW data is excellent in each 

instance, although there is a suggestion that the original acoustic liner (TTT) performed slightly better in 

the DNW at 16 kHz (Fig. 37) through the mid range of the acoustic traverse. 

The UPS fan exhibits maximum MPT generation at 12 k rpmc. Figures 39 to 41 show directivity 

comparisons at this speed for, respectively, broadband at 4 kHz, bypass 2BPF and core BPF at 10 kHz, 

and bypass 4BPF and core 2BPF at 20 kHz. Although not as good as for 10 k rpmc, the agreement 

between corresponding data is still acceptable. At 4 kHz (Fig. 40) the TTT configuration data shows good 

agreement between the two facilities. Multiple pure tones are strongly present in the HTH data, showing 

slightly more generation in the DNW data near a peak emission angle of 60. Difference in multiple pure 

tone generation may still be a factor in the small differences between configuration directivities at 10 and 

20 kHz. 

Figures 42 to 45 show directivity comparisons at the overspeed, 13.5 k rpmc condition. The fan noise 

is highly aft dominated at this rotational speed. Directivities are shown in Figures 42 to 45, respectively, 

for the bypass BPF (strongly cuton) at 5 kHz, broadband at 8 kHz, bypass 2BPF and core BPF at 10 kHz, 

and bypass 4BPF and core 2BPF at 20 kHz. The data compares favorable through 10 kHz (Figs. 42 to 

44). At 20 kHz (Fig. 45) the 915 LSWT data is consistently higher than the corresponding DNW data. 

The reason for this difference is unknown. 

Free Jet Shear Layer Effects 

The DNW data afforded an excellent opportunity to further investigate the shear layer induced tone 

diffraction which was noted in the LSAF data. DNW constant bandwidth (36 Hz) data are available for 

both the 120-in. sideline within the free jet airflow, and out of the flow at a 36-ft sideline. Figures 46 to 

48 compare constant bandwidth spectra acquired within and outside of the free jet shear layer for the 

hardwall (HTH) configuration. Data are shown for 12 k rpmc at emission angles of 60, 90, and 120. 

The comparisons are similar to those seen for the 915 LSWT/LSAF data, showing significant tone 

scattering through the freejet shear layer. The strong MPT content at 60 (Fig. 46) is barely evident 

outside of the free jet, being essentially limited to frequencies below 4 kHz. Rotor/stator interaction tones 

which are readily seen in the in flow spectra at 90 and 120 are barely evident in the far field spectra 

taken outside of the free jet (Figs. 47 and 48). These comparisons again illustrate the difficulty in using 

fan data taken outside of a free jet to gain insights into fan noise generation mechanisms. 

Acoustic Sideline Distance 

As was previously mentioned, there is some question concerning the minimum acoustic sideline data 

required to obtain valid far field measurements. Again, the DNW test provided an insight with in flow 

sideline data at the nominal 915 LSWT distance of 89-in. and also in flow sideline data at a somewhat 

greater 120-in. The out of flow data at 36 ft is clearly in the far field, but may be compromised by shear 

layer effects. 

Figures 49 to 54 show constant bandwidth (36 Hz) directivities along these three sidelines for the 

UPS hardwall HTH configuration at 12 k rpmc. Directivities are shown for the first 4 bypass tone orders 

and first 2 core tone orders. The constant bandwidth data are instrument corrected, but not adjusted for 

atmospheric absorption. The general conclusion from these figures is that directivities for the two in flow 

sidelines (88- and 120-in.) are essentially similar, giving credibility to the 89-in. sideline used in the 

915 LSWT. The tone directivities in the far field (through the shear layer) reasonably follows that of the 
NASA/TM—2012-217608 9 

in flow data for the BPF tone (approximately 4500 Hz, Fig. 49), but is not very descriptive at higher 

frequencies (tone orders). This result is constant with the previous observation that tonal information is 

significantly compromised through a Mach number of 0.20 free jet shear layer at frequencies above 

4000 Hz. 

Comparison of DNW and 915 LSWT Directivities 

It is desirable to compare the constant bandwidth directivities using the same bandwidth (and acoustic 

energy content). The sound pressure levels in three adjacent 36 Hz acoustic bands were logarithmically 

added to effectively obtain an equivalent 118 Hz band SPL for selected DNW UPS 88-in. sideline 

directivities at 10 k rpmc. This was done for the TTT and HTH configuration data for the first 4 bypass 

and 2 core tone orders. These adjusted directivities are compared with corresponding (118 Hz) results 

from the 915 LSWT in Figures 55 and 56. 

The hardwall comparisons are presented in Figure 55. The data agreement varies for the various 

bypass tone orders. The bypass BPF tone (Fig. 55(a)) shows fairly good agreement except for the sideline 

emission angles around 120. The DNW sideline survey extended somewhat further downstream than did 

that of the 915 LSWT, more clearly showing the reduction in SPL at further downstream angles 

(desirable for EPNL calculations). 

The directivity agreement for the bypass 2BPF tone (Fig. 55(b)) was not especially good, with the 

DNW results being nearly 10 dB higher at some angles. Directivity comparisons for the 3 and 4BPF 

bypass tones (Figs. 55(c) and (d)) were somewhat better. 

Interestingly, the directivity comparisons for the first 2 core tone orders (Figs. 55(e) and (f)) were 

quite good between the two facilities. Unlike the bypass tones, the core tones are mostly aft-radiating. 

Perhaps this simplifies the acoustic resolution since forward and aft radiation interaction (as for the 

bypass tones) is not a consideration. 

There has been some question as to the origin of the “periodic” nature of the bypass tone directivity 

as illustrated in the preceding plots. An initial concern was that the treated walls of the 915 LSWT were, 

in reality, reflecting some noise, resulting in a cancellation pattern. The comparisons between the 915 

LSWT and the DNW are useful in exploring this mechanism, in that the DNW with its open free jet does 

not have the potential for near wall reflection. 

Reference 14 explores an analytical solution for fan tone directivity along a similar sideline distance 

with consideration of forward and aft tone reinforcement and cancellation effects. Predicted bypass tone 

directivities presented in Reference 14 show a periodicity similar to that seen for the UPS data, 

reinforcing the idea that this periodicity is due to interaction between forward and aft radiated fan tones. 

This analytical result and the directivity comparisons between the 915 LSWT and the DNW UPS data 

show that the acoustically-treated walls of the 915 LSWT are not a significant source of reflection 

contamination of the data. 

Figure 56 presents directivity comparisons for these bypass and core tones for the treated, TTT 

configuration at 10 k rpmc. Figures 56(a) and (b) shows good agreement between data from the two 

facilities for the bypass BPF and 2BPF tones. However, at 3BPF and 4BPF (Figs. 56(c) and (d)) the 

915 LSWT data is consistently higher. This results contrast with those of for the HTH configuration 

(Figs. 55(c) and (d)) which showed relatively good agreement between results for the two facilities. 

There was considerable evidence that the acoustic treatment (TTT) tested in the 915 LSWT was 

somehow not as effective compared to the UPS TTT performance in LSAF. It is possible that installationinduced changes in liner performance are causing with higher bypass 3BPF and 4BPF tone levels in the 

915 LSWT seen for these comparisons. 

The core stage interactions tones for the TTT configuration again showed good agreement between 

the two facilities (Figs. 56(e) and (f)). These tones are essentially unaffected by the presence of the bypass 

duct acoustic liner. 
NASA/TM—2012-217608 10 

Concluding Remarks 

A model advanced turbofan was acoustically tested in the 915 LSWT, the Boeing Low Speed 

Aeroacoustic Facility (LSAF) and the German-Dutch Wind Tunnel (DNW). The Universal Propulsion 

Simulator (UPS) fan was designed and manufactured by the General Electric Aircraft Engines (GEAE) 

Company, and featured powered core, as well as bypass, flow paths. The reference test configurations 

were with the unswept baseline “M4” rotor with hardwall and acoustically treated bypass flow ducts. 

These tests afforded an opportunity to compare relative merits of fan acoustic testing within airflow 

(915 LSWT and DNW) and with acoustic measurements taken outside of a free jet (LSAF and DNW) 

using common test hardware and operating conditions. 

The Boeing LSAF tests were with the fan installed in a free jet and far field noise measurements 

taken outside of the free jet. The UPS acoustic liner was more effective in the LSAF installation than in 

the 915 LSWT. The reason for this difference is unknown, but may relate to small differences between 

successive builds of the model in the two facilities. The LSAF results showed significant shear layer 

diffraction of fan tones measured outside of the shear layer. In particular, a significant amount of the 

diagnostic fan tonal information may be lost by transmission through a shear layer. However, overall 

noise levels seem to be essentially the same when measured within the flow (915 LSWT) or outside of 

the flow (LSAF). 

The German Dutch DNW results provided an excellent opportunity to compare far field acoustic data 

taken concurrently both within and outside of a free jet. The free jet in this facility was sufficiently large 

to allow in flow acoustic sideline measurements as well as simultaneous far field (outside of the shear 

layer) measurements. The shear layer tone diffraction noted for the LSAF tests was further quantified in 

the DNW. In-flow measurements were made at the DNW using the same microphone holder assembly 

that was used for the 915 LSWT tests and utilizing the same sideline distance as for the NASA wind 

tunnel tests. These results showed excellent acoustic agreement between the 915 LSWT and DNW tests. 

An additional result of the DNW tests was to quantify the effect of sideline distance. In-flow sideline data 

were acquired in the DNW at 88 in. (nominal 915 LSWT sideline), 120 in., and outside the free jet at 

36 ft. The sideline directivities were slightly influenced by fan inlet/exhaust radiation patterns at closer 

sidelines and higher frequencies; however, the results generally showed that the 89-in. (nominal 4 fan 

diameter) sideline employed in the 915 LSWT should be adequate to acquire “far field” sideline data. 

References 

1. Gliebe, P.R., Ho, P.Y., and Mickol, J.D., “Low-Speed Wind Tunnel (LSWT)/Universal Propulsion 

Simulator (UPS) Acoustic Calibration,” GEAE Technical Memorandum, August, 1996. 

2. Tyler, J.M., and Sofrin, T.G., “Axial Flow Compressor Noise Studies,” Society of Automotive 

Engineers Transactions, Vol. 70, 1962, pp. 309–332. 

3. Rice, E.J., and Heidmann, M.F., “Modal Propagation Angles in a Cylindrical Duct With Flow and 

their Relation to Sound Radiation,” AIAA-79-0183, January, 1979. 

4. Woodward, R.P., and Hughes, C.E., “Acoustic Performance of the GEAE UPS Research Fan in the 

NASA Glenn 9- by 15-Foot Low Speed Wind Tunnel,” NASA/TM—2012-217450. 

5. Balan, C., and Hoff, G.E., “Propulsion Simulator for High Bypass Turbofan Performance 

Evaluation,” SAE Paper 931410, Jan. 1993. 

6. Dahl, Milo D., and Woodward, Richard P., “Comparison Between Design and Installed Acoustic 

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

NASA TP-2996, April, 1990. 

7. Dahl, Milo D., and Woodward, Richard P., “Acoustical Evaluation of the NASA Glenn 9- by 15-Foot 

Low Speed Wind Tunnel,” NASA TP-3274, November, 1992. 
NASA/TM—2012-217608 11 

8. Woodward, Richard P., Dittmar, James H., Hall, David G., and Kee-Bowling, Bonnie, “Background 

Noise Levels Measured in the NASA Glenn 9- by 15-Foot Low-Speed Wind Tunnel,” AIAA-95-

0720, NASA TM 106817, January, 1995. 

9. Chestnutt, D., “Flight Effects of Fan Noise,” NASA CP-2242, January, 1982. 

10. Allen, R.M., and Reed, D.H., “Development of the Boeing Low Speed Aeroacoustic Facility 

(LSAF),” In DGLR (AIAA 14th Aeroacoustics Conference, Aachen Germany, May 11-14, 1992) 

Proceedings. Vol. 1 (A93-19126 05-71) pp 187-195. 

11. Jaarsma, F., and Seidel, M., “The German-Dutch Wind Tunnel DNW - Design Aspects and Status of 

Construction,” Proceedings, International Council of the Aeronautical Sciences (DGLR), Sept. 1978, 

Vol. 1 (A79-20076 06-01) pp 449-460. 

12. Van Ditshuizen, J.C.A., Courage, G.D., Ross, R., and Schultz, K.J., “Acoustic Capabilities of the 

German-Dutch Wind Tunnel DNW,” AIAA Paper 83-0146, Jan. 1983. 

13. Heller, H.H., Splettstoesser, W.R., Dobrzynski, W.M., and Schultz, K.J., “Aeroacoustics at the 

German-Dutch Wind Tunnel, Proceedings, ICAS 15th Congress, Sept., 1986, Vol. 2 (A86-48976 24-

01), AIAA, pp 786-800. 

14. Envia, Edmane, and Nallasamy, M., “Design Selection and Analysis of a Swept & Leaned Stator 

Concept,” NASA TM-1998-208662, Dec. 1998. 

TABLE 1.—UPS DESIGN PARAMETERS 

TABLE 2.—ACOUSTIC TEST SPEEDS 

[Nominal Values.] 

Corrected, 

rpm 

Point of interest Corrected tip speed m/sec, 

ft/sec 

Tip Mach, 

Tangential a

1330 Windmill 38.9 (127.7) 0.11 

7400 Low approach 216.5 (710.3) 0.63 

8200 High approach 239.9 (787.1) 0.70 

10000 Low cutback 292.6 (959.9) 0.85 

11000 High cutback 321.8 (1055.9) 0.94 

12000 MPT peak 351.1 (1151.9) 1.02 

13000 Low takeoff 380.4 (1247.9) 1.11 

13500 High takeoff 395.0 (1295.9) 1.15 

14000 Overspeed 409.6 (1343.9) 1.19 a

Windmill speed is approximate, depending on tunnel conditions

Bypass Stage: 

Rotor blades................................................................................ 22 

Stator vanes ................................................................................ 54 

Core (booster): 

Inlet guide vanes ........................................................................ 90 

Rotor blades................................................................................ 48 

Outlet guide vanes ...................................................................... 70 

Deswirl vanes ............................................................................. 50 

Forward load struts ..................................................................................... 8 

Full passage screen ...................................................................... 1 

Aft load struts ............................................................................... 8 

Rotor-stator axial spacing (mean rotor chords) .................................... 2.75 

Bypass stage: 

Pressure ratio ........................................................................... 1.49 

Bypass ratio: ............................................................................ 8.85 

Mass flow, kg/sec (lbm/sec): ..................................... 46.3 (102.1) 

Rotor diameter, cm (in.) ............................................... 55.9 (22.0) 

Rotor tip speed, m/sec (ft/sec): .................................................. 370 (1214) 

Acoustic Rating Rotor Tip Speeds, m/sec (ft/sec) 

Approach ........................................................................ 216 (710) 

Cutback ........................................................................... 293 (960) 

Sideline ......................................................................... 351 (1152) 
NASA/TM—2012-217608 12 

TABLE 3.—DATA COMPARISON BETWEEN GRC 915 LSWT AND BOEING LSAF 

[0 AOA, Except As Noted.] 

LSAF entry 2: Mach as shown, 20 ft radius upstream and 20-ft sideline aft. 

LSAF entry 3: 15-ft radius upstream and 15-ft sideline aft. 

Acoustic Treatment—Treated (T) or Hardwall (H): [Inlet]–[Between Rotors and Stator]–[Exhaust Duct] 

Corrected, 

rpm 

915 (0.20 Mach) LSAF entry 2 LSAF entry 3 

(0.20 Mach) 

Acoustic 

treatment 

configuration 

Data 

taken 

Acoustic 

treatment 

configuration 

Mach Data taken Acoustic 

treatment 

configuration 

Data 

taken 

Windmill TTT Yes TTT 0.20 Yesa HTT Yes

7000 N.A. TTT 0.25 Yes N.A. 

7000 N.A. HTH 0.20 Yes N.A. 

7400 TTT Yes TTT 0.25 Yes TTT Yes 

7400 HTH Yes HTH 0.20 Yes HTT Yes 

7400 N.A. HTH 0.25 Yes N.A. 

7400 N.A. HTH 0.06 Yes N.A. 

8200 TTT Yes TTT 0.25 Yes TTT Yes 

8200 HTH Yes HTH 0.20 Yes HTT Yes 

8200 N.A. HTH 0.25 Yes N.A. 

10000 TTT Yes TTT 0.25 Yes TTT Yes 

10000 HTH Yes HTH 0.20 Yes HTT Yes 

11000 TTT Yes TTT 0.25 Yes TTT Yes 

11000 HTH Yes HTH 0.25 Yes HTT Yes 

11700 N.A. HTH 0.25 Yes TTT Yes 

11700 N.A. N.A. HTT Yes 

12000 TTT Yes TTT 0.25 Yes TTT Yes 

12000 HTH Yes N.A. HTT Yes 

13000 TTT Yes TTT 0.25 Yes TTT Yes 

13000 HTH Yes HTH 0.25 Yes HTT Yes 

13500 TTT Yes N.A. TTT Yesb

13500 HTH Yes N.A. HTT Yesc

14300 N.A. TTT 0.25 Yes N.A. 

14300 N.A. HTH 0.25 Yes N.A. 

a

Windmill data, 3 Angle-of-Attack. b

Angle-of-Attack is really 3.86 c

Slight loss of hardwall taping, therefore questionable data

 
NASA/TM—2012-217608 13 

TABLE 4.—GE UPS DATA TAKEN IN THE DNW FREE JET FACILITY 

[M4 Rotor, Free jet with Mach Number 0.20.] 

Corrected, rpm 

Hardwall (HTH) Treated (TTT) 

Windmill ---------------------- ---------------------- 

6700 D1/3rd D1/3rd

7300 N1/3rd, D1/3rd, SL4 N1/3rd, D1/3rd, SL4 

8100 N1/3rd, D1/3rd, SL2, SL4 N1/3rd, D1/3rd, SL2, SL4 

10000 N1/3rd, D1/3rd, SL2, SL4 N1/3rd, D1/3rd, SL2, SL4 

10800 N1/3rd, D1/3rd, SL2, SL3, SL4 N1/3rd, D1/3rd, SL4 

12000 N1/3rd, D1/3rd, SL2, SL4 N1/3rd, D1/3rd, SL2, SL4 

13000 N1/3rd, D1/3rd, SL2, SL4 N1/3rd, D1/3rd, SL2, SL4 

13500 N1/3rd, D1/3rd, SL3, SL4 N1/3rd, D1/3rd, SL4 

13900 D1/3rd D1/3rd 

Available data: 

N1/3rd—1/3rd octave taken with the NASA mike in flow at an 88-in. sideline 

D1/3rd—1/3rd octave taken with the DNW in flow translating mic at a 120-in. sideline 

SL2—36 Hz narrowband data taken with the DNW translating probe, middle mic 

SL3—36 Hz narrowband data taken with the DNW translating probe, lower mic 

SL4—36 Hz narrowband data taken with the NASA inflow microphone probe 
NASA/TM—2012-217608 14 
NASA/TM—2012-217608 15 
NASA/TM—2012-217608 16 
NASA/TM—2012-217608 17 
NASA/TM—2012-217608 18 

Figure 8.—Fan stage aerodynamic performance in the 915 LSWT for the M4 rotor. 

Figure 9.—Effect of rotor bypass duct acoustic treatment for the baseline M4 metal rotor. (EPNL calculated 

from 915 LSWT sideline data, 0 AOA, 5.6 scale factor, 304.8-m (1000-ft) flyover). 

40 60 80 100 120

Correct Inlet Weight Flow, lbm/sec

1.10

1.20

1.30

1.40

1.50

1.60

1.70

Bypass

Pressure 

Ratio

Hardwall, HTH 

Acoustic treatment, TTT 

600 700 800 900 1000 1100 1200 1300 1400

Corrected tip speed, ft./sec

10

EPNdB

Hardwall, HTH 

Acoustic treatment, TTT 
NASA/TM—2012-217608 19 

Figure 10.—UPS bypass and core tone frequencies as a function of rotor speed. 

Figure 11.—Constant bandwidth (6 Hz) spectra. (M4 metal rotor, 74 sideline emission angle, 

89 in. sideline, 12 k rpmc, NASA 915 LSWT). 

6000 7000 8000 9000 10000 11000 12000 13000 14000

Actual Rotor RPM

0

5000

10000

15000

20000

25000

Frequency,Hz

6000 7000 8000 9000 10000 11000 12000 13000 14000

Nominal Corrected Rotor RPM

BPF

2BPF

3BPF

4BPF

5BPF

1xCore BPF

2xCore BPF

0 2000 4000 6000 8000 10000

Frequency, Hz

60

70

80

90

100

110

 

60

70

80

90

100

110

SPL,

dB

Acoustic treatment, TTT 

Hardwall, HTH

 BPF 

 |

 2BPF 

 |
NASA/TM—2012-217608 20 

Figure 12.—1/3rd octave directivities for hard-wall and acoustic treatment configurations (Baseline M4 

metal rotor, 915 LSWT). 

20 30 40 50 60 70 80 90 100 110 120 130 140 150

Emission angle relative to inlet highlight, deg.

95

100

105

110

 

85

90

95

100

SPL,

dB

Hardwall, HTH

Acoustic treatment, TTT

85

90

95

100

(a) 8200 rpmc, 8 kHz, contains broadband

(b) 8200 rpmc, 10 kHz, contains bypass 3BPF tone

(c) 12000 rpmc, 2 kHz, contains broadband and MPTs
NASA/TM—2012-217608 21 

Figure 12.—Concluded. 

20 30 40 50 60 70 80 90 100 110 120 130 140 150

Emission angle relative to inlet highlight, deg.

95

100

105

110

 

95

100

105

110

SPL,

dB

Hardwall, HTH

Acoustic treatment, TTT

(d) 12000 rpmc, 4 kHz, contains bypass BPF tone and MPTs

(e) 12000 rpmc, 8 kHz, contains bypass 2BPF tone and MPTs
NASA/TM—2012-217608 22 

Figure 13.—Effect of inlet and exhaust acoustic liner for NASA 915 LSWT and Boeing LSAF entries (8.2 k rpmc,

1/3rd octave directivities at 5 kHz (broadband spectral region), LSAF data adjusted to 88-in. sideline). 

20 30 40 50 60 70 80 90 100 110 120 130 140 150

Emission angle relative to inlet highlight, deg.

75

80

85

90

95

 

LSAF, M4, TTT, entry 3, 0.20 M

LSAF, M4, HTT, entry 3, 0.20 M

80

85

90

95

100

SPL,

dB

LSAF, M4, TTT, entry 2, 0.25 M, 

LSAF, M4, HTH, entry 2, 0.20 M

LSAF, M4, HTH, entry 2, 0.25 M

80

85

90

95

100

9x15, M4, TTT, 0.20 M

9x15, M4, HTH, 0.20 M

9x15, M4, TTT, 0.20 M, Windmill
NASA/TM—2012-217608 23 

Figure 14.—Effect of inlet and exhaust acoustic liner for NASA 915 LSWT and Boeing LSAF entries (8.2 k rpmc,

1/3rd octave directivities at 8 kHz (broadband spectral region), LSAF data adjusted to 88-in. sideline). 

20 30 40 50 60 70 80 90 100 110 120 130 140 150

Emission angle relative to inlet highlight, deg.

80

85

90

95

100

 

LSAF, M4, TTT, entry 3, 0.20 M

LSAF, M4, HTT, entry 3, 0.20 M

80

85

90

95

100

SPL,

dB

LSAF, M4, TTT, entry 2, 0.25 M, 

LSAF, M4, HTH, entry 2, 0.20 M

LSAF, M4, HTH, entry 2, 0.25 M

80

85

90

95

100

9x15, M4, TTT, 0.20 M

9x15, M4, HTH, 0.20 M

9x15, M4, TTT, 0.20 M, Windmill
NASA/TM—2012-217608 24 

Figure 15.—Effect of inlet and exhaust acoustic liner for NASA 915 LSWT and Boeing LSAF entries 

(10 k rpmc, 1/3rd octave directivities at 6.3 kHz (broadband spectral region), LSAF data adjusted to 88-in. 

sideline). 

20 30 40 50 60 70 80 90 100 110 120 130 140 150

Emission angle relative to inlet highlight, deg.

80

85

90

95

100

 

LSAF, M4, TTT, entry 3, 0.20 M

LSAF, M4, HTT, entry 3, 0.20 M

85

90

95

100

105

SPL,

dB

LSAF, M4, TTT, entry 2, 0.25 M

LSAF, M4, HTH, entry 2, 0.20 M

85

90

95

100

105

9x15, M4, TTT, 0.20 M

9x15, M4, HTH, 0.20 M
NASA/TM—2012-217608 25 

Figure 16.—Effect of inlet and exhaust acoustic liner for NASA 915 LSWT and Boeing LSAF entries (10 k rpmc, 

1/3rd octave directivities at 8 kHz (1/3rd octave band contains bypass 2BPF and core BPF tones), LSAF data 

adjusted to 88-in. sideline). 

 

20 30 40 50 60 70 80 90 100 110 120 130 140 150

Emission angle relative to inlet highlight, deg.

85

90

95

100

105

 

LSAF, M4, TTT, entry 3, 0.20 M

LSAF, M4, HTT, entry 3, 0.20 M

90

95

100

105

110

SPL,

dB

LSAF, M4, TTT, entry 2, 0.25 M

LSAF, M4, HTH, entry 2, 0.20 M

85

90

95

100

105

9x15, M4, TTT, 0.20 M

9x15, M4, HTH, 0.20 M
NASA/TM—2012-217608 26 

Figure 17.—Effect of inlet and exhaust acoustic liner for NASA 915 LSWT and Boeing LSAF entries (11 k rpmc, 

1/3rd octave directivities at 4 kHz (1/3rd octave band contains MPT and bypass BPF tones), LSAF data adjusted 

to 88-in. sideline). 

20 30 40 50 60 70 80 90 100 110 120 130 140 150

Emission angle relative to inlet highlight, deg.

90

95

100

105

110

 

LSAF, M4, TTT, entry 3, 0.20 M

LSAF, M4, HTT, entry 3, 0.20 M

90

95

100

105

110

SPL,

dB

LSAF, M4, TTT, entry 2, 0.25 M

LSAF, M4, HTH, entry 2, 0.20 M

90

95

100

105

110

9x15, M4, TTT, 0.20 M

9x15, M4, HTH, 0.20 M
NASA/TM—2012-217608 27 

Figure 18.—Effect of inlet and exhaust acoustic liner for NASA 915 LSWT and Boeing LSAF entries (11 k rpmc, 

1/3rd octave directivities at 8 kHz (1/3rd octave band contains MPT, bypass 2BPF and core BPF tones), LSAF 

data adjusted to 88-in. sideline). 

20 30 40 50 60 70 80 90 100 110 120 130 140 150

Emission angle relative to inlet highlight, deg.

90

95

100

105

110

 

LSAF, M4, TTT, entry 3, 0.20 M

LSAF, M4, HTT, entry 3, 0.20 M

90

95

100

105

110

SPL,

dB

LSAF, M4, TTT, entry 2, 0.25 M

LSAF, M4, HTH, entry 2, 0.20 M

90

95

100

105

110

9x15, M4, TTT, 0.20 M

9x15, M4, HTH, 0.20 M
NASA/TM—2012-217608 28 

Figure 19.—Effect of inlet and exhaust acoustic liner for NASA 915 LSWT and Boeing LSAF entries 

(12 k rpmc, 1/3rd octave directivities at 4 kHz (1/3rd octave band contains MPT and bypass BPF tones), 

LSAF data adjusted to 88-in. sideline). 

20 30 40 50 60 70 80 90 100 110 120 130 140 150

Emission angle relative to inlet highlight, deg.

95

100

105

110

115

 

LSAF, M4, TTT, entry 3, 0.20 M

LSAF, M4, HTT, entry 3, 0.20 M

90

95

100

105

110

SPL,

dB

LSAF, M4, TTT, entry 2, 0.25 M

LSAF, M4, HTH -- data not available

90

95

100

105

110

9x15, M4, TTT, 0.20 M

9x15, M4, HTH, 0.20 M
NASA/TM—2012-217608 29 

Figure 20.—Effect of inlet and exhaust acoustic liner for NASA 915 LSWT and Boeing LSAF entries (12 k rpmc 

1.3rd octave directivities at 5 kHz (1/3rd octave band contains MPT and bypass BPF tones), LSAF data 

adjusted to 88-in. sideline). 

20 30 40 50 60 70 80 90 100 110 120 130 140 150

Emission angle relative to inlet highlight, deg.

95

100

105

110

115

 

LSAF, M4, TTT, entry 3, 0.20 M

LSAF, M4, HTT, entry 3, 0.20 M

90

95

100

105

110

SPL,

dB

LSAF, M4, TTT, entry 2, 0.25 M

LSAF, M4, HTH -- data not available

90

95

100

105

110

9x15, M4, TTT, 0.20 M

9x15, M4, HTH, 0.20 M
NASA/TM—2012-217608 30 

Figure 21.—Effect of inlet and exhaust acoustic liner for NASA 915 LSWT and Boeing LSAF entries (12 k rpmc,

1/3rd octave directivities at 8 kHz (1/3rd octave band contains MPT and bypass 2BPF tones), LSAF data 

adjusted to 88-in. sideline). 

20 30 40 50 60 70 80 90 100 110 120 130 140 150

Emission angle relative to inlet highlight, deg.

95

100

105

110

115

 

LSAF, M4, TTT, entry 3, 0.20 M

LSAF, M4, HTT, entry 3, 0.20 M

90

95

100

105

110

SPL,

dB

LSAF, M4, TTT, entry 2, 0.25 M

LSAF, M4, HTH -- data not available

90

95

100

105

110

9x15, M4, TTT, 0.20 M

9x15, M4, HTH, 0.20 M
NASA/TM—2012-217608 31 

Figure 22.—Effect of inlet and exhaust acoustic liner for NASA 915 LSWT and Boeing LSAF entries (13 k rpmc,

1/3rd octave directivities at 4 kHz (MPT and broadband spectral region), LSAF data adjusted to 88-in. sideline). 

20 30 40 50 60 70 80 90 100 110 120 130 140 150

Emission angle relative to inlet highlight, deg.

95

100

105

110

115

 

LSAF, M4, TTT, entry 3, 0.20 M

LSAF, M4, HTT, entry 3, 0.20 M

95

100

105

110

115

SPL,

dB

LSAF, M4, TTT, entry 2, 0.25 M

LSAF, M4, HTH, entry 2, 0.25 M

90

95

100

105

110

9x15, M4, TTT, 0.20 M

9x15, M4, HTH, 0.20 M
NASA/TM—2012-217608 32 

Figure 23.—Effect of inlet and exhaust acoustic liner for NASA 915 LSWT and Boeing LSAF entries (13 k rpmc,

1/3rd octave directivities at 5 kHz (1/3rd octave band contains MPT and bypass BPF tones), LSAF data 

adjusted to 88-in. sideline). 

20 30 40 50 60 70 80 90 100 110 120 130 140 150

Emission angle relative to inlet highlight, deg.

100

105

110

115

120

 

LSAF, M4, TTT, entry 3, 0.20 M

LSAF, M4, HTT, entry 3, 0.20 M

95

100

105

110

115

SPL,

dB

LSAF, M4, TTT, entry 2, 0.25 M

LSAF, M4, HTH, entry 2, 0.25 M

95

100

105

110

115

9x15, M4, TTT, 0.20 M

9x15, M4, HTH, 0.20 M
NASA/TM—2012-217608 33 

Figure 24.—Effect of inlet and exhaust acoustic liner for NASA 915 LSWT and Boeing LSAF entries 

(13 k rpmc, 1/3rd octave directivities at 10 kHz (1/3rd octave band contains MPT, bypass 2BPF and 

core BPF tones), LSAF data adjusted to 88-in. sideline). 

20 30 40 50 60 70 80 90 100 110 120 130 140 150

Emission angle relative to inlet highlight, deg.

95

100

105

110

115

 

LSAF, M4, TTT, entry 3, 0.20 M

LSAF, M4, HTT, entry 3, 0.20 M

95

100

105

110

115

SPL,

dB

LSAF, M4, TTT, entry 2, 0.25 M

LSAF, M4, HTH, entry 2, 0.25 M

95

100

105

110

115

9x15, M4, TTT, 0.20 M

9x15, M4, HTH, 0.20 M
NASA/TM—2012-217608 34 

Figure 25.—Comparison of 6 Hz bandwidth spectra taken in the NASA 915 LSWT and the 

Boeing LSAF showing shear layer distortion of the tonal content (8.2 k rpmc, 130 sideline 

emission angle, HTH). 

Figure 26.—Comparison of 6 Hz bandwidth spectra taken in the NASA 915 LSWT and the 

Boeing LSAF showing shear layer distortion of the tonal content (11 k rpmc, 75 sideline 

emission angle, HTH). 

0 2000 4000 6000 8000 10000

Frequency, Hz

 

LSAF, M4, entry 2, 0.25 M

 9x15, M4, 0.20 M

 BPF 

 | 2BPF 

 |

CORE

 BPF

 |

10 dB

0 2000 4000 6000 8000 10000

Frequency, Hz

 

LSAF, M4, entry 2, 0.25 M

 9x15, M4, 0.20 M

 BPF 

 |

 2BPF 

 |

10 dB
NASA/TM—2012-217608 35 

Figure 27.—Comparison of 6 Hz bandwidth spectra taken in the NASA 915 LSWT 

and the Boeing LSAF showing shear layer distortion of the tonal content (12 k rpmc, 

50 sideline emission angle, TTT). 

Figure 28.—Comparison of 6 Hz bandwidth spectra taken in the NASA 915 LSWT and the Boeing LSAF 

showing shear layer distortion of the tonal content (12 k rpmc, 75 sideline emission angle, HTH). 

0 2000 4000 6000 8000 10000

Frequency, Hz

 

LSAF, M4, entry 2, 0.25 M

 9x15, M4, 0.20 M

 BPF 

 |

 2BPF 

 |

10 dB

0 2000 4000 6000 8000 10000

Frequency, Hz

 

LSAF, M4, entry 2, 0.25 M

 9x15, M4, 0.20 M

 BPF 

 |

 2BPF 

 |

10 dB
NASA/TM—2012-217608 36 

Figure 29.—Comparison of 6 Hz bandwidth spectra taken in the NASA 915 LSWT and the 

Boeing LSAF showing shear layer distortion of the tonal content (13 k rpmc, 50 sideline 

emission angle, HTH). 

Figure 30.—Comparison of 6 Hz bandwidth spectra taken in the NASA 915 LSWT and the 

Boeing LSAF showing shear layer distortion of the tonal content (13 k rpmc, 100 sideline 

emission angle, TTT). 

0 2000 4000 6000 8000 10000

Frequency, Hz

 

LSAF, M4, entry 2, 0.25 M

 9x15, M4, 0.20 M

 BPF 

 |

 2BPF 

 |

10 dB

0 2000 4000 6000 8000 10000

Frequency, Hz

 

LSAF, M4, entry 2, 0.25 M

 9x15, M4, 0.20 M

 BPF 

 | 2BPF 

 |

10 dB
NASA/TM—2012-217608 37 

Figure 31.—Comparison of 1/3rd octave directivities obtained within a Mach number 0.20 free jet in the DNW 

facility at 88- and 120-in. sidelines (10 k rpmc, data adjusted to a 20-ft sideline, HTH). 

20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

Emission angle relative to inlet highlight, deg.

70

75

80

85

90

95

100

 

75

80

85

90

95

100

105

SPL,

dB

120 in sideline adjusted to 20 ft.

88 in. sideline adjusted to 20 ft.

75

80

85

90

95

100

105

(a) 4 kHz (contains bypass BPF)

(b) 8 kHz (contains bypass 2BPF and core BPF)

(c) 12.5 kHz (contains bypass 3BPF)
NASA/TM—2012-217608 38 

Figure 31.—Concluded.

20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

Emission angle relative to inlet highlight, deg.

55

60

65

70

75

80

85

 

65

70

75

80

85

90

95

SPL,

dB

120 in sideline adjusted to 20 ft.

88 in. sideline adjusted to 20 ft.

70

75

80

85

90

95

100

(d) 16 kHz 

(e) 25 kHz 

(f) 40 kHz 
NASA/TM—2012-217608 39 

Figure 32.—Comparison of UPS data acquired in the NASA 915 LSWT and within the free 

jet of the DNW free-jet facility. Both data were acquired with the NASA streamlined 

microphone holder on a nominal 88 in. sideline (8.1 k rpmc, 1/3rd directivities at 6.3 kHz 

(contains bypass 2BPF and core BPF tones), Mach number 0.20). 

Figure 33.—Comparison of UPS data acquired in the NASA 915 LSWT and within 

the free jet of the DNW freejet facility. Both data were acquired with the NASA 

streamlined microphone holder on a nominal 88-in. sideline (8.1 k rpmc, 1/3rd

directivities at 10 kHz (broadband spectral region), Mach number 0.20). 

20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

Emission angle relative to inlet highlight, deg.

80

85

90

95

100

105

110

 

80

85

90

95

100

105

110

SPL,

dB

NASA 9x15 data

DNW data

(a) M4, TTT

(b) M4, HTH

20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

Emission angle relative to inlet highlight, deg.

80

85

90

95

100

105

110

 

80

85

90

95

100

105

110

SPL,

dB

NASA 9x15 data

DNW data

(a) M4, TTT

(b) M4, HTH
NASA/TM—2012-217608 40 

Figure 34.—Comparison of UPS data acquired in the NASA 915 LSWT and within the free 

jet of the DNW free-jet facility. Both data were acquired with the NASA streamlined 

microphone holder on a nominal 88-in. sideline (8.1 k rpmc, 1/3rd directivities at 20 kHz 

(broadband spectral region), Mach number 0.20). 

Figure 35.—Comparison of UPS data acquired in the NASA 915 LSWT and within the free 

jet of the DNW free-jet facility. Both data were acquired with the NASA streamlined 

microphone holder on a nominal 88-in. sideline (10 k rpmc, 1/3rd directivities at 4 kHz 

(broadband spectral region), Mach number 0.20). 

20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

Emission angle relative to inlet highlight, deg.

80

85

90

95

100

105

110

 

80

85

90

95

100

105

110

SPL,

dB

NASA 9x15 data

DNW data

(a) M4, TTT

(b) M4, HTH

20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

Emission angle relative to inlet highlight, deg.

80

85

90

95

100

105

110

 

80

85

90

95

100

105

110

SPL,

dB

NASA 9x15 data

DNW data

(a) M4, TTT

(b) M4, HTH
NASA/TM—2012-217608 41 

Figure 36.—Comparison of UPS data acquired in the NASA 915 LSWT and within the free 

jet of the DNW free-jet facility. Both data were acquired with the NASA streamlined 

microphone holder on a nominal 88-in. sideline (10 k rpmc, 1/3rd directivities at 8 kHz 

(contains bypass 2BPF and core BPF tones), Mach number 0.20). 

Figure 37.—Comparison of UPS data acquired in the NASA 915 LSWT and within the free 

jet of the DNW free-jet facility. Both data were acquired with the NASA streamlined 

microphone holder on a nominal 88-in. sideline (10 k rpmc, 1/3rd directivities at 16 kHz 

(contains bypass 4BPF and core 2BPF tones), Mach number 0.20). 

20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

Emission angle relative to inlet highlight, deg.

80

85

90

95

100

105

110

 

80

85

90

95

100

105

110

SPL,

dB

NASA 9x15 data

DNW data

(a) M4, TTT

(b) M4, HTH

20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

Emission angle relative to inlet highlight, deg.

80

85

90

95

100

105

110

 

80

85

90

95

100

105

110

SPL,

dB

NASA 9x15 data

DNW data

(a) M4, TTT

(b) M4, HTH
NASA/TM—2012-217608 42 

Figure 38.—Comparison of UPS data acquired in the NASA 915 LSWT and within the free 

jet of the DNW free-jet facility. Both data were acquired with the NASA streamlined 

microphone holder on a nominal 88-in. sideline (10 k rpmc, 1/3rd directivities at 25 kHz 

(contains bypass 6BPF and core 3BPF tones), Mach number 0.20). 

Figure 39.—Comparison of UPS data acquired in the NASA 915 LSWT and within the free 

jet of the DNW free-jet facility. Both data were acquired with the NASA streamlined 

microphone holder on a nominal 88-in. sideline (12 k rpmc, 1/3rd directivities at 4 kHz 

(broadband spectral region), Mach number 0.20). 

20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

Emission angle relative to inlet highlight, deg.

80

85

90

95

100

105

110

 

80

85

90

95

100

105

110

SPL,

dB

NASA 9x15 data

DNW data

(a) M4, TTT

(b) M4, HTH

20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

Emission angle relative to inlet highlight, deg.

85

90

95

100

105

110

115

 

85

90

95

100

105

110

115

SPL,

dB

NASA 9x15 data

DNW data

(a) M4, TTT

(b) M4, HTH
NASA/TM—2012-217608 43 

Figure 40.—Comparison of UPS data acquired in the NASA 915 LSWT and within the free 

jet of the DNW free-jet facility. Both data were acquired with the NASA streamlined 

microphone holder on a nominal 88-in. sideline (12 k rpmc, 1/3rd directivities at 10 kHz 

(contains bypass 2BPF and core BPF tones), Mach number 0.20). 

Figure 41.—Comparison of UPS data acquired in the NASA 915 LSWT and within the free 

jet of the DNW free-jet facility. Both data were acquired with the NASA streamlined 

microphone holder on a nominal 88-in. sideline (12 k rpmc, 1/3rd directivities at 20 kHz 

(contains bypass 4BPF and core 2BPF tones), Mach number 0.20). 

20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

Emission angle relative to inlet highlight, deg.

85

90

95

100

105

110

115

 

85

90

95

100

105

110

115

SPL,

dB

NASA 9x15 data

DNW data

(a) M4, TTT

(b) M4, HTH

20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

Emission angle relative to inlet highlight, deg.

85

90

95

100

105

110

115

 

85

90

95

100

105

110

115

SPL,

dB

NASA 9x15 data

DNW data

(a) M4, TTT

(b) M4, HTH
NASA/TM—2012-217608 44 

Figure 42.—Comparison of UPS data acquired in the NASA 915 LSWT and within the free 

jet of the DNW free-jet facility. Both data were acquired with the NASA streamlined 

microphone holder on a nominal 88-in. sideline (13.5 k rpmc, 1/3rd directivities at 5 kHz 

(contains bypass BPF tone), Mach number 0.20). 

 

Figure 43.—Comparison of UPS data acquired in the NASA 915 LSWT and within the free 

jet of the DNW free-jet facility. Both data were acquired with the NASA streamlined 

microphone holder on a nominal 88-in. sideline (13.5 k rpmc, 1/3rd directivities at 8 kHz 

(broadband spectral region), Mach number 0.20). 

20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

Emission angle relative to inlet highlight, deg.

90

95

100

105

110

115

120

 

85

90

95

100

105

110

115

SPL,

dB

NASA 9x15 data

DNW data

(a) M4, TTT

(b) M4, HTH

20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

Emission angle relative to inlet highlight, deg.

90

95

100

105

110

115

120

 

85

90

95

100

105

110

115

SPL,

dB

NASA 9x15 data

DNW data

(a) M4, TTT

(b) M4, HTH
NASA/TM—2012-217608 45 

Figure 44.—Comparison of UPS data acquired in the NASA 915 LSWT and within the free 

jet of the DNW free-jet facility. Both data were acquired with the NASA streamlined 

microphone holder on a nominal 88-in. sideline (13.5 k rpmc, 1/3rd directivities at 10 kHz 

(contains bypass 2BPF and core BPF tones), Mach number 0.20). 

Figure 45.—Comparison of UPS data acquired in the NASA 915 LSWT and within the free jet of the 

DNW free-jet facility. Both data were acquired with the NASA streamlined microphone holder on a 

nominal 88-in. sideline (13.5 k rpmc, 1/3rd directivities at 20 kHz (contains bypass 4BPF and core 2BPF 

tones), Mach number 0.20). 

20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

Emission angle relative to inlet highlight, deg.

90

95

100

105

110

115

120

 

85

90

95

100

105

110

115

SPL,

dB

NASA 9x15 data

DNW data

(a) M4, TTT

(b) M4, HTH

20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

Emission angle relative to inlet highlight, deg.

85

90

95

100

105

110

115

 

85

90

95

100

105

110

115

SPL,

dB

NASA 9x15 data

DNW data

(a) M4, TTT

(b) M4, HTH
NASA/TM—2012-217608 46 

Figure 46.—Comparison of constant bandwidth (36 Hz) spectra acquired in the DNW 

facility within a Mach number 0.20 free jet and outside the freejet showing tone 

diffraction through the free jet shear layer. (12 k rpmc, 60 emission angle, HTH). 

Figure 47.—Comparison of constant bandwidth (36 Hz) spectra acquired in the DNW 

facility within a Mach number 0.20 free jet and outside the free jet showing tone 

diffraction through the free-jet shear layer. (12 k rpmc, 90 emission angle, HTH). 

0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000

Frequency, Hz

 

(a) Data taken within freejet

(b) Data taken outside freejet

10 dB

BPF

 |

2BPF

|

Core

BPF

|

Core

2BPF

|

3BPF

|

4BPF

|

0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000

Frequency, Hz

 

(a) Data taken within freejet

(b) Data taken outside freejet

10 dB

BPF

 | 2BPF

|

Core

BPF

| Core

2BPF

|

3BPF

|

4BPF

|
NASA/TM—2012-217608 47 

Figure 48.—Comparison of constant bandwidth (36 Hz) spectra acquired in the DNW facility 

within a Mach number 0.20 free jet and outside the free jet showing tone diffraction through 

the free jet shear layer. (12 k rpmc, 120 emission angle, HTH). 

0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000

Frequency, Hz

 

(a) Data taken within freejet

(b) Data taken outside freejet

10 dB

BPF

 |

2BPF

|

Core

BPF

| Core

2BPF

|

3BPF

|

4BPF

|
NASA/TM—2012-217608 48 

Figure 49.—Comparison of constant bandwidth (36 Hz) directivities acquired in the DNW facility within a 

Mach number 0.20 free jet and outside the freejet showing tone diffraction through the free jet shear layer 

(12 k rpmc, bypass BPF tone, M4, HTH). 

20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

Emission angle relative to inlet highlight, deg.

70

80

90

100

110

 

70

80

90

100

110

SPL,

dB

60

70

80

90

100

Fixed mics on 36 ft. sideline -- outside freejet

Traverse on 120 in. sideline -- inside freejet

Traverse on 88 in. sideline -- inside freejet
NASA/TM—2012-217608 49 

Figure 50.—Comparison of constant bandwidth (36 Hz) directivities acquired in the DNW facility within a 

Mach number 0.20 free jet and outside the free jet showing tone diffraction through the free jet shear layer 

(12 k rpmc, bypass 2BPF tone, M4, HTH). 

20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

Emission angle relative to inlet highlight, deg.

70

80

90

100

110

 

70

80

90

100

110

SPL,

dB

60

70

80

90

100

Fixed mics on 36 ft. sideline -- outside freejet

Traverse on 120 in. sideline -- inside freejet

Traverse on 88 in. sideline -- inside freejet
NASA/TM—2012-217608 50 

Figure 51.—Comparison of constant bandwidth (36 Hz) directivities acquired in the DNW facility within a 

Mach number 0.20 free jet and outside the free jet showing tone diffraction through the free jet shear layer 

(12 k rpmc, bypass 3BPF tone, M4, HTH). 

20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

Emission angle relative to inlet highlight, deg.

60

70

80

90

100

 

60

70

80

90

100

SPL,

dB

50

60

70

80

90

Fixed mics on 36 ft. sideline -- outside freejet

Traverse on 120 in. sideline -- inside freejet

Traverse on 88 in. sideline -- inside freejet
NASA/TM—2012-217608 51 

Figure 52.—Comparison of constant bandwidth (36 Hz) directivities acquired in the DNW facility within a 

Mach number 0.20 free jet and outside the free jet showing tone diffraction through the free jet shear 

layer (12 k rpmc, bypass 4BPF tone, M4, HTH). 

20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

Emission angle relative to inlet highlight, deg.

60

70

80

90

100

 

60

70

80

90

100

SPL,

dB

40

50

60

70

80

Fixed mics on 36 ft. sideline -- outside freejet

Traverse on 120 in. sideline -- inside freejet

Traverse on 88 in. sideline -- inside freejet
NASA/TM—2012-217608 52 

Figure 53.—Comparison of constant bandwidth (36 Hz) directivities acquired in the DNW facility within a 

Mach number 0.20 free jet and outside the free jet showing tone diffraction through the free jet shear layer 

(12 k rpmc, core BPF tone, M4, HTH). 

20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

Emission angle relative to inlet highlight, deg.

60

70

80

90

100

 

60

70

80

90

100

SPL,

dB

50

60

70

80

90

Fixed mics on 36 ft. sideline -- outside freejet

Traverse on 120 in. sideline -- inside freejet

Traverse on 88 in. sideline -- inside freejet
NASA/TM—2012-217608 53 

Figure 54.—Comparison of constant bandwidth (36 Hz) directivities acquired in the DNW facility within a Mach 

number 0.20 free jet and outside the free jet showing tone diffraction through the free jet shear layer (12 k rpmc, 

core 2BPF tone, M4, HTH). 

20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

Emission angle relative to inlet highlight, deg.

60

70

80

90

100

 

60

70

80

90

100

SPL,

dB

40

50

60

70

80

Fixed mics on 36 ft. sideline -- outside freejet

Traverse on 120 in. sideline -- inside freejet

Traverse on 88 in. sideline -- inside freejet
NASA/TM—2012-217608 54 

Figure 55.—Comparison of “in-flow” constant bandwidth directivities acquired in the DNW and in the 

NASA 915 LSWT on a nominal 88-in. sideline (10 k rpmc, 0.20 M, M4, HTH). 

20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

Emission angle relative to inlet highlight, deg.

70

80

90

100

 

75

85

95

105

SPL,

dB

9x15 data, 118 Hz BW

DNW data, 118 Hz BW (sum of three adjacent bands)

70

80

90

100

(a) Bypass BPF tone

(b) Bypass 2BPF tone

(c) Bypass 3BPF tone
NASA/TM—2012-217608 55 

Figure 55.—Concluded. 

20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

Emission angle relative to inlet highlight, deg.

70

80

90

100

 

75

85

95

105

SPL,

dB

9x15 data, 118 Hz BW

DNW data, 118 Hz BW (sum of three adjacent bands)

70

80

90

100

(d) Bypass 4BPF tone

(e) Core BPF tone

(f) Core 2BPF tone
NASA/TM—2012-217608 56 

Figure 56.—Comparison of “in-flow” constant bandwidth directivities acquired in the DNW and in the 

NASA 915 LSWT on a nominal 88-in. sideline (10 k rpmc, Mach number 0.20, M4, TTT). 

20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

Emission angle relative to inlet highlight, deg.

70

80

90

100

 

75

85

95

105

SPL,

dB

9x15 data, 118 Hz BW

DNW data, 118 Hz BW (sum of 3 adjacent bands)

70

80

90

100

(a) Bypass BPF tone

(b) Bypass 2BPF tone

(c) Bypass 3BPF tone
NASA/TM—2012-217608 57 

Figure 56.—Concluded. 

20 30 40 50 60 70 80 90 100 110 120 130 140 150 160

Emission angle relative to inlet highlight, deg.

70

80

90

100

 

75

85

95

105

SPL,

dB

9x15 data, 118 Hz BW

DNW data, 118 Hz BW (sum of 3 adjacent bands)

70

80

90

100

(d) Bypass 4BPF tone

(e) Core BPF tone

(f) Core 2BPF tone
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control number. 

PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 

1. REPORT DATE (DD-MM-YYYY)

01-06-2012 

2. REPORT TYPE

Technical Memorandum 

3. DATES COVERED (From - To)

4. TITLE AND SUBTITLE

Acoustic Performance of an Advanced Model Turbofan in Three Aeroacoustic Test Facilities 

5a. CONTRACT NUMBER

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

Woodward, Richard, P.; Hughes, Christopher, E. 

5d. PROJECT NUMBER

5e. TASK NUMBER

5f. WORK UNIT NUMBER

WBS 561581.02.08.03.45.02.04 

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-18189 

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

National Aeronautics and Space Administration 

Washington, DC 20546-0001 

10. SPONSORING/MONITOR'S

 ACRONYM(S)

NASA 

11. SPONSORING/MONITORING

 REPORT NUMBER

NASA/TM-2012-217608 

12. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified-Unlimited 

Subject Category: 01 

Available electronically at http://www.sti.nasa.gov 

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

13. SUPPLEMENTARY NOTES

14. ABSTRACT

A model advanced turbofan was acoustically tested in the NASA Glenn 9- by 15-Foot-Low-Speed Wind Tunnel (LSWT), and in two other 

aeroacoustic facilities. The Universal Propulsion Simulator (UPS) fan was designed and manufactured by the General Electric Aircraft 

Engines (GEAE) Company, and featured active core, as well as bypass, flow paths. The reference test configurations were with the metal, 

M4, rotor with hardwall and treated bypass flow ducts. The UPS fan was tested within an airflow at a Mach number of 0.20 (limited flow 

data were also acquired at a Mach number of 0.25) which is representative of aircraft takeoff and approach conditions. Comparisons were 

made between data acquired within the airflow (9×15 LSWT and German-Dutch Wind Tunnel (DNW)) and outside of a free jet (Boeing 

Low Speed Aero acoustic Facility (LSAF) and DNW). Sideline data were acquired on an 89-in. (nominal 4 fan diameters) sideline using the 

same microphone assembly and holder in the 9×15 LSWT and DNW facilities. These data showed good agreement for similar UPS 

operating conditions and configurations. Distortion of fan spectra tonal content through a free jet shear layer was documented, suggesting 

that in-flow acoustic measurements are required for comprehensive fan noise diagnostics. However, there was good agreement for overall 

sound power level (PWL) fan noise measurements made both within and outside of the test facility airflow. 

15. SUBJECT TERMS

Acoustic emission; Jet aircraft noise; Engine noise; Noise reduction 

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF

 ABSTRACT

UU 

18. NUMBER

 OF 

 PAGES

63 

19a. NAME OF RESPONSIBLE PERSON

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

a. REPORT

U 

b. ABSTRACT

U 

c. THIS 

PAGE

U 

19b. TELEPHONE NUMBER (include area code)

443-757-5802 

Standard Form 298 (Rev. 8-98)

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