Richard P. Woodward and Christopher E. Hughes

Glenn Research Center, Cleveland, Ohio

Acoustic Performance of the GEAE UPS Research 

Fan in the NASA Glenn 9- by 15-Foot Low-Speed 

Wind Tunnel

NASA/TM—2012-217450

May 2012
NASA STI Program . . . in Profi le

Since its founding, NASA has been dedicated to the 

advancement of aeronautics and space science. The 

NASA Scientifi c and Technical Information (STI) 

program plays a key part in helping NASA maintain 

this important role.

The NASA STI Program operates under the auspices 

of the Agency Chief Information Offi cer. It collects, 

organizes, provides for archiving, and disseminates 

NASA’s STI. The NASA STI program provides access 

to the NASA Aeronautics and Space Database and 

its public interface, the NASA Technical Reports 

Server, thus providing one of the largest collections 

of aeronautical and space science STI in the world. 

Results are published in both non-NASA channels 

and by NASA in the NASA STI Report Series, which 

includes the following report types:

• TECHNICAL PUBLICATION. Reports of 

completed research or a major signifi cant phase 

of research that present the results of NASA 

programs and include extensive data or theoretical 

analysis. Includes compilations of signifi cant 

scientifi c and technical data and information 

deemed to be of continuing reference value. 

NASA counterpart of peer-reviewed formal 

professional papers but has less stringent 

limitations on manuscript length and extent of 

graphic presentations.

• TECHNICAL MEMORANDUM. Scientifi c 

and technical fi ndings that are preliminary or 

of specialized interest, e.g., quick release 

reports, working papers, and bibliographies that 

contain minimal annotation. Does not contain 

extensive analysis.

• CONTRACTOR REPORT. Scientifi c and 

technical fi ndings by NASA-sponsored 

contractors and grantees.

• CONFERENCE PUBLICATION. Collected 

papers from scientifi c and technical 

conferences, symposia, seminars, or other 

meetings sponsored or cosponsored by NASA.

• SPECIAL PUBLICATION. Scientifi c, 

technical, or historical information from 

NASA programs, projects, and missions, often 

concerned with subjects having substantial 

public interest.

• TECHNICAL TRANSLATION. Englishlanguage translations of foreign scientifi c and 

technical material pertinent to NASA’s mission.

Specialized services also include creating custom 

thesauri, building customized databases, organizing 

and publishing research results.

For more information about the NASA STI 

program, see the following:

• Access the NASA STI program home page at 

http://www.sti.nasa.gov

• E-mail your question via the Internet to help@

sti.nasa.gov

• Fax your question to the NASA STI Help Desk 

at 443–757–5803

• Telephone the NASA STI Help Desk at

 443–757–5802

• Write to:

 NASA Center for AeroSpace Information (CASI)

 7115 Standard Drive

 Hanover, MD 21076–1320
Richard P. Woodward and Christopher E. Hughes

Glenn Research Center, Cleveland, Ohio

Acoustic Performance of the GEAE UPS Research 

Fan in the NASA Glenn 9- by 15-Foot Low-Speed 

Wind Tunnel

NASA/TM—2012-217450

May 2012

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135
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://www.sti.nasa.gov

Trade names and trademarks are used in this report for identifi cation 

only. Their usage does not constitute an offi cial endorsement, 

either expressed or implied, by the National Aeronautics and 

Space Administration.

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—2012-217450 1 

Acoustic Performance of the GEAE UPS Research Fan in the 

NASA Glenn 9- by 15-Foot Low-Speed Wind Tunnel 

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 in 1994. The Universal Propulsion Simulator fan was designed and manufactured by General 

Electric Aircraft Engines, and included an active core, as well as bypass, flow paths. The fan was tested with 

several rotors featuring unswept, forward-swept and aft-swept designs of both metal and composite 

construction. Sideline acoustic data were taken with both hard and acoustically treated walls in the flow 

passages. The fan was tested within an airflow at a Mach number of 0.20, which is representative of aircraft 

takeoff/approach conditions. All rotors showed similar aerodynamic performance. However, the composite 

rotors typically showed higher noise levels than did corresponding metal rotors. Aft and forward rotor 

sweep showed at most modest reductions of transonic multiple pure tone levels. However, rotor sweep often 

introduced increased rotor-stator interaction tone levels. Broadband noise was typically higher for the 

composite rotors and also for the aft-swept metal rotor. Transonic MPT generation was reduced with 

increasing fan axis angle of attack (AOA); however, higher downstream noise levels did increase with AOA 

resulting in higher overall Effective Perceived Noise Level. 

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 1994 UPS 

fan tests were conducted in the NASA Glenn 9- by 15-Foot Low-Speed Wind Tunnel (henceforth referred 

to as the 915 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 inlet and exhaust flow passages. Acoustic testing 

was performed with air flowing in the tunnel at a Mach number of 0.20, which is representative of aircraft 

takeoff/approach conditions. 

The primary focus of these tests was to acquire representative UPS fan data in the NASA Glenn 

Research Center 915 LSWT and in two other world class facilities—the Boeing Low-Speed 

Aeroacoustic Facility (LSAF) free jet, and the German-Dutch Wind Tunnel (DNW) free jet facility. The 

acoustic results of the UPS fan tests in these three facilities can be found in References 1 and 2. Data 

comparisons for the UPS fan in these three facilities showed the NASA 915 LSWT to be an acceptable 

facility for fan far-field aeroacoustic measurements under simulated flight conditions. 

Description of Test 

Research Fan 

The UPS fan is representative of current state-of-the-art high bypass ratio turbofan engines. Figure 1 

is a cross-sectional sketch of the UPS fan. The bypass rotor diameter is 55.9 cm (22.0 in.). The rotor 

bypass-vane ratio is adequate to achieve cutoff of the fundamental interaction tone (Refs. 3 and 4). The 

UPS fan has an active core flow that includes a powered rotor (same rotational speed as the bypass fan) 

with inlet and outlet vanes. The core flow passage has de-swirl struts slightly downstream of the core 
NASA/TM—2012-217450 2 

outlet guide vanes, and aft load struts further downstream which have the potential of generating rotorstrut interaction noise. 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. The fan 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 wind tunnel test section floor. 

The UPS fan stage was tested with several bypass rotor configurations as shown in Figure 2. (The 

bypass stator and core stage were the same throughout this test series.) The baseline rotor, designated 

“M4” was unswept and fabricated of metal. Additional test rotors allowed investigation of rotor forward 

and aft sweep effects, and relative performance of composite versus metal rotor construction. 

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 stator. Letter designations are used in this 

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

outlet sections of the bypass duct. The letter “H” designates a hard-wall panel. The initial acoustic 

treatment or the original acoustic treatment as provided by GEAE, is designated by the letter “T.” A new 

or alternative acoustic treatment, designed by NASA, is designated by the letter “N.” Thus, the hard-wall 

configuration is designated “HTH” and the treated configurations are designated “TTT” or “NTN.” 

915 LSWT and Acoustic Instrumentation 

The NASA Glenn 915 LSWT is located in the low speed return leg of the 86 Supersonic Wind 

Tunnel (Fig. 3). The tunnel test section walls, floor and ceiling have acoustic treatment to produce an 

anechoic test environment (Refs. 6 to 8). Figure 4 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 5) 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 226 cm (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 at a tunnel Mach number of 0.20, which is 

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

Acoustic data were taken at 0, 3, and 9 of fan axis angles of attack. 

Acoustic data acquired in the 915 LSWT were processed as constant bandwidth spectra. Spectra 

were acquired and averaged at each translating probe position with 6 and 118 Hz bandwidths. These 

constant bandwidth spectra were electronically merged and used to generate 1/3rd octave spectra. The 

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. Geometric (observed) sideline angles were converted to emission angles 

according to the relationship: 

 em = geom - sin-1(Mo sin geom) 

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

section Mach number. 
NASA/TM—2012-217450 3 

There was initially some concern as to the validity of data acquired with the translating microphone 

probe 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 UPS test were used to compare fixed and translating microphone data quality (Ref. 8). 

Wakes from upstream microphone holders were shown to persist a significant distance downstream, thus 

possibly impinging on downstream microphones with a consequent compromise in the data quality from 

these microphones. Also, the vertical stagger used to minimize this wake interaction introduced a new, 

azimuthal variation in the sideline data—a problem not associated with a single traversing microphone. 

The traversing microphone probe is not restricted as to the number of discrete measurement positions (48 

positions were used for this test). Acoustic data presented herein is for the translating microphone probe. 

Results and Discussion 

Aerodynamic Performance 

Limited aerodynamic results are available for the UPS tests in the NASA 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 tip speed (Table 1) was 1214 ft/sec (metal 

rotors, such as M4) and 1274 ft/sec (composite rotors). 

The UPS fan was tested in the 915 LSWT with several rotor configurations (Table 3). As discussed 

previously, acoustic treatment was always present between the rotor and the stator on the bypass duct 

outer wall (see Fig. 1). Data were taken with two types of acoustic treatment on the inlet and bypass ducts 

as well as for hard-wall in those locations. Acoustic data were acquired for the first 9 configurations, 

listed as C-1 to C-9 in Table 3, followed by a series of aerodynamic and flow visualization tests (not 

reported herein). A rather severe drive system oil leak developed at the end of these non-acoustic tests, 

necessitating the insertion of an oil drain pipe extending from the drive through the downstream flow 

passages. Consequently, aeroacoustic results for the last four test configurations (listed as C-44 a and b 

and C-45 a and b in Table 3) utilizing the advanced unswept composite rotor were compromised with 

extraneous noise by the insertion of this oil drainpipe, and are not included herein. 

Representative fan aerodynamic performance for the UPS tests are shown in Figures 6 and 7. 

Figure 6 shows the aerodynamic performance in terms of the bypass pressure ratio as a function of bypass 

corrected weight flow for the hard-wall test configurations. These results show similar performance for 

each of the 4 bypass rotors; the unswept (M4) and the aft-swept metal rotors, and the unswept and 

forward-swept composite rotors (see Fig. 2). Figure 7 shows corresponding results for the test 

configurations with acoustically treated inlet and exhaust ducts. 

Acoustic Performance 

Expected Acoustic Propagation 

Table 4 shows the expected frequencies for the first four rotor bypass rotor-stator interaction tone 

orders and first two core stage tone orders for each of the fan test speeds. These results are presented in 

graphical form in Figure 8. Blade and vane numbers for the bypass and core stages were selected to 

acoustically cutoff the propagation of the fundamental blade passing frequency (BPF) tone at lower fan 

speeds, according to the acoustic mode theory of References 3 and 4. 
NASA/TM—2012-217450 4 

Effective Perceived Noise Level 

The Effective Perceived Noise Level (EPNL) provides a subjective measure of the aircraft flyover 

and sideline noise levels. This value is derived from the flyover or sideline sound pressure level profiles 

and is a function of frequency, duration, and tone content. Effective perceived noise levels were 

calculated by GEAE using the NASA 915 LSWT results. The furthest downstream emission angle 

measured by the traverse microphone at M0 = 0.20 flow was 130, which was not sufficiently downstream 

to define a 10 dB drop off from the peak sideline values. (Later acoustic tests in the 915 LSWT used 

three fixed downstream microphones to better define aft fan noise.) Therefore, an assumed downstream 

directivity shape was used to complete the EPNL calculations. A scale factor of 5.6 was used. EPNL 

values are calculated from “full-scale engine” sound pressure data up to 10 kHz. Thus, with this scale 

factor, model acoustic data up to about 60 kHz were utilized. 

An unexpected tone in the acoustic spectra was associated with the composite rotor (configurations 

4 through 7, Table 3). The tones were found to be caused by the presence of bolt access holes in the rotor 

spinner used for the composite blade configurations. Another spinner with slightly different bolt hole 

geometry was used for the metal rotor configurations and did not generate these unexpected tones. (The 

acoustic impact of the spinner holes was investigated with the advanced unswept composite rotor of 

configurations 44 and 45 using metallic tape to cover the spinner holes.) The spinner-induced tones were 

electronically removed from the spectra for the composite rotor configurations. Figure 9 shows the 

adverse effect of these spinner bolt holes as a function of rotor tip speed, with the noise difference being 

most significant at lower tip speeds. 

Figure 10 compares EPNL levels for several hard-wall (HTH) configurations at 0 fan axis angle of 

attack. The noise levels for the metal baseline M4 rotor are significantly lower than those for the aft-swept 

metal rotor or the unswept and forward-swept composite rotors—especially near 950 ft/sec rotor tip 

speed. The relatively higher noise levels for the aft-swept metal rotor may be the result of increased rotor 

wake-vane interaction because of reduced blade-vane spacing toward the tip region. The composite rotors 

were consistently noisier than their metal counterparts. This may be due, at least in part, to adverse 

flexing of the composite rotors under load. 

Figure 11 shows corresponding EPNL results for the test configurations with inlet and bypass exhaust 

duct treatment. Two wall treatment configurations were tested, as provided by GEAE. As indicated 

before, the original treatment configurations are designated TTT. New treatment panels, designated NTN 

were introduced for some of the later configurations. Once again, the lowest EPNL values were 

associated with the baseline M4 metal rotor. The M4 rotor with the original wall treatment (TTT) was 

typically slightly quieter than with the new treatment (NTN). The composite rotors were typically noisier 

than the M4 rotor, although the difference between metal and composite rotors was not as pronounced as 

for the hardwall configurations of Figure 10. 

Figure 12 compares the baseline M4 configurations with (TTT) and without (HTH) wall treatment. 

The wall treatment varied in effectiveness through the range of test speeds from about 2 EPNdB at the 

lowest speeds to about 5 EPNdB at the higher speeds—the exception was near 950 ft/sec rotor tip speed, 

which showed no treatment benefit. Rotor multiple pure tone generation will occur as the tip Mach 

number approaches unity. The results of Figure 12 show lower perceived noise levels with liner 

treatment, most likely due to MPT absorption by the liner. 

Effect of Rotor Design and Construction 

The UPS fan was tested with several metal and composite rotors featuring mild forward and aft sweep 

as well as metal and composite unswept rotors (see Fig. 2). The EPNL results, given in the previous 

section, showed that, in general, the noise levels were somewhat lower with the metal rotors than with 

composite rotors, even though all rotors showed comparable aerodynamic performance, 

(Figs. 6 and 7). The following discussion presents spectral and directivity comparisons for these test 

 
NASA/TM—2012-217450 5 

rotors. Results are presented for six rotor comparisons first showing EPNL versus fan speed. Results are 

then presented for constant bandwidth (6 Hz) spectra at 10 and 12 k corrected rpm, or rpmc at 47, 102, 

and 130 sideline emission angles. The fan tangential tip speed is subsonic at 10 k rpmc (nominal 

980 ft/sec), and supersonic at 12 k rpmc (nominal 1180 ft/sec), which is the speed where maximum MPT 

generation occurs. These comparisons are then concluded with 1/3rd octave sideline directivities at these 

two fan speeds. 

Unswept Rotor 

Figures 13 to 30 compare acoustic performance of the baseline unswept M4 metal rotor and the 

unswept composite rotor. Figures 13 to 21 are for the hardwall duct, and Figures 22 to 30 are for the 

“new” duct acoustic treatment (NTN). These results continue to show higher noise levels associated with 

the composite rotor. 

Figure 13 compares EPNL for the two rotors as a function of rotor tip speed, showing the composite 

rotor configuration to be up to 4 EPNdB noisier than the M4 metal rotor. Figure 14 compares constant 

bandwidth spectra at 10 k rpmc at the upstream, 47 emission angle. There is a “haystack” noise region 

associated with the composite rotor near 2 kHz that is not seen for the metal rotor. It is possible that MPT 

generation occurs slightly sooner (at a lower tip speed) for the composite rotor than for the metal rotor. 

Likewise, there are several pure tones above the bypass blade passage frequency (BPF) which are only 

seen for the composite rotor. There is evidence of the fundamental rotor tone (BPF) in these spectra even 

though the blade and vane numbers were chosen to cutoff the fundamental BPF tone. The fan tip speed is 

approaching transonic at 10 k rpmc such that a rotor-alone BPF tone is possible. The bypass 2BPF tone, 

which is clearly seen for the metal rotor, is essentially missing from the spectra for the composite rotor at 

this sideline angle. Broadband levels tend to be higher for the composite rotor. The 2 kHz “haystack” is 

not seen for the composite rotor at the 102 and 130 emission angles (Figs. 15 and 16). Broadband levels 

are still slightly higher for the composite rotor at the further aft sideline locations. MPT generation 

appears to be well established for both rotors (Figs. 17 to 19) at 12 k rpmc, where the broadband level is 

still higher for the composite rotor. 

Figure 20 compares 1/3rd octave directivities for the metal and composite unswept rotors at 

10 k rpmc. Noise levels for the composite rotor are especially higher toward upstream angles at 2 and 

2.5 kHz (Figs. 20(a) and (b)), which correspond to the spectral “haystack” (possibly early MPT 

generation) observed in the spectra of Figure 15. Higher noise levels for the composite rotor become more 

consistent across the directivity survey with increasing frequency, eventually becoming aft dominated at 5 

kHz (Fig. 20(e)). The directivity surveys for the bypass 2BPF and core BPF tones (8 kHz, Fig. 20(f), See 

also Table 4) show a somewhat higher level for the composite rotor, although these noise levels are 

significantly affected by differences in broadband levels for the two rotors. 

Directivities at 12 k rpmc (Fig. 21) again show high noise levels associated with the composite rotor 

at forward sideline angles and low frequencies. However, unlike the directivity results at 10 k rpmc, noise 

level differences between the two rotors become insignificant at frequencies above 4 kHz. 

Figures 22 to 30 present a similar comparison for the unswept metal and composite rotors with the 

“new” bypass duct acoustic treatment (NTN) in place. EPNL differences are significantly smaller with 

duct acoustic treatment, although the composite rotor is typically still noisier (Fig. 22, compare with 

Fig. 13). The EPNL difference tends to be less as the rotor tip speed exceeds the sonic speed where MPT 

energy (rather than broadband) tends to dominate the noise spectra. 

The constant bandwidth spectral comparisons at 10 k and 12 k rpmc (Figs. 23 to 28) correspond to the 

previously discussed figures for the hard-wall (HTH) configuration (Figs. 14 to 19). At 10 k rpmc the new 

acoustic treatment greatly reduced the 2BPF tone—especially at 47 and 102 sideline angles. However, 

there was some increase in the fundamental, BPF tone associated with the NTN treatment. 
NASA/TM—2012-217450 6 

There is considerable MPT generation at 12 k rpmc for both the hard-wall and treated bypass ducts, 

although subjectively, duct treatment somewhat reduced the severity of these MPT tones. Also, the new 

duct treatment was more effective in reducing the fundamental tone level at this fan speed than was seen 

at the lower, 10 k rpmc fan speed. 

Figures 29 and 30 show, respectively, 1/3rd octave directivities at 10 k and 12 k rpmc for the unswept 

metal and composite rotors with duct wall acoustic treatment (NTN). The 10 k rpmc results are similar to 

those for the hard-wall duct (higher noise levels associated with the composite rotor), although the noise 

level differences between the two rotors are less with duct treatment in place. At 12 k rpmc the composite 

rotor shows significantly higher noise levels at upstream angles for 2 and 2.5 kHz (Figs. 30(a) and (b)). 

However, noise differences between the two rotors become minimal at 3.15 kHz. (Fig. 30(c)) and above. 

In summary, comparisons between the unswept metal and composite rotors consistently showed 

higher noise levels associated with the composite rotor. These differences are primarily in the broadband, 

and are more pronounced at lower frequencies. There are also consistent spectral differences between the 

metal and composite rotors. In particular, an upstream “haystack” region is exclusively seen for the 

composite rotor in the constant bandwidth spectra near 2 kHz. The composite rotor tends to have a higher 

bypass BPF tone at 10 k rpmc; however, the bypass 2BPF tone for this rotor and fan speed is much lower 

than that tone for the metal rotor. 

Effect of Rotor Aft Sweep 

Rotor aft sweep may retard and/or reduce MPT generation. However, aft rotor sweep may decrease 

the rotor-stator separation distance toward the tip region, thereby increase the potential for rotor-stator 

interaction noise. Figures 31 to 39 compare acoustic results for the unswept M4 metal rotor and the aftswept metal rotor (Fig. 2) with the hardwall bypass duct (HTH). Similar results are presented for the 

unswept M4 and modified aft-swept metal rotors with the “new” bypass duct acoustic treatment (NTN) in 

Figures 40 to 48. 

Figure 31 compares EPNL’s as a function of fan speed for the baseline M4 unswept and aft-swept 

metal rotors for the hard-wall configuration. Noise levels are consistently higher for the aft-swept rotor, 

especially for near transonic tip speeds, being 4 EPNdB higher than the baseline rotor at 970 ft/sec rotor 

tip speed. 

Figures 32 to 37 present constant bandwidth spectra at 10 and 12 k rpmc for 47, 102, and 130

emission angles. There are several spectral differences between the two rotors at 10 k rpmc (Figs. 32 to 

34). The fundamental bypass interaction tone is consistently higher for the aft-swept rotor as might be 

expected with the somewhat closer rotor-stator axial spacing toward the tip region. However, the bypass 

2BPF tone is much stronger for the baseline M4 rotor. Additionally, broadband levels for the aft-swept 

rotor are as much as 6 dB higher than those for the baseline rotor. 

Fundamental bypass interaction tone levels continue to be higher for the aft-swept rotor at 12 k rpmc

(Figs. 35 to 37), especially at further aft sideline angles. Again, broadband noise levels are higher for the 

aft-swept rotor. There is some indication that MPT generation may be slightly less for the aft-swept rotor, 

although the difference is insignificant. 

Figures 38 and 39 present 1/3rd octave directivities for the unswept and aft-swept metal rotors. At 

10 k rpmc (Fig. 38) broadband levels are consistently higher for the aft-swept rotor throughout the sideline 

survey. The directivities at 4 kHz (Fig. 38(d)), which contain the bypass BPF tone, are significantly 

higher for the aft-swept rotor compared to the other frequency bands shown, suggesting increased rotorstator wake interaction for this rotor (or possibly rotor-alone BPF tone as a consequence of transonic flow 

over the rotor). The directivities at 8 kHz (Fig. 38(f)), which contain the bypass 2BPF and core BPF tones 

are also somewhat higher for the aft-swept rotor. However, it is likely that the higher broadband levels for 

the aft-swept rotor largely control these levels. 
NASA/TM—2012-217450 7 

The directivities at 12 k rpmc (Fig. 39) tell a different story, suggesting that there may be a 

measurable reduction in MPT noise for the aft-swept rotor. As seen in the constant bandwidth spectra of 

Figures 35 to 37, both rotors generate significant MPTs at this rotor speed with somewhat higher 

broadband levels associated with the aft-swept rotor. At 2 kHz (Fig. 39(a)), the directivities for both 

rotors are essentially similar, if slightly higher for the unswept rotor. Directivity levels continue to be 

lower for the aft-swept rotor at 2.5 and 3.15 kHz. However a tendency for higher noise for the aft-swept 

rotor at downstream angles begins to be seen at 3.15 kHz and above. This is especially evident for the 

bypass BPF tone at 5 kHz, which is much stronger for the aft-swept rotor than for the unswept rotor. 

Increased tone noise for the aft-swept rotor is consistent with the idea that decreased blade-vane tip 

spacing should show increased rotor-stator interaction noise. 

The EPNL for the unswept M4 and modified aft-swept metal rotors with the “new” acoustic treatment 

(NTN) are in good agreement at subsonic and supersonic tip speeds (Fig. 40). The modified aft-swept 

rotor is about 2 EPNdB noisier than the baseline rotor in the transonic tip speed region. 

The constant bandwidth spectral comparisons for the two rotors are shown in Figures 41 to 46. The 

bypass stage interaction tones are typically higher for the baseline rotor at 10 k rpmc. Relative BPF and 

2BPF tone levels vary with sideline angles (Figs. 41 to 43). However, at 12 k rpmc (Figs. 44 to 46) the 

fundamental bypass interaction tone is typically higher for the modified aft-swept rotor. The modified aftswept rotor was consistently effective in reducing MPT generation at 12 k rpmc. 

Figure 47 presents 1/3rd octave directivities for the unswept and modified aft-swept rotors with bypass 

duct acoustic treatment at 10 k rpmc. These results are again similar to the hardwall results of Figure 38, 

showing somewhat higher noise levels for the modified aft-swept rotor, especially in the aft part for the 

directivities at 4 kHz (Fig. 47(d)) which contain the bypass BPF tone. 

Figure 48 presents the corresponding 1/3rd octave directivities at 12 k rpmc. There is clear evidence 

that MPT generation for the modified aft-swept rotor is significantly less than for the unswept rotor at 

frequencies below bypass BPF at upstream sideline angles. However, the bypass BPF tone is higher for 

the modified aft-swept rotor at further downstream sideline angles, consistent with increased rotor-stator 

interaction for the aft-swept rotor. 

The aft-swept rotor was expected to show reduced MPT generation, but with possibly increased rotorstator interaction tones due to reduced blade row spacing (especially near the tip region). These results 

showed that the modified aft-swept rotor did a better job of reducing MPTs than did the original aft-swept 

design, although this observation is somewhat qualified in that the original aft-swept rotor was tested with 

a hard bypass duct (HTH) while the modified aft-swept rotor was tested with a treated duct (NTN). In 

particular, the modified aft-swept rotor showed significantly less MPT generation in the region of 

transonic tip speed. However, the fundamental rotor-stator interaction tone, in particular, was higher for 

the aft-swept rotors. In addition, there is evidence of higher broadband levels associated with the aftswept design, especially at subsonic tip speeds. 

Effect of Rotor Forward Sweep 

In concept, rotor forward sweep could combine the MPT reductions associated with aft sweep while 

further increasing the blade row spacing in the tip region with resultant reductions in rotor-stator tone 

noise levels. Mechanically, forward sweep imposes additional blade stress considerations, which could 

include a tendency to “untwist” under aerodynamic loading. Test results were obtained with the unswept 

and forward-swept composite rotors in both the hard-wall (HTH) and “new” acoustic treatment (NTN) 

configurations. Results for the hardwall bypass duct are shown in Figures 49 to 57, while corresponding 

results with the new bypass duct acoustic treatment are shown in Figures 58 to 66. 

Figure 49 compares EPNLs for the unswept and forward-swept composite rotors (Fig. 2) for the 

hardwall bypass duct. Noise levels are essentially the same for both rotors. Figure 50 compares constant 

bandwidth spectra at the 47 emission angle and 10 k rpmc for the two rotors. The spectra are mostly 

similar, showing the previously seen “haystack” at 2 kHz, which was previously shown for composite 

 
NASA/TM—2012-217450 8 

rotor noise (Fig. 14). The bypass 2BPF tone is significantly higher for the forward-swept rotor at this 

sideline angle. Spectra at 102 and 130 sideline emission angles (Figs. 51 and 52) do not show the 

“haystack” region; however, the bypass BPF and 2BPF tones are both higher for the forward-swept rotor. 

There is little difference in the MPT generation for the two rotors at 12 k rpmc at 47 and 130

sideline angles, with some decrease in MPT generation for the forward-swept rotor at 102 sideline angle 

(Figs. 53 to 55). The bypass rotor-stator interaction tones (BPF and 2BPF) continue to be somewhat 

stronger for the forward-swept rotor. 

Figure 56 shows 1/3rd octave directivities at 10 k rpmc. There is an indication of reduced broadband 

noise level associated with the forward-swept rotor (in contrast to the aft-swept rotor results of Figure 38 

in which the broadband noise for the aft-swept rotor was greater than that for the unswept rotor). There is 

essentially no difference in blade row interaction tone levels at 4 and 8 kHz (Figs. 56(d) and (f)). 

The 1/3rd octave directivity results at 12 k rpmc (Fig. 57) show little difference in the broadband levels 

for the two rotors at 2 and 2.5 kHz. (there is significant MPT content at this speed). There is an indication 

of reduced broadband level for the forward-swept rotor at 3.15 k and especially 4 kHz. The stronger 

bypass BPF tone for the forward-swept rotor, noted in the spectra of Figure 55, is evident in the 

directivities at 5 kHz (Fig. 57(e)) which include the bypass BPF tone. 

The comparison of forward-swept and unswept composite rotors (with the hard-wall duct 

configuration) showed mixed relative benefits for the two rotor designs. There was little evidence that 

MPT generation was significantly reduced with the forward-swept rotor, although that was the main 

expected benefit of the forward-swept design. Surprisingly, broadband levels were sometimes lower for 

the forward-swept rotor. Somewhat higher bypass interaction tone levels for the forward-swept rotor 

suggest that downstream wakes from this rotor were somewhat higher despite the increased rotor tipstator axial spacing. 

Figures 58 to 66 show the corresponding comparisons between the unswept and forward-swept 

composite rotors with the “new” bypass duct acoustic treatment (NTN). EPNL is essentially the same for 

the two rotors throughout the range of test speeds (Fig. 58). Representative constant bandwidth spectra at 

10 k and 12 k rpmc for the two rotors are shown in Figures 59 to 64. The forward-swept composite rotor 

again shows higher bypass BPF tone levels at aft angles. MPT generation is about the same for the two 

rotors at 12 k rpmc. 

There is little difference in the 1/3rd octave directivity levels for the two rotors at 10 k rpmc (Fig. 65), 

although broadband levels are slightly lower for the forward-swept composite rotor at downstream 

sideline angles at 3.15 k and 5 kHz (Figs. 65(c) and (e)). The 1/3rd octave directivities at 12 k rpmc

(Fig. 66) are essentially the same for the two rotors. There is a small increase in the bypass BPF tone level 

for the forward-swept rotor at 5 kHz, but Figure 66(e) shows the apparent effect of absorption by the 

acoustic liner (compare with Fig. 57(e)). 

The acoustic results for the forward-swept and unswept composite rotor with bypass duct acoustic 

treatment suggest that forward sweep may slightly reduce broadband levels at some fan speeds and 

frequencies. Expected reductions in MPT noise with forward sweep relative to unswept were not 

observed. The bypass BPF tone level tended to increase, rather than decrease with forward sweep, 

indicating an increase in the forward-swept rotor wake. 

Fan Axis Angle of Attack 

The UPS fan was tested at fan axis angles-of-attack (AOA) of 0, 3, and 9. Figures 67 to 69 show 

EPNL levels for these AOAs as a function of rotor tip speed for the baseline M4 metal rotor with hardwall bypass duct and two types of bypass inlet and exhaust wall treatment. The EPNL levels typically 

increase with AOA. 

Figures 70 to 72 show representative constant bandwidth (6 Hz) spectra for these three configurations 

for 0, 3, and 9 AOA at 12 k rpmc. The spectra of Figure 70 are for the hard-wall, HTH, configuration. 

MPT generation is significant at this transonic fan speed. There is a significant decrease in MPT activity as 
NASA/TM—2012-217450 9 

the AOA is increased from 0 to 9. Data were not taken at 3 AOA for this configuration and speed. 

Similar results are seen for the M4 rotor with wall treatment in Figures 71 and 72. 

Figures 73 to 78 show 1/3rd octave directivities taken with the translating sideline microphone for 

these three M4 rotor configurations. Figure 73 shows directivities for 8 kHz (broadband) noise at 

8200 rpmc. The broadband levels are particularly high for 9 AOA toward the aft (typically peak noise) 

angles. There is a small decrease in noise levels for the TTT configuration at 3 AOA that is not observed 

for the HTH or NTN configurations. Noise levels at upstream angles are seen to decrease slightly with 

AOA for the TTT and NTN configurations. 

Figure 74 shows directivity changes with AOA for the 3BPF bypass interaction tone with the fan 

operating at 8200 rpmc. Noise levels are again seen to increase with AOA at aft angles, with some 

decrease in the upstream levels with increasing AOA. 

The UPS fan shows maximum MPT generation near 12 k rpmc Figure 75 shows 1/3rd octave 

directivities for the three M4 rotor configurations at 2 kHz. These results illustrate the reduction in MPT 

generation that was seen in the previously discussed constant bandwidth spectra. In particular, there is a 

significant reduction in noise level with increasing AOA for the hard-wall configuration. Earlier results 

presented in this paper (Fig. 11) suggested that the initial duct wall treatment (TTT) was somewhat more 

effective than was the redesigned (NTN) treatment. It was also shown that duct wall treatment can 

significantly reduce MPT levels. This observation is further confirmed in Figure 76 where changes in 

MPT generation with AOA are essentially not seen for the TTT configuration, since these tones are 

effectively removed by the duct wall treatment. Such was not the case for the NTN treatment, which still 

showed reductions in MPT levels with increasing AOA. 

Finally, Figure 77 shows 1/3rd octave directivities at 12 k rpmc and 8 kHz, which contains the bypass 

2BPF tone. There is still significant MPT content at this frequency (see Figs. 70 to 72) and the results are 

somewhat similar to those of the two preceding figures, showing a level reduction with increasing AOA. 

However, this effect is also seen for the TTT configuration, possibly due to the presence of the bypass 

2BPF tone which was not as easily absorbed by the duct wall treatment. 

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

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

LSWT were, in fact, reflecting some noise, resulting in a cancellation pattern. Directivity results for the 

UPS fan tested in the German-Dutch Wind Tunnel (DNW) likewise showed this periodic nature (Ref. 1). 

Tests were made with the same UPS configuration using the same microphone assembly and holder as 

was used for the NASA 915 LSWT tests and data were taken at a 224 cm (88 in.) sideline within a 

M0 = 0.20 airflow. However, as a free jet facility, the DNW did not introduce the possibility of 

acoustically reflecting tunnel walls. These DNW directivity results show that the likely source of the 

“periodic” noise levels is acoustic interaction (periodic reinforcement and cancellation) between fan noise 

at a particular frequency radiating from the fan inlet and exhaust. Reference 10 is a theoretical study of 

model fan noise radiating from separate inlet and exhaust sources. Tone directivity results in this 

reference likewise show this periodic nature. 

Concluding Remarks 

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

Engines to explore advanced fan stage concepts for future quiet turbofan engines. The fan stage was 

tested in the NASA Glenn 915 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. Acoustic testing was performed within a M0 = 0.20 tunnel flow, which is representative 

of aircraft takeoff and approach conditions. 

 
NASA/TM—2012-217450 10 

Noise levels were compared for the various rotors and bypass duct treatments. These comparisons 

showed that there was a significant noise increase associated with the composite rotors relative to that for 

metal rotors. This noise increase appears to be largely due to increases in broadband noise for the 

composite rotors (although a modest reduction in broadband noise was sometimes observed for the 

composite forward-swept rotor). There was a significant spectral “haystack” noise region associated with 

the composite rotors at upstream sideline locations. Aerodynamic performance of the various rotors was 

essentially similar. 

The use of aft or forward rotor sweep could somewhat reduce multiple pure tone (MPT) generation 

for transonic rotational speeds. However, aft rotor sweep introduces the potential for increased rotorstator interaction noise due to reduced blade-vane spacing. Acoustic results for two aft-swept metal rotor 

designs were compared with those for the baseline, unswept metal rotor. While MPT generation was 

reduced for the aft-swept rotors, there was also an increase in the bypass stage BPF tone associated with 

the reduced blade-vane spacing. Also, there was evidence of higher broadband levels associated with the 

aft-swept rotors. Consequently, overall EPNL were similar for the aft-swept and unswept rotors. 

The effect of rotor forward sweep was explored with composite forward-swept and unswept rotor 

designs. These comparisons suggest that there may be a slight reduction in broadband noise level 

associated with forward sweep. However, the bypass BPF tone was higher for the forward-swept rotor, 

indicating that the wake from the forward-swept rotor is more severe than that for the unswept rotor. 

EPNL comparisons for the forward-swept and upswept rotor were essentially the same for both 

configurations. 

The UPS fan was tested at three fan axis angles-of-attack in the NASA 915 LSWT. The fan was 

shown to exhibit reduced MPT generation with increased AOA, although overall effective perceived 

noise levels typically increased with AOA. Additionally, EPNL values were typically higher for bypass 

rotors of composite material compared to the metal rotors. This may be due to increased flexure of the 

composite rotors changing their acoustic (but apparently not gross aerodynamic) properties under load. 

References 

1. Woodward, R.P., and Hughes, C.E., “Acoustic Performance of Several GEAE UPS Research Fans in 

Three Test Facilities,” Pending NASA TM. 

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

Simulator (UPS) Acoustic Calibration,” GEAE Technical Memorandum 96-166, August, 1996. 

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

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

4. 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. 

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. 

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

Concept,” NASA TM-1998-208662, 1998. 
NASA/TM—2012-217450 11 

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: 

M4 rotor ................................................................................... 1.49 

Composite rotors ..................................................................... 1.53 

Bypass ratio: 

M4 rotor ................................................................................... 8.85 

Composite rotors ..................................................................... 8.24 

Mass flow, kg/sec (lbm/sec): 

M4 rotor ...................................................................... 46.3 (102.1) 

Composite rotors ........................................................ 47.5 (104.7) 

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

Rotor tip speed, m/sec (ft/sec): 

M4 rotor ........................................................................ 370 (1214) 

Composite rotors .......................................................... 388 (1274) 

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

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

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

Sideline......................................................351 (1152) 
NASA/TM—2012-217450 12 

TABLE 3.—ACOUSTIC TEST CONFIGURATIONS IN THE NASA 915 LSWT 

Blade design Duct treatment 

 Inlet Fan case Exhaust 

C-1, Baseline (M4, metal) T 

(treated) 

T T 

C-2, Baseline (M4, metal) H 

(hard-wall) 

T H 

C-3, Aft-Swept (metal) H T H 

C-4, Unswept (composite) H T H 

C-5, Forward-Swept 

(composite) 

H T H 

C-6, Forward-Swept 

(composite) 

N 

(new treatment) 

T N 

C-7, Unswept (composite) N T N 

C-7, Modified Aft-Swept 

(metal) 

N T N 

C-9, Baseline (M4, metal) N T N 

C-44(a), Advanced 

Unswepta

 (composite) 

H T H 

C- 44(b), Advanced 

Unswepta,b (composite) 

H T H 

C-45, Advanced Unswepta,b

(composite) 

N T H 

C-45(a), Advanced 

Unswepta,b (composite) 

T T H 

a

Lube oil scavenge line in bypass aft duct 

b

Taped spinner to eliminate extraneous tones 

TABLE 4.—NOMINAL BLADE PASSING FREQUENCY (BPF) TONES AS A FUNCTION OF FAN SPEED 

Nominal, 

rpm 

Bypass tones, 

Hz 

Core tones, 

Hz 

Corrected 

speed 

Actual 

speed 

BPF 2BPF 3BPF 4BPF 5BPF BPFC 2BPFC

7400 7500 2750 5500 8250 11000 13750 6000 12000 

8200 8300 3043 6087 9130 12173 15217 6640 13280 

10000 10220 3747 7495 11242 14989 18737 8176 16352 

11000 11150 4088 8177 12265 16353 20442 8920 17840 

12000 12275 4501 9002 13503 18003 22504 9820 19640 

13000 13300 4877 9753 14630 19507 24383 10640 21280 

13500 13800 5060 10120 15180 20240 25300 11040 22080 
NASA/TM—2012-217450 13 

Figure 1.—Cross-sectional view of the UPS fan stage. 

Figure 2.—UPS rotors tested in the NASA Glenn 915 LSWT. 
NASA/TM—2012-217450 14 

Figure 3.—NASA Glenn 915 low-speed anechoic wind tunnel. 

Figure 4.—Sketch of the UPS model installed in the NASA Glenn 915 LSWT (dimensions are cm (in.)). 
NASA/TM—2012-217450 15 

Figure 5.—Photograph of the UPS model installed in the NASA Glenn 915 LSWT. 

Figure 6.—Fan stage aerodynamic performance for the hard-wall flow duct configurations. 

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

M4 metal rotor

Aft-swept metal rotor

Unswept composite rotor

Forward-swept composite rotor
NASA/TM—2012-217450 16 

Figure 7.—Fan stage aerodynamic performance for the treated flow duct configurations. 

Figure 8.—UPS bypass and core tone frequencies as a function of rotor speed. 

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

M4 metal rotor, TTT

M4 metal rotor, NTN

Forward-swept composite rotor, NTN

Unswept composite rotor, NTN

Modified aft-swept metal rotor, NTN

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
NASA/TM—2012-217450 17 

Figure 9.—Effect of electronically removing the “spinner tone” from the unswept composite rotor, HTH 

configuration (EPNL calculated from 915 LSWT sideline data, 0 AOA, 5.6 scale factor, 304.8-m 

(1000-ft) flyover). 

Figure 10.—Effect of rotor configuration with hardwall bypass duct. (EPNL calculated from 915 LSWT 

sideline data, 0 AOA, 5.6 scale factor, 304.8-m (1000-ft) flyover). 

700 800 900 1000

Corrected tip speed, ft./sec

Spinner tone present

Spinner tone removed

10

EPNdB

600 700 800 900 1000 1100 1200 1300 1400

Corrected tip speed, ft./sec

10

EPNdB

M4 metal rotor, HTH (C-2)

Aft-swept metal rotor, HTH (C-3)

Unswept composite rotor, HTH (C-4)

Forward-swept composite rotor, HTH (C-5)
NASA/TM—2012-217450 18 

Figure 11.—Effect of rotor configuration with acoustically treated bypass duct. (EPNL calculated 

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

Figure 12.—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). 

600 700 800 900 1000 1100 1200 1300 1400

Corrected tip speed, ft./sec

10

EPNdB

M4 metal rotor, TTT (C-1)

Forward-swept composite rotor, NTN (C-6)

Unswept composite rotor, NTN (C-7)

Modified aft-swept composite rotor, NTN (C-8)

M4 metal rotor, NTN (C-9)

600 700 800 900 1000 1100 1200 1300 1400

Corrected tip speed, ft./sec

10

EPNdB

M4 metal rotor, TTT (C-1)

M4 metal rotor, HTH (C-2)
NASA/TM—2012-217450 19 

Figure 13.—Comparison of unswept metal M4 and composite rotors (HTH). 

Figure 14.—Comparison of constant (6 Hz) bandwidth spectra for the unswept metal M4 and 

composite rotors at 10 k rpmc (47 sideline emission angle, HTH). 

600 700 800 900 1000 1100 1200 1300 1400

Corrected tip speed, ft./sec

10

EPNdB

M4 metal rotor, HTH (C-2)

Unswept composite rotor, HTH (C-4)

0 2000 4000 6000 8000 10000

Frequency, Hz

60

70

80

90

100

 

60

70

80

90

100

SPL,

dB 

(a) M4 metal rotor (C-2)

(b) Unswept composite rotor (C-4)

BPF

 |

2BPF

|

Core

BPF

|
NASA/TM—2012-217450 20 

Figure 15.—Comparison of constant (6 Hz) bandwidth spectra for the unswept metal M4 and 

composite rotors at 10 k rpmc (102 sideline emission angle, HTH). 

Figure 16.—Comparison of constant (6 Hz) bandwidth spectra for the unswept metal M4 and 

composite rotors at 10 k rpmc (130 sideline emission angle, HTH). 

0 2000 4000 6000 8000 10000

Frequency, Hz

60

70

80

90

100

 

60

70

80

90

100

SPL,

dB 

(a) M4 metal rotor (C-2)

(b) Unswept composite rotor (C-4)

BPF

 |

2BPF

| Core

BPF

|

0 2000 4000 6000 8000 10000

Frequency, Hz

60

70

80

90

100

 

60

70

80

90

100

SPL,

dB 

(a) M4 metal rotor (C-2)

(b) Unswept composite rotor (C-4)

BPF

 |

2BPF

|

Core

BPF

|
NASA/TM—2012-217450 21 

Figure 17.—Comparison of constant (6 Hz) bandwidth spectra for the unswept metal M4 and 

composite rotors at 12 k rpmc (47 sideline emission angle, HTH). 

Figure 18.—Comparison of constant (6 Hz) bandwidth spectra for the unswept metal M4 and composite 

rotors at 12 k rpmc (102 sideline emission angle, HTH). 

0 2000 4000 6000 8000 10000

Frequency, Hz

70

80

90

100

110

 

70

80

90

100

110

SPL,

dB 

(a) M4 metal rotor (C-2)

(b) Unswept composite rotor (C-4)

BPF

 |

2BPF

|

0 2000 4000 6000 8000 10000

Frequency, Hz

70

80

90

100

110

 

70

80

90

100

110

SPL,

dB 

(a) M4 metal rotor (C-2)

(b) Unswept composite rotor (C-4)

BPF

 |

2BPF

|
NASA/TM—2012-217450 22 

Figure 19.—Comparison of constant (6 Hz) bandwidth spectra for the unswept metal M4 and composite 

rotors at 12 k rpmc (130 sideline emission angle, HTH). 

0 2000 4000 6000 8000 10000

Frequency, Hz

70

80

90

100

110

 

70

80

90

100

110

SPL,

dB 

(a) M4 metal rotor (C-2)

(b) Unswept composite rotor (C-4)

BPF

 |

2BPF

|
NASA/TM—2012-217450 23 

Figure 20.—Comparison of 1/3rd octave directivities for the M4 unswept metal and unswept composite 

rotors at 10 k rpmc (HTH). 

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

Emission angle relative to inlet highlight, deg.

85

90

95

100

105

 

85

90

95

100

105

SPL,

dB

Unswept metal rotor, M4 (C-2)

Unswept composite rotor (C-4)

Windmill noise level (M4, TTT, C-1)

85

90

95

100

105

(a) 2 kHz (contains broadband)

(b) 2.5 kHz (contains broadband)

(c) 3.15 kHz (contains broadband)
NASA/TM—2012-217450 24 

Figure 20.—Concluded. 

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

Emission angle relative to inlet highlight, deg.

85

90

95

100

105

 

85

90

95

100

105

SPL,

dB

Unswept metal rotor, M4 (C-2)

Unswept composite rotor (C-4)

Windmill noise level (M4, TTT, C-1)

85

90

95

100

105

(d) 4 kHz (contains bypass BPF)

(e) 5 kHz (contains broadband)

(f) 8 kHz (contains bypass 2BPF and core BPF)
NASA/TM—2012-217450 25 

Figure 21.—Comparison of 1/3rd octave directivities for the M4 unswept metal and unswept composite 

rotors at 12 k rpmc (HTH). 

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

Emission angle relative to inlet highlight, deg.

95

100

105

110

115

 

95

100

105

110

115

SPL,

dB

Unswept metal rotor, M4 (C-2)

Unswept composite rotor (C-4)

95

100

105

110

115

(a) 2 kHz (contains broadband)

(b) 2.5 kHz (contains broadband)

(c) 3.15 kHz (contains broadband)
NASA/TM—2012-217450 26 

Figure 21.—Concluded. 

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

Emission angle relative to inlet highlight, deg.

95

100

105

110

115

 

95

100

105

110

115

SPL,

dB

Unswept metal rotor, M4 (C-2)

Unswept composite rotor (C-4)

95

100

105

110

115

(d) 4 kHz (contains broadband)

(e) 5 kHz (contains bypass BPF)

(f) 8 kHz (contains bypass 2BPF)
NASA/TM—2012-217450 27 

Figure 22.—Comparison of unswept metal M4 and composite rotors (NTN). 

Figure 23.—Comparison of constant (6 Hz) bandwidth spectra for the unswept metal M4 and 

composite rotors at 10 k rpmc (47 sideline emission angle, NTN). 

600 700 800 900 1000 1100 1200 1300 1400

Corrected tip speed, ft./sec

10

EPNdB

M4 metal rotor, NTN (C-9)

Unswept composite rotor, NTN (C-7)

0 2000 4000 6000 8000 10000

Frequency, Hz

60

70

80

90

100

 

60

70

80

90

100

SPL,

dB 

(a) M4 metal rotor (C-9)

(b) Unswept composite rotor (C-7)

BPF

 |

2BPF

|

Core

BPF

|
NASA/TM—2012-217450 28 

Figure 24.—Comparison of constant (6 Hz) bandwidth spectra for the unswept metal M4 and 

composite rotors at 10 k rpmc (102 sideline emission angle, NTN). 

Figure 25.—Comparison of constant (6 Hz) bandwidth spectra for the unswept metal M4 and 

composite rotors at 10 k rpmc (130 sideline emission angle, NTN). 

0 2000 4000 6000 8000 10000

Frequency, Hz

60

70

80

90

100

 

60

70

80

90

100

SPL,

dB 

(a) M4 metal rotor (C-9)

(b) Unswept composite rotor (C-7)

BPF

 |

2BPF

|

Core

BPF

|

0 2000 4000 6000 8000 10000

Frequency, Hz

60

70

80

90

100

 

60

70

80

90

100

SPL,

dB 

(a) M4 metal rotor (C-9)

(b) Unswept composite rotor (C-7)

BPF

 |

2BPF

|

Core

BPF

|
NASA/TM—2012-217450 29 

Figure 26.—Comparison of constant (6 Hz) bandwidth spectra for the unswept metal M4 and 

composite rotors at 12 k rpmc (47 sideline emission angle, NTN). 

Figure 27.—Comparison of constant (6 Hz) bandwidth spectra for the unswept metal M4 and 

composite rotors at 12 k rpmc (102 sideline emission angle, NTN). 

0 2000 4000 6000 8000 10000

Frequency, Hz

70

80

90

100

110

 

70

80

90

100

110

SPL,

dB 

(a) M4 metal rotor (C-9)

(b) Unswept composite rotor (C-7)

BPF

 |

2BPF

|

0 2000 4000 6000 8000 10000

Frequency, Hz

70

80

90

100

110

 

70

80

90

100

110

SPL,

dB 

(a) M4 metal rotor (C-9)

(b) Unswept composite rotor (C-7)

BPF

 |

2BPF

|
NASA/TM—2012-217450 30 

Figure 28.—Comparison of constant (6 Hz) bandwidth spectra for the unswept metal M4 and 

composite rotors at 12 k rpmc (130 sideline emission angle, NTN). 

0 2000 4000 6000 8000 10000

Frequency, Hz

70

80

90

100

110

 

70

80

90

100

110

SPL,

dB 

(a) M4 metal rotor (C-9)

(b) Unswept composite rotor (C-7)

BPF

 | 2BPF

|
NASA/TM—2012-217450 31 

Figure 29.—Comparison of 1/3rd octave directivities for the M4 unswept metal rotor and unswept 

composite rotors at 10 k rpmc (NTN). 

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

Emission angle relative to inlet highlight, deg.

85

90

95

100

105

 

85

90

95

100

105

SPL,

dB

Unswept metal rotor, M4 (C-9)

Unswept composite rotor (C-7)

85

90

95

100

105

(a) 2 kHz (contains broadband)

(b) 2.5 kHz (contains broadband)

(c) 3.15 kHz (contains broadband)
NASA/TM—2012-217450 32 

Figure 29.—Concluded. 

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

Emission angle relative to inlet highlight, deg.

85

90

95

100

105

 

85

90

95

100

105

SPL,

dB

Unswept metal rotor, M4 (C-9)

Unswept composite rotor (C-7)

85

90

95

100

105

(d) 4 kHz (contains bypass BPF)

(e) 5 kHz (contains broadband)

(f) 8 kHz (contains bypass 2BPF and core BPF)
NASA/TM—2012-217450 33 

Figure 30.—Comparison of 1/3rd octave directivities for the M4 unswept metal rotor and unswept 

composite rotors at 12 k rpmc (NTN). 

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

Emission angle relative to inlet highlight, deg.

95

100

105

110

115

 

95

100

105

110

115

SPL,

dB

Unswept metal rotor, M4 (C-9)

Unswept composite rotor (C-7)

95

100

105

110

115

(a) 2 kHz (contains broadband)

(b) 2.5 kHz (contains broadband)

(c) 3.15 kHz (contains broadband)
NASA/TM—2012-217450 34 

Figure 30.—Concluded. 

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

Emission angle relative to inlet highlight, deg.

95

100

105

110

115

 

95

100

105

110

115

SPL,

dB

Unswept metal rotor, M4 (C-9)

Unswept composite rotor (C-7)

95

100

105

110

115

(d) 4 kHz (contains broadband)

(e) 5 kHz (contains bypass BPF)

(f) 8 kHz (contains bypass 2BPF)
NASA/TM—2012-217450 35 

Figure 31.—Comparison of unswept M4 and aft-swept metal rotors (HTH). 

Figure 32.—Comparison of constant (6 Hz) bandwidth spectra for the unswept and aft-swept metal 

rotors at 10 k rpmc (47 sideline emission angle, HTH). 

600 700 800 900 1000 1100 1200 1300 1400

Corrected tip speed, ft./sec

10

EPNdB

M4 metal rotor, HTH (C-2)

Aft swept metal rotor, HTH (C-3)

0 2000 4000 6000 8000 10000

Frequency, Hz

60

70

80

90

100

 

60

70

80

90

100

SPL,

dB 

(a) M4 metal rotor (C-2)

(b) Aft swept metal rotor (C-3)

BPF

 |

2BPF

|

Core

BPF

|
NASA/TM—2012-217450 36 

Figure 33.—Comparison of constant (6 Hz) bandwidth spectra for the unswept and aft-swept 

metal rotors at 10 k rpmc (102 sideline emission angle, HTH). 

Figure 34.—Comparison of constant (6 Hz) bandwidth spectra for the unswept and aft-swept metal 

rotors at 10 k rpmc (130 sideline emission angle, HTH). 

0 2000 4000 6000 8000 10000

Frequency, Hz

60

70

80

90

100

 

60

70

80

90

100

SPL,

dB 

(a) M4 metal rotor (C-2)

(b) Aft swept metal rotor (C-3)

BPF

 |

2BPF

| Core

BPF

|

0 2000 4000 6000 8000 10000

Frequency, Hz

60

70

80

90

100

 

60

70

80

90

100

SPL,

dB 

(a) M4 metal rotor (C-2)

(b) Aft swept metal rotor (C-3)

BPF

 |

2BPF

|

Core

BPF

|
NASA/TM—2012-217450 37 

Figure 35.—Comparison of constant (6 Hz) bandwidth spectra for the unswept and aft-swept metal 

rotors at 12 k rpmc (47 sideline emission angle, HTH). 

Figure 36.—Comparison of constant (6 Hz) bandwidth spectra for the unswept and aft-swept 

metal rotors at 12 k rpmc (102 sideline emission angle, HTH). 

0 2000 4000 6000 8000 10000

Frequency, Hz

70

80

90

100

110

 

70

80

90

100

110

SPL,

dB 

(a) M4 metal rotor (C-2)

(b) Aft swept metal rotor (C-3)

BPF

 |

2BPF

|

0 2000 4000 6000 8000 10000

Frequency, Hz

70

80

90

100

110

 

70

80

90

100

110

SPL,

dB 

(a) M4 metal rotor (C-2)

(b) Aft swept metal rotor (C-3)

BPF

 |

2BPF

|
NASA/TM—2012-217450 38 

Figure 37.—Comparison of constant (6 Hz) bandwidth spectra for the unswept and aft-swept 

metal rotors at 12 k rpmc (130 sideline emission angle, HTH). 

0 2000 4000 6000 8000 10000

Frequency, Hz

70

80

90

100

110

 

70

80

90

100

110

SPL,

dB 

(a) M4 metal rotor (C-2)

(b) Aft swept metal rotor (C-3)

BPF

 |

2BPF

|
NASA/TM—2012-217450 39 

Figure 38.—Comparison of 1/3rd octave directivities for the unswept M4 and aft-swept metal rotors at 

10 k rpmc (HTH). 

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

Emission angle relative to inlet highlight, deg.

85

90

95

100

105

 

85

90

95

100

105

SPL,

dB

Unswept metal rotor, M4 (C-2)

Aft swept metal rotor (C-3)

85

90

95

100

105

(a) 2 kHz (contains broadband)

(b) 2.5 kHz (contains broadband)

(c) 3.15 kHz (contains broadband)
NASA/TM—2012-217450 40 

Figure 38.—Concluded. 

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

Emission angle relative to inlet highlight, deg.

90

95

100

105

110

 

90

95

100

105

110

SPL,

dB

Unswept metal rotor, M4 (C-2)

Aft swept metal rotor (C-3)

90

95

100

105

110

(d) 4 kHz (contains bypass BPF)

(e) 5 kHz (contains broadband)

(f) 8 kHz (contains bypass 2BPF and core BPF))
NASA/TM—2012-217450 41 

Figure 39.—Comparison of 1/3rd octave directivities for the unswept M4 and aft-swept metal rotors at 

12 k rpmc (HTH). 

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

Emission angle relative to inlet highlight, deg.

90

95

100

105

110

 

95

100

105

110

115

SPL,

dB

Unswept metal rotor, M4 (C-2)

Aft swept metal rotor (C-3)

90

95

100

105

110

(a) 2 kHz (contains broadband)

(b) 2.5 kHz (contains broadband)

(c) 3.15 kHz (contains broadband)
NASA/TM—2012-217450 42 

Figure 39.—Concluded. 

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

Emission angle relative to inlet highlight, deg.

95

100

105

110

115

 

95

100

105

110

115

SPL,

dB

Unswept metal rotor, M4 (C-2)

Aft swept metal rotor (C-3)

95

100

105

110

115

(d) 4 kHz (contains broadband)

(e) 5 kHz (contains bypass BPF)

(f) 8 kHz (contains bypass 2BPF)
NASA/TM—2012-217450 43 

Figure 40.—Comparison of unswept M4 and aft-swept metal rotors (NTN). 

Figure 41.—Comparison of constant (6 Hz) broadband spectra for the unswept metal M4 and modified 

aft-swept metal rotors at 10 k rpmc (47 emission angle, NTN). 

600 700 800 900 1000 1100 1200 1300 1400

Corrected tip speed, ft./sec

10

EPNdB

M4 metal rotor, NTN (C-9)

Modified aft swept, NTN (C-8)

0 2000 4000 6000 8000 10000

Frequency, Hz

60

70

80

90

100

 

60

70

80

90

100

SPL,

dB 

(a) M4 metal rotor (C-9)

(b) Modified aft swept metal rotor (C-8)

BPF

 |

2BPF

|

Core

BPF

|
NASA/TM—2012-217450 44 

Figure 42.—Comparison of constant (6 Hz) broadband spectra for the unswept metal M4 and 

modified aft-swept metal rotors at 10 k rpmc (102 emission angle, NTN). 

Figure 43.—Comparison of constant (6 Hz) broadband spectra for the unswept metal M4 and 

modified aft-swept metal rotors at 10 k rpmc (130 emission angle, NTN). 

0 2000 4000 6000 8000 10000

Frequency, Hz

60

70

80

90

100

 

60

70

80

90

100

SPL,

dB 

(a) M4 metal rotor (C-9)

(b) Modified aft swept metal rotor (C-8)

BPF

 |

2BPF

|

Core

BPF

|

0 2000 4000 6000 8000 10000

Frequency, Hz

60

70

80

90

100

 

60

70

80

90

100

SPL,

dB 

(a) M4 metal rotor (C-9)

(b) Modified aft swept metal rotor (C-8)

BPF

 |

2BPF

|

Core

BPF

|
NASA/TM—2012-217450 45 

Figure 44.—Comparison of constant (6 Hz) broadband spectra for the unswept metal M4 and modified 

aft-swept metal rotors at 12 k rpmc (47 emission angle, NTN). 

Figure 45.—Comparison of constant (6 Hz) broadband spectra for the unswept metal M4 and modified 

aft-swept metal rotors at 12 k rpmc (102 emission angle, NTN). 

0 2000 4000 6000 8000 10000

Frequency, Hz

70

80

90

100

110

 

70

80

90

100

110

SPL,

dB 

(a) M4 metal rotor (C-9)

(b) Modified aft swept metal rotor (C-8)

BPF

 |

2BPF

|

0 2000 4000 6000 8000 10000

Frequency, Hz

70

80

90

100

110

 

70

80

90

100

110

SPL,

dB 

(a) M4 metal rotor (C-9)

(b) Modified aft swept metal rotor (C-8)

BPF

 |

2BPF

|
NASA/TM—2012-217450 46 

Figure 46.—Comparison of constant (6 Hz) broadband spectra for the unswept metal M4 and 

modified aft-swept metal rotors at 12 k rpmc (130 emission angle, NTN). 

0 2000 4000 6000 8000 10000

Frequency, Hz

70

80

90

100

110

 

70

80

90

100

110

SPL,

dB 

(a) M4 metal rotor (C-9)

(b) Modified aft swept metal rotor (C-8)

BPF

 |

2BPF

|
NASA/TM—2012-217450 47 

Figure 47.—Comparison of 1/3rd octave directivities for the M4 unswept and modified aft-swept metal 

rotors at 10 k rpmc (NTN). 

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

Emission angle relative to inlet highlight, deg.

85

90

95

100

105

 

85

90

95

100

105

SPL,

dB

Unswept metal rotor, M4 (C-9)

Modified aft swept metal rotor (C-8)

85

90

95

100

105

(a) 2 kHz (contains broadband)

(b) 2.5 kHz (contains broadband)

(c) 3.15 kHz (contains broadband)
NASA/TM—2012-217450 48 

Figure 47.—Concluded. 

 

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

Emission angle relative to inlet highlight, deg.

85

90

95

100

105

 

85

90

95

100

105

SPL,

dB

Unswept metal rotor, M4 (C-9)

Modified aft swept metal rotor (C-8)

85

90

95

100

105

(d) 4 kHz (contains bypass BPF)

(e) 5 kHz (contains broadband)

(f) 8 kHz (contains bypass 2BPF and core BPF) 
NASA/TM—2012-217450 49 

Figure 48.—Comparison of 1/3rd octave directivities for the M4 unswept and modified aft-swept metal 

rotors at 12 k rpmc (NTN). 

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

Emission angle relative to inlet highlight, deg.

90

95

100

105

110

 

90

95

100

105

110

SPL,

dB

Unswept metal rotor, M4 (C-9)

Modified aft swept metal rotor (C-8)

90

95

100

105

110

(a) 2 kHz (contains broadband)

(b) 2.5 kHz (contains broadband)

(c) 3.15 kHz (contains broadband)
NASA/TM—2012-217450 50 

Figure 48.—Concluded. 

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

Emission angle relative to inlet highlight, deg.

90

95

100

105

110

 

90

95

100

105

110

SPL,

dB

Unswept metal rotor, M4 (C-9)

Modified aft swept metal rotor (C-8)

90

95

100

105

110

(d) 4 kHz (contains broadband)

(e) 5 kHz (contains bypass BPF)

(f) 8 kHz (contains bypass 2BPF)
NASA/TM—2012-217450 51 

Figure 49.—Comparison of unswept and forward-swept composite rotors (HTH). 

Figure 50.—Comparison of constant (6 Hz) bandwidth spectra for the unswept and forward-swept composite 

rotors at 10 k rpmc (47 sideline emission angle, HTH). 

600 700 800 900 1000 1100 1200 1300 1400

Corrected tip speed, ft./sec

10

EPNdB

Unswept composite rotor, HTH (C-4)

Forward swept composite rotor, HTH (C-5)

0 2000 4000 6000 8000 10000

Frequency, Hz

60

70

80

90

100

 

60

70

80

90

100

SPL,

dB 

(a) Unswept composite rotor (C-4)

(b) Forward swept composite rotor (C-5)

BPF

 |

2BPF

|

Core

BPF

|
NASA/TM—2012-217450 52 

Figure 51.—Comparison of constant (6 Hz) bandwidth spectra for the unswept and forward-swept 

composite rotors at 10 k rpmc (102 sideline emission angle, HTH). 

Figure 52.—Comparison of constant (6 Hz) bandwidth spectra for the unswept and forward-swept composite 

rotors at 10 k rpmc (130 sideline emission angle, HTH). 

0 2000 4000 6000 8000 10000

Frequency, Hz

60

70

80

90

100

 

60

70

80

90

100

SPL,

dB 

(a) Unswept composite rotor (C-4)

(b) Forward swept composite rotor (C-5)

BPF

 |

2BPF

|

Core

BPF

|

0 2000 4000 6000 8000 10000

Frequency, Hz

70

80

90

100

110

 

70

80

90

100

110

SPL,

dB 

(a) Unswept composite rotor (C-4)

(b) Forward swept composite rotor (C-5)

BPF

 |

2BPF

| Core

BPF

|
NASA/TM—2012-217450 53 

Figure 53.—Comparison of constant (6 Hz) bandwidth spectra for the unswept and forward-swept composite 

rotors at 12 k rpmc (47 sideline emission angle, HTH). 

Figure 54.—Comparison of constant (6 Hz) bandwidth spectra for the unswept and forwardswept composite rotors at 12 k rpmc (102 sideline emission angle, HTH). 

0 2000 4000 6000 8000 10000

Frequency, Hz

70

80

90

100

110

 

70

80

90

100

110

SPL,

dB 

(a) Unswept composite rotor (C-4)

(b) Forward swept composite rotor (C-5)

BPF

 | 2BPF

|

0 2000 4000 6000 8000 10000

Frequency, Hz

70

80

90

100

110

 

70

80

90

100

110

SPL,

dB 

(a) Unswept composite rotor (C-4)

(b) Forward swept composite rotor (C-5)

BPF

 |

2BPF

|
NASA/TM—2012-217450 54 

Figure 55.—Comparison of constant (6 Hz) bandwidth spectra for the unswept and forwardswept composite rotors at 12 k rpmc (130 sideline emission angle, HTH). 

0 2000 4000 6000 8000 10000

Frequency, Hz

70

80

90

100

110

 

70

80

90

100

110

SPL,

dB 

(a) Unswept composite rotor (C-4)

(b) Forward swept composite rotor (C-5)

BPF

 | 2BPF

|
NASA/TM—2012-217450 55 

Figure 56.—Comparison of 1/3rd octave directivities for the unswept and forward-swept composite rotors at 

10 k rpmc (HTH). 

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

Emission angle relative to inlet highlight, deg.

90

95

100

105

110

 

90

95

100

105

110

SPL,

dB

Unswept composite rotor (C-4)

Forward swept composite rotor (C-5)

90

95

100

105

110

(a) 2 kHz (contains broadband)

(b) 2.5 kHz (contains broadband)

(c) 3.15 kHz (contains broadband)
NASA/TM—2012-217450 56 

Figure 56.—Concluded. 

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

Emission angle relative to inlet highlight, deg.

90

95

100

105

110

 

90

95

100

105

110

SPL,

dB

Unswept composite rotor (C-4)

Forward swept composite rotor (C-5)

90

95

100

105

110

(d) 4 kHz (contains bypass BPF)

(e) 5 kHz (contains broadband)

(f) 8 kHz (contains bypass 2BPF and core BPF)
NASA/TM—2012-217450 57 

Figure 57.—Comparison of 1/3rd octave directivities for the unswept and forward-swept composite rotors at 

12 k rpmc (HTH). 

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

Emission angle relative to inlet highlight, deg.

95

100

105

110

115

 

95

100

105

110

115

SPL,

dB

Unswept composite rotor (C-4)

Forward swept composite rotor (C-5)

95

100

105

110

115

(a) 2 kHz (contains broadband)

(b) 2.5 kHz (contains broadband)

(c) 3.15 kHz (contains broadband)
NASA/TM—2012-217450 58 

Figure 57.—Concluded. 

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

Emission angle relative to inlet highlight, deg.

95

100

105

110

115

 

95

100

105

110

115

SPL,

dB

Unswept composite rotor (C-4)

Forward swept composite rotor (C-5)

95

100

105

110

115

(d) 4 kHz (contains broadband)

(e) 5 kHz (contains bypass BPF)

(e) 8 kHz (contains bypass 2BPF)
NASA/TM—2012-217450 59 

Figure 58.—Comparison of unswept and forward-swept composite rotors (NTN). 

Figure 59.—Comparison of constant (6 Hz) bandwidth spectra for the unswept and forward-swept 

composite rotors at 10 k rpmc (47 sideline emission angle, NTN). 

600 700 800 900 1000 1100 1200 1300 1400

Corrected tip speed, ft./sec

10

EPNdB

Unswept composite rotor, NTN (C-7)

Forward swept composite rotor, NTN (C-6)

0 2000 4000 6000 8000 10000

Frequency, Hz

60

70

80

90

100

 

60

70

80

90

100

SPL,

dB 

(a) Unswept composite rotor (C-7)

(b) Forward swept composite rotor (C-6)

BPF

 |

2BPF

|

Core

BPF

|
NASA/TM—2012-217450 60 

Figure 60.—Comparison of constant (6 Hz) bandwidth spectra for the unswept and forwardswept composite rotors at 10 k rpmc (102 sideline emission angle, NTN). 

Figure 61.—Comparison of constant (6 Hz) bandwidth spectra for the unswept and forward-swept 

composite rotors at 10 k rpmc (130 sideline emission angle, NTN). 

0 2000 4000 6000 8000 10000

Frequency, Hz

60

70

80

90

100

 

60

70

80

90

100

SPL,

dB 

(a) Unswept composite rotor (C-7)

(b) Forward swept composite rotor (C-6)

BPF

 |

2BPF

|

Core

BPF

|

0 2000 4000 6000 8000 10000

Frequency, Hz

60

70

80

90

100

 

60

70

80

90

100

SPL,

dB 

(a) Unswept composite rotor (C-7)

(b) Forward swept composite rotor (C-6)

BPF

 | 2BPF

| Core

BPF

|
NASA/TM—2012-217450 61 

Figure 62.—Comparison of constant (6 Hz) bandwidth spectra for the unswept and forward-swept composite 

rotors at 12 k rpmc (47 sideline emission angle, NTN). 

Figure 63.—Comparison of constant (6 Hz) bandwidth spectra for the unswept and forward-swept 

composite rotors at 12 k rpmc (102 sideline emission angle, NTN). 

0 2000 4000 6000 8000 10000

Frequency, Hz

70

80

90

100

110

 

70

80

90

100

110

SPL,

dB 

(a) Unswept composite rotor (C-7)

(b) Forward swept composite rotor (C-6)

BPF

 | 2BPF

|

0 2000 4000 6000 8000 10000

Frequency, Hz

70

80

90

100

110

 

70

80

90

100

110

SPL,

dB 

(a) Unswept composite rotor (C-7)

(b) Forward swept composite rotor (C-6)

BPF

 |

2BPF

|
NASA/TM—2012-217450 62 

Figure 64.—Comparison of constant (6 Hz) bandwidth spectra for the unswept and forward-swept 

composite rotors at 12 k rpmc (130 sideline emission angle, NTN). 

0 2000 4000 6000 8000 10000

Frequency, Hz

70

80

90

100

110

 

70

80

90

100

110

SPL,

dB 

(a) Unswept composite rotor (C-7)

(b) Forward swept composite rotor (C-6)

BPF

 |

2BPF

|
NASA/TM—2012-217450 63 

Figure 65.—Comparison of 1/3rd octave directivities for the unswept and forward-swept composite rotors 

at 10 k rpmc (NTN). 

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

Emission angle relative to inlet highlight, deg.

85

90

95

100

105

 

85

90

95

100

105

SPL,

dB

Unswept composite rotor (C-7)

Forward swept composite rotor (C-6)

85

90

95

100

105

(a) 2 kHz (contains broadband)

(b) 2.5 kHz (contains broadband)

(c) 3.15 kHz (contains broadband)
NASA/TM—2012-217450 64 

Figure 65.—Concluded. 

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

Emission angle relative to inlet highlight, deg.

85

90

95

100

105

 

85

90

95

100

105

SPL,

dB

Unswept composite rotor (C-7)

Forward swept composite rotor (C-6)

85

90

95

100

105

(d) 4 kHz (contains bypass BPF)

(e) 5 kHz (contains broadband)

(f) 8 kHz (contains bypass 2BPF and core BPF)
NASA/TM—2012-217450 65 

Figure 66.—Comparison of 1/3rd octave directivities for the unswept and forward-swept composite rotors 

at 12 k rpmc (NTN). 

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

Emission angle relative to inlet highlight, deg.

95

100

105

110

115

 

95

100

105

110

115

SPL,

dB

Unswept composite rotor (C-7)

Forward swept composite rotor (C-6)

95

100

105

110

115

(a) 2 kHz (contains broadband)

(b) 2.5 kHz (contains broadband)

(c) 3.15 kHz (contains broadband)
NASA/TM—2012-217450 66 

Figure 66.—Concluded. 

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

Emission angle relative to inlet highlight, deg.

95

100

105

110

115

 

95

100

105

110

115

SPL,

dB

Unswept composite rotor (C-7)

Forward swept composite rotor (C-6)

95

100

105

110

115

(d) 4 kHz (contains broadband)

(e) 5 kHz (contains bypass BPF)

(f) 8 kHz (contains bypass 2BPF)
NASA/TM—2012-217450 67 

Figure 67.—Effect of fan axis angle-of-attack for the baseline M4 metal rotor, hardwall configuration (EPNL 

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

Figure 68.—Effect of fan axis angle-of-attack for the baseline M4 metal rotor, with acoustic treatment 

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

600 700 800 900 1000 1100 1200 1300 1400

Corrected tip speed, ft./sec

10

EPNdB

M4 metal rotor, HTH (C-2)

0 degrees AOA

3 degrees AOA

9 degrees AOA

600 700 800 900 1000 1100 1200 1300 1400

Corrected tip speed, ft./sec

10

EPNdB

M4 metal rotor, TTT (C-1)

0 degrees AOA

3 degrees AOA

9 degrees AOA
NASA/TM—2012-217450 68 

Figure 69.—Effect of fan axis angle-of-attack for the baseline M4 metal rotor, with “new” acoustic treatment 

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

600 700 800 900 1000 1100 1200 1300 1400

Corrected tip speed, ft./sec

10

EPNdB

M4 metal rotor, NTN (C-9)

0 degrees AOA

3 degrees AOA

9 degrees AOA
NASA/TM—2012-217450 69 

Figure 70.—Constant bandwidth (6 Hz) spectra. (M4 metal rotor, hardwall (HTH, C-2), 74 emission 

sideline angle on 89-in. sideline, 12 k rpmc). 

0 2000 4000 6000 8000 10000 12000

Frequency, Hz

60

70

80

90

100

110

 

60

70

80

90

100

110

SPL,

dB

60

70

80

90

100

110

 0 degree AOA

 3 degree AOA

 9 degree AOA

 -- Data not available --

 BPF 

 |

 2BPF 

 |

CORE

 BPF

 |
NASA/TM—2012-217450 70 

Figure 71.—Constant bandwidth (6 Hz) spectra. (M4 metal rotor, treated (TTT, C-1), 74 emission sideline 

angle on 89-in. sideline, 12 k rpmc). 

0 2000 4000 6000 8000 10000 12000

Frequency, Hz

60

70

80

90

100

110

 

60

70

80

90

100

110

SPL,

dB

60

70

80

90

100

110

 0 degree AOA

 3 degree AOA

 9 degree AOA

 BPF 

 | 2BPF 

 |

CORE

 BPF

 |
NASA/TM—2012-217450 71 

Figure 72.—Constant bandwidth (6 Hz) spectra. (M4 metal rotor, treated (NTN, C-9), 74 emission sideline 

angle on 89-in. sideline, 12 k rpmc). 

0 2000 4000 6000 8000 10000 12000

Frequency, Hz

60

70

80

90

100

110

 

60

70

80

90

100

110

SPL,

dB

60

70

80

90

100

110

 0 degree AOA

 3 degree AOA

 9 degree AOA

 BPF 

 | 2BPF 

 |

CORE

 BPF

 |
NASA/TM—2012-217450 72 

Figure 73.—1/3rd octave directivities at 8200 rpmc showing fan axis angle-of-attack effects 

(Baseline M4 metal rotor, 8 kHz (broadband spectral region)). 

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

Emission angle relative to inlet highlight, deg.

85

90

95

 

90

95

100

SPL,

dB

0 deg. AOA

3 deg. AOA

9 deg. AOA

85

90

95

TTT, C-1

HTH, C-2

NTN, C-9
NASA/TM—2012-217450 73 

Figure 74.—1/3rd octave directivities at 8200 rpmc showing fan axis angle-of-attack effects (Baseline M4 

metal rotor, 10 kHz (1/3rd octave band contains bypass 3BPF tone)). 

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

Emission angle relative to inlet highlight, deg.

85

90

95

 

90

95

100

SPL,

dB

0 deg. AOA

3 deg. AOA

9 deg. AOA

90

95

100

TTT, C-1

HTH, C-2

NTN, C-9
NASA/TM—2012-217450 74 

Figure 75.—1/3rd octave directivities at 12000 rpmc showing fan axis angle-of-attack effects (Baseline M4 

metal rotor, 2 kHz (1/3rd octave band contains multiple pure tones and broadband)). 

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

Emission angle relative to inlet highlight, deg.

95

100

105

 

95

100

105

110

SPL,

dB

0 deg. AOA

3 deg. AOA

9 deg. AOA

95

100

105

TTT, C-1

HTH, C-2

NTN, C-9
NASA/TM—2012-217450 75 

Figure 76.—1/3rd octave directivities at 12000 rpmc showing fan axis angle-of-attack effects (Baseline 

M4 metal rotor, 4 kHz (1/3rd octave band contains bypass BPF and multiple pure tones)). 

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

Emission angle relative to inlet highlight, deg.

95

100

105

 

95

100

105

110

SPL,

dB

0 deg. AOA

3 deg. AOA

9 deg. AOA

95

100

105

TTT, C-1

HTH, C-2

NTN, C-9
NASA/TM—2012-217450 76 

Figure 77.—1/3rd octave directivities at 12000 rpmc showing fan axis angle-of-attack effects (Baseline 

M4 metal rotor, 8 kHz (1/3rd octave band contains bypass 2BPF and multiple pure tones)). 

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

Emission angle relative to inlet highlight, deg.

95

100

105

 

95

100

105

110

SPL,

dB

0 deg. AOA

3 deg. AOA

9 deg. AOA

95

100

105

TTT, C-1

HTH, C-2

NTN, C-9
REPORT DOCUMENTATION PAGE Form Approved 

OMB No. 0704-0188 

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the 

data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this 

burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. 

Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB 

control number. 

PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 

1. REPORT DATE (DD-MM-YYYY)

01-05-2012 

2. REPORT TYPE

Technical Memorandum 

3. DATES COVERED (From - To)

4. TITLE AND SUBTITLE

Acoustic Performance of the GEAE UPS Research Fan in the NASA Glenn 9- by 15-Foot 

Low-Speed Wind Tunnel 

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-18180 

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-2012-217450 

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 in 1994. The Universal 

Propulsion Simulator fan was designed and manufactured by General Electric Aircraft Engines, and included an active core, as well as 

bypass, flow paths. The fan was tested with several rotors featuring unswept, forward-swept and aft-swept designs of both metal and 

composite construction. Sideline acoustic data were taken with both hard and acoustically treated walls in the flow passages. The fan was 

tested within an airflow at a Mach number of 0.20, which is representative of aircraft takeoff/approach conditions. All rotors showed similar 

aerodynamic performance. However, the composite rotors typically showed higher noise levels than did corresponding metal rotors. Aft and 

forward rotor sweep showed at most modest reductions of transonic multiple pure tone levels. However, rotor sweep often introduced 

increased rotor-stator interaction tone levels. Broadband noise was typically higher for the composite rotors and also for the aft-swept metal 

rotor. Transonic MPT generation was reduced with increasing fan axis angle of attack (AOA); however, higher downstream noise levels did 

increase with AOA resulting in higher overall Effective Perceived Noise Level.

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

82 

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)

Prescribed by ANSI Std. Z39-18