Blade-Vortex Interaction Noise of a Full-Scale XV-15 Rotor ... · BLADE-VORTEX INTERACTION NOISE OF...

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NASA/TM–1999-208789 Blade-Vortex Interaction Noise of a Full-Scale XV-15 Rotor Tested in the NASA Ames 80- by 120-Foot Wind Tunnel C. Kitaplioglu July 1999

Transcript of Blade-Vortex Interaction Noise of a Full-Scale XV-15 Rotor ... · BLADE-VORTEX INTERACTION NOISE OF...

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NASA/TM–1999-208789

Blade-Vortex Interaction Noise of a Full-Scale XV-15 RotorTested in the NASA Ames 80- by 120-Foot Wind Tunnel

C. Kitaplioglu

July 1999

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NASA/TM–1999-208789

Blade-Vortex Interaction Noise of a Full-Scale XV-15 RotorTested in the NASA Ames 80- by 120-Foot Wind Tunnel

C. KitapliogluAmes Research Center, Moffett Field, California

July 1999

National Aeronautics andSpace Administration

Ames Research CenterMoffett Field, California 94035-1000

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NASA Center for AeroSpace Information National Technical Information Service7121 Standard Drive 5285 Port Royal RoadHanover, MD 21076-1320 Springfield, VA 22161(301) 621-0390 (703) 487-4650

NOTICEUse of trade names or names of manufacturers in this document does not constitute an officialendorsement of such products or manufacturers, either expressed or implied, by the NationalAeronautics and Space Administration.

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BLADE-VORTEX INTERACTION NOISE OF AFULL-SCALE XV-15 ROTOR TESTED IN THE

NASA AMES 80- BY 120-FOOT WIND TUNNEL

C. Kitaplioglu

Ames Research Center

SUMMARY

A full-scale isolated XV-15 rotor was tested in the NASA Ames 80- by 120-Foot Wind Tunnel todetermine the baseline blade-vortex interaction (BVI) noise signature at typical descending flightconditions. The test is briefly described. Representative samples of the acoustic data are presented.All of the acoustic data are included on an enclosed CD-ROM.

NOMENCLATURE

BLSPL Band-Limited Sound Pressure Level

CT rotor thrust coefficient

CQ rotor torque coefficient

dBA A-weighted Sound Pressure Level

Mtip rotor tip Mach number

OASPL Overall Sound Pressure Level

p sound pressure

R rotor radius

V¥ tunnel velocity

Xm streamwise location of microphone traverse

as rotor shaft angle, deg (as is measured from normal to tunnel flow)

aTPP rotor tip-path-plane angle, deg

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b1C blade longitudinal flapping angle, deg

m rotor advance ratio

s rotor solidity

TEST OBJECTIVES AND APPROACH

An isolated, full-scale XV-15 rotor was tested in the NASA Ames 80- by 120-Foot Wind Tunnel(fig. 1) of the National Full-Scale Aerodynamics Complex (NFAC) to establish the baseline blade-vortex interaction (BVI) noise signature of a full-scale tiltrotor in descending flight. This was accom-plished by systematically varying the rotor advance ratio and tip path plane angle for several fixedvalues of rotor thrust coefficient and tip Mach number. Another major objective of the test was tovalidate these wind tunnel data against similar data obtained on the XV-15 aircraft in flight (ref. 1). Forthis purpose the rotor was operated in the wind tunnel in a manner to closely simulate the state of therotor in flight under the same operating conditions.

Because of the highly directional nature of BVI noise (for counterclockwise rotation BVI noise has apeak directivity angle to starboard and down from the rotor plane) and the opposite rotation of the tworotors (and, therefore, their highly divergent peak BVI directivities) on an XV-15 aircraft, the BVInoise of one rotor has little contribution in the direction where the BVI noise of the opposite rotor isdominant. This allowed an effective comparison of an isolated rotor tested in the wind tunnel with afull aircraft tested in flight.

To measure the BVI noise field of the rotor, a microphone was placed at a position of estimated peakBVI noise directivity, identical during both the in-flight test and the wind tunnel test. A second micro-phone was used in the wind tunnel to test the validity of simulating the BVI noise field of a dual tiltrotor with a single rotor.

An additional set of microphones mounted on a traverse in the wind tunnel was used to characterize theacoustic footprint under the advancing side of the rotor.

An analysis of the acoustic data and comparison to flight test data were presented in reference 1.Analyses of the rotor performance data were presented in references 2 and 3. This technicalmemorandum presents the complete acoustic data set.

TEST DESCRIPTION

Test Hardware

A single, full-scale, XV-15 rotor was tested on the Ames Rotor Test Apparatus (RTA). The rotationdirection of the rotor was the same as the starboard rotor of the aircraft. The RTA is a special-purpose

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test stand for operating full-scale rotors in the NFAC. The RTA houses electric drive motors, a right-angle transmission, a five-component rotor balance, and primary and dynamic control systems. TheRTA was mounted in the wind tunnel on a three-strut support system placing the rotor hub 31 ft(2.5 rotor radii) above the tunnel floor. The rotor shaft angle could be changed by adjusting the heightof the tail strut. The rotor hub center was 11.58 ft above the pitch axis.

The XV-15 rotor has three highly twisted, metal blades with a radius of 12.5 ft. The rotor and bladecharacteristics are summarized in table 1. More detailed descriptions can be found in reference 4. Rotorcollective and cyclic pitch controls were input through the swashplate by three electro-mechanical/hydraulic actuators.

The wind tunnel test section walls are treated with acoustically absorbent material to reduce reflectionsthat can contaminate the noise field. This provides an absorptivity of greater than 90% down to afrequency of approximately 250 Hz. To reduce contamination by hard surfaces on the test model andhardware, additional absorptive material was added to the Rotor Test Apparatus, the struts, themicrophone traverse, and selected hard spots on the test section floor.

Instrumentation and Data Acquisition

Figure 2 shows the arrangement of the microphones in the wind tunnel test section. Figure 3 illustratesthe coordinate system. The origin is coincident with the rotor hub center when the shaft angle is set tozero (as = 0). The positions of the microphones are given in table 2. Microphones #1 through #4 weremounted on a streamwise traversing mechanism to probe the acoustic footprint under the advancingside of the rotor where the highest BVI noise levels would be encountered. Microphone #5 was placedat a position of estimated peak BVI noise directivity. Microphone #6 was positioned to simulate themeasurement of the noise of the second rotor at Microphone #5.

Instrumentation-grade 0.5-in. condenser microphones (Bruel & Kjaer type 4133) were used for theacoustic measurements. The microphone signals were preamplified at the source to minimize signalloss over the long wiring runs. Microphone power supplies provided proper impedance matching. Thesignals were further amplified to maximize signal-to-noise ratio at the measurement system. In additionto the microphone signals, encoders on the rotor shaft provided a 1/rev trigger signal, as well as a2048/rev clocking signal.

The data acquisition system consisted of anti-aliasing filters and 16-bit digitizers. The data weredigitized at 2048 samples/revolution (20480 samples/sec at a nominal RPM of 600) using the clockingsignal from the rotor encoder. All channels were triggered and sampled simultaneously. The anti-aliasing filters were set at a cutoff frequency of 4 kHz for the rotor operating at 600 RPM.

Sixteen revolutions of data were digitized and stored at each test condition. Preliminary processing ofthe data after the completion of each run provided an averaged time history and power spectrum foreach microphone. A dBA metric was also calculated and provided guidance for choice of a test matrixfor subsequent data runs.

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An end-to-end calibration of each microphone channel was performed prior to each data run. A fixedfrequency pistonphone (Bruel & Kjaer type 4220) of known output (nominally 124 dB at 250 Hz)traceable to the NASA Ames Calibration Lab was utilized for the calibrations. These calibrationsprovided engineering units conversions that were updated prior to the run.

Test Matrix

The initial task was to map out the BVI noise variations as a function of rotor operating condition andto locate the operating condition at which maximum BVI noise occurred. This was done at fixed rotortip Mach number and fixed thrust coefficient, while varying rotor tip-path-plane angle and advanceratio. Once this was accomplished, the next steps were to obtain the advancing side acoustic footprintat the peak BVI condition and to document how the acoustic field changed with operating parametersfrom this peak BVI noise condition.

The relatively quick preliminary processing of data allowed a strategy of successive refinement of thetest matrix as the test progressed and data accumulated. During this phase of testing, the rotor wastrimmed to zero flapping, so that the rotor tip-path-plane angle was essentially equal to the shaft angle.

Matching wind tunnel test conditions with those measured during flight required a different approach.The rotor trim state was not matched exactly between the wind tunnel and flight test. The longitudinalflapping on the aircraft results from balancing aircraft moments for a given flight condition. Thesevalues of longitudinal flapping were not obtained in the wind tunnel due to control system load con-straints. Therefore, the rotor tip-path-plane angle (aTPP = as + b1C) was matched between the twotests, rather than the shaft angle and longitudinal flapping individually. As there was no direct measureof rotor thrust on the aircraft, and estimating the rotor thrust from the aircraft weight and wing lift wasproblematic, the rotor torque coefficient was used as a matching parameter. The rotor torque is a directmeasurement from the rotor shaft for both the XV-15 aircraft and the wind tunnel model. It wasassumed that by matching m, Mtip, aTPP, and CQ, the rotor thrust for the two tests would be equal.

Table 3 shows the complete test matrix. The table has been sorted by operating condition, rather thanby test sequence. Surveys of the acoustic field under the advancing side of the rotor are outlined indark. Lighter outlines delineate operating parameters of constant value.

TEST DATA

Data Processing

During data acquisition, 16 revolutions of data, each revolution consisting of 2048 points, weredigitized and written to disk. Initial examination of the data showed excellent rev-to-rev repeatability ofthe data as illustrated in figure 4(a), which includes each individual revolution of data (light lines) aswell as the averaged data (dark line). The high amplitude pulses indicative of the BVI events haveidentical azimuth phases when each revolution of the total 16 revolution record is superimposed asdetailed on figures 4(b), 4(c), and 4(d). Therefore, a straightforward synchronous average of the data

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in the time domain, based on the 1/rev trigger, preserves the pulse-like nature of the BVI events. Theoverall procedure for post-test processing of the data is illustrated in figure 5. The 16 revolutions oftime history data were synchronously averaged based on the 1/rev trigger pulses, resulting in anaveraged time history of one revolution duration of 2048 points. The Fourier transform of thisaveraged time history yielded a power spectrum of 1/rev resolution (10 Hz for 600 RPM). An addi-tional step yielded an A-weighted Sound Power Spectrum. The averaged time history was filtered, asdescribed in the next paragraph, to focus on the BVI event. Three noise level metrics were obtained byintegrating the respective sound pressure power spectra: OASPL from the unfiltered spectra, dBAfrom the A-weighted power spectra, and BLSPL from the bandpass filtered spectra.

Figure 6 compares the time history of a high BVI noise case to one where BVI noise is essentiallyabsent. The main feature of the BVI is the high amplitude double pulse. To highlight these BVI events,the averaged time history was digitally filtered to attenuate frequency content below the 10th and abovethe 50th blade passage harmonics. The 10th harmonic was selected for the lower cutoff frequency,rather than the 5th harmonic used by some investigators (e.g. ref. 5), because of the potential contami-nation of the lower frequency components by wind tunnel reflections as well as wind tunnel drive fannoise. The 50th harmonic (rather than the 40th) was selected to include significant BVI acoustic energyat the higher frequencies. Figure 7 compares data that were bandpass filtered to include the 10th to50th blade passage harmonics to the same data filtered to include the 5th to 40th harmonics, and tounfiltered data. The figure illustrates that the selected method of bandpass filtering the 10th to 50thharmonics adequately preserves the peak-to-peak amplitude and pulse width of the high amplitudeacoustic pulse indicative of the BVI event, while effectively attenuating the (potentially contaminated)low frequency content unrelated to BVI.

Data Quality

Several aspects of data quality are discussed. As mentioned in the “Test Hardware” section, in additionto the sound-absorbing material permanently installed in the wind tunnel test section walls, additionalfoam was added to minimize reflections from the test hardware. To test the efficacy of this additionaltreatment, an impulsive sound source (a starter pistol), located at estimated BVI source positions, wasused to check for the presence of reflections before and after the application of the additional treatment.

Figure 8 illustrates a typical case at Microphone #5. Prior to treatment (Fig 8(a)), a strong reflectedpulse is present at a delay time (from the direct pulse) of 4 msec. This represents a path length differ-ence between the direct and reflected signals of approximately 4.5 ft at a source-to-receiver distance of75 ft, indicating that the reflection point was most likely somewhere on the surface of the test modelfuselage. There are several other, weaker, reflections, most likely from tunnel floor hard points. Aftercovering with foam the portion of the fuselage on the side facing the microphones (the forward,advancing side), we show, in figure 8(b), that the primary reflection was effectively eliminated. Wewere less successful in eliminating the other, weaker reflections, presumably because we were unableto pinpoint the reflection points. Although some obvious hard points on the floor were covered withfoam, a more extensive treatment was impractical. Nevertheless, we are reasonably comfortable withthe overall acoustic quality of the final configuration due to the weaker nature of these secondaryreflections. In addition, the secondary reflections occur at delay times of approximately 25 msec

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(around 1/4 revolution) and, therefore, are unlikely to contaminate the BVI pulses, which occur atintervals of 1/3 revolution.

The background noise due to a combination of wind noise over the microphones and tunnel drivenoise was measured with the rotor hub spinning and all test hardware present except the rotor blades.Figure 9 shows the sound power spectra at Microphone #5 (obtained in the same manner as for rotornoise data described above) at several tunnel speeds. The high level peaks at the low frequencies arisefrom the tunnel drive fans. Figure 10 is a comparison of high BVI noise data at Microphone #5 tobackground noise at similar tunnel speeds. It can be seen that for this high BVI noise case, there isadequate signal-to-noise ratio within the frequency range of interest (300–1500 Hz) for BVI noise.Figure 11, on the other hand, shows a similar comparison for a relatively low BVI noise case. In thisinstance, it is apparent that the signal-to-noise is not adequate. It should be noted that although thesecomparisons are straightforward in the frequency domain, they cannot be easily done in the timedomain because of lack of information regarding the relative phases of the rotor and the drive fans.Therefore, no attempt has been made to correct the time history data for background noise.

Data Files

Acoustic metrics (OASPL, DBA, and BLSPL) are presented in table 4 in Run/Point order. Contourplots of BLSPL levels under the forward advancing side (obtained from Mics #1-4 for the Runs/Pointsoutlined in dark in table 3) are shown in figure 12. A range of operating conditions, as noted on theplots, near maximum BVI noise are provided. Note that in several cases these surveys wereincomplete.

The complete set of acoustic data, including background noise data, is provided on a CD-ROM. Thedisk and file formats are described in the Appendix.

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REFERENCES

1. Kitaplioglu, C; McCluer, M.; and Acree, Jr., C. W.: Comparison of XV-15 Full-Scale WindTunnel and In-Flight Blade-Vortex Interaction Noise. American Helicopter Society 53rdAnnual Forum, Virginia Beach, VA, April 1997.

2. Light, J.: Results of an XV-15 Test in the National Full-Scale Aerodynamics Complex. AmericanHelicopter Society 53rd Annual Forum, Virginia Beach, VA, April 1997.

3. Light, J.; Kitaplioglu, C.; and Acree, C. W.: XV-15 Aeroacoustic Testing at NASA Ames. 23rdEuropean Rotorcraft Forum, Dresden, Germany, September 1997.

4. Maisel, M.: NASA/Army XV-15 Tilt Rotor Research Aircraft Familiarization Document. NASATM X-62,407, January 1975.

5. Martin, R. M.; and Hardin, J. C.: Spectral Characteristics of Rotor Blade/Vortex Interaction Noise.Journal of Aircraft, vol. 25, no. 1, January 1988.

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Table 1. XV-15 rotor characteristics

Blade number 3

Rotor radius 12.5 ft

Blade chord at tip 14 in

Rotor solidity 0.089

Blade twist -41° (nonlinear)

Hub pre-cone angle 1.5°

Rotor airfoils NACA 64-series

Table 2. Microphone positions

Mic # x/R y/R z/R

1 variable 0.575 1.82

2 variable 0.752 1.82

3 variable 1.11 1.82

4 variable 1.46 1.82

5 4.87 2.82 2.05

6 3.6 -4.20 2.05

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Table 3. Test matrix

Mtip RPMCT/ s CQ/ s m aTPP

Xm RUN POINT

0.691 590.6 0.0417 0.00258 0.125 0.06 225 9 13

0.690 588.0 0.0617 0.00413 0.150 -6.42 0 13 420.690 587.9 0.0617 0.00412 0.150 -6.42 37.5 13 410.691 588.2 0.0618 0.00412 0.150 -6.42 75 13 400.690 588.2 0.0618 0.00411 0.150 -6.43 112.5 13 390.690 588.1 0.0617 0.00411 0.150 -6.42 150 13 380.689 587.3 0.0617 0.00411 0.150 -6.42 187.5 13 370.690 587.4 0.0617 0.00410 0.150 -6.42 225 13 360.690 587.6 0.0618 0.00410 0.150 -6.42 262.5 13 350.690 587.8 0.0618 0.00409 0.150 -6.43 300 13 34

0.690 585.7 0.0608 0.00277 0.148 3.03 225 12 1080.690 585.3 0.0608 0.00269 0.159 3.05 225 12 1070.689 584.6 0.0609 0.00296 0.170 1.01 225 12 1050.690 586.0 0.0605 0.00279 0.170 1.97 225 12 104

0.690 585.4 0.0609 0.00264 0.170 3.03 0 12 1010.690 585.5 0.0608 0.00264 0.170 3.02 37.5 12 1000.691 585.6 0.0609 0.00263 0.170 3.02 75 12 990.690 585.1 0.0610 0.00263 0.170 3.03 112.5 12 980.690 585.5 0.0606 0.00264 0.170 3.01 150 12 970.690 585.3 0.0608 0.00263 0.170 3.01 187.5 12 960.690 585.5 0.0606 0.00263 0.170 3.01 225 12 950.690 585.5 0.0614 0.00262 0.170 3.09 262.5 12 940.690 585.5 0.0611 0.00262 0.170 3.08 300 12 93

0.690 585.3 0.0607 0.00248 0.170 4.03 225 12 1020.690 585.3 0.0608 0.00234 0.170 5.00 225 12 1030.690 585.6 0.0608 0.00260 0.181 3.03 225 12 106

0.690 587.6 0.0756 0.00648 0.125 -15.04 225 13 480.690 587.5 0.0757 0.00635 0.125 -14.03 225 13 490.689 590.6 0.0754 0.00607 0.126 -12.00 225 9 710.691 591.8 0.0761 0.00584 0.125 -9.99 225 9 700.690 591.2 0.0752 0.00544 0.125 -7.96 225 9 690.690 591.0 0.0756 0.00529 0.125 -6.94 225 9 680.689 589.9 0.0759 0.00514 0.126 -5.97 225 9 670.690 591.0 0.0759 0.00498 0.126 -4.93 225 9 660.690 591.0 0.0762 0.00484 0.125 -3.90 225 9 650.690 590.8 0.0760 0.00471 0.125 -2.88 225 9 64

0.690 591.8 0.0752 0.00442 0.125 -1.95 -112.5 9 630.691 591.5 0.0750 0.00441 0.125 -1.94 -75 9 620.690 591.2 0.0752 0.00442 0.126 -1.94 -37.5 9 610.690 590.6 0.0750 0.00441 0.125 -1.94 0 9 600.691 591.9 0.0751 0.00443 0.125 -1.95 37.5 9 590.690 591.4 0.0750 0.00443 0.125 -1.93 75 9 580.689 590.1 0.0752 0.00442 0.126 -1.94 112.5 9 570.690 591.2 0.0749 0.00441 0.125 -1.93 150 9 560.690 590.4 0.0749 0.00442 0.125 -1.94 187.5 9 550.690 591.4 0.0750 0.00442 0.125 -1.94 225 9 540.690 591.3 0.0749 0.00441 0.125 -1.94 262.5 9 530.690 591.1 0.0751 0.00442 0.125 -1.95 300 9 52

0.689 590.1 0.0753 0.00440 0.126 -1.95 225 9 510.689 590.0 0.0754 0.00425 0.126 -0.93 225 9 500.690 590.1 0.0751 0.00384 0.125 0.11 225 9 140.690 590.2 0.0756 0.00374 0.125 0.99 225 9 15

0.691 590.9 0.0752 0.00359 0.125 1.95 -112.5 9 270.690 590.6 0.0752 0.00360 0.125 1.95 -75 9 260.691 591.0 0.0749 0.00359 0.125 1.95 -37.5 9 250.691 590.8 0.0754 0.00358 0.125 1.95 0 9 24

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Mtip RPMCT/ s CQ/ s m aTPP

Xm RUN POINT

0.691 590.9 0.0753 0.00358 0.125 1.95 37.5 9 230.691 591.3 0.0755 0.00357 0.125 1.96 75 9 220.691 591.1 0.0753 0.00357 0.125 1.95 112.5 9 210.690 590.7 0.0754 0.00358 0.125 1.94 150 9 200.691 591.3 0.0754 0.00358 0.125 1.95 187.5 9 190.690 591.1 0.0755 0.00359 0.125 1.95 225 9 180.689 590.2 0.0753 0.00359 0.125 1.95 262.5 9 170.691 591.1 0.0750 0.00358 0.125 1.92 300 9 16

0.689 590.0 0.0762 0.00349 0.125 2.95 225 9 28

0.691 591.4 0.0758 0.00338 0.125 3.96 -112.5 9 400.691 591.5 0.0762 0.00337 0.125 3.95 -75 9 390.690 591.0 0.0759 0.00339 0.125 3.95 -37.5 9 380.690 591.1 0.0762 0.00338 0.125 3.95 0 9 370.691 591.3 0.0761 0.00337 0.125 3.95 37.5 9 360.690 591.1 0.0761 0.00337 0.125 3.93 75 9 350.690 590.9 0.0760 0.00337 0.125 3.96 112.5 9 340.691 591.0 0.0756 0.00336 0.125 3.96 150 9 330.690 591.0 0.0760 0.00337 0.125 3.95 187.5 9 320.691 590.9 0.0761 0.00335 0.125 3.94 225 9 310.690 591.0 0.0763 0.00336 0.125 3.95 262.5 9 300.690 590.7 0.0760 0.00334 0.125 3.96 300 9 29

0.689 590.2 0.0761 0.00322 0.126 4.97 225 9 410.690 590.7 0.0756 0.00306 0.125 5.95 225 9 420.690 590.3 0.0756 0.00291 0.125 6.91 225 9 430.690 590.5 0.0754 0.00274 0.125 7.97 225 9 440.689 590.9 0.0765 0.00263 0.125 8.82 225 9 450.690 590.9 0.0756 0.00246 0.125 9.86 225 9 460.690 587.0 0.0757 0.00251 0.125 9.96 225 13 500.690 590.7 0.0755 0.00217 0.125 11.78 225 9 470.690 591.1 0.0765 0.00192 0.125 13.69 225 9 480.689 590.2 0.0763 0.00178 0.126 14.65 225 9 490.690 587.4 0.0755 0.00664 0.150 -15.04 225 13 470.690 587.8 0.0757 0.00646 0.150 -13.99 225 13 460.690 587.9 0.0757 0.00608 0.150 -11.96 225 13 450.691 588.2 0.0759 0.00572 0.150 -9.97 225 13 440.690 587.7 0.0755 0.00531 0.150 -8.00 225 13 430.690 583.7 0.0755 0.00485 0.151 -5.96 225 11 34

0.690 588.1 0.0727 0.00421 0.150 -3.71 0 13 250.690 587.8 0.0727 0.00421 0.150 -3.71 37.5 13 260.690 587.9 0.0726 0.00422 0.150 -3.71 75 13 270.690 587.7 0.0727 0.00422 0.150 -3.71 112.5 13 280.690 587.8 0.0728 0.00422 0.150 -3.70 150 13 290.690 587.7 0.0727 0.00423 0.150 -3.70 187.5 13 30

0.690 583.4 0.0759 0.00450 0.151 -4.01 225 11 330.690 587.8 0.0726 0.00423 0.150 -3.71 225 13 310.690 587.4 0.0725 0.00424 0.151 -3.72 262.5 13 320.690 587.5 0.0726 0.00424 0.150 -3.70 300 13 330.690 583.3 0.0758 0.00407 0.150 -1.91 225 11 320.690 582.6 0.0757 0.00385 0.150 -0.91 225 11 310.690 594.5 0.0754 0.00344 0.150 0.01 225 15 70.689 583.1 0.0759 0.00364 0.151 0.04 225 11 240.690 590.8 0.0757 0.00341 0.150 0.09 225 14 120.689 589.1 0.0760 0.00356 0.150 0.07 300 14 320.690 583.9 0.0758 0.00345 0.150 1.00 225 11 250.691 584.3 0.0757 0.00326 0.150 1.99 225 11 260.690 582.9 0.0758 0.00306 0.150 3.06 225 11 300.690 583.9 0.0756 0.00286 0.150 3.96 225 11 270.689 583.3 0.0759 0.00248 0.151 6.02 225 11 280.689 583.3 0.0759 0.00215 0.151 7.95 225 11 290.690 587.2 0.0758 0.00202 0.150 9.89 225 13 540.690 587.4 0.0759 0.00170 0.150 11.89 225 13 510.690 587.0 0.0756 0.00142 0.150 13.78 225 13 52

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11

Mtip RPMCT/ s CQ/ s m aTPP

Xm RUN POINT

0.689 586.6 0.0758 0.00130 0.150 14.67 225 13 53

0.690 585.1 0.0758 0.00303 0.159 3.07 0 12 760.690 585.2 0.0755 0.00304 0.159 3.05 37.5 12 750.690 585.3 0.0757 0.00304 0.159 3.06 75 12 740.690 585.0 0.0757 0.00304 0.159 3.05 112.5 12 730.690 585.4 0.0758 0.00303 0.159 3.05 150 12 720.690 585.2 0.0756 0.00304 0.159 3.05 187.5 12 710.690 585.2 0.0758 0.00304 0.159 3.05 225 12 700.690 585.2 0.0757 0.00303 0.159 3.06 262.5 12 690.690 585.3 0.0758 0.00302 0.159 3.06 300 12 68

0.684 578.6 0.0801 0.00463 0.164 -3.96 225 11 230.691 597.0 0.0753 0.00673 0.170 -15.01 225 15 430.690 596.4 0.0753 0.00652 0.170 -13.99 225 15 420.690 596.6 0.0760 0.00614 0.170 -11.97 225 15 410.690 596.3 0.0756 0.00569 0.170 -9.98 225 15 400.690 596.9 0.0759 0.00529 0.170 -8.03 225 15 390.690 584.4 0.0759 0.00479 0.170 -5.93 225 11 220.690 584.1 0.0755 0.00432 0.170 -3.94 225 11 210.690 583.7 0.0756 0.00387 0.170 -1.96 225 11 200.690 584.0 0.0756 0.00364 0.170 -0.89 225 11 190.690 583.7 0.0757 0.00342 0.170 0.01 225 11 110.690 584.0 0.0755 0.00321 0.170 0.97 225 11 12

0.689 583.6 0.0758 0.00319 0.170 1.07 0 12 200.689 583.7 0.0758 0.00319 0.170 1.07 37.5 12 190.689 583.7 0.0758 0.00318 0.170 1.07 75 12 180.690 583.8 0.0759 0.00318 0.170 1.07 112.5 12 170.690 583.9 0.0758 0.00319 0.170 1.07 150 12 160.690 583.8 0.0760 0.00318 0.170 1.07 187.5 12 150.690 584.2 0.0758 0.00320 0.170 1.07 225 12 140.690 584.4 0.0758 0.00320 0.170 1.07 262.5 12 130.690 584.5 0.0758 0.00320 0.170 1.06 300 12 12

0.690 584.3 0.0758 0.00301 0.170 1.97 225 11 13

0.690 584.1 0.0757 0.00299 0.170 2.01 0 12 210.689 583.8 0.0758 0.00299 0.170 2.00 37.5 12 220.689 583.7 0.0759 0.00298 0.170 2.03 75 12 230.690 584.3 0.0759 0.00299 0.170 2.04 112.5 12 240.690 584.3 0.0759 0.00299 0.170 2.04 150 12 250.690 584.5 0.0757 0.00299 0.170 2.04 187.5 12 260.690 584.4 0.0759 0.00299 0.170 2.04 187.5 12 270.690 584.3 0.0759 0.00299 0.170 2.04 225 12 280.690 584.4 0.0757 0.00299 0.170 2.03 262.5 12 290.690 584.5 0.0757 0.00300 0.170 2.03 300 12 30

0.690 584.8 0.0758 0.00282 0.170 3.03 0 12 400.690 584.7 0.0758 0.00281 0.170 3.03 37.5 12 390.691 585.1 0.0762 0.00281 0.170 3.06 37.5 12 380.690 584.7 0.0761 0.00281 0.170 3.07 75 12 370.690 584.8 0.0761 0.00280 0.170 3.06 112.5 12 360.690 584.8 0.0762 0.00280 0.170 3.05 150 12 350.690 584.8 0.0759 0.00280 0.170 3.04 187.5 12 340.690 584.1 0.0759 0.00279 0.170 3.03 225 12 330.690 584.2 0.0759 0.00280 0.170 3.04 262.5 12 320.690 584.3 0.0755 0.00278 0.170 2.99 300 12 31

0.690 583.7 0.0759 0.00279 0.170 3.08 225 11 180.690 584.1 0.0757 0.00260 0.170 3.97 225 11 14

0.690 584.7 0.0759 0.00262 0.170 4.01 0 12 410.690 584.4 0.0759 0.00263 0.170 4.01 37.5 12 420.690 584.9 0.0756 0.00264 0.170 4.01 75 12 430.690 585.0 0.0757 0.00263 0.170 4.01 112.5 12 440.690 585.1 0.0759 0.00263 0.170 4.01 150 12 450.690 584.8 0.0757 0.00263 0.170 4.01 187.5 12 460.690 584.8 0.0756 0.00264 0.170 4.01 225 12 47

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12

Mtip RPMCT/ s CQ/ s m aTPP

Xm RUN POINT

0.690 585.0 0.0758 0.00264 0.170 4.01 262.5 12 480.690 585.1 0.0758 0.00264 0.170 4.01 300 12 49

0.690 585.1 0.0759 0.00248 0.170 5.00 0 12 580.691 585.6 0.0758 0.00248 0.170 5.00 37.5 12 570.691 585.4 0.0759 0.00247 0.170 5.01 75 12 560.690 585.0 0.0755 0.00246 0.170 5.00 112.5 12 550.690 585.0 0.0757 0.00247 0.170 5.00 150 12 540.690 585.1 0.0758 0.00245 0.170 5.00 187.5 12 530.690 585.1 0.0756 0.00245 0.170 5.00 225 12 520.691 585.3 0.0757 0.00244 0.170 5.00 262.5 12 510.691 585.2 0.0757 0.00245 0.170 4.98 300 12 50

0.690 583.9 0.0757 0.00239 0.170 5.04 225 11 170.690 584.0 0.0759 0.00222 0.170 5.95 225 11 150.689 583.6 0.0760 0.00184 0.170 7.97 225 11 160.690 595.7 0.0754 0.00158 0.170 9.92 225 15 350.690 596.0 0.0754 0.00125 0.170 11.83 225 15 360.690 596.2 0.0757 0.00094 0.171 13.73 225 15 370.690 596.5 0.0757 0.00080 0.170 14.71 225 15 38

0.689 584.3 0.0756 0.00282 0.177 3.04 0 12 590.690 585.2 0.0757 0.00283 0.177 3.05 37.5 12 600.690 584.7 0.0757 0.00283 0.177 3.04 75 12 610.690 584.8 0.0756 0.00284 0.177 3.04 112.5 12 620.690 584.9 0.0761 0.00285 0.177 3.08 150 12 630.690 585.0 0.0758 0.00285 0.177 3.02 187.5 12 640.690 584.9 0.0756 0.00287 0.177 3.04 225 12 650.690 584.9 0.0758 0.00287 0.177 3.03 262.5 12 660.690 585.0 0.0757 0.00286 0.177 3.02 300 12 67

0.690 588.3 0.0845 0.00456 0.150 -1.96 0 13 240.690 588.2 0.0845 0.00456 0.150 -1.95 37.5 13 230.690 588.2 0.0845 0.00456 0.150 -1.96 75 13 220.690 588.4 0.0844 0.00456 0.150 -1.95 112.5 13 210.691 588.6 0.0845 0.00456 0.150 -1.96 150 13 200.690 588.5 0.0845 0.00455 0.150 -1.96 187.5 13 190.691 588.7 0.0844 0.00455 0.150 -1.95 225 13 180.690 588.5 0.0844 0.00455 0.150 -1.95 262.5 13 170.689 587.2 0.0846 0.00454 0.150 -1.95 300 13 16

0.690 585.7 0.0910 0.00399 0.148 3.02 225 12 92

0.690 590.0 0.0909 0.00562 0.157 -4.89 225 14 310.690 589.7 0.0853 0.00497 0.157 -3.99 225 14 290.689 589.7 0.0939 0.00562 0.157 -3.93 225 14 300.690 589.9 0.0889 0.00494 0.157 -2.91 225 14 270.689 589.7 0.0844 0.00441 0.157 -2.06 225 14 250.690 590.4 0.0925 0.00495 0.157 -1.95 225 14 260.690 589.5 0.0881 0.00439 0.157 -0.98 225 14 230.689 589.0 0.0919 0.00438 0.157 -0.00 225 14 210.690 595.0 0.0907 0.00392 0.156 1.58 225 15 170.690 585.6 0.0911 0.00376 0.159 3.06 225 12 910.690 594.3 0.0907 0.00350 0.156 3.11 225 15 120.691 588.6 0.0895 0.00258 0.156 7.02 225 13 150.690 585.6 0.0908 0.00412 0.170 1.04 225 12 890.690 585.7 0.0909 0.00384 0.170 2.05 225 12 88

0.690 584.4 0.0913 0.00354 0.170 3.09 0 12 770.690 584.8 0.0914 0.00355 0.170 3.09 37.5 12 780.690 585.2 0.0913 0.00355 0.170 3.08 75 12 790.690 585.0 0.0912 0.00355 0.170 3.09 112.5 12 800.690 585.2 0.0912 0.00355 0.170 3.09 150 12 810.690 585.1 0.0913 0.00355 0.170 3.09 187.5 12 820.690 585.3 0.0911 0.00355 0.170 3.09 225 12 83

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13

Mtip RPMCT/ s CQ/ s m aTPP

Xm RUN POINT

0.690 585.2 0.0913 0.00355 0.170 3.09 262.5 12 840.690 585.3 0.0912 0.00355 0.170 3.09 300 12 85

0.689 584.7 0.0909 0.00331 0.170 4.02 225 12 860.690 585.3 0.0914 0.00307 0.170 5.01 225 12 870.689 584.7 0.0910 0.00345 0.181 3.08 225 12 90

0.690 595.5 0.0998 0.00441 0.148 3.07 225 15 330.690 590.5 0.0964 0.00554 0.157 -2.92 225 14 280.690 590.3 0.0964 0.00496 0.157 -0.90 225 14 240.690 589.5 0.1006 0.00499 0.157 0.10 225 14 220.691 591.0 0.0964 0.00440 0.156 1.03 225 14 190.690 590.1 0.1044 0.00499 0.156 1.07 225 14 200.690 594.9 0.1022 0.00459 0.156 1.28 225 15 130.690 594.9 0.1013 0.00462 0.156 1.55 225 15 140.690 591.0 0.0990 0.00439 0.157 1.55 225 14 170.691 595.2 0.0957 0.00427 0.156 1.55 225 15 160.690 594.7 0.1035 0.00477 0.156 1.59 225 15 150.690 590.9 0.1034 0.00437 0.157 2.61 225 14 160.690 594.6 0.1025 0.00407 0.156 2.96 225 15 80.690 594.2 0.0964 0.00381 0.156 3.11 225 15 110.690 595.8 0.1016 0.00423 0.159 3.14 225 15 320.690 594.6 0.1010 0.00406 0.156 3.15 225 15 90.691 588.7 0.0970 0.00326 0.156 5.54 225 13 140.690 596.0 0.0991 0.00446 0.170 1.03 225 15 300.689 594.5 0.1023 0.00435 0.171 2.06 225 15 290.690 596.0 0.1022 0.00407 0.171 3.09 225 15 340.690 595.3 0.1017 0.00392 0.180 3.06 225 15 31

0.690 590.9 0.1068 0.00497 0.157 1.63 225 14 180.690 594.1 0.1068 0.00445 0.157 3.22 225 15 100.690 591.0 0.1077 0.00439 0.157 3.53 225 14 15

0.690 595.7 0.1061 0.00428 0.170 3.06 0 15 280.690 595.3 0.1054 0.00428 0.170 3.06 37.5 15 270.690 594.6 0.1058 0.00426 0.170 3.06 75 15 260.690 594.7 0.1058 0.00427 0.171 3.06 112.5 15 250.689 594.6 0.1057 0.00427 0.170 3.05 150 15 240.689 594.6 0.1056 0.00426 0.171 3.07 187.5 15 230.690 595.2 0.1056 0.00425 0.170 3.06 225 15 220.690 595.1 0.1055 0.00422 0.170 3.06 262.5 15 210.690 595.4 0.1055 0.00423 0.170 3.07 300 15 20

0.690 594.5 0.1049 0.00388 0.170 4.04 225 15 190.690 594.7 0.1054 0.00358 0.170 5.03 225 15 18

0.690 590.5 0.1124 0.00439 0.157 4.61 225 14 140.690 590.5 0.1118 0.00398 0.157 5.60 225 14 13

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15

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Page 19: Blade-Vortex Interaction Noise of a Full-Scale XV-15 Rotor ... · BLADE-VORTEX INTERACTION NOISE OF A FULL-SCALE XV-15 ROTOR TESTED IN THE NASA AMES 80- BY 120-FOOT WIND TUNNEL C.

16

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Page 20: Blade-Vortex Interaction Noise of a Full-Scale XV-15 Rotor ... · BLADE-VORTEX INTERACTION NOISE OF A FULL-SCALE XV-15 ROTOR TESTED IN THE NASA AMES 80- BY 120-FOOT WIND TUNNEL C.

17

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Page 21: Blade-Vortex Interaction Noise of a Full-Scale XV-15 Rotor ... · BLADE-VORTEX INTERACTION NOISE OF A FULL-SCALE XV-15 ROTOR TESTED IN THE NASA AMES 80- BY 120-FOOT WIND TUNNEL C.

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Page 22: Blade-Vortex Interaction Noise of a Full-Scale XV-15 Rotor ... · BLADE-VORTEX INTERACTION NOISE OF A FULL-SCALE XV-15 ROTOR TESTED IN THE NASA AMES 80- BY 120-FOOT WIND TUNNEL C.

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.33

11

9.4

11

11

.25

11

4.2

21

18

.59

11

0.6

11

13

.27

11

7.2

10

9.8

71

12

.57

11

3.5

41

03

.33

10

5.2

31

12

.93

94

.52

96

.89

15

34

12

0.2

61

12

.52

11

6.6

11

20

.52

11

2.9

21

17

.05

12

0.3

51

12

.46

11

6.2

11

19

.85

11

2.1

91

15

.13

11

3.5

41

05

10

7.7

31

13

.95

97

.39

99

.79

15

35

11

8.9

10

8.0

71

10

.87

11

9.5

71

08

.73

11

1.5

31

19

.73

10

9.4

31

12

.31

11

8.9

31

10

.08

11

2.9

61

10

.79

10

2.2

61

04

.28

11

5.0

99

0.8

69

3.5

81

53

61

17

.68

10

5.7

51

09

.44

11

8.2

11

06

.35

10

9.6

91

18

.39

10

7.0

51

10

.61

11

7.6

51

07

.33

11

0.5

81

09

.87

99

.74

10

2.2

61

15

.19

89

.79

93

.36

15

37

11

6.6

11

02

.83

10

6.4

11

17

.12

10

3.0

21

06

.38

11

7.3

61

03

.03

10

6.2

21

16

.52

10

3.2

10

6.7

41

08

.98

96

.16

98

.57

11

5.2

78

8.2

69

0.2

91

53

81

16

.35

10

01

02

.87

11

6.8

51

00

.86

10

2.8

81

16

.99

9.9

81

02

.82

11

6.0

81

00

.21

10

2.9

61

09

.03

94

.65

97

.46

11

4.7

38

8.2

19

1.4

41

53

91

15

.51

10

4.2

81

05

.74

11

5.1

71

03

.99

10

4.9

31

13

.95

10

1.7

61

02

.37

11

2.2

91

00

.29

10

0.9

31

09

.05

92

.23

91

.81

11

.65

87

.15

90

.02

15

40

11

4.6

19

9.3

29

9.1

51

14

.23

99

.41

99

.13

11

2.9

99

7.4

29

6.4

11

1.0

69

5.9

49

5.7

41

08

.84

91

.12

89

.94

11

1.2

28

5.5

78

8.6

11

54

11

14

.07

10

1.5

81

02

.72

11

3.6

51

01

.24

10

2.2

21

12

.31

98

.45

99

.17

11

0.5

79

6.8

69

7.9

61

08

.97

91

.74

89

.31

10

.75

86

.04

86

.79

15

42

11

3.3

11

00

.96

10

2.0

81

12

.78

10

0.2

81

01

.24

11

0.9

49

7.5

39

8.2

21

09

.67

95

.89

6.9

41

08

.98

91

.55

86

.93

11

0.0

88

6.7

86

.53

15

43

11

3.0

59

5.9

96

.03

11

2.5

95

.54

95

.58

11

0.9

92

.74

92

.48

10

9.6

29

1.0

79

11

09

.23

91

.75

87

.84

10

9.8

88

5.2

48

4.4

3

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20

Figure 1. The XV–15 right-hand rotor mounted in the Ames 80- by 120-Foot Wind Tunnel.

Mic 6

Mic 5

Mics12 3 4

Microphonetraverse

XV-15starboardrotor

Rotor image(port rotor)

Figure 2. Schematic of microphone positions for the XV-15 test in the NASA Ames 80- by 120-FootWind Tunnel.

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21

x

yz

rotor hub(as=0) V¥

Äpitchaxis

11.58 ft

3.08 ft

Figure 3. Coordinate system.

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22

- 4 0

- 2 0

0

2 0

4 0

6 0

8 0

0 0 . 2 0 . 4 0 . 6 0 . 8 1

Sou

nd P

ress

ure

(Pas

cals

)

R e v

Figure 4(a). Comparing individual revs (light lines) to the average (dark line).

- 4 0

- 2 0

0

2 0

4 0

6 0

8 0

0 .18 0 . 2 0 .22 0 .24 0 .26 0 .28

Sou

nd P

ress

ure

(Pas

cals

)

R e v

Figure 4(b). Expanded azimuth near the first BVI pulse.

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23

- 4 0

- 2 0

0

2 0

4 0

6 0

8 0

0 .52 0 .54 0 .56 0 .58 0 . 6 0 .62

Sou

nd P

ress

ure

(Pas

cals

)

R e v

Figure 4(c). Expanded azimuth near the second BVI pulse.

- 4 0

- 2 0

0

2 0

4 0

6 0

8 0

0 .84 0 .86 0 .88 0 . 9 0 .92 0 .94

Sou

nd P

ress

ure

(Pas

cals

)

R e v

Figure 4(d). Expanded azimuth near the third BVI pulse.

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24

unaveraged data

averaged time history

filtered averaged time

history

power spectrum of averaged time

history

A-weighted power spectrum of

averaged time history

power spectrum of filtered,

averaged time history

OASPL dBA

BLSPL

Figure 5. Data processing procedure.

- 4 0

- 2 0

0

2 0

4 0

6 0

0 9 0 1 8 0 2 7 0 3 6 0

high BVIno BVI

Sou

nd P

ress

ure

(Pas

cals

)

Azimuth (deg)

Figure 6. Comparison of a high BVI noise case with a case where no BVI noise is present,Microphone #5. Unfiltered data.

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25

- 4 0

- 2 0

0

2 0

4 0

6 0

0 9 0 1 8 0 2 7 0 3 6 0

unfilteredfiltered [5th - 40th b.p.h.]filtered [10th - 50th b.p.h.]

Sou

nd P

ress

ure

(Pas

cals

)

Azimuth (deg)

Figure 7(a). Comparison of unfiltered data with data filtered at two bandpass frequencies.

- 4 0

- 2 0

0

2 0

4 0

6 0

6 0 7 0 8 0 9 0 1 0 0 1 1 0

unfilteredfiltered [5th - 40th b.p.h.]filtered [10th - 50th b.p.h.]

Sou

nd P

ress

ure

(Pas

cals

)

Azimuth (deg)

Figure 7(b). Expanded azimuth scale.

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26

-1 .5

- 1

-0 .5

0

0 . 5

1

- 1 0 0 1 0 2 0 3 0 4 0 5 0

Sca

led

Am

plitu

de

Time (msec)

Figure 8(a). Reflection data without foam treatment, Mic #5.

-1 .5

- 1

-0 .5

0

0 . 5

1

- 1 0 0 1 0 2 0 3 0 4 0 5 0

Sca

led

Am

plitu

de

Time (msec)

Figure 8(b). Reflection data after adding foam treatment.

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27

4 0

5 0

6 0

7 0

8 0

9 0

0 1000 2000 3000 4000

81.8 knots

SP

L (d

B;

ref.

2e-

5 P

a)

Frequency (Hz)

Mic #5

4 0

5 0

6 0

7 0

8 0

9 0

0 1000 2000 3000 4000

62.3 knots

SP

L (d

B;

ref.

2e-5

Pa)

Frequency (Hz)

Mic #5

4 0

5 0

6 0

7 0

8 0

9 0

0 1000 2000 3000 4000

43.7 knots

SP

L (d

B;

ref.

2e-5

Pa)

Frequency (Hz)

Mic #5

Figure 9. Power spectra of background noise at several tunnel speeds.

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28

4 0

5 0

6 0

7 0

8 0

9 0

1 0 0

1 1 0

0 1000 2000 3000 4000

DATA-80.2 knotsBKGND-81.8 knots

SP

L (d

B;

ref.

2e-5

Pa)

Frequency (Hz)

Figure 10. Comparison of data to background noise at a high BVI noise condition.

4 0

5 0

6 0

7 0

8 0

9 0

1 0 0

1 1 0

0 1000 2000 3000 4000

DATA-57.5 knotsBKGND-62.3 knots

SP

L (d

B;

ref.

2e-5

Pa)

Frequency (Hz)

Figure 11. Comparison of data to background noise at a low BVI noise condition.

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29

Fig 12. Contour plots of Band Limited Sound Pressure Level (BLSPL) under the forward advancingside of the starboard XV-15 rotor at operating conditions near maximum BVI noise.

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30

Fig 12. Continued.

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31

Fig 12. Continued.

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32

Fig 12. Continued.

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33

Fig 12. Continued.

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34

Fig 12. Continued.

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35

Fig 12. Continued.

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36

Fig 12. Continued.

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37

Fig 12. Continued.

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38

Fig 12. Continued.

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39

Fig 12. Continued.

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40

Fig 12. Continued.

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41

Fig 12. Continued.

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42

Fig 12. Continued.

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43

Fig 12. Continued.

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44

Fig 12. Concluded.

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45

APPENDIX

XV-15 ACOUSTIC DATA FILES

All of the acoustic data from the full-scale XV-15 rotor test in the NASA Ames 80- by 120-Foot WindTunnel are provided on a CD-ROM. The CD has been produced in ISO 9660 format readable on awide variety of computers. The files are in text format.

The file names reflect the specific Run and Point with reference to table 3. For example, fileT832R12P020 refers to Test 832 (the XV-15 test), Run 12, Point 20.

The files are organized into four directories:

(1) The “-FA” directory contains the filtered (10th through 50th blade passage harmonics) averagedtime histories. The microphone data values are Sound Pressure in Pascals. Each file contains a headerrow, followed by 2048 rows representing the 2048/rev sampling. The data are in tab delimitedcolumns as follows:

Index Rev Azimuth Mic#1................ Mic#6

1

2

.

.

.

2048

Figure A.1 is a representative filtered, averaged time history.

(2) The “-PS” directory contains the unfiltered, time-averaged power spectra. Each file contains aheader, followed by approximately 400 rows representing the 400 blade-passage harmonics (up to the4 kHZ anti-aliasing filter limit). The data are in tab delimited columns as follows:

Order Frequency (Hz) Mic#1..................Mic#6

1

2

.

.

.

400

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46

Note that the values in these spectra files are in units of sound power (sound pressure squared) inPascals2. To obtain the equivalent decibel values, the following conversion must be made:

dB = 10 * log10 (p2/(2e-5)2)

where p2 is the value in the file (units of Pascal2). Figure A.2 is a representative unfiltered, averagedpower spectrum, including the corresponding background noise spectrum.

(3) The “-dBA” directory contains, in seven files, one for each of the data runs, the A-weighted soundpower metric (dBA) values for each data point and microphone. Each file contains a header row,followed by a variable number (depending on the number of data points obtained during that particularrun) of rows of dBA data. The data are in tab delimited columns as follows:

Point Mic#1................... Mic#6

0n

.

.

.

nn

(4) The “-F2_BLdB” directory contains, in six files, one for each of the data runs, the band-limited(filtered 10th through 50th blade-passage harmonics) sound power metric (BLSPL) values for eachdata point and microphone. Each file contains a header row, followed by a variable number(depending on the number of data points obtained during that particular run) of rows of BLSPL data.The data are in tab delimited columns as follows:

Point Mic#1................... Mic#6

0n

.

.

.

nn

Note that only unfiltered power spectra of background noise (Run 19) data are included. Therefore,“T832R19Pnn-xx.dat” files appear only in the “-PS” and “-dBA” directories.

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47

-40

-20

0

2 0

4 0

6 0

0 9 0 180 270 360

Sou

nd P

ress

ure

(Pas

cals

)

Azimuth (deg)

Fig A.1. Filtered, averaged time history. Run 12, Point 65 (Mtip = 0.69, CT/s = 0.076, m = 0.177,aTPP = 3.04°), Mic #5.

4 0

5 0

6 0

7 0

8 0

9 0

100

110

0 1000 2000 3000 4000

D a t aBackground noise

SP

L (d

B;

ref.

2e-5

Pa)

Frequency (Hz)

Fig A.2. Unfiltered sound power spectrum for Run 12, Point 65, Mic #5.

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REPORT DOCUMENTATION PAGE

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OMB No. 0704-0188

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20. LIMITATION OF ABSTRACT19. SECURITY CLASSIFICATION OF ABSTRACT

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13. ABSTRACT (Maximum 200 words)

Standard Form 298 (Rev. 2-89)Prescribed by ANSI Std. Z39-18298-102

NSN 7540-01-280-5500

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 thiscollection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for information Operations and Reports, 1215 JeffersonDavis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503.

11. SUPPLEMENTARY NOTES

Unclassified Unclassified

Unclassified — UnlimitedSubject Category 05 Distribution: StandardAvailability: NASA CASI (301) 621-0390

A-99V0029

NASA/TM–1999-208789

July 1999

Ames Research CenterMoffett Field, CA 94035-1000

National Aeronautics and Space AdministrationWashington, DC 20546-0001

51

A04

Blade-Vortex Interaction Noise of a Full-Scale XV-15 Rotor Tested in theNASA Ames 80- by 120-Foot Wind Tunnel

C. Kitaplioglu

A full-scale isolated XV-15 rotor was tested in the NASA Ames 80- by 120-Foot Wind Tunnel todetermine the baseline blade-vortex interaction (BVI) noise signature at typical descending flight condi-tions. The test is briefly described. Representative samples of the acoustic data are presented.All of the acoustic data are included on an enclosed CD-ROM.

Rotorcraft, Acoustics, Blade-vortex interaction, XV-15

Technical Memorandum

Point of Contact: C. Kitaplioglu, Ames Research Center, MS T12B, Moffett Field, CA 94035-1000 (650) 604-6679

581-10-12