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LOCITY ON THE GENERATION OF LIFT FANT NOISE IN VTOL AIRCRAFT (Generalectric Co.) 43 p HC $4.25 CSCL 01C

ASA-CR-114

,1 Report No. 2. Government Accession No. 3. Recipient's Catalog No.NASA CR 114571

4. Title and Subtitle 5. Report DateEffect of Crossflow Velocity on the Generation of Lift Fan Jet r Q7tNoise in VTOL Aircraft 6. Performing Organization Code

7. Authorzs) 8. Performing Organization Report No.D.L. Stimpert, R.G. Fogg

10. Work Unit No.9. Performing Organization Name and AddressGeneral Electric CompanyAircraft Engine Group 11. Contract or Grant No.Cincinnati, Ohio 45215 NAS2-5462

13. Type of Report and Period Covered12. Sponsoring Agency Name and Address Contractor Report

National Aeronautics & Space Administration 14. Sponsoring Agency CodeWashington, D.C. 20546

15. Supplementary NotesProject Manager, D.H. HickeyNASA Ames Research CenterMoffett Field, California

16. Abstract

Analytical studies based on a turbulent mixing noise prediction technique indicatethat jet noise power levels are increased when a jet is situated in a crossflow. V/STOLmodel transport acoustic test data obtained in the NASA Ames 40' x 80' (12.2 m x 24.4 m)wind tunnel confirmed this jet noise power level increase due to crossflow. Increases

up to 6 dB at a Strouhal number of 2.5 and crossflow velocity to jet velocity ratio of0.58 were observed. The power level increases observed in the experimental data confirm

the predicted power level increases.

17. Key Words (Suggested by Author(s)) 18. Distribution StatementCrossflow Velocity

Jet Noise Unclassified - Unlimited

Lift Fan

VTOL Aircraft

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price'Unclassified Unclassified 36

* For sale by the National Technical Information Service, Springfield, Virginia 22151

FOREWORD

The authors wish to acknowledge the cooperation of D. Hickey, J. Kirk

and A. Atencio of NASA Ames in making available the data sources used in the

experimental analysis portion of this report.

ii

TABLE OF CONTENTS

Page

FOREWORD ii

LIST OF FIGURES iv

SYMBOLS vi

SUMMARY 1

INTRODUCTION 2

ANALYTICAL STUDY 3

Crosswind Adjustment to Jet Noise

EXPERIMENTAL ANALYSIS 6

V/STOL Model and Data Acquisition

Lift/Cruise Fans

Lift Fans

COMPARISON OF ANALYTICAL AND EXPERIMENTAL RESULTS 9

CONCLUSIONS 10

FIGURES 11

REFERENCES 36

iii

LIST OF FIGURES

Figure

1. Schematic of Jet in Crossflow

2. Predicted Power Spectra Change for Jetsin Crossflow

3. Microphone and V/STOL Model TransportLocation in Ames Wind Tunnel

4. V/STOL Model Transport Schematic

5. Effect of Crossflow onModel Lift/Cruise Fans










15.

16.

Page

11

12

13

14

15

16

17

18

19

50 Hz SPL of V/STOL(Downstream Microphones)

50 Hz SPL of V/STOL(Upstream Microphones)









20

21

22

23

24

25V/STOL Model Lift/Cruise Fan Jet Noise Directiv-ity Pattern at Vo/VJet = 0 and 0.396

V/STOL Model Lift/Cruise Fan Jet Noise Direc-tivity Pattern at Vo/Vjet = 0 and 0.396

26

iv

LIST OF FIGURES - Concluded

Figure PagU

17. Jet Noise Power Level Increase with Increased 27Crossflow at Various Strouhal Numbers

18. Jet Noise Power Level Change as a Function of 28Strouhal Number for Various Crossflow VelocityRatios

19. Effect of Crossflow on 100 Hz Signal from V/STOL 29Model Lift Fans (Downstream Microphones)

20. Effect of Crossflow on 100 Hz Signal from V/STOL 30Model Lift Fans (Upstream Microphones)

21. V/STOL Model Lift Fan Jet Noise Directivity 31Pattern at 100 Hz

22. Comparison of Crossflow Effect on Jet Noise 32Power Level of V/STOL Model Lift Fans andLift/Cruise Fans

23. Comparison of Measured and Predicted Power 33Spectra at Vo/VJet = 0.091

24. Comparison of Measured and Predicted Power 34Spectra at Vo/Vjet = 0.2

25. Comparison of Measured and Predicted Power 35Spectra at Vo/Vjet = 0.33

v

SYMBOLS

Units

2 2A(y) Jet area FT m

dj Diameter of jet at exit plane FT m

f Frequency Hz

K1

Empirical constant

K2 Empirical constant

P Power watts

PWL Sound Power Level Re 10 watts dB

r Radius FT m

Sn Strouhal number, fdj/VjetSPL Sound pressure level Re 0.0002 microbar dB

V Jet Velocity FT/sec m/sec

Vjet Jet Exit Velocity FT/sec m/sec

V(X,Y) Velocity distribution in a plane perpendicular

to the jet trajectory axis FT/sec m/sec

V Crossflow velocity FT/sec m/seco

V Relative velocity FT/sec m/secr

x Space coordinate parallel to crossflow velocity

in jet exhaust plane FT m

X Space coordinate in a plane perpendicular to

the jet axis FT m

y Space coordinate parallel to jet exhaust

velocity at jet exhaust plane FT m

Y Space coordinate in a plane perpendicular to

the jet axis FT m

a Jet trajectory slope, dy/dx Degrees

a1 V/STOL model transport yaw angle Degrees

V Exhaust louver angle of V/STOL model lift fans Degrees

aCN V/STOL model transport lift/cruise nozzle

exhaust exit angle Degrees

Jet trajectory coordinate FT m

vi

SUMMARY

Possible installations for lift fans in future V/STOL aircraft include

vertical mounting in wing pods, vertical mounting in the fuselage, and lift-

cruise mounting on the fuselage with the Jet being vectored for lift and cruise.

In all these possible configurations, the jet will experience various degrees

of crossflow during flight. An investigation was conducted into the effects of

crossflow velocity on the generation of lift fan Jet noise. This investigation

included an analytical study and an examination of experimental data, both of

which confirmed an increase in jet noise sound power level with increasing

crossflow velocities. The aero-acoustic analysis utilized a turbulent mixing

noise prediction technique which is based upon a velocity profile method that

was modified to handle deflected jet velocity profiles. Confirmation of the

aero-acoustic analysis was obtained by examining acoustic data recorded during

testing of a V/STOL model in the NASA Ames 40 foot by 80 foot (12.2m by 24.4m)

wind tunnel.

INTRODUCTION

Research is currently being directed toward the design of V/STOL air-

craft to be used as commercial subsonic transports. Many of the configurations

being considered by NASA and the airframe manufacturers incorporate lift fans

which are fixed in wing pods or mounted in the fuselage with the inlets oriented

vertically. During transition from vertical to horizontal flight on takeoff

or the reverse on landing, exhaust jets from these lift fans experience various

degrees of crossflow velocities.

During aerodynamic and acoustic investigations of a large scale lift fan

model in the NASA Ames 40' by 80' (12.2m x 24.4m) wind tunnel, sound pressure

levels in the jet noise region of the spectrum were observed to increase when

the jet was issuing perpendicular to the crossflow (Reference 1). This paper

reports on analysis of additional noise measurements taken in the NASA Ames

40' by 80' (12.2m by 24.4m) wind tunnel with a complete lift fan aircraft

model. The results were analyzed to give an empirical understanding of jet

noise in a crossflow and to provide verification of an analytical study.

2

ANALYTICAL STUDY

CROSS WIND ADJUSTMENT TO JET NOISE

The Jet noise adjustment used in the prediction model to account for in-

troducing a cross wind component to the Jet flow is based on several fundamental

theoretical noise relationships with modifying assumptions. This cross wind

adjustment factor is applied to the undisturbed Jet noise spectra to arrive at

a predicted Jet noise with cross wind.

The reference jet noise spectra is prepared using the method delineated

in Reference 2. The flight Strouhal curve is used as being representative of

the free field sound generating conditions experienced in aircraft flyover.

This Jet noise spectra is calculated for a Jet exhausting into an undisturbed

area with the assumption that complete mixing occurs between the fan and Jet

stream so that the characteristics of a single jet stream are used to obtain

the Jet spectra.

The evaluation of the acoustic power spectra of a Jet in a crossflow is

based on a turbulent mixing noise analysis using a velocity profile method as

outlined in Reference 3. To compute the acoustic quantities two basic

assumptions are employed:

1. For static Jets or Jets without crossflow, the sound power, P, generated

by a slice of a circular jet obeys Lighthill's eighth power law

dP X v8 dA (1)

where V is the mean velocity which varies with axial location y and radial

distance r from the Jet centerline and A (y) is the cross section area of the

Jet at the axial location y.

2. The nomdimensional sound frequency (Reference 3 and 4) is directly

proportional to nondimensional axial location as defined by the empirical

relationship

fd -K2fdj = (K1 y/d) (2)Vjet

3

where f is the frequency, dj the Jet exit diameter, Vjet the jet exit velocity,

and K1 and K2

are experimentally determined constants which have values of 1.25

and 1.22 respectively.

To evaluate equation 1, the velocity profiles at each axial location are

needed. In this way, the power per slice of Jet can be readily converted to

a power per frequency band (or power spectral level). For a jet in a cross-

flow, the trajectory, jet spread, and velocity profiles are computed from the

model of Bowley and Sucec in Reference 5. Their analysis treats the deflected

jet as a jet composed of two regions - an initial mixing region and a fully

mixed region. Figure 1 presents the coordinates and form of the deflected jet

characteristics.

Acoustically, the splitting of the jet into two aerodynamic regions

also splits the acoustic analysis represented by equation 1 into two regions.

There is a high frequency region associated with the initial mixing region

and a low frequency region associated with the fully mixed region of the de-

flected jet. The superposition of these regions results in the total power

of the jet.

The frequency location along the axis of the deflected jet is represented

by equation 2 where the axial location y for a static jet is replaced by the

deflected jet trajectory location i; therefore equation 2 becomes

fd -Ket = (K1 /dj) (3)

jet

By assuming that the static velocity profiles in equation 1 may be replaced

by relative velocity profiles of a deflected jet or

V R V (X,Y) - V cos a (4)R o

a complete computational system is set for calculating the power spectral

properties of a jet in a crossflow. In equation 4, VR is the relative velocity,

V (X,Y) is the velocity in a plane perpendicular to the deflected jet axis,

VO is the crossflow velocity, and a is the jet trajectory slope. As in Refer-

ence 5, the shape of the jet in a plane perpendicular to the deflected jet

4

axis is assumed rectangular. Typical results of these calculations are shown

on Figure 2 with the peak sound power level occurring at the transition point

between the initial mixing region and the fully mixed region. For V /V jet 0,

the spectra correspond to those predicted by reference 2. This sound power

level increment in decibels is assumed equal to the sound pressure level

change. Since this increment is based on the SAE reference acoustic angle of

135°, the increment is allocated to all acoustic angles using a jet spectra

directivity factor currently in use accounting for the deflection angle for

each frequency. Consequently, the result of the calculation is a noise spectra

in units of SPL for all frequencies and acoustic angles adjusted for cross wind

effects.

Preliminary analysis of predicted power level spectra had indicated a

crossover or decrease in power level at high frequencies as crosswind in-

creased. This was not consistent with experimental data (see Section IV) and

a modification to the method of reference 5 was made. This modification

assumed no deflection of the jet axis in the initial region or more specifi-

cally the deflection angle a = 90° and cos a = 0. Consequently, on the power

frequency plot presented in Figure 2, the lines representing varying cross

flow strengths are regular without any crossover in the range of frequencies

generated in the initial region. It is noted, however, that the transition

point on the jet axis between the initial and turbulent region still varies

as a function of crossflow strength.

5

EXPERIMENTAL ANALYSIS

V/STOL Model and Data Acquisition

A scale model aircraft configured as a V/STOL transport was tested in

the 40' x 80' (12.2 m x 24.4 m) wind tunnel at NASA Ames. The aircraft had

four X376B fans of which two were mounted in deep inlets in the nose and two

were mounted as lift/cruise fans near the tail. The exhaust of the lift/

cruise fans could be vectored downward simulating a lift mode. Exhaust from a

T58 gas generator drove the tip turbine of each 36 inch (.914 m) diameter fan.

Each fan had a design pressure ratio of 1.08 and a tip speed of 640 feet per

second (195 m/ sec). Figure 3 identifies the fan locations on the model and

the microphone locations in the wind tunnel, while Figure 4 is a schematic

of the V/STOL model transport.

Noise measurements were recorded on magnetic tape at various tunnel

speeds for various combinations of lift fans and lift/cruise fans in operation

by NASA Ames personnel. The data were processed at General Electric Edwards

Flight Test Center to give 1/3 octave band sound pressure levels at each micro-

phone for each test point. All data for this report were referenced to a

120 foot (36.5 m) radius by extrapolating the SPL's measured at each microphone

under the assumption of spherical divergence. No corrections for tunnel

reverberation effects are included in the data.

Lift/Cruise Fans

To understand the effect of crossflow on jet noise, data from runs with

the lift/cruise exhaust nozzle in the lift mode (6CN = 90° ) were analyzed for

various tunnel speeds. Figures 5 through 14 show the effect of crossflow

velocity (expressed here as the ratio of tunnel velocity to jet exit velocity)

on 1/3 octave band sound pressure levels at all microphones and at frequencies

of 50, 100, 200, 400 and 800 Hz. It should be noted that the levels measured

are above the tunnel "floor" or background noise. Reference 6 indicates that

the tunnel broadband noise floor is on the order of 80 dB up to velocity ratios

of 0.4. As tunnel velocity and therefore crossflow velocity ratio decreases,

the tunnel noise floor which is broadband in nature drops accordingly.

Reference 6 places the broadband floor at low tunnel speeds at 65 dB + 5 dB.

6

There is a definite increase due to crossflow indicated for all microphones

up to and including 400 Hz. 800 Hz data show only a slight increase in SPL

as crossflow velocity increases. For this frequency and presumably higher

frequencies, the noise may be dominated by fan broadband noise. Reference 7

has shown that the fan pure tone noise of the lift/cruise fans does not increase

with increasing tunnel velocity since the fan inlet is aligned with the flow

and does not experience a true crossflow. Assuming that the fan broadband

noise follows the same trend and that fan broadband noise is dominant at 800 Hz

would account for the data of Figures 13 and 14. The downstream microphones

(numbers 1 through 5) at 50 Hz exhibit large change in SPL with crossflow.

Whether this is an actual increase due to crossflow or the result of inaccuracies

involved in measuring low frequency noise is not certain at this time.

The data of Figures 4 through 14 were used to determine the change in

jet noise at selected crossflow velocity ratios for five 1/3 octave bands

(50, 100, 200, 400, and 800 Hz). The procedure is demonstrated for a cross-

flow velocity ratio of 0.396. Shown in Figures 15 and 16 are plots of 1/3

octave band SPL at frequencies of 50, 100, 200, 400, and 800 Hz both with

and without crossflow. The acoustic angles for each microphone were calcu-

lated relative to the lift/cruise fan exhaust axis. At each frequency, there

is a change due to crossflow which is approximately constant for all angles.

This means that one can assume that the power level change due to crossflow

is equal to the measured SPL change. With the exception of the 50 Hz data in

Figure 15, upstream and downstream microphones show the same increase with

crossflow.

Similar analysis at velocity ratios of 0.175 generated the curves shown

on Figure 17 which are the power level changes due to an increase in cross-

flow velocity at five frequencies. Each frequency was normalized to a

Strouhal number (S n de).jet

Figure 18 was generated by reading the APWL values of the lines drawn

through the data of Figure 16 and represents the measured power level in-

crease as a function of Strouhal number for various crossflow to jet

velocity ratios.

7

Lift Fans

Another source of Jet noise data was noise measurements taken with the

forward lift fans of the V/STOL model in operation at various tunnel speeds.

The data were evaluated in the same manner as the lift/cruise fans. Figures

19 and 20 show the change in 100 Hz 1/3 octave band sound pressure level for

increasing crossflow. To date, only the 100 Hz data has been analyzed. After

calculating the acoustic angle "seen" by each microphone relative to the ex-

haust axis of lift fan number one, the plots of Figure 21 were made. The data

points represent the value of the lines through the data of Figures 19 and 20

read at the corresponding crossflow ratio. For each crossflow ratio, there

is an SPL increase which is constant over all acoustic angles. As a result,

one can assume that the jet noise power level increase is identical to the

SPL increase. Figure 22 compares the Jet noise power level increase indicated

by the lift fan data of Figure 21 with the lift/cruise results obtained by

reading Figure 18 at S = 1.82. The resulting comparison is good although the

forward lift fan increase at this selected frequency is higher than that of

the lift/cruise fans.

8

COMPARISON OF THEORETICAL AND EXPERIMENTAL RESULTS

Figures 23, 24, and 25 represent a comparison of the analytical and ex-

perimental results of the lift/cruise fans. For these comparisons at three

crossflow velocity ratios, the experimental incremental change in power level

from Figure 18 was added to the zero crossflow curve of Figure 2. The result-

ing comparisons indicate that the predicted power level increase and experi-

mental increase due to increasing crossflow are in good agreement.

9

CONCLUSIONS

This investigation included both an analytical study and an examination

of experimental data to determine the effect of crossflow velocity on the Jet

noise generation of lift fans. It was found that an increase in Jet noise

power level is associated with an increase in crossflow velocity perpendicular

to the jet exhaust axis. This predicted increase is confirmed by experimental

data from wind tunnel tests of a V/STOL model. It is recommended that the

analytically predicted Jet noise power levels with crossflow effects be

incorporated into current prediction techniques.

10

y AXIS

Vo0

(CROSS WIND)

INITIALREGION -

high frequency noisegeneration region

JET AXIS

/low frequencynoise generationregion

- TRANSITION POINT

x AXIS

VJET

INITIAL JET

FIGURE 1 SCHEMATIC OF JET IN CROSS FLOW11

LIo r

l rH

~/ x

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0 .2 .4 .6

V/STOL MODEL

* FANS 3 & 4 @ 3600 RPM* REFERENCED TO 120' RADIUS

(36.6m)

*· cn9i °O

.4

Vo/VJet

FIGURE 5 EFFECT OF CROSSFLOW ON 50 Hz SPL OF V/STOL MODELLIFT/CRUISE FANS (DOWNSTREAM MICROPHONES).

15

1001

A

a)

tO

8

0Lu'

MIKE 5

_~~~~~1 ,..6.2

100

0MIKE 6

90o

80

100

90

80

100

90

80

V/STOL MODEL


(36.6m)

* 61c0

· 6cn=90

Vo/VJet

FIGURE 6 EFFECT OF CROSSFLOW ON 50 Hz SPL OF V/STOL MODELLIFT/CRUISE FANS (UPSTREAM MICROPHONES)

16

8rnr-4

0

MIKB 8

I I I

V/STOL MODEL

* FANS 3 & 4 e 3600 RPM* REFERENCED TO 120' RADIUS

(36.6m)

* 5cn90 °* 6 in900cn

0 .2 .4 .6

Vo/VJet

FIGURE 7 EFFECT OF CROSSFLOW ON 100 Hz SPL OF V/STOL MODELLIFr/CRUISE FANS (DIWNSTREAM MICROPHONES).

17

100

90

0o;C-1

Y 80

h)

100

90

80Ec

r-

N

8r4

100

90

80

MIKE 5

I'- I- I

.2 .4

V/STOL MODEL


(36.6m)

· 6 =90 °

cn

.6 0 .2 .4 .6

Vo/VJet

FIGURE 8 EFFECT OF CROSSFLOW ON 100 Hz SPL OF V/STOL MODELLIFT/CRUISE FANS (UPSTREAM MICROPHONES).

18

jUL

9c-

O

MIKE 6

iL.

0)

8

Ec

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MIKE 7

I L I

MIKE 8

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94

100

90

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80

1

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V/STOL MODEL


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Vo/VJet

FIGURE 9 EFFECT OF CROSSFLOW ON 200 Hz SPL OF V/STOL MODELLIFT/CRUISE FANS (DOWNSTREAM MICROPHONES).

19

MIKE 1

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0

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0

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0 .2 .4

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* 6 900cn

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Vo/VJet

.2 .4

FIGURE 10 EFFECT OF CROSSFLOW ON 200 Hz SPL OF V/STOL MODELLIFT/CRUISE FANS (UPSTREAM MICROPHONES).

100

90 o 0

MIKE 6

I I I

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Vo/VJet

EFFECT OF CROSSFLOW ON 400 Hz SPL OF V/STOL MODELLIFT/CRUISE FANS (DOWNSTREAM MICROPHONES).

21

100

90

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80

100

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100

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V/STOL MODEL

* FANS 3 & 4 @ 3600 RPM* RVFERENCED TO 120' RADIUS

(36,6m)* aI 90 0

· 5cn=90°

.6 0

Vo/VJet

.2 .4

EFFECT CP CROSSFLOW O0 400 Hz SPL OF V/STOL MODELLIFT/CRUISE FANS (UPSTREAM MICROPHONES).

100

90

80

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MIKE 6

I I I

. 100

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MIKE 7

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V/STOL MODEL


(36.6m)· al 0 °

1 6 900 cnm9

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Vo/VJet

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EFFECT OF CROSSFLOW ON 800 Hz SPL OF V/STOL MODELLIFT/CRUISE FANS (DOWNSTREAM MCRAOPONES).

23

C)DY:

MIKE 1

I I I

MIKE 2

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MIKE 3

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FIGURE 13

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V/STOL MODEL

* FANS 3 & 4 @ 3600 RPM* RWEBfRCED TO 120' RADIUS

(36.6m)

*· 690°

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Vo/VJet

EFFECT OF CROSSFLOW ON 800 Hz SPL OF V/STOL MODELLIFT/CRUISE FANS (UPSTREAM MICROPHONES).

MIKE 6

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24

V/STOL MODEL

* FANS 3 & 4 @ 3600 RPM* REFERENCED TO 120' RADIUS (36.6m)* SOLID SYMBOLS DENOE. DOWNSTREAM MICROPHONES V /e

t

* CY=' o Jet

* 6n =900 0 0Una 3 0.396- 0~~

50 Hz

Sn -.625

]--

O "-"

90 100 110 120 130

ACOUSTIC ANGLE RELATIVE TO EXHAUST AXIS

140

V/STOL MODEL LIFT/CRUISE FAN JET NOISE DIRECTIVITYPATTERN AT Vo/VE = 0 and 0.396.

25

ioo

.

90 _

80 _

(V

8

-4

FIGURE 15

I I II

v/s0

0

3TOL MODEL

FANS 3 & 4 @ 3600 RPMREFERENCED TO 120' RADIUS (36.6m)

SOLID SYMBOLS DENOTE DOWNSTREAM MICROPHONES

C1 = O°

6cn 90° Vo/Vjet

o0o 0.396

100

800 Hz

~~90 0 4 _S n - 10

I I I 140100 110 120 130

ACOUSTIC ANGLE RELATIVE TO EXHAUST AXIS

V/STOL MODEL LIFT/CRUISE FAN JET NOISE DIRECTIVITY

PATTERN AT Vo/VJET - 0 AND 0.396 ·

o

0

o0

..co

-4

90

FIGURE 16

26

V/STOL MODEL* FANS 3 & 4 @ 3600 RPM* REFERENCED TO 120' RADIUS (36.6m)

* 6cn=90* cn C

I , I , I IF .--

.2

Vo/VJet

50 Hz

Sn = .625

100 Hz

Sn = 1.25

200 Hz

Sn

= 2.5

400 Hz

Sn 5

800 Hz

Sn

- 10

.6

FIGURE 17 JET NOISE LEVEL INCREASE WITH INCREASED CROSSFLOWAT VARIOUS STROUHAL NUMBERS.

27

10

O

10

0

10

0

10

0

10

0

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F I I I I

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00

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p

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28

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m;

r1-*

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so

9,

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8

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00

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r4

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N

Z

a

29

to. 0H

P

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cO r0

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rdv

bc

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IH

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00r4

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0 0

oa oa

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to'.0

r4rr4H

00oo

0

0oI

ooC

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o

kD

I>:Noc

;I0 :li

cu0

30

V/STOL MODEL* LIFT FANS 1 & 2 @ 3600 RPM* REFIIRNCED TO 120' RADIUS (36.6m)* SOLID SYMBOLS DENB!TE DOWNSTREAM MICROPHOIES

· vA

I I I

Vo/VJet

oo.2

0.4V.6

0

i m I I I I I

V

0

I I I I I I100 120 140 160

ACOUSTIC ANGLE REZATIVE TO LIFT FAN 1 EXHAUST EXIT AXIS, DEGREES

FIGURE 21 V/STOL MODEL LIFT FAN JET NOISE DIRECTIVITY PATTERNAT 100 Hz

90

80

70

090

80

70

100

90

I

,

2

..

80 _

70

31

I I I I

I .I I I I I II

I

V/STOL MODEL

* LIFT FANS 1 & 2 @ 3600 RPM· l-o4-av-o°

· 6cn900

0 .2 .4 .6

Vo/VJet

FIGURE 22 COMPARISON OF CROSSFLOW EFFBCT ON JET NOISEPOWER LEVEL OF V/STOL MODEL LIFT FANS ANDLIFT/CRUISE FAIRS

32

0Ul

/ -r.

I .

I~

o

I

trt -.

.S

I

/

SEC

. I

Eal4

',O:"

33

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//

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r- r4

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34

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Fcr)

/~/ 0_ C

~/a

~~

~

o

0

/ C

,,~~

MC

Y

/ 1 qp 1

Iu

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~~

~~

U~

so uoo

us

i

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4~

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35

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r4

REFERENCES

1. Kirk, J.V., Hall, L.P., and Hodder, B.K., "Aerodynamics of Lift Fan V/STOL

Aircraft," NASA TM X-62, 086, September 1971.

2. "Jet Noise Prediction," Aerospace Information Report 876, Society

of Automotive Engineers, Inc., July 10, 1965

3. Lee, R., et al, "Research Investigation of the Generation and Suppression

of Jet Noise," General Electric Flight Propulsion Division, Prepared

under Bureau of Naval Weapons, Contract #NOas 59-6160-C, June 1961.

4. NASA Report #1338, "Near Field Noise of a Jet Engine Exhaust."

5. Bowley, W.W., and Sucec, J., "Trajectory and Spreading of a Turbulent

Jet in the Presence of a Crossflow of Arbitrary Velocity Distribution,"

ASME Paper presented at Gas Turbine Conference & Products Show,.

Cleveland, Ohio, March 9 - 13, 1969.

6. Hickey, D.H., Soderman, P.T., and Kelly, M.W., "Noise Measurements

in Wind Tunnels," pp. 399-408, Basic Aerodynamic Noise Research,

NASA SP-207, July 14, 1969.

7. Stimpert, D.L., "Effect of Crossflow Velocity on VTOL Lift Fan Blade

Passing Frequency Noise Generation," NASA CR 114566, February 1973.

36

; c a ; ' o k...wind tunnel confirmed this jet noise power level increase due to crossflow....

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