N94-33490

COMMUNITY NOISE TECHNOLOGY NEEDS

BOEINGS PERSPECTIVE

G. L. Nihart

Boeing Commercial Airplane Group

Seattle, Washington

High Speed Research

First Annual WorkshopMay 14-16, 1991

PRECEDING PAGE BLANK NOT FILMED 1105

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COMMUNITY NOISE TECHNOLOGY NEEDS

BOEING PERSPECTIVE

:_ NOISE REQUIREMENTS (NOISE CONTOURS)

:_ NOISE SOURCES

JET NOISE PREDICTION TECHNOLOGY

- JEN3RC (EMPIRICAL)

' JEN8 (SEMI-EMPIRICAL)

FLOW UNDERSTANDING:

- FLOW VISUALIZATION

- CFD MODELING

:_ OTHER PREDICTION TECHNOLOGY NEEDS

:_ PREDICTION ACCURACY AND CONFIDENCE LEVELS

:_ CONCLUSIONS

FIGURE 1

FIGURE 2

FIGURE 3

FIGURE 4

FIGURE 5

FIGURES 6, 7

FIGURE 8

FIGURES 9, 10

FIGURES 11, 12

1106

AIRPORTCOMMUNITY ACCEPTANCE

Airport communityacceptanceof HSCT noiselevelswill dependon the relativenoiselevelsto airplanesflying at the time of introduction. The 85 dBA noise contours for the range of

large subsonic airplanes that are expected to be in service in the early 21st century areshown as a shaded area. A certifiable HSCT noise contour, as shown, would be somewhat

wider along the runway but about the same in the residential areas downrange. An HSCTnoise rule should insure this noise capability.

COMMUNITY NOISE

85 dBA FOOTPRINTS

HSCT Range of Large Subsonic Airplanes

1<_ 1 Mite _>l

FIGURE I

1107

COMMUNITY NOISE SOURCES

Jet noiseis theprimarynoisesourceat the sidelinemeasuringpoint but at the downrangeand approachmeasuringpointsburnernoise isalsoimportantIn addition turbine and air-framenoiseare importantsourcesduringapproach.Predictionaccuracyfor all of thesourcesandfor noisereductionfeatures,suchastile jet exhaustnoisesuppressionnozzle,will havea major impacton designfeaturessuchasenginesizing.

120

116

112

108

104

EPNdBo o

96

92

i

84

80

_Hardwall NWith Suppression I

I CUTBACK 20% PLR 1

UYolal Comp. BurnerTurbine Jet

110

108-

106-

104

102-

EPNdB 100

98-

96

94

92

90-

Stage 3

Figure 2

12°/116 --

112

108 ._

EPNdB 1°4

1oo

96

92

88

84

80

APPROACH

SIDELINE 20% PLR

Total Comp. BurnerTurbine Jei ,,

_ Stage 3

-NaN

88Total Comp. BurnerTurbino Jet Airframe

Noise Components Turbine Bypass Turbojet Engine

Stage 3

1108

JET NOISE PREDICTION TECHNOLOGY

CURRENT PROCEDURES ARE :

* EMPIRICAL

* PREDICT UNSUPPRESSED JET ; ie, R-C

* PREDICT SPECIFIC SUPPRESSION CONFIGURATIONS

IDEAL PROCEDURE :

* ANALYTICAL PROCEDURE THAT PREDICTS ABSOLUTE LEVELS

" FLEXIBLE SUCH THAT SUPPRESSION DEVICES CAN BE SCREENED

* USES PREDICTABLE FLOW PARAMETERS OR RESULTS OF CFD

MODELING

FIGURE 3

1109

NFM NOZZLE PREDICTION VERSUS DATA

The basic low bypass ratio jet noise prediction program at Boeing is empirical

and is for a round convergent (RC) nozzle. This program was used to predictexternally generated noise based on the fully mixed stream and the internal noisefrom one of the primary nozzles using the aspirated flow as the free stream. The

predicted noise levels are then added. Shock cell noise predicted for the primarynozzle is reduced by 7 dB to account for the convergent-divergent (CD)expansion of the primary nozzle.

25

20

t

Z

o

a. 15

10

1110

_[ Pre-TestPrediction ]

7"

I{.W.

X

X = Prediction

0= Data

X = ModifiedPrediction.

• Long Shroud

X

Medium Shroud

"ShortShroud

t I 1___1.... 1 I I I I

"EFFECTIVE" LINING LENGTH - AI/,'_I

I I 1 I I I 1

[ FI__._GURE4, NFM NOZZLE PREDICTION VS DATA ]

JET NOISE PREDICTION PROCEDURE DE\,'ELOPMENT

A computer prediction program is being developed at Boeing incorporating the recentnozzle test data modeling externally generated mixing noise, internally generatedmi:,dng noise and internal shock cell noise components. A status comparison to testdata in the forward and aft arc are shown.

H S C T JET NOISE

SEMI-EMPIRICAL COMPONENT MODELLINGTO GUIDE NOZZLE / AIRPLANE DEVELOPMENT

Forward Radiated Aft Radiated

:'°t _ r i

:_°1 ; t A

85

"70

oo.11

I I I I It mas_re_--k

/-A_ i\_ . -_ -

xmg--q_ _

Sh4ck I_ I t 'X.

22 24 26 28 30 .32 34 36 38 40 42 44

_JAND

,,_! d I15 ur -"--""_ I

_,,o-r ' I ._t ,

.... ][..... !' Z2

22 24 26 28 30 32 34 36 38 40 42 44 46

1111FIGURE 5

CROSS-CORRELATIONSTUDIES

Techniquesarebeingstudiedto cross-correlateinternal fluctuatingjet velocitieswith far field soundpressure.If this is successful,noisesourcelocationsandtheir frequencycharacteristicscanbedeterminedinsidethe ejector.This wouldbe usefulin improvingthemixer nozzleandejector lining designs.

z_Zg;2WzT,6_f_'

APPLICATION OF CROSS CORRELATION TECHNIQUES

Present Opportunities for Better Under-

standing of Internal Noise Sources

<:_ Nozzle

P/

Signal Processing:

Sampling, Recording, Fil-

tering, Differentiating,

Multiplying, Cross-Corre-

lating

1112FIGURE 6

SIMULATED CROSS-CORRELATIONRESULTS

In order to determinethe numberof samples(proportional to processingtime) neededto obtain usefulcross-correlationfunctions,a digitally simulatedrandomtest signalwasburied in a noisesignalanddelayed.Resultingcross-correlationsbetweenthesecondderivativeof the original testsignalandthe testandnoisesignalcombination,areshownwherethesignalto noiseratio isabout 10.The reducionin thevarianceinthe correlationwith increasingnumberof samplesisevident.Frequencycharacteristicsareobtainedby fourier transformingthecrosscorrelation.

SIMULATED CROSS-CORRELATION

Results- Time Domain- Noise > Signal

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c,..)

¢...,

._o

O

16K

Samples

Time Delay

.c2

O

64K co,

Samples

Time Delay

32K

Samples

Time Delay

128K

Samples

Time Delay

Idealized

Shape forband-limitednoise:

I

FIGURE 7

1113

CFD AND NOZZLE DESIGN

ComputationalFluid Dynamics(CFD) hasthepotential of beinga veryusefultool in nozzledesign.CurrentlyCFD is usedto evaluatenewdesigns,prior to fabrication,in order to find potential flow problems.Datagatheredduringwind tunnel testingis usedto validateCFDmodelingincreasingconfidencein theCFD results.

Comparison of Coarse and Fine Grid Pressure Contours

Flow Conditions: PR1=3.5, TR1=1.01, PR2=1.16, TR2=1.01, M_--0.24

Coarse Grid

P/7P_

D. B2OO

D. BD50

O. 79DO

O. 775D

O, 76DO

D, 7450

l=il- o. 7a0o- D.7150

- D, ?ODD

O. EBSO

O. GTOO

O. G550

- O. 6.400

- O. 525D

1- O. 5950

0. SOD0

- D. 5650

- D, 55D0

1114 FIGURE 8

OTHER PREDICTION TECHNOLOGY NEEDS

SIDELINE SHIELDING AND GROUND REFLECTION / ATTENUATION

* CURRENT METHODS ARE BASED ON H'BPR ENGINES AND SUBSONICAIRPLANE CONFIGURATIONS

INSTALLATION EFFECTS

* EFFECT ON SUPPRESSION SYSTEM

* NO[SE REFLECTION, ETC.

OTHER NOISE SOURCES

* TURBOMACHINERY

* BURNER NOISE (LOW EMISSION BURNERS)

* AIRFRAME NOISE

FIGURE 9

1115

SIDELINE SHIELDING PREDICTION

Current sideline shielding prediction programs were developed using sideline noise

measurements of 747 and 767 airplanes with the same engines. The shielding is

then for high bypass ratio engines mounted off of the leading edge of the wing andwith many configuration differences from current HSCT designs. There is currently

little capability to accuratly predict shielding sensitivities to configuration layout

changes.

Size ComparisonHSCT Versus 747-400

747-400

23! ft 10 in

311 ft

211 ft 5 in

132 ft

CO-318R1

G-8-1

P 1642,29 H

m

=

1116 FIGURE 10

DESIGN MARGIN IMPORTANCE

A designmarginon theorder of 80% confidencewill be requiredto launchan ItSCTproductionprogram.The currentstatusis lessthan 50% with a one sigma variation of5. To reach 80% confidence will require irnprovements in the airplane, such as an im-

provements in the jet suppression nozzle, but will also require improved predictioncapability to reduce the variation.

9O

8O

VJET NOISE SUPPRESSION AND

PREDICTION ACCURACY

EFFECT ON CONFIDENCE LEVEL

o 2 GOAL

g

7O

60

5O

4O

3O

[] 17

I I I I I I I I I I I I I I18 19 20

Jet Suppression, delta EPNdB

FIGURE 11

1117

PREDICTION UNCERTAINTY SOURCES

Predictionuncertaintyincludesthe uncertaintyof eachof thecontributingnoisesources(A-D). The total accumulatedmeasurementvariation includes(E) thesingletestvariability (datascatter)but also(F) any true error (bias).To improvethe totalpredictionto demonstrationuncertainty(G) eachnoisesourcepredictionprocedureshouldbeevaluatedfor accuracyand improvedif possible.Improvementsin predictionof propagation,installationeffects,shielding,groundreflectionandairplaneperformancewill alsobe required.

VALUE

PREDICTION UNCERTAINTY

(_( DISPLACED BY BIAS G )

+VARIABILITY IN 1 ,,SCATTER, '

SINGLE TEST / • L ..

VAR,ABIL,T .

MEASURED

_ _MEAN (X)

"-TNRU E (p].%

DICTED []./}

I PREDICTION/I TOOE,.:O/!UNCERT, 'N I

CONDITION

1118 FIGURE 12

CONCLUSIONS

JET NOISE PREDICTIONS ARE PRIMARILY EMPIRICAL AND PREDICT TESTED NOZZLE

CONFIGURATIONS.

FLEXIBLE AND MORE ANALYTICAL PREDICTION PROCEDURES ARE NEEDED THAT

ACCURATELY PREDICT ABSOLUTE LEVELS.

ALSO, IMPROVEMENTS ARE NEEDED IN PREDICTION PROCEDURES FOR THE OTHER

NOISE SOURCES TOGETHER WITH IMPROVEMENTS IN INSTALLATION EFFECTS, SIDELINE

SHIELDING AND GROUND REFLECTION PREDICTIONS.

1119

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