AIRFRAME NOISE MODELING APPROPRIATE FOR MULTIDISCIPLINARY DESIGN AND

OPTIMIZATION

42nd AIAA Aerospace Sciences Meeting and ExhibitReno, NV, January 7, 2004

AIAA-2004-0689

Serhat Hosder, Joseph A. Schetz, Bernard Grossman and William H. Mason

Virginia TechWork sponsored by NASA Langley Research

Center, Grant NAG 1-02024

2

Introduction

Aircraft noise: an important performance criterion and constraint in aircraft design

Noise regulations limit growth of air transportation

Reduction in noise needed

To achieve noise reduction – Design revolutionary aircraft with innovative configurations

– Improve conventional aircraft noise performance

– Optimize flight performance parameters for minimum noise

All these efforts require addressing noise in the aircraft conceptual design phase

3

Aircraft Noise Components

Airframe

Aircraft Noise

Engine

Engine/airframe interference

Include aircraft noise as an objective function or constraint in MDO– Requires modeling of each noise source

Airframe noise – Now comparable to engine noise at approach

– Our current focus

4

Trailing Edge Noise: noise mechanism of a clean wing – scattering of acoustic waves generated due to the passage of turbulent boundary layer over the trailing edge of a

wing or flap

In our study, we have developed a new Trailing Edge Noise metric appropriate for MDO

5

Why Do We Model Trailing Edge Noise?

Trailing Edge Noise: a lower bound value of airframe noise at approach (a measure of merit)

Trailing Edge Noise can be significant contributor to the airframe noise for a non-conventional configuration– traditional high-lift devices not used on approach– A Blended-Wing-Body (BWB) Aircraft

• Large Wing Area and span– A conventional aircraft or BWB with distributed propulsion

• Jet-wing concept for high lift – An airplane with a morphing wing

A Trailing Edge Noise Formulation based on proper physics may be used to model the noise from flap trailing edges or flap-side edges at high lift conditions

First step towards a general MDO model

6

Outline of the Current Work

Objective: To develop a trailing edge noise metric– construct response surfaces for aerodynamic noise minimization

Noise metric– Should be a reliable indicator of noise– Not necessarily the magnitude of the absolute noise– Should be relatively inexpensive to compute

• Computational Aeroacoustics too expensive to use• Still perform 3-D, RANS simulations with the CFD code GASP

Parametric Noise Metric Studies– 2-D and 3-D cases– The effect of different wing design variables on the noise metric

7

The Trailing Edge Noise Metric

dyyyDyH

yCosylyu

aI

b

NM )(),()(

)()()(

2 02

30

50

23

ref

NM

I

IdBNM log10)(

)log(10120)( NMIdBNM

wing TE

z y

V

receiver

noise source

H

x

u0 characteristic velocity for turbulence

l0 characteristic length scale for turbulence

free-stream density

a free-stream speed of soundH distance to the receiver trailing edge sweep anglepolar directivity angle azimuthal directivity angle

SinSinD

22],[ 2

Following classical aeroacoustics theories from Goldstein and Lilley, we derive a noise intensity indicator (INM)

Noise Metric:

(directivity term)

, with Iref=10-12 (W/m2)

8

Modeling of u0 and l0

)()(0 zTKEMaxyu

)()(0

zTKEMaxyl

Characteristic turbulence velocity scale at the trailing edge

New characteristic turbulence length scale at the trailing edge

is the turbulence frequency observed at the maximum TKE location for each spanwise location. TKE and obtained from the solutions of TKE- (k-) turbulence model equations used in RANS calculations Previous semi-empirical trailing edge noise prediction methods use orfor the length scale

– Related to mean flow– Do not capture the turbulence structure

9

Unique Features of the Noise Metric

Expected to be an accurate relative noise measure suitable for MDO studies

Written for any wing configuration

Spanwise variation of the characteristic turbulence velocity and length scale taken into account

Sensitive to changes in design variables (lift coefficient, speed, wing geometry etc.)

The choice of turbulence length scale (l0) more soundly based than previous ones used in semi-empirical noise predictions

10

Noise Metric Validation

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1 2 3 4 5 6 7

OASPLsi

NMsi

1.122

2.0

1.4971.1640.8310.4990.6651.497Recx10-6

1.50.01.52.00.00.0deg

1.122

2.0

1.4971.1640.8310.4990.6651.497Recx10-6

1.50.01.52.00.00.0deg

NM and OASPL results are scaled with the values obtained for case 1

Experimental NACA 0012 cases from NASA RP 1218 (Brooks et al.)

All cases subsonic Predicted Noise Metric

(NM) compared with the experimental OASPL

The agreement between the predictions and the experiment is very good

Experimental

11

Parametric Noise Metric Studies

Two-Dimensional Cases– Subsonic Airfoils

• NACA 0012 and NACA 0009– Supercritical Airfoils

• SC(2)-0710 (t/c=10%) SC(2)-0714 (t/c=14%)

– C-grid topology (38864 cells) Three-Dimensional Cases

– Energy Efficient Transport (EET) Wing• Sref=511 m2, MAC=9.54 m• AR=8.16, =30 at c/4• t/c=14% at the root t/c=12% at the break t/c=10% at the tip

– C-O topology, 4 blocks (884,736 cells) Steady RANS simulations with GASP

– Menter’s SST k- turbulence model

-0.08

-0.04

0.00

0.04

0.08

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

SC(2)-0710

SC(2)-0714

z/c

x/c

X

Y

Z

12

Parametric Noise Metric Studies with NACA 0012 and NACA 0009

58.00

59.00

60.00

61.00

62.00

63.00

64.00

65.00

0.70 0.80 0.90 1.00 1.10

1

2

3

2.453 dB

1.164 dB

NACA 0012, c=0.3048 m, Cl=1.046, lift=1010 N

NACA 0012, c=0.3741 m, Cl=0.853, lift=1011 N

NACA 0009, c=0.3741 m,

Cl=0.860, lift=1018 N

NM

(dB

)

Cl

V=71.3 m/s, Mach=0.2, Rec=1.497106 & 1.837106

Investigated noise reduction by decreasing Cl and t/c

– Increased chord length to keep lift and speed constant – Total noise reduction=3.617 dB

Simplified representation of increasing the wing area and reducing the overall lift coefficient at constant lift and speed– Additional benefit: eliminating or minimizing the use of high lift devices

13

Parametric Noise Metric Studies with SC(2)-0710 and SC(2)-0714

0.0

0.4

0.8

1.2

1.6

2.0

2.4

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0

Cl

SC(2)-0710

SC(2)-0714

0.0

0.4

0.8

1.2

1.6

2.0

2.4

0.00 0.01 0.02 0.03 0.04 0.05 0.06

Cl

Cd

SC(2)-0710

SC(2)-0714

Realistic approach conditions

– Rec=44106

– V= 68 m/s, Mach=0.2

Corresponds to typical transport aircraft– With MAC=9.54 m

– Flying at H=120 m

– Approximately the point for the noise certification at the approach before landing

Directivity terms– =90 and =90

Investigate the effect of the thickness ratio and the lift coefficient

14

Noise Metric Values for the Supercritical Airfoils at different Cl values

20.0

25.0

30.0

35.0

40.0

45.0

50.0

0.3 0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1 2.3

NM

(dB

)

Cl

SC(2)-0710

SC(2)-0714

At relatively lower lift coefficients (Cl < 1.3) – Noise metric almost constant

– The thicker airfoil has a larger noise metric

At higher lift coefficients (Cl >1.3) – Sharp increase in the noise metric

– The thinner airfoil has a larger noise metric

15

3-D Parametric Noise Metric Studies with the EET Wing

0.00

0.15

0.30

0.45

0.60

0.75

0.90

1.05

1.20

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.00

4386

128 171

214 257

300 343

CL

W/S

(kg

/m2 )

0.00

0.15

0.30

0.45

0.60

0.75

0.90

1.05

1.20

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14

CL

CD

Realistic approach conditions– Rec=44106, V= 68 m/s, M=0.2– Flying at H=120 m

Stall observed at the highest CL

– CLmax= 1.106

W/Smax=315.7 kg/m2 (64.8 lb/ft2)

– Less than realistic CL and W/S (~430 kg/m2) values

Investigate the effect of the lift coefficient on the noise metric with a realistic geometry

Investigate spanwise variation of u0 and l0

16

Section Cl and Spanload distributions for the EET Wing

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0.0 0.2 0.4 0.6 0.8 1.0

Inboard Outboard

2y/b

Cl

0.836

0.534

0.375

0.970

CL= 0.219

0.689

1.0841.106

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0.0 0.2 0.4 0.6 0.8 1.0

Inboard Outboard

0.836

0.534

0.375

0.970

CL= 0.219

0.689

1.0841.106

Cl c

/ca

Loss of lift on the outboard sections at the highest lift coefficient

Large region of separated flow Shows the need to increase the

wing area of a clean wing– To obtain the required lift on

approach with lower CL

• Lower noise

17

Skin Friction Contours at the Upper Surface of the EET Wing for different CL values

y/b0.20 0.40 0.60 0.80 1.00

Cf

0.00940.00860.00780.00700.00620.00540.00460.00380.00300.00230.00150.0007

-0.0001-0.0009-0.0017

y/b0.20 0.40 0.60 0.80 1.00

y/b0.20 0.40 0.60 0.80 1.00

y/b0.20 0.40 0.60 0.80 1.00

0 0

0 0

2 2

2 2

CL=0.375, =2

CL=0.689, =6

CL=0.970, =10

CL=1.106, =14

18

0.0E+00

1.0E-02

2.0E-02

3.0E-02

4.0E-02

5.0E-02

6.0E-02

7.0E-02

0.0 0.2 0.4 0.6 0.8 1.0

Inboard Outboard

CL=0.836CL=0.534

CL=1.084

CL=1.106

CL=0.970

2y/b

TKE and l0 Distributions at the Trailing Edge of the EET Wing for different CL values

0.0

25.0

50.0

75.0

100.0

125.0

150.0

175.0

200.0

225.0

0.0 0.2 0.4 0.6 0.8 1.0CL=0.836CL=0.534

CL=1.084

CL=1.106

CL=0.970

2y/b

Inboard Outboard

TK

Em

ax

(J/k

g)

l 0 (m

)

Maximum TKE and l0 get larger starting from CL=0.836, especially at the outboard section

Dramatic increase for the separated flow case

Maximum TKE and l0 not constant along the span at high CL

19

Noise Metric Values for the EET Wing at different CL values

15.0

25.0

35.0

45.0

55.0

65.0

75.0

0.2 0.4 0.6 0.8 1.0 1.2

NM

(dB

)

CL

NMtotal

NMupper NMlower

At lower lift coefficients – Noise metric almost constant

– Contribution to the total noise from the lower surface significant At higher lift coefficients

– Noise metric gets larger

• Dramatic increase for the separated flow case

– Upper surface is the dominant contributor to the total noise

20

Conclusions

A new trailing edge noise metric has been developed

– For response surfaces in MDO– For any wing geometry– Introduced a length scale directly related to the turbulence structure – Spanwise variation of characteristic velocity and length scales considered

Noise metric an accurate relative noise measure as shown by validation studies

Parametric noise metric studies performed– Studied the effect of the lift coefficient and the thickness ratio – Noise reduction possible with decreasing the lift coefficient and the

thickness ratio while increasing the wing area – Noise constant at lower lift coefficients and gets larger at higher lift

coefficients. Sharp increase when there is large separation– Characteristic velocity and length scales not constant along the span at

high lift coefficients due to 3-D effects

21

Future Work