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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
u Aircraft noise: an important performance criterion and constraint in aircraft design
u Noise regulations limit growth of air transportation
u Reduction in noise needed
u To achieve noise reduction – Design revolutionary aircraft with innovative configurations– Improve conventional aircraft noise performance– Optimize flight performance parameters for minimum noise
u All these efforts require addressing noise in the aircraft conceptual design phase
3
Aircraft Noise Components
Airframe
Aircraft Noise
Engine
Engine/airframe interference
u Include aircraft noise as an objective function or constraint in MDO– Requires modeling of each noise source
u Airframe noise – Now comparable to engine noise at approach – Our current focus
4
Trailing Edge Noise
u Trailing Edge Noise– Airframe noise component– Main noise mechanism of a clean wing – scattering of acoustic waves generated due to the passage of
turbulent boundary layer over the trailing edge
u In our study, we have developed a new Trailing Edge Noise metric appropriate for MDO
5
Why Do We Model Trailing Edge Noise?
u Trailing Edge Noise: a lower bound value of airframe noise at approach (a measure of merit)
u 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
u 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
u First step towards a general MDO noise model
6
Outline of the Current Work
u Objective: To develop a trailing edge noise metric– construct response surfaces for aerodynamic noise minimization
u 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
u 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
yCosylyua
Ib
NM )(),()(
)()()(2 0
2
30
50
23 ψθβ
πρ
∫∞
∞=
=
ref
NM
II
dBNM log10)(
)log(10120)( NMIdBNM +=
wing TE
θ
z y
V∞
receiver
noise source
H
x ψ
u0 characteristic velocity for turbulencel0 characteristic length scale for turbulenceρ∞ free-stream densitya ∞ free-stream speed of soundH distance to the receiverβ trailing edge sweep angleθ polar directivity angleψ azimuthal directivity angle
( )ψθ
ψθ SinSinD
=
22],[ 2
u Following classical aeroacoustics theories from Goldstein and Lilley, we derive a noise intensity indicator (INM)
u Noise Metric:
(directivity term)
, with Iref=10-12 (W/m2)
8
Modeling of u0 and l0
{ })()(0 zTKEMaxyu =
{ }ω
)()(0
zTKEMaxyl =
u Characteristic turbulence velocity scale at the trailing edge
u New characteristic turbulence length scale at the trailing edge
u ω is the turbulence frequency observed at the maximum TKE location for each spanwise location.
u TKE and ω obtained from the solutions of TKE-ω (k-ω)turbulence model equations used in RANS calculations
u Previous semi-empirical trailing edge noise prediction methods use δ or δ∗ for the length scale– Related to mean flow– Do not capture the turbulence structure
9
Unique Features of the Noise Metric
u Expected to be an accurate relative noise measure suitable for MDO studies
u Applicable to any wing configuration
u Spanwise variation of the characteristic turbulence velocity and length scale taken into account
u Sensitive to changes in design variables (lift coefficient, speed, wing geometry etc.)
u 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
1.50.01.52.00.00.0α (deg)
1.122
2.0
1.4971.1640.8310.4990.6651.497Recx10-6
1.50.01.52.00.00.0α (deg)
NM and OASPL results are scaled with the values obtained for case 1
u Experimental NACA 0012 cases from NASA RP 1218 (Brooks et al.)
u All cases subsonic u Predicted Noise Metric
(NM) compared with the experimental OASPL
u The agreement between the predictions and the experiment is very good
Experimental
11
Parametric Noise Metric Studies
u 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 (388×64 cells)
u Three-Dimensional Cases– Energy Efficient Transport (EET) Wing
• Sref=511 m2, MAC=9.54 m• AR=8.16, Λ=30° at c/4• t/c=14% at the root
t/c=12% at the breakt/c=10% at the tip
– C-O topology, 4 blocks (884,736 cells)u Steady RANS simulations with GASP
– Menter’s SST k-ω 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
u V∞=71.3 m/s, Mach=0.2, Rec=1.497×106 & 1.837×106
u Investigated noise reduction by decreasing Cl and t/c– Increased chord length to keep lift and speed constant – Total noise reduction=3.617 dB
u 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
α
SC(2)-0710
SC(2)-0714
u Realistic approach conditions– Rec=44×106
– V∞= 68 m/s, Mach=0.2
u 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
u Directivity terms– Directivity term=1.0
(θ =90° and ψ=90°)
u 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
u At relatively lower lift coefficients (Cl < 1.3) – Noise metric almost constant– The thicker airfoil has a larger noise metric
u 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 16.0
0
4386
128 171 214 257 300 343
CL
α
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
u Realistic approach conditions– Rec=44×106, V∞= 68 m/s, M=0.2– Flying at H=120 m
u 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
u Investigate the effect of the lift coefficient on the noise metric with a realistic geometry
u Investigate spanwise variation of u0 and l0
16
0.00.20.40.60.81.01.21.41.61.82.0
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
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
u Loss of lift on the outboard sections at the highest lift coefficient
u Large region of separated flow
u Shows the value to increase the wing area of a clean wing– To obtain the required
lift on approach with lower CL
– Lower noise
2y/b
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, α=2°
CL=0.689, α=6°
CL=0.970, α=10°
CL=1.106, α=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 (u02) 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 1.0
CL=0.836CL=0.534
CL=1.084
CL=1.106
CL=0.970
2y/b
Inboard Outboard
TK
Em
ax (J
/kg
)l 0
(m)
u Maximum TKE and l0 get larger starting from CL=0.836, especially at the outboard section
u Dramatic increase for the separated flow case
u Maximum TKE and l0not 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
u At lower lift coefficients – Noise metric almost constant– Contribution to the total noise from the lower surface significant
u 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
u A new trailing edge noise metric has been developed– For noise 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
u Noise metric an accurate relative noise measure as shown by validation studies
u Parametric noise metric studies performed– Studied the effect of the lift coefficient and the thickness ratio – Noise reduction possible with decreasing the lift coefficient
• Leads to increase in chord length (wing area) for constant lift and speed• Leads to decrease in thickness ratio (further reduction in noise)
– 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
u Trailing Edge Noise– Investigate the effect of other design parameters
• Twist distribution
– Wider parameter space– Extend approach to flaps and slats
u Consider other noise components