AIRFRAME NOISE MODELING APPROPRIATE FOR MULTIDISCIPLINARY DESIGN AND OPTIMIZATION AIAA-2004-0689 Serhat Hosder, Joseph A. Schetz, Bernard Grossman and William H. Mason Virginia Tech Work sponsored by NASA Langley Research Center, Grant NAG 1-02024 42 nd AIAA Aerospace Sciences Meeting and Exhibit Reno, NV, January 7, 2004
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 2
Aircraft Noise Components Engine Aircraft Noise Engine/airframe interference Airframe 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 3
Trailing Edge Noise 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 In our study, we have developed a new Trailing Edge Noise metric appropriate for MDO 4
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 noise model 5
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 6
The Trailing Edge Noise Metric Following classical aeroacoustics theories from Goldstein and Lilley, we derive a noise intensity indicator (I NM ) ( β ( y) ) b 5 3 ρ u0 ( y) l0 ( y) Cos I NM = D ψ ) 3 2 2 π a H ( y) 2 0 [ θ ( y), ( y ] dy Noise Metric: NM ( db) I = 10log I NM ref, with I ref =10-12 (W/m 2 ) NM ( db) = 120 + 10log( I NM ) V wing TE y y H noise source q x z receiver 2 θ D[ θ, ψ ] = 2 Sin Sin ( ψ ) (directivity term) 2 u 0 characteristic velocity for turbulence l 0 characteristic length scale for turbulence ρ free-stream density a free-stream speed of sound H distance to the receiver β trailing edge sweep angle θ polar directivity angle ψ azimuthal directivity angle 7
Modeling of u 0 and l 0 Characteristic turbulence velocity scale at the trailing edge { TKE ( ) } u 0 ( y) = Max z New characteristic turbulence length scale at the trailing edge l ( y) = 0 Max { TKE ( z) } ω is the turbulence frequency observed at the maximum TKE location for each spanwise location. TKE and ω obtained from the solutions of TKE-ω (k-ω) turbulence model equations used in RANS calculations ω 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 8
Unique Features of the Noise Metric Expected to be an accurate relative noise measure suitable for MDO studies Applicable to 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 (l 0 ) more soundly based than previous ones used in semiempirical noise predictions 9
Noise Metric Validation 1.40 1.20 NM si 1.00 0.80 0.60 0.40 0.20 0.00 Experimental OASPL si 1 2 3 4 5 6 7 a (deg) 0.0 0.0 2.0 1.5 0.0 2.0 1.5 Re c x10-6 1.497 0.665 0.499 0.831 1.164 1.122 1.497 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 NM and OASPL results are scaled with the values obtained for case 1 10
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 (388 64 cells) Three-Dimensional Cases Energy Efficient Transport (EET) Wing S ref =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 break t/c=10% at the tip C-O topology, 4 blocks (884,736 cells) Steady RANS simulations with GASP Menter s SST k-ω turbulence model z/c 0.08 0.04 0.00-0.04 SC(2)-0710 SC(2)-0714-0.08 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 X Z x/c Y 11
Parametric Noise Metric Studies with NACA 0012 and NACA 0009 V =71.3 m/s, Mach=0.2, Re c =1.497 10 6 & 1.837 10 6 Investigated noise reduction by decreasing C l NM (db) 65.00 64.00 63.00 62.00 61.00 60.00 59.00 58.00 NACA 0012, c=0.3741 m, C l =0.853, lift=1011 N 2 NACA 0009, c=0.3741 m, 3 C l =0.860, lift=1018 N NACA 0012, c=0.3048 m, C l =1.046, lift=1010 N 0.70 0.80 0.90 1.00 1.10 C l 12 2.453 db 1.164 db 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 1
Parametric Noise Metric Studies with SC(2)-0710 and SC(2)-0714 C l 2.4 2.0 1.6 1.2 0.8 0.4 0.0 SC(2)-0714 SC(2)-0710 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 a Realistic approach conditions Re c =44 10 6 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 Directivity term=1.0 (θ =90 and ψ=90 ) Investigate the effect of the thickness ratio and the lift coefficient 13
Noise Metric Values for the Supercritical Airfoils at different C l values 50.0 NM (db) 45.0 40.0 35.0 30.0 25.0 SC(2)-0710 SC(2)-0714 20.0 0.3 0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1 2.3 C l At relatively lower lift coefficients (C l < 1.3) Noise metric almost constant The thicker airfoil has a larger noise metric At higher lift coefficients (C l >1.3) Sharp increase in the noise metric The thinner airfoil has a larger noise metric 14
3-D Parametric Noise Metric Studies with the EET Wing C L C L 1.20 1.05 0.90 0.75 0.60 0.45 0.30 0.15 0.00 1.20 1.05 0.90 0.75 0.60 0.45 0.30 0.15 0.00 343 300 257 214 171 128 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 a 86 43 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 C D 0 W/S (kg/m 2 ) Realistic approach conditions Re c =44 10 6, V = 68 m/s, M=0.2 Flying at H=120 m Stall observed at the highest C L CL max = 1.106 W/S max =315.7 kg/m 2 (64.8 lb/ft 2 ) Less than realistic C L and W/S (~430 kg/m 2 ) values Investigate the effect of the lift coefficient on the noise metric with a realistic geometry Investigate spanwise variation of u 0 and l 0 15
Section C l and Spanload distributions for the EET Wing C l C l c/c a 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 1.106 1.084 0.970 0.836 0.689 0.534 0.375 C L = 0.219 Inboard Inboard 1.106 1.084 0.970 0.836 0.689 0.534 0.375 C L = 0.219 0.0 0.2 0.4 0.6 0.8 1.0 2y/b Outboard Outboard 0.0 0.2 0.4 0.6 0.8 1.0 2y/b 16 Loss of lift on the outboard sections at the highest lift coefficient Large region of separated flow Shows the value to increase the wing area of a clean wing To obtain the required lift on approach with lower C L Lower noise
Skin Friction Contours at the Upper Surface of the EET Wing for different CL values Cf 0.0094 0.0086 0.0078 0.0070 0.0062 0.0054 0.0046 0.0038 0.0030 0.0023 0.0015 0.0007-0.0001-0.0009-0.0017 CL=0.375, α=2 0 0.20 0.40 2 y/b 0.60 0.80 CL=0.970, α=10 1.00 0 0.20 0.40 2 y/b 0.60 0.40 2 y/b 0.60 0.80 1.00 0.80 1.00 CL=1.106, α=14 CL=0.689, α=6 0 0.20 0.80 0 1.00 17 0.20 0.40 2 y/b 0.60
TKE (u 02 ) and l 0 Distributions at the Trailing Edge of the EET Wing for different C L values l 0 (m) TKE max (J/kg) 225.0 200.0 175.0 150.0 125.0 100.0 75.0 50.0 25.0 0.0 0.0 0.2 0.4 0.6 0.8 1.0 2y/b 7.0E-02 6.0E-02 5.0E-02 4.0E-02 3.0E-02 2.0E-02 1.0E-02 0.0E+00 Inboard Inboard C L =0.534 C L =0.836 Outboard C L =0.534 Outboard C L =1.106 C L =1.084 C L =0.970 C L =0.836 C L =1.106 C L =1.084 C L =0.970 0.0 0.2 0.4 0.6 0.8 1.0 2y/b 18 Maximum TKE and l 0 get larger starting from CL=0.836, especially at the outboard section Dramatic increase for the separated flow case Maximum TKE and l 0 not constant along the span at high C L
Noise Metric Values for the EET Wing at different C L values 75.0 65.0 NM (db) 55.0 45.0 35.0 25.0 NM upper NM total NM lower 15.0 At lower lift coefficients 0.2 0.4 0.6 0.8 1.0 1.2 C L 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 19
Conclusions 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 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 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 20
Future Work Trailing Edge Noise Investigate the effect of other design parameters Twist distribution Wider parameter space Extend approach to flaps and slats Consider other noise components 21