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Experimental Validation of TNO Trailing Edge Noise Model and Application to Airfoil Optimization. Franck Bertagnolio, Helge Aa. Madsen, and Christian Bak Aero-Elastic Design, Wind Energy Division Risø DTU, National Laboratory for Sustainable Energy Roskilde, Denmark. Outline. - PowerPoint PPT Presentation
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Experimental Validation ofTNO Trailing Edge Noise Modeland Application to Airfoil Optimization
Franck Bertagnolio, Helge Aa. Madsen, and Christian Bak
Aero-Elastic Design, Wind Energy DivisionRisø DTU, National Laboratory for Sustainable EnergyRoskilde, Denmark
EWEC 2009, Marseille, 16-19 March 20092 Risø-DTU, Technical University of Denmark
Outline
• Trailing Edge Noise
• TNO Trailing Edge Noise Model
• Validation against Measurements
• Aeroacoustic Optimizationof a Wind Turbine Airfoil
EWEC 2009, Marseille, 16-19 March 20093 Risø-DTU, Technical University of Denmark
Trailing Edge Noise
2y3y
1y
1 2( )U y
( , )P k
1 2 3, ,u u u Far field sound ( )PS
EWEC 2009, Marseille, 16-19 March 20094 Risø-DTU, Technical University of Denmark
TNO Trailing Edge Noise Model
2
22 21 10 2 2 2 22 1 22 2 0
1 3 2
( , ) 4 ( ) ( , ) e dkym c
k UP L y u U k y
k k y
k k
Parchen (1998) combines a diffraction problem solution with knowledge of the turbulent fluctuations in the boundary layer
• Airfoil Surface Pressure Spectrum (Blake,1986) Lighthill analogy in spectral domain
Solution for the Mean shear-Turbulence interaction:
• Far Field Noise (Ffwocs Williams and Hall, 1970 ; Chandiramani, 1974; Chase, 1975; Howe, 1978; Brooks and Hodgson, 1981)
1 120 1
( ) ( , )d4span
P
LS P k k
R c k
EWEC 2009, Marseille, 16-19 March 20095 Risø-DTU, Technical University of Denmark
Model Practical Implementation
Input data originates either from XFOIL or EllipSys2D
Boundary layer quantities required as input are:
• Directly obtained from the codes (U1 (y2), Shear, kt (CFD), …)
• Classical turbulence theory results for 22 (Isotropic
turbulence spectrum, Von Karman), m (Gaussian), …
• Integral length scale: (Lutz et al, 2007)
3/ 2t
2 2( ) 0.387k
L y
EWEC 2009, Marseille, 16-19 March 20096 Risø-DTU, Technical University of Denmark
Validation: LM Glasfiber Wind Tunnel
Aerodynamic Test Facility
NACA0015 Airfoil Section
Surface Pressure Measurement Holes
EWEC 2009, Marseille, 16-19 March 20097 Risø-DTU, Technical University of Denmark
NACA0015: Surface Pressure Spectrum
Re=1.6x10^6 - No Turbulence Grid - x/C = 0.567=0o =4o
=8o =12o
EWEC 2009, Marseille, 16-19 March 20098 Risø-DTU, Technical University of Denmark
Validation: NACA0012 [Brooks and Hodgson]Anaechoic Wind Tunnel Facility at NASA Langley (1981)Re=1.6M, 2.9M – Aoa=0o
Surface Pressure
Far Field SPL
EWEC 2009, Marseille, 16-19 March 20099 Risø-DTU, Technical University of Denmark
Discussion on Validation
• Quantitative model results might be erroneous (Difference in conventions?? )
• but it may be that TNO model fails to accurately predict measurements(However, no fundamental differences between experiments NACA0015-LM / NACA0012-NASA…??)
• TNO model correctly captures tendencies observed
in measurements
• TNO model (using XFOIL) is a good candidate for aeroacoustic optimization
EWEC 2009, Marseille, 16-19 March 200910 Risø-DTU, Technical University of Denmark
Airfoil Optimization
• Goal: Reduce trailing edge noise
• AirfoilOpt: SIMPLEX algorithm (gradient based method) Cost function minimization subject to non-linear constraints Both cost function and constraints can involve:
1) Aerodynamic characteristics (XFOIL)2) Geometric characteristics
TNO model implemented in the code
• Noise Optimization Procedure: Maximum SPL from TNO model used as cost function Various constraints to preserve aerodynamic and geometrical
characteristics of original airfoil (PARAMETER STUDY, see paper)
EWEC 2009, Marseille, 16-19 March 200911 Risø-DTU, Technical University of Denmark
Relaxing Geometric Constraints
Initial airfoil: RISØ-B1-18Constraints relaxation: - Preserve all constraints - ymin and ymax along chord
- y,xx (Airfoil curvature)
EWEC 2009, Marseille, 16-19 March 200912 Risø-DTU, Technical University of Denmark
Relaxing Geometric Constraints
Far Field SPL A-Weighted SPL
EWEC 2009, Marseille, 16-19 March 200913 Risø-DTU, Technical University of Denmark
Mechanism Behind SPL Reduction Boundary Layer Development along Chord
Turbulent Kinetic Energy Profile
Near TrailingEdge
Original
Optimized
Original Optimized
EWEC 2009, Marseille, 16-19 March 200914 Risø-DTU, Technical University of Denmark
Conclusions
• TNO model validation gave mixed results (Convention problem / Model error ???)
• Airfoil noise optimization: SPL ~ -1 to 2dB
• Noise reduction reached through:reducing camber flattening of suction side
Reduction of TKE at trailing edge