experimental validation of tno trailing edge noise model and application to airfoil optimization
DESCRIPTION
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 PresentationTRANSCRIPT
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