Application of a Beamforming Technique to the Measurement of Airfoil Leading Edge Noise

The present paper describes the use of microphone array technology and beamforming algorithms for the measurement and analysis of noise generated by the interaction of a turbulent flow with the leading edge of an airfoil. Experiments were performed using a setup in an aeroacoustic wind tunnel, where the turbulent inflow is provided by different grids. In order to exactly localize the aeroacoustic noise sources and, moreover, to separate airfoil leading edge noise from grid-generated noise, the selected deconvolution beamforming algorithm is extended to be used on a fully three-dimensional source region. The result of this extended beamforming are three-dimensional mappings of noise source locations. Besides acoustic measurements, the investigation of airfoil leading edge noise requires the measurement of parameters describing the incident turbulence, such as the intensity and a characteristic length scale or time scale. The method used for the determination of these parameters in the present study is explained in detail. To demonstrate the applicability of the extended beamforming algorithm and the experimental setup as a whole, the noise generated at the leading edge of airfoils made of porous materials was measured and compared to that generated at the leading edge of a common nonporous airfoil.

[1]  M. R. Fink.  Experimental evaluation of trailing edge and incidence fluctuation noise theories , 1975 .

[2]  Paul T. Soderman,et al.  Microphone Measurements In and Out of Airstream , 2002 .

[3]  Ennes Sarradj,et al.  A fast signal subspace approach for the determination of absolute levels from phased microphone array measurements , 2010 .

[4]  Daniel J. Stead,et al.  Measurement of the Noise Resulting from the Interaction of Turbulence with a Lifting Surface , 2011 .

[5]  Robert P. Dougherty,et al.  Beamforming In Acoustic Testing , 2002 .

[6]  P. E. Roach,et al.  The generation of nearly isotropic turbulence by means of grids , 1987 .

[7]  Damon Honnery,et al.  Autocorrelation Functions and the Determination of Integral Length with Reference to Experimental and Numerical Data , 2004 .

[8]  Ennes Sarradj,et al.  Acoustic and aerodynamic design and characterization of a small-scale aeroacoustic wind tunnel , 2009 .

[9]  Marc B. Parlange,et al.  Analysis of land surface heat fluxes using the orthonormal wavelet approach , 1995 .

[10]  Stefan Oerlemans,et al.  Wind Tunnel Aeroacoustic Tests of Six Airfoils for Use on Small Wind Turbines , 2004 .

[11]  R. K. Amiet,et al.  Acoustic radiation and surface pressure characteristics of an airfoil due to incident turbulence , 1976 .

[12]  J. Sanford.  Acoustic Refraction: A Three-Dimensional Shear Layer Correction for Microphone Measurements in an Open-Jet Acoustic Wind Tunnel , 2008 .

[13]  S. Oerlemans,et al.  Quantification of Airframe Noise Using Microphone Arrays in Open and Closed wind Tunnels , 2007 .

[14]  R. K. Amiet,et al.  Refraction and Scattering of Sound by A Shear Layer , 1980 .

[15]  M. R. Fink.  Investigation of scrubbing and impingement noise , 1975 .

[16]  R. Amiet.  Refraction of sound by a shear layer , 1977 .

[17]  Thomas F. Brooks,et al.  A Deconvolution Approach for the Mapping of Acoustic Sources (DAMAS) Determined from Phased Microphone Arrays , 2004 .

[18]  J. Gershfeld,et al.  Leading edge noise from thick foils in turbulent flows , 2004 .

[19]  F. Fahy,et al.  Mechanics of flow-induced sound and vibration , 1989 .

[20]  I. J. Sharland.  Sources of noise in axial flow fans , 1964 .

[21]  J. Bendat,et al.  Random Data: Analysis and Measurement Procedures , 1987 .

[22]  T. Geyer,et al.  Porous Airfoils: Noise Reduction and Boundary Layer Effects , 2009 .

[23]  R. Amiet.  Acoustic radiation from an airfoil in a turbulent stream , 1975 .

[24]  Joshua Staubs.  Real Airfoil Effects on Leading Edge Noise , 2008 .

[25]  Ennes Sarradj,et al.  Measurement of the noise generation at the trailing edge of porous airfoils , 2010 .

[26]  Stefan Oerlemans,et al.  Aeroacoustic wind tunnel tests of wind turbine arfoils , 2004 .

[27]  Takao Suzuki.  A review of diagnostic studies on jet-noise sources and generation mechanisms of subsonically convecting jets , 2010 .

[28]  F. Grosveld.  Prediction of broadband noise from horizontal axis wind turbines , 1985 .

[29]  Michel Roger,et al.  Effect of Angle of Attack and Airfoil Shape on Turbulence-Interaction Noise , 2005 .

[30]  Stefan Oerlemans,et al.  Wind Tunnel Aeroacoustic Tests of Six Airfoils for Use on Small Wind Turbines: Preprint , 2003 .

[31]  Aiaa Paper,et al.  CLEAN based on spatial source coherence , 2007 .