A Comparison of Microphone Phased Array Methods Applied to the Study of Airframe Noise in Wind Tunnel Testing

In this werk, various microphone phased array data processing techniques are applied to two existing datasets from aeroacoustic wind tunnel tests. The first of these is from a !arge closed-wall facility, DLR's Kryo-Kanal Koln (DNW·KKK), and is a measurement cf the high-lift noise cf a semispan model. The second is from a small-scale open-jet facility, the NASA Langley Quiet Flow Facility (QFF), and is a measurement cf a clean airfoil selfnoise. The data had been made publicly available in 2015, and were analyzed by several research groups using multiple analysis techniques. This procedure allows the assessment of the variability of individual methods across various organizational implementations, as weil as the variability cf results produced by different array analysis methods. This paper summarizes the results presented at panel sessions held at AIAA conferences in 2015 and 2016. Results show that with appropriate handling of background noise, all advanced methods can identify dominant acoustic sources for a broad range cf frequencies. Lowerlevel sources may be masked er underpredicted. lntegrated levels are more robust and in closer agreement between methods than narrowband maps for individual frequencies. Overall there is no obvious best method, though multiple methods may be used to bound expected behavior.

[1]  Charles L. Lawson,et al.  Solving least squares problems , 1976, Classics in applied mathematics.

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

[3]  Pieter Sijtsma,et al.  CLEAN Based on Spatial Source Coherence , 2007 .

[4]  J. Antoni,et al.  Empirical Bayesian regularization of the inverse acoustic problem , 2015 .

[5]  Thomas F. Brooks,et al.  Effects of Angle of Attack and Velocity on Trailing Edge Noise , 2004 .

[6]  Renaud Davy,et al.  2D high-lift airfoil noise measurements in an aerodynamic wind tunnel , 2015 .

[7]  R. Bro,et al.  A fast non‐negativity‐constrained least squares algorithm , 1997 .

[8]  Jr William M. Humphreys,et al.  Design and Use of Microphone Directional Arrays for Aeroacoustic Measurements , 1998 .

[9]  C. Bahr,et al.  Advanced Background Subtraction Applied to Aeroacoustic Wind Tunnel Testing , 2015 .

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

[11]  T. Brooks,et al.  Measurement of Trailing EDGE Noise Using Directional Array and Coherent Output Power Methods , 2002 .

[12]  Gert Herold,et al.  A Microphone Array Method Benchmarking Exercise using Synthesized Input Data , 2017 .

[13]  Thomas Ahlefeldt,et al.  Aeroacoustic Measurements of a Scaled Half-Model at High Reynolds Numbers , 2010 .

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

[15]  Pieter Sijtsma,et al.  Experimental techniques for identification and characterisation of noise sources , 2004 .