An Analysis of Different Measurement Techniques for Airfoil Trailing Edge Noise

Different processing methodologies are applied to experimental trailing edge noise data from a NACA 63-215 Mod B airfoil in the University of Florida Aeroacoustic Flow Facility. Methods vary in complexity from a single microphone analysis to array-based techniques. Intermediate steps evaluated include the classic coherent power method, a three-microphone technique for removing uncorrelated contaminated noise from the measured autospectra, and a generalized least-squares extension of the three-microphone method to an arbitrary number of microphones. These intermediate steps all involve the use of Single- Input/Multiple-Output (SIMO) modeling for the removal of mutually uncorrelated noise sources. All of the coherence-based methodologies mentioned above successfully remove uncorrelated noise from the signal of interest. The least-squares denoising approach is also applied to Delay-and-Sum (DAS) beamforming and improves beamforming maps similar to but without diagonal removal. All of the methods are applied to directivity measurements and successfully match theory when integrated over an appropriate bandwidth corresponding to trailing edge noise.