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The scattering of acoustic waves by a turbulence shear layer is investigated experimentally.The acoustic field is measured with an antenna of microphones, while the shear layer is characterised with Particle Image Velocimetry (PIV).In agreement with previous studies, microphones measurements highlight a broadening of the power spectral density and the formation of two sidelobes around the source tone.The bicoherence spectrum is computed on the microphones signals and evidences a non-linear interaction between the source tone and low frequencies in the shear layer.Spectral proper orthogonal decomposition (SPOD) is applied to the PIV data.The spatio-temporal mode decomposition reveals that the the dominant mode of the spanwise velocity component has a hump that corresponds to the range of frequencies of the sidelobes.This suggests that the spanwise velocity fluctuations are responsible for the interaction with the acoustic field and are the cause of the modification in the acoustic transmission observed in the acoustic measurements.The characteristic turbulent lengthscale that interacts with the acoustic transmission is calculated with several methods and compared with previous studies and turbulent features of the shear layer.
Scarano et al. (Thu,) studied this question.