Numerical simulation of spectral broadening of an acoustic wave by a spatially growing turbulent mixing layer

The scattering of an acoustic wave by a fully turbulent mixing layer is investigated by means of a Large Eddy Simulation. The turbulent characteristics of the mixing layer have been validated by comparison to experimental and numerical studies. Computational Aero Acoustics (CAA) methods have been used to minimize spurious pression fluctuations created while the turbulent structures leave the computational domain. Then, an acoustic source has been placed inside a uniform flow and the acoustic propagation has been validated. Finally, both the turbulent mixing layer and the acoustic field are calculated and the scattering phenomenon is investigated. The ’double-humped’ structures of the far field power spectral density is recovered and a parametrical study, involving the tonal frequency of the source is carried out. The comparison to previous experimental works have been enabled thanks to the definition of a relevant scattering parameter. The spectra are in good agreement with experimental works on acoustic scattering. The frequency shift of the sidelobes and the spectra’s decrease are well predicted and in a good agreement with the ones found in the literature.