On the role of coherent turbulent structures on the noise emitted by non-straight trailing edges

Abstract

This work addresses the importance of considering the coherent organization of turbulence structures when predicting the noise from serrated trailing edges. Turbulent flow is the source of broadband trailing-edge noise. The existence of coherence in the turbulent flow departs from the state-of-the-art assumption for noise prediction based on the sum of the different wavenumbers excitations in an incoherent manner. This study addresses whether the latter hypothesis is the underlying cause of the noise underestimation observed from theoretical models for serrated trailing edges at high frequencies. A simplified hairpin model in the form of a bounded vortex filament is used as input to the scattering solution. The vortex filament is used to compute the turbulent velocity and wall-pressure fluctuations induced by the modelled coherent structure. This coherent wall-pressure structure is given as input to a numerical acoustic solver of the diffraction problem, yielding the scattered acoustic field. Results focus on the differences between coherent and incoherent assumptions. It is demonstrated that the acoustic scattering of coherent structures differs from the incoherent sum of the wavenumber spectrum of such structures, showing more consistent results with experimental evidences. The results indicates that modelling of the noise from serrated trailing edges can be improved with a detailed description of the turbulent flow.