Noise due to unsteady flow past trailing edges

Abstract

This paper presents two-dimensional direct numerical simulations (DNS) of noise generated at trailing edges (TE) with zero thickness. The simulations are conducted specifying either no-slip or slip walls in order to investigate viscous effects. In both cases, small amplitude disturbances are introduced close to the inflow boundary that serve as pressure disturbances at the trailing edge. DNS data reveals that the unsteady Kutta condition is not satisfied, irrespective of the wall boundary condition. However, it appears that the validity of the unsteady Kutta condition is not essential for making an accurate prediction of the far field noise. The far field pressure is predicted as a function of the surface pressure difference using a 2-D modification of Amiets classical theory, and compared with the far field pressure computed directly. Directivity plots provide evidence that the presence of boundary layers and noise generated by an unsteady wake in the no-slip cases lead to smearing of individual obes, and that the downstream pointing lobes in no-slip wall cases are probably due to nonlinear noise generation in the wake. The simulations are conducted using a high-order accurate numerical method which is free of upwinding, artificial dissipation or any form of explicit filtering, and employs a novel boundary treatment.