An Investigation of the Flow Field Around a Flat Plate Aerofoil Emitting Discrete Frequency Noise and the Generation Mechanism of the Noise.

Abstract

Coherent flow fields around a two-dimensional flat plate aerofoil emitting discrete frequency noise in a uniform flow have been determined using phase-locked averaging technique, from which the generation mechanism of the noise has been discussed. The frequency and the noise level were artificially modified using a small circular cylinder inserted in the near wake region. The organized flow details such as velocity fluctuations in the boundary layer, pressure fluctuations on the aerofoil surface as well as the detailed structures of the shedding vortices in the turbulent wake have been presented. The generation mechanism of the discrete frequency noise has been examined in relation to the organized structures in the turbulent wake. It is confirmed that the source of the discrete frequency noise is generated by the organized fluctuating pressures on the aerofoil due to the fluctuating velocities induced by the organized turbulent shedding vortices in the wake.