Deterministic Model of AcousticWave Propagation in a Cavity

A mathematical model is proposed that evaluates acoustic propagation of turbulent boundary layer waves on top of a cavity enclosing a microphone. The goal is to optimize these cavity geometries to improve the signal-to-noise ratio of acoustic measurements. This model predicts the attenuation of the turbulent boundary layer fluctuations propagating within the cavity for a given wind tunnel speed, porous surface resistance and cavity geometry. Duct acoustics predict that the spatial wave numbers of the turbulent boundary layer pressure fluctuations are shorter than the acoustic wavelength and are therefore evanescent in the cavity. These cavities are also covered with a porous material such as a metallic mesh or kevlar, to attenuate hydrodynamic fluctuations through the cavity. This model supports the investigation of 3D cylindrical cavities and incorporates both soft and hard cavity walls. Good agreement was found with experimental data