Aeroacoustic Investigation of an Open Cavity at Low Mach Number

Abstract

The laminar flow and the near-field acoustics of an open cavity at Mach number 0.15 is computed by direct solution (two-dimensional) of the compressible Navier-Stokes equations. The radiated sound is also computed by an acoustic analogy, a modified version of Curle's equation, and compared to the directly computed sound field. The agreement is found to be good. The contributions from the various source terms in Curle's equation are quantified, and the terms involving wall-pressure fluctuations are found to account for most of the radiated intensity. These main source terms are investigated further, and it is found that they are especially large in the downstream part of the cavity, and for about two cavity lengths downstream of the cavity. The upstream dominance of the radiated sound is explained by the fact that the downstream cavity wall contributes primarily to the upstream direction. Correlations between the radiated sound and the source terms, coupled with where the source terms are large, suggest that the near-field terms display a stronger upstream dominance than the far-field terms, and hence the far-field directivity is expected to be flatter.