Numerical Simulation of a Slit Resonator in a Grazing Flow (AIAA-2006-0799)

It is known experimentally that a grazing flow has significant influence on the performance of a resonant acoustic liner. As yet, detailed understanding of the effect in fluid dynamics or acoustics terms is not available. One principal reason for this is the smallness of the openings of the resonators of present day acoustic liners. The smallness of the holes makes in-depth experimental observation and mapping of the fluid flow field around the opening of a resonator in the presence of a grazing flow extremely difficult. As a result, there is a genuine lack of data leading directly to a lack of understanding. In this study, numerical simulations of the flow field around a slit resonator in the presence of a grazing flow under acoustic forcing are carried out. It is observed that at high sound pressure level, vortices are shed from the corners of the resonator opening. Some of these vortices merge together. Others are absorbed by the wall boundary layer. The simulated results indicate that a strong merged vortex is convected downstream by the grazing flow and persists for a long distance. This suggests possible fluid mechanical interaction between neighboring resonators of an acoustic liner when there is a grazing flow. This possible interaction, as far as is known, has not been included in any theoretical or semi-empirical model of acoustic liners. Detailed formulation of the computational model, as well as computational algorithm, are provided. The computation code is verified by comparing computed results with an exact linear solution and validated by comparing with measurements of a companion experiment. It is shown that the computation code is of high quality and accuracy.

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