The Effect of Boundary Layers on Bulk Reacting Liners at Low Mach Number Flows

Sound absorbing linings are effective noise treatments in many applications in order to meet noise emission requirements. Stricter noise requirements set harder demands on the performance of the liners, why better prediction models of their performance have to be developed. As of today, several models to predict the sound reducing properties in the presence of flow exist and are shown to give diverging absorption properties for locally reacting liners exposed to high Mach number flows. The effect of flow on absorption properties is often seen as an issue that only needs to be addressed at high Mach number flows. In this paper, the existing models are applied to bulk reacting liners exposed to low Mach number flows and the resulting absorption coefficients are compared. Predictions of absorption coefficients clearly show that the effect of flow needs to be considered also at low Mach number flows and that the difference between the prediction models is indeed significant at low Mach number flows. This shows the importance in choosing the correct model for a specific application in order to avoid introducing erroneous prediction on the effect of flow. This study thus gives well-grounded evidence of the importance to include flow effects in modeling of sound absorptive linings even at low Mach number flows.QC 20130913