An experimental study of sound diffraction at an airfoil trailing edge

Abstract

Spark photography with a sensitive schlieren system has been used to show the interaction between an incident acoustic wave and the flow around an airfoil trailing edge. Impact of the wave did not show any significant observable effect on the wake or trailing-edge boundary layer. The intensity of the wave diffracted from the edge varied considerably with the prevailing flow conditions. In the event of unsteadiness in the flow or boundary-layer separation the diffracted wave was strongly visible. In smooth flows with attached boundary layers the diffracted wave was very weak. These observations tend to support the recent conclusion of Howe (1976) that trailing-edge flows are quieter if they do not show singular behaviour. This is in contrast to the predictions of earlier theoretical models of the edge diffraction problem.