Cross-correlation analysis of synchronized PIV and microphone measurements of an oscillating airfoil

Abstract

The present study focuses on the correlation between the flow structures evolving during the dynamic stall processes of a two-dimensional NACA64-618 airfoil, which performs a sinusoidal movement about its quarter chord axis, and their aeroacoustic response in the far field. Experiments are conducted in an anechoic wind tunnel at a Reynolds number of 8x105 based on the chord length and include simultaneous velocity field measurements in the vicinity of the airfoil and microphone measurements in the acoustic far field. A causality correlation method based on phase locked snapshots of the velocity field allows for the identification of specific structures at different phases of the dynamic stall life cycle that contribute to the sound generation process. The sound emission during the stall development and flow reattachment phases is attributed to coherent structures evolving downstream of the trailing edge. When the flow is fully stalled, the region that contributes to the sound emission increases. The position of the sound emitting coherent structures also fluctuates stronger between oscillation cycles during full stall.