Tomographic PIV for Beveled Trailing Edge Aeroacoustics

摘要

This study investigates the flow field around beveled trailing, defined by the ratio of radius of curvature R to plate thickness T and the enclosed 25° trailing edge angle, which parametrically resembles a variety of trailing edge flows ranging from sharp to blunt. In particular, for aeroacoustically generated trailing edge noise and vibro-structural problems the characteristics of the unsteady surface pressure near the trailing edge are of interest under these different conditions. Complementary to unsteady surface pressure sensors, highspeed tomographic Particle Image Velocimetry (PIV) can provide time-resolved and volumetric information on the flow field. Recent advances of multi-frame correlation methods and the introduction of pressure reconstruction methods based on PIV data allow for estimation of quantities related to the unsteady pressure, which otherwise requires complex instrumentation of the model. The present contribution focuses on the case R/T=10. Acoustic phased array microphone measurements have been performed and the sound pressure level has been determined by integration of the source maps over the relevant source region. Visualizations of the high-speed tomographic PIV measurements reveal the structure of the adverse pressure gradient, separating flow close to the trailing edge. PIV based reconstructed and measured unsteady surface pressure spectra show agreement over an extended range of frequencies. Estimates of the spanwise coherence length of velocity fluctuations are obtained, showing a decrease of the coherence length in the lower part of the separating shear layer. In contrast to a zero pressure gradient boundary layer, the reconstructed pressure spectra show a decrease of unsteady surface pressure convection velocities with increasing frequency for the beveled edge.