High-speed camera-based measurement system for aeroacoustic investigations

Abstract

The interaction of sound and flow enables an efficient noise damping. Inevitable for understanding of this aeroacoustic damping phenomenon is the simultaneous measurement of flow and sound fields. Optical sensor systems have the advantage of non-contact measurements. The necessary simultaneous determination of sound levels and flow velocities with high dynamic range has major hurdles. We present an approach based on frequency-modulated Doppler global velocimetry, where a high-speed CMOS camera with data rates over 160 MSamples s-1 of velocity samples is employed. Using the proposed system, two-component flow velocity measurements are performed in a three-dimensional region of interest with a spatial resolution of 224 μm, based on single-pixel evaluation, and a measurement rate of 10 kHz. The sensor system can simultaneously capture sound and turbulent flow velocity oscillations down to a minimal power density of 40.5 (mms-1)2 Hz-1 in a frequency range up to 5 kHz. The presented measurements of the interaction of sound and flow support the hypothesis that the sound energy is transferred into flow energy.