Multi-scale measurement of acoustic particle velocity and flow velocity for liner investigations

Abstract

The optimization of liners for noise reduction lacks a thorough comprehension of the inherent aeroacoustic damping phenomena. Therefore, the interaction of the acoustic particle velocity (APV) and the flow velocity field at liners has to be investigated. Hence, the simultaneous measurement of both quantities, differing by several orders of magnitude, is aspired. However, the required high dynamic range is challenging. In order to analyse the energy transfer from the acoustic wave to the flow turbulence, turbulence spectra must be resolved which necessitates a high measurement rate as well. Doppler global velocimetry with sinusoidal laser frequency modulation (FM-DGV) fulfils these demanding requirements. First, the capability of FM-DGV for APV measurements was successfully validated with microphone measurements. Finally, a multi-point measurement at a bias flow liner was performed with a high dynamic range of 7,000 and a high measurement rate of 50 kHz. Hence, a deeper understanding of the aeroacoustics at liners can be gained in future investigations.