Statistical estimation of aeroacoustic source terms in cold subsonic turbulent jets using Multiplane Stereo PIV and BOS

Abstract

The dataset of Multiplane Stereo Particle Image Velocimetry (MSPIV) measurements on a cold subsonic jet at Mach number M ≈ 0.65 is analysed in order to obtain information of the turbulent flow with relevance for noise prediction methods. After Reynolds-decomposition the two-point space-time correlations of the axial fluctuating velocity components are calculated. Thus, it is possible to determine the turbulent kinetic energy k, the axial integral length-scale L , the decorrelation time-scale t and the convection velocity u of the axial velocity correlations. In a second experiment the sound generation in a cold jet at Mach number M ≈ 0.9 has been investigated by means of simultaneous and synchronized Background Oriented Schlieren (BOS) measurements in the near-field and microphone measurements in the far-field. From 20000 recorded BOS snapshots in the region of the potential core the density gradient fields are determined and cross-correlated with the acoustic far-field pressure signal. The correlation maps show regularities in the flow field which are related to the radiated noise.