Stereoscopic PIV and POD applied to the far turbulent axisymmetric jet

Recent experiments on asymptotic high Reynolds number turbulent jet have shown a difference between results from the slice POD applied to the full velocity vector and to the streamwise component of velocity only. In particular, the evolution of the peak in the energy toward azimuthal mode-2 in the streamwise velocity component decomposition noted in earlier experiments, shifted to mode-1 if all three components of velocity were considered. This is in contrast to what appears to be the case for the jet mixing layer and the axisymmetric wake6 where no such differences were observed. The work reported here applies stereoscopic PIV to the far field of the same jet in which the mode-2 phenomenon was first noticed. Indeed azimuthal mode-1 is maximal if all three velocity components are considered, so the new findings are confirmed. This work also addresses a number of outstanding issues from all the previous measurements, including questions of whether the spatial resolution was adequate and whether the results were influenced by the short-comings of using hot-wire probes in such high intensity turbulent flows.