Application of particle image velocimetry and proper orthogonal decomposition to the study of a jet in a counterflow

Particle image velocimetry (PIV) experiments were carried out on a round jet in a uniform counterflow. The complex dynamics of this flow has so far hindered its understanding, and PIV appears to be a promising investigation method to help fill this gap. In fact PIV allows the dynamics of single vorticity structures to be followed, at least within the limits of its spatial and temporal resolution. In particular, the combination of PIV and proper orthogonal decomposition (POD) analysis showed that it is possible to isolate a few typical patterns out of the apparently chaotic fluctuations of the jet. A POD analysis at high velocity ratios was performed to investigate the fluctuations typical of the far field of the jet, while one at the critical velocity ratio of 1.3 delivered further information on the transition between the stable and the unstable flow condition.