Spatiotemporal Development of Transitional Wall Jets

Wall jets have many applications in engineering ranging from active flow control to film cooling. A typical wall jet is characterized by both spatial and temporal variation. Here we use Time Resolved-Digital Particle Image Velocimetry (TR-DPIV) to deliver high spatially and temporally resolved investigation of wall jets across a wide range of Reynolds numbers (150–10,000). We employ Proper Orthogonal Decomposition (POD) to post-process the data and generate low-order models describing the underlying physics. The results show the presence of near wall structures forming at the jet exit and convecting downstream directly influencing the transition to turbulence. Using the time coefficients associated with the POD modes, the frequency content of the individual modes is determined and the mechanism of energy transfer between the modes is quantified. This study provides the first spatiotemporally resolved experimental investigation of the transition to turbulence of a rectangular wall jet.