Dynamics of Variable Density Jets in Crossflow

The equidensity jet in crossflow (JICF) is known to demonstrate absolute/global instability characteristics in the upstream shear layer (USL) at relatively low jet-to-crossflow momentum flux ratios, approximately J < 10, and to produce relatively weak, convective instability at larger J values [Megerian, et al., JFM 2007]. Reducing the jet-to-crossflow density ratio S to values well below unity (S < 0.45) has been shown to generally produce global instability, as would be expected when compared with the classic free jet [Getsinger, et al, Exp Fluids 2012]. Yet in gas-phase experiments there can be anomalous trends as one gradually reduces jet density while fixing J and jet Reynolds number [Shoji, et al., JFM 2020]. The present experiments examine the variable density transverse jet in detail, focusing in addition on higher density JICF conditions (1.0 < S < 2.0), which have useful practical applications. Here jet dynamics and USL transition are studied via simultaneous acetone PLIF and PIV as well as hotwire anemometry. Experimental observations of shear layer stability transition are compared with those predicted in linear stability analysis, making use of the counter-current shear layer analogy with curvature and viscous effects [Souza, et al, PR Fluids 2021] but now with variable density conditions.