Mixing in nearwall regions downstream of a sonic jet in a supersonic crossflow at Mach 2.7

The mixing status downstream of a transverse sonic jet in a supersonic crossflow at a Mach number of 2.7 was studied. Direct numerical simulations were performed to investigate the transport of a passive scalar of jet fluid for jet-to-cross-flow momentum flux ratios (denoted as J) of 1.85 and 5.5. Results showed that a counter-rotating vortex pair (CVP) with two branches generates in the jet nearfield, grows, and breaks into small eddies in the farfield, which enhances the local mixing. A nearwall region in the jet lee between the CVP branches is identified to have a low mass fraction of the jet fluid and this region expands as J increases. Analysis of the streamlines originating from the jet orifice and the crossflow suggests that the jet fluid in the downstream nearwall region is entrained by the lateral crossflow upstream of the jet, which travels around the jet and mixes with the injectants downstream of the jet. Higher J leads to a lower mass fraction of the jet fluid in the nearwall region of the jet nearfield, but produces a higher mass fraction in the nearwall region of the farfield. A three-dimensional schematic of the jet wakes is presented and explains the formation of the nearwall low mass fraction zone in the jet nearfield.