Transient start-up of a sonic jet in hypersonic crossflow

Abstract

This paper presents a numerical study of the transient start-up of a sonic jet into a hypersonic crossflow. Implicit large-eddy simulations were performed using OpenFOAM for a round, sonic, perfect air jet issuing normal to a Mach 5 crossflow, over a flat plate with a laminar boundary layer, at a jet-to-crossflow momentum ratio of 5.3. The evolution of shock and vortex structures, the jet penetration, and the control force have been quantified during the jet start-up. Initially, a lead shock forms, which is quickly deformed and convected downstream by the crossflow. The obstruction caused by the jet leads to formation of barrel shocks, a bow shock, and a Mach disk. The obstruction also results in upstream flow separation, which facilitates the formation of the horseshoe vortices within an upstream recirculation region. Shear-layer vortices begin to form and shed periodically once the barrel shock structure is established, while longitudinal counter-rotating vortices and wake vortices are not formed until the jet flow has penetrated far downstream. The control force develops on the same time-scale as the longitudinal counter-rotating vortices. An overshoot is observed in the control force after the lead shock and initial jet flow has convected downstream beyond the edge of the plate, and is related to the re-compression of the free-stream flow downstream of the jet outlet, and the development of re-circulation regions.