Forced Injection of a Spanwise-Inclined Jet in Supersonic Crossflow

Abstract

Beneficial effects of forced air-jet vortex generators in controlling shock-induced flow separation motivated us to study forced jet injection in detail to understand the advantageous control effects. We performed implicit large-eddy simulations to examine the influence of sinusoidally forced injection of a spanwise-inclined jet in supersonic crossflow. Two forcing frequencies were considered (with and 0.0062) in a crossflow at Mach 2.5 and momentum-thickness Reynolds number of 7000. The underexpansion of the jet has a near-linear dependence on the injection pressure. Consequently, in the near field, the major vortices pulsate with the injection pressure. Statistical analysis using triple decomposition revealed that periodic oscillations of the major counter-rotating vortex pair (CVP) result in momentum transfer by major CVPs, also on their lateral sides, leading to enhanced mixing and lateral spreading, which is beneficial for separation control. Three-dimensional dynamic mode decomposition revealed that forced injection induces a large-scale clockwise rotation of the major vortex. These effects are weak at low forcing frequency. High-frequency jet forcing thus leads to more efficient control of flow separation. On the other hand, periodic oscillations cause these vortical structures to dissipate and breakdown faster in the midfield region than for steady jets. The placement of forced jets is therefore an important parameter when used for separation-control purposes.