Experimental investigation of underexpanded transverse jet interaction with supersonic crossflow

Abstract

Transverse jet interaction with crossflow is one of the most canonical and studied flow phenomena in fluid dynamics. It is possible come across to this kind of flow even in nature and daily life; smoke blowing out of the chimney in windy weather could be given as a typical example. Despite different flow structures observed, this interaction is matter of interest in both subsonic and supersonic crossflows. As regards to aerospace discipline, this particular flow event becomes prominent in high-speed applications. Two main research area comprises most of the studies in this context; lateral thrust vectoring without any control surface of supersonic missiles and effective injection for fuel mixing in combustion chamber of supersonic combustion ramjets which have key role in modern aerospace systems. Even minor changes in incidence angles of supersonic missile control surfaces could lead to complex flow structures and prevent effective maneuverability. Lateral control with jets injected to supersonic crossflow becomes advantageous on account of much less response time in comparison with conventional control surfaces. On the other hand, maxiumum mixing of fuel with flow in combustion chamber is a must for scramjet engines. Flow structures, their stability and penetration to flow domain is very crucial. Furthermore, pressure gradients; thus, momentum losses and their minimization in the downstram region of the jet should be evaluated. Realization of jet interaction with supersonic crossflow will contribute to competitive new-generation aerospace solutions. As a result of interaction, various zones occur in both upstream and downstream regions of the jet. The most distinct one is the bow shock which occurs at a certain upstream distance from the jet exit. High-pressure jet behaves just like an obstacle against the crossflow and forces it to go around. Since jet mixing evolves with increasing distance from the surface, its dominance and resistance against crossflow diminishes. As a result, bow shock is bent towards the surface. Bow shock induces flow separation with adverse pressure gradient. Therefore; a recirculation zone, and more importantly, a horseshoe vortex is observed. On the other hand, jet accelerates by expansion in the vicinity of injection surface. Then, it is surrounded by a barrel shock, which defines compression. As a result, supersonic nature of the jet concludes with a Mach disk which is normal to trajectory of the jet. In downstream of the Mach disk, vortical events take place. The most characteristic one is a counter-rotating vortex pair which enlarges as distance to jet exit increases. When surface activities are inspected, a V-shaped separation zone draws attention. When moved to streamwise symmetry axis of the jet, reattachment occurs. In streamwise direction, this zone terminates and then, reflection shocks appear. Briefly, flow structures as a result of jet interaction with supersonic crossflow are summarized as such.