Jet-Spike Bifurcation in High-Speed Flows

In recent plasma injection experiments, counterflow jet interaction has been identified as one of the mechanisms that significantly reduces the drag. There is a sudden change of the dynamic state from an oscillatory to nearly steady motion of this jet-shock interaction which depends on the relative magnitude of injection and the stagnation pressure. The shock-wave bifurcation associated with a counterflow jet from a hemispherical cylinder is investigated by a side-by-side experimental and computational effort. Shock-wave bifurcation has been discovered by the present experiments over the entire range of tested conditions in the Mach 6 wind tunnel. This oscillatory motion is sustained by the upstream propagation of selectively amplified frequencies from the free-shear layer to the Mach disk through the embedded subsonic domain. The breakdown of this feedback loop occurs when a higher injecting jet pressure creates a supersonic zone separating the interconnecting embedded subsonic domains