Jet-spike bifurcation in high-speed flows

In recent plasma injection experiments, counterflow jet interaction has bee n 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 bifurcat ion associated with a counterflow jet from a hemispherical cylinder is inve stigated by a side-by-side experimental and computational effort. Shock-wav e bifurcation has been discovered by the present experiments over the entir e range of tested conditions in the Mach 6 wind tunnel. This oscillatory mo tion is sustained by the upstream propagation of selectively amplified freq uencies from the free-shear layer to the Mach disk through the embedded sub sonic domain. The breakdown of this feedback loop occurs when a higher inje cting jet pressure creates a supersonic zone separating the interconnecting embedded subsonic domains.