Drag and Heat Transfer Reductions in High-Speed Flows

A numerical investigation of forward-facing injection from blunt bodies in high-speed flows when coupled with upstream deposition of energy is shown to result in large decreases in overall drag and heat transfer. The problem of upstream-directed injection jet instability is shown to be significantly reduced by the coupling of the two techniques (injection and upstream energy deposition); this allows the jet to penetrate far upstream and stabilize within bounds. When hydrogen is used as the core injectant, the substantial production of water in and near the zone of upstream energy deposition may assist in the efficiency of energy deposition systems. Additionally, by sheathing the hydrogen core with an inert injectant such as nitrogen, the body is cooled and the heat release and resulting zones of water production are removed from the vicinity of the blunt body. Cases are shown in which the overall drag is only 20-30% of the baseline drag, heat transfer is minimal, and jet stabilization and forward penetration is ensured. The impact of turbulence on drag reduction and flow stability (for combined energy deposition and forward-facing injection) is also shown. Although the impact of turbulence on drag reduction results is found to be similar to laminar flow, the turbulence generally increases the stability of the forward-facing injection, delays the partial collapse of the forward-facing jet, and increases the mixing of hydrogen and air. This increase in mixing is shown to result in a more effective energy release associated with the reaction, which is found to further stabilize the injection and results in lower drag. Further studies also indicate that minimum drag and maximum penetration and stability of the jet at the point of maximum penetration can be maintained by active control of the energy deposition location