Shock-induced combustion in high-speed wedge flows.

摘要

Oblique detonation waves are essentially oblique shocks closely followed by a combustion front, and have been proposed for application to the combustors of high-speed propulsion systems. While the theory governing oblique detonation waves in the limit of equilibrium chemistry is relatively well understood, there is a comparative lack of understanding of the transition from oblique shocks to oblique detonations under non-equilibrium conditions. The purpose of this study is to improve understanding of these phenomena. The study is primarily computational in nature, and employed a dedicated multi-species, finite-rate chemistry (H₂/air combustion) CFD code developed by the author.; Rankine-Hugoniot and shock polar theory describe a number of regimes for supersonic, exothermic wedge flows, based on the frozen- and equilibrium-chemistry polar curves, and the wedge turning angle. Within one range of turning angles, solutions on both the frozen and equilibrium polars are possible, and the flowfield will typically involve an initial frozen oblique shock attached to the tip of the wedge, followed by transition to an oblique detonation wave as energy is released by combustion. The numerical model was used to investigate the critical role of the energy-release rate in governing the characteristics of the transition process. The study found that the transition varied from smooth at relatively slow rates of energy release, to a discontinuous transition for relatively fast energy release.; Another study investigated whether an oblique detonation can be stabilized at wedge angles less than the nominal wedge angle which generates an oblique Chapman-Jouguet (C-J) detonation. The investigation found that a solution consisting of an oblique C-J detonation, followed by a Prandtl-Meyer expansion wave which turns the flow parallel to the wedge surface, is indeed possible.; Wedge angles larger than the detachment point on the equilibrium polar resulted in an initial frozen shock attached to the wedge tip, followed by a locally detached detonation wave. The results showed that this locally detached detonation is unstable, and will eventually propagate forward toward the wedge tip to form a fully detached flow. Comparisons of the numerical model with experimental OH PLIF and schlieren flow visualization results in this regime show generally good agreement.