Numerical Study of the Oblique Detonation Initiation Induced by Spheres

The oblique detonation wave engine is a new kind of engine which has a simple structure, low cost, and high specific impulse. In order to ensure the initiation, blunt body is used to induce the oblique detonation wave. The oblique detonation wave flow field induced by spheres in supersonic hydrogen/air mixture is numerically simulated, based on the Euler equations and a detailed hydrogen-oxygen chemical reaction model. Unlike the oblique detonation wave induced by a wedge, the reacting flow around a sphere is much more complex. First, a normal shock wave/detonation wave is formed, then oblique shock wave/detonation wave is developed in the presence of a rarefaction wave. The numerical simulation results show that after the gases being compressed by the blunt body and reaching the auto-ignition temperature, two kinds of flowfileds will appear. When Mach numbers are low, the combustion will be quenched and can not appear downstream of the blunt body due to the influence of the rarefaction wave. When Mach numbers are high, combustion can spread to the downstream region. When the scales of blunt body are small, energy around the stationary point is not enough to induce detonation initiation and an obvious decoupling of combustion and shock wave is formed. As the sphere becomes large enough, decoupling of combustion and shock wave will not appear in the flow and this feature is indpendent of the Mach number. By adjusting the spheric diameter, the flow structures with partial coupling of shock wave and combustion zone was obtained which does not exist in a wedgy-induced oblique detonation. The present investigations suggest that the interaction between rarefaction wave and detonation wavefront is the key issue for detonation initiation induced by a spheric body.