Numerical Investigation of the Effects of Nonuniform Premixing on Shock-Induced Combustion

Abstract

A parametric numerical study was performed to study effects of the nonuniform premixing of a hydrogen–air mixture on the structures of oblique detonation and shock-induced combustion formed on the surface of a hypersonic spherical projectile. Axisymmetric two-dimensional Navier–Stokes equations were solved with a detailed chemical kinetic mechanism involving nine species. A smooth-front oblique detonation formed on the hypersonic projectile at a Mach number of 6.46 under a uniformly stoichiometric condition was taken as the completely premixed case. For nonuniform cases, hydrogen mole fraction was distributed at the inlet boundary based on the Gaussian function. As the nonuniformity was increased, the following occurred: 1) deformed oblique detonation, 2) oscillating shock-induced combustions with nonuniform corrugated structures, 3) steady shock-induced combustions with (and without) the minimum induction length located outside the centerline, and 4) nose-confined combustion. Analyses on distributions of induction lengths combined with zero-dimensional additional simulations demonstrated that a reactivity gradient became strongly influential on the nonuniformly premixed structures as the nonuniformity was increased, and finally the postshock flowfield became the most determinant factor.