Numerical investigation of 2-dimensional H2-air flame holding over ramps and rearward facing steps

The time-dependent Navier-Stokes equations, including the effects of finite rate chemistry, are numerically integrated to predict the steady state behavior of several model supersonic flame holders. The conservation equations governing chemically reacting flows are solved using a technique based on the idea of rescaling the equations in time such that all convective and chemical processes evolve on similar 'pseudo' time scales. To accomplish this, the conservation equations are preconditioned to remove the stiffness associated with these equations. The method can be used to compute the steady state solution very efficiently regardless of whether the flow is frozen, finite rate or in equilibrium. Two candidate supersonic flame holders are analyzed to assess their operating characteristics. The geometries include a ramp and a rearward facing step. Several different kinds of flow field are generated depending upon the level of heat release. For each geometry it is suggested that the different flow fields can be summarized on a plot of equivalence ratio vs inlet Mach number or the equivalence ratio vs the ratio of the maximum temperature to the fuel ignition temperature. All flows considered a premixed H2-air stream and used the global chemistry model of Rogers & Chinitz.