Computation of nonequilibrium chemically reacting flows in hypersonic flow field

In recent years a renewed interest in the design of various hypersonic vehicles has necessitated the inclusion of chemically reacting flows for the solution of hypersonic flowfields. From the physical point of view, all chemical reactions take some time to reach equilibrium state. Therefore, finite-rate (nonequilibrium) chemistry models must be utilized for hypersonic flowfield computations. A compelling difficulty in the numerical simulation of chemically reacting flow is the selection of the marching time step. Usually the characteristic time scale of the gas dynamic equations is different from that of the chemistry equations. A numerical algorithm that determines the chemistry marching time step is developed in this investigative work. Von Neumann stability analysis is applied to the chemistry equations to provide a criteria for the selection of time step for a stable solution. Both the quasi one-dimensional nozzle problem and the two-dimensional/axisymmetric blunt body problem are used for numerical validation. Unsteady Euler equations and chemistry equations are written in the conservative form so that the shock capturing scheme can be applied. A five species model is selected for the air compositions. The governing equations are discretized by an implicit, flux-splitting finite difference formulation to provide a better stability characteristic and faster convergence. The gas dynamic equations and chemistry equations are solved interactively and communicated by the loosely-coupled scheme.