Numerical simulation of high-speed and high temperature reacting flows using a commercial CFD software.

Hypersonic flows are a field of great interest since the sixties of last century because they occur in the planetary entry of space probes and they have recently attracted renovated attention due to development of hypersonic cruise missiles. Currently, the dominating method of study for high Mach number flows is Computational Fluid Dynamics (CFD), which have become sufficiently powerful, and have replaced the old analytic methods. In the present work, a computational model has been developed for simulating flows of a multicomponent air mixture around a hypersonic cruise missile (HCM) using the commercial CFD software STAR-CCM+. The investigations aim at verifying, first of all, the effective occurrence of chemical reactions of an air mixture of eleven species (N, N2, O, O2, NO, N+, O+, N2+, O2+, NO+, e-), then to evaluate the possible presence of the ionized particles species and finally to assess whether their amount is high enough to generate an appreciable electric field or not. The software set-up choices were made to match assumptions required for analytical models which describe aerothermo-chemical effects in the proximity to the missile nose. Starting from a Mach number equal to 10, several simulations have been carried out, applied to the basic geometry of the nose, and different thermo-chemical models have been considered. Furthermore, since the considered model included a multicomponent gas mixture, multicomponent diffusive mechanisms have been implemented, where binary diffusion coefficients and gradients of temperature effects have been considered. Good convergence of solution was observed for all cases presented since every investigation has been carried out with a proper numeric discretization scheme and fine enough grids to avoid numerical instabilities and to guarantee adequately accurate results. The investigations showed the occurring of reactions and revealed the appearance of ionized particles. These phenomena strongly affect flow field properties. Reactions influence heat flow at wall in stagnation region, while a distribution of charged particles induces an electric field which may give to the missile a stealth property, as well as conditioning transport mechanisms. These considerations make hypersonic flow fields fundamental to investigate and our results confirmed how significant thermo-chemical effects are for HCMs features.