Keywords: heat protection, slot and uniform gas injection, hydrogen combustion, hypersonic flow, exponential box-scheme, direct-simulation Monte-Carlo method.

Three numerical methods have been developed for analyses of hypersonic flows and heat transfer under the conditions of intensive gas blowing from the blunt body surface for various continuum and rarefied-gas flow regimes. Non-equilibrium parameters in the multicomponent media were evaluated for slot and uniform injections of air, helium, and hydrogen. Numerical results indicate that the most effective cooling of the probe surface occurs at moderate uniform injections and moderate Reynolds numbers.

The direct simulation Monte-Carlo technique [1] has been used to study the influence of the blowing parameter (the ratio of outgas mass flux to upstream mass flux) and the rarefaction factor (Knudsen number) on the airflow structure about a sphere. It has been found that at transitional flow conditions (Knudsen number = 0.0163), when the mass injection rate equals 0.7 of the free-stream mass flux, the viscous layer is blown completely off the surface, and the heat transfer is zero. The displacement effect of blowing spreads both in the counterflow direction and along the surface. This effect is more pronounced at lower values of the Knudsen number, less than 0.075. The width of the injection-influenced "displacement" zone increases by the factor of 3 at decreasing the Knudsen number from 1.5 to 0.016.

The temperature contours are disturbed more significantly for helium injection than in the case of air-to-air blowing. Even at moderate helium mass blowing rates (in the range from 0.32 to 0.7), diffuse outgas flow displaces completely the viscous layer off the sphere surface. Numerical results correlate well with experimental data obtained in hypersonic wind-tunnels.

The present results demonstrate that the moderate blowing leads to decreasing both the friction and heat flux on the surface at the continuum airflow regime. The flow parameters in this case have been calculated by using the two-point exponential box scheme that has a property of uniform second-order convergence in the full range of blowing parameters.

The third numerical method has been developed for studying the processes of diffusive hydrogen combustion in a thin viscous shock layer at moderate Reynolds numbers [2]. The algorithm combines a matrix-factorization variant of the two-point exponential box scheme and the Newton-Raphson method for solving the nonlinear grid equations that approximate Navier-Stokes equations. The numerical results indicate that the major products of non-equilibrium chemical reactions are water and hydroxyl, which could be used for the identification of the excess/deficient hydrogen zones. It is found that he most effective cooling of the surface occurs at moderate uniform hydrogen injections.

1

V.V. Riabov, "Numerical study of interference between simple-shape bodies in hypersonic flows", Computers and Structures, 87, 651-663, 2009. doi:10.1016/j.compstruc.2008.10.010

2

V.V. Riabov, A.V. Botin, "Hypersonic hydrogen combustion in the thin viscous shock layer", Journal of Thermophysics and Heat Transfer, 9(2), 233-239, 1995. doi:10.2514/3.651

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