V.L. Kovalev (MSU)

To calculate the heat loads and predict the life-time of the reusable heat shield it is necessary to have basic information on the processes of thermo chemical interaction between dissociated air and heat shield materials. The most important processes are catalytic atom recombination. The heat fluxes to surfaces with different catalytic properties can differ by several times. Despite the fact that since the fifties it has been well known that heterogeneous atom recombination significantly affects heat transfer at hypersonic flight velocities, the mechanisms and rates of the processes which determine the interaction between the gas and the surface have been much less closely studied than the kinetics and the homogeneous chemical reaction rates. The complexity of the problem of determining the catalytic properties of the surface is associated with the fact that there are no direct methods of measuring the recombination coefficients and chemical energy accommodation.

Molecular dynamics models are useful to understand the surface chemical reactions from a molecular point of view. Molecular dynamics simulations predict some quantities that cannot be easily measured in experimental observations, such as: state-to-state surface coefficients and their dependence upon the internal energy content of reactive molecule; translational and internal energy distributions of the product states; energy exchanged between the surface and the chemical system reaction mechanism and reaction pathways.

In this report 'MD Trajectory' software complex was developed to investigate mechanisms of heterogeneous catalytic processes. 'MD Trajectory' was tested on supercomputer clusters of Moscow State University and Russian Academy of Sciences and very high efficiency was achieved.

Using molecular dynamics approach the elementary catalytic heterogeneous reactions on SiO₂ or SiC based coatings have been studied in details and all its significant characteristics including both recombination and accommodation coefficients, distributions of molecules formed during recombination over vibrational and rotational states have been determined. Good agreements between our results and calculations or experimental results of other authors were revealed. It was revealed that silicon carbide surface will be heated more effective due to oxygen recombination than SiO₂ one because chemical energy accommodation coefficient for this surface is higher than last one on the full range of collision energy.