Book Description

The research was concerned with a theoretical description of shock wave structure in gaseous mixtures when diffusive effects are important. The problem considered in detail is the structure of a shock wave in a helium-argon mixture in which the argon is present in very small concentration. An anomalous result, cited in the literature, suggesting that the argon undergoes an initial pre-expansion before compression, was analysed to show the theoretical origin of this effect. The velocity distribution of a trace of heavy gas (and its lower moments) are watched as the heavy particles pass through a Mott-Smith background shock of lighter particles. The Mott-Smith background is chosen because its bimodal Maxwellian form provides an analytical determination of the free path to the next event for the heavy test particle at any point along its trajectory. This so-called Monte Carlo solution to the idealized diffusion shock problem can be used as a standard for evaluating the diffusion equations derived from various kinetic theory approximations. A number of systems of moment equations of the heavy particle Boltzmann equation were solved and the resulting heavy particle moment profiles compared with those of the Monte Carlo solution. A second strong diffusion problem was analysed from a kinetic theory point of view. It was found experimentally that the ion density profile through a shock in a weakly ionized plasma with elevated electron temperature is much more diffuse than the neutral atom shock. The theoretical analysis shows that this strong diffusion effect can be attributed to the electrical coupling between the ions and the hotter electron gas. (Author).