Initiation and propagation of shock and detonation waves in gases due to power deposition.

摘要

This thesis is in two parts. In part 'A' the problem of unsteady planar shock wave generation and propagation in an inert gas, confined between two infinite parallel plane walls, due to time-dependent power deposition at the boundary is investigated. A numerical solution is obtained for the system of Euler equations that describe the flow driven by the moving edge of an expanding conduction layer described by Clarke et al. (1984 b). The MacCormack finite-difference, explicit second-order accurate scheme is used with the Flux-Corrected Transport technique to reduce the oscillations that appear near the large gradients.; The results show that the numerical code is capable of capturing the shock wave with excellent accuracy. The results also show that the pressure and speed of the edge of the conduction layer increase as the power deposition at the boundary increases with time and accordingly, the shock speed and strength increase with time. The increase in the pressure level with time provides a source of compression heating to the gas contained in the conduction layer. This study indicates also that the fluid properties between the edge of the conduction layer and the generated shock wave are time and space-dependent.; In part 'B' the deflagration to detonation transition (DDT) and the unsteady behavior of the planar detonation wave is studied in a reactive mixture contained between two parallel plane walls. It is assumed that the gas undergoes a one-step exothermic chemical reaction with an Arrhenius law. The reactants and products behave as an ideal gas. The mixture is ignited by bulk power deposition of limited duration in a thin layer adjacent to the wall.; The resulting gas dynamic and chemical phenomena lead to the formation of several localized shock and combustion waves. An exothermic reaction center forms behind the lead shock. The forward moving front of the expanding reaction center drives a new shock wave which overtakes the lead shock. The coalesced shock is strong enough to induce a strongly coupled reaction zone in the gas just behind it. As a result, an over-driven detonation wave appears and exhibits oscillatory phenomena. This is associated with a time-dependent variation in the net chemical heat release and in the lead shock strength. The mean properties of the detonation asymptotes to the C.J. values for the gas considered.