Dark Space ahead of a Shock in Ionized Gas Flows

The dark space, which is formed ahead of a detached shock of a blunt body in a flow of ionized argon, was theoretically investigated, and its mechanism was revealed. The electron energy equation, electron continuity equation and continuity equation of the first excited-level atoms were formulized separatly in a shock layer and in a free stream, and then the free-stream solutions were connected with the shock-layer solutions in such a way that the boundary conditions on the wall of the blunt body are satisfied. The method of solving is described here. The calculations were carried out for the case that atom density is 10 particles/m, atom temperature is 500 K, Mach number is 4.5, electron density is 5 X 10 particles/m in the free stream and that the wall temperature is 300 K. The results show that the region of the elevated electron temperature exists ahead of the shock and that this elevation causes the decrease in the population densities of excited levels higher than the 5s level. The dark space can be explained as the reduction in the population densities due to the elevation in the electron temperature.