Two-dimensional outflow of an inhomogeneous streaming gas into a vacuum

A study is made of two-dimensional nonisentropic flows of an ideal polytropic gas arising in the case of an instantaneous removal of a smooth surface separating specified gas flow from a vacuum. The problem of the decay of such a discontinuity is solved in a space of special variables in the form of converging characteristic series. Based on an analysis of the series convergence region, it is shown that during a certain period of time, each gas particle at the vacuum boundary moves along its own straight path at its own constant velocity. The case where a gas and a vacuum are contiguous, with a smooth free surface between them, is also examined.