Predicition and simulation of compressive shocks with lower perturbed density for increasing shock strength in real gases.

In this paper we predict and simulate a peculiar type of compressive shock in a real gas modeled by the van der Waals constitutive equation. This shock produces a phase transition from the gas to the liquid phase and, under some special circumstances, back to the gas phase. This shock has a quite unusual property that when the perturbed pressure the pressure after a shock increases, the perturbed density decreases and tends to a limit value from above, in contrast with the ordinary well-known compressive shock in which the density tends to the limit value from below. To achieve such a compressive upper shock, it is necessary to choose the unperturbed state the state before the shock in a very thin region in the p plane, characterized by low values of density and pressure, near the gas-liquid coexistence curve. This region, which depends on the internal degrees of freedom of a constituent molecule, is completely identified.