Van der Waals shock polars with multiple or supersonic critical points

Abstract

It is shown that the γ-van der Waals equation of state (eos) permits shock polars with supersonic critical points, corresponding to critical or strong-type shock reflections that are supersonic, which is not possible for ideal gas. It is also shown that general van der Waals eos permits polars with multiple critical points, corresponding to four or more reflected shocks for the same deflection angle. Of these reflected shocks, at least two are weak-type, i.e., deflection angle increasing with increasing shock strength, so that standard literature has no criteria to select one of the two. Both phenomena can be found with Hugoniot curves entirely in the region of convex and thermodynamically stable eos, avoiding the coexistence region and satisfying various shock stability criteria.