1The expansion of a dilute gas through a gasdynamics convergent-divergent nozzle can occur in three different regimes, depending on the inlet and discharge conditions and on the type of gas: via a fully subsonic expansion, via a subsonic-supersonic flow with transition to supersonic flow at the minimum area section or via a subsonic-supersonic-subsonic expansion embedding a compression shock wave within the divergent portion of the nozzle.
Modern thermodynamic models of molecularly complex fluids operating in the non-ideal regime indicate that eighteen additional different flow configurations are possible, each including multiple compression classical shocks as well as non-classical rarefaction ones, also called negative shock waves.
These exotic configurations can possibly occur in compressible flows of molecularly complex fluids such as hydrocarbons, siloxanes or perfluorocarbons operating close to the liquid-vapour saturation curve and critical point.