Numerical study of the reverse flow behind the Mach disk in an underexpanded supersonic jet

Numerical simulations of an underexpanded supersonic jet exhausting from a circular nozzle are reported. The study is performed in a three-dimensional formulation using two different approaches: Navier–Stokes equations and Direct Simulation Monte Carlo method. In both cases, a reverse flow zone is formed behind the Mach disk in the first shock cell. Thus, this phenomenon, which was previously observed in axisymmetric simulations, cannot be attributed to inaccuracies of approximation of these equations near the axis of symmetry.