Numerical study of shock-reflection hysteresis in an underexpanded jet

Shock-reflection hysteresis and plume structure in a low-density, axisymmetric highly underexpanded air jet is examined using a Navier-Stokes dow solver. This type of jet is found in a number of applications, e.g., rocket exhausts and fuel injectors. The plume structure is complex, involving the interaction of several flow features, making this a demanding problem. Two types of shock reflection appear to occur in the plume, regular and Mach, depending on the jet pressure ratio. The existence of a dual solution domain where either type may occur has been predicted, in agreement with experiment where the same phenomenon has been observed for a nitrogen jet. There is a hysteresis in the shock-reflection type; the reflection type observed in the dual-solution domain depends on the time history of the plume development. A quasi-steady approach is employed to calculate the entire hysteresis loop. An implicit, multiblock structured, finite volume flow solver is used. The results of the computational study are used to examine the structure of the plume and are compared with experimental data where possible. Some flow features not initially recognized from experiment have been identified, notably curvature of the Mach disk, recirculation behind the Mach disk, and the regular reflection having Mach-reflection characteristics.