Blast-Wave Dynamics in a Circular Duct with a Sudden Expansion

Abstract

In this study, the problem of a planar blast wave in a duct with a sudden expansion is considered. An incident blast wave that contains two shock waves is arranged so that one pair of vortex rings induced by the first shock wave interacts with the second shock wave of the blast wave and with the reflected shock associated with the first shock wave. A high-resolution Euler/Navier-Stokes solver using a fifth-order weighted essentially nonoscillation scheme is employed to investigate the problem. After the Euler/Navier-Stokes solver is validated to be reasonably accurate, the flow fields induced by the shock/vortex interactions are investigated by computational shadowgraph and computational schlieren techniques. It is found that the trajectories formed by major ring-vortex centers may be different case by case, depending on the arrival time sequence of the second shock wave and the reflected shock wave. In particular, a third vortex ring may be developed, causing the trajectory's turn at some critical time in viscous-flow models. Because of viscous dissipation, consequently stronger vortex-ring strength predicted by the inviscid-flow model than that for the viscous-flow model can result in 14-32% lower pressures at the major ring-vortex centers in the inviscid flow compared with the turbulent flow during the time interval investigated for case A, and 20-32% for case B, and 21-38% for case C. Because of the boundary layer development along the duct wall after the sudden expansion, the reflection type of the first shock wave is changed from a regular reflection in the inviscid-flow case to a single Mach reflection that directly affects the arrival time of the reflected shock wave at the sharp corner. Moreover, the mechanism of the vortex ring formation based on the inviscid-flow model is analyzed. It is found that the term due to the dilation effect also plays a more important role in vorticity generation than the baroclinic term.