Unsteady pseudo-shock wave in a shock tube

The unsteady flows in shock tubes are typical where the reflection of a shock wave falling on the tube end face takes place. A particular pattern of the unsteady flow can form in these cases which includes a series of shocks typical of a pseudo-shock wave in the steady flows. Forming of this unsteady flow pattern is an interesting but little-studied phenomenon. Results of a numerical simulation of the unsteady flow with the pseudo-shock wave forming in an axisymmetric shock tube are presented and discussed. The investigated flow was initiated by the process derived from the sudden rupture of a thin diaphragm separating two sections of the shock tube of which one section is filled with the high-pressure gas and another with the low-pressure gas. The same operating gas in both the sections was assumed to be ideal of an equal room temperature. The sudden rupture of the diaphragm generates such wave entities as an unsteady expansion fan propagating into the high-pressure section, as well as a primary shock wave and a following contact discontinuity both propagating into the low-pressure section. The initial velocity of the primary shock wave corresponded to the Mach number M = 2.6. The unsteady flow evolution was numerically simulated with the use of a Reynolds-averaged Navier–Stokes code and the k-ω SST turbulence model. The process of moving the said wave entities was investigated with emphasizing the reflection of the primary shock wave and contact discontinuity from the end face of the shock tube. The revealed conditions of forming the unsteady pseudo-shock wave are analyzed in comparison with some known experimental and computational data.