Experimental and Numerical Study of Stationary Throat Plug in Shock Tunnel

Abstract

A throat plug is a device in a shock tunnel to prevent fragments, produced by the bursting of the primary diaphragm, from entering the nozzle and damaging the model. In the present study, a series of experimental and numerical studies has been carried out to investigate the flows around stationary throat plugs in a shock tunnel. For this purpose, conical, circular, and double circular stationary throat plugs that have a 19.4% areal blockage were used as the test models. The primary shock velocity was set at 1.19 km/s, and the shock generated a tailored condition when helium and air were used as the driver and driven gases at room temperature. In the experiment, the nozzle reservoir pressure and the pitot pressure at the nozzle exit were measured to examine the influence of the throat plug. It was found that, from both the experiment and the calculation, all types of the plugs generate a pressure bump in the nozzle reservoir during the transient period of interaction between the reflected shock and the plugs. After the transient period, the difference between the plug-distorted and -undistorted nozzle flows is small and can practically be neglected. When the driven tube diameter is increased in the region in which the throat plug is located, the pressure bump is almost eliminated. However, according to the calculation, the increased diameter causes an augmentation in the temporal enthalpy and the entropy at the nozzle exit. The spatial distribution of the entropy in the radial direction shows little change. The configuration of the plug has little influence on the shock-tunnel flow when the plug is placed in the region in which the plug does not distort the nozzle flow.