Study of a throat plug in a shock tunnel

Abstract

When a shock tunnel flow is initiated by the rupture of the primary metallic diaphragm, the rupturing produces many small fragments of the diaphragm material. These diaphragm fragments move slowly toward the nozzle throat. After the useful test flow is finished, these fragments may pass through the nozzle via the throat and blast the model. This results in scratching of the model surface, in damage to instrumentation and in disturbing of the boundary layer flow around the model necessitating frequent model replacement. If a plug for the throat of the nozzle is present the fragments are stopped in front of the nozzle; however, the influence of this part on the shock tunnel nozzle flow is not well known. It is the purpose of present research ultimately to design this plug for a new large shock tunnel. To investigate the characteristics of flow around the throat plug and flow in the test section affected by the presence of the throat plug, experimental and theoretical approaches are carried out. Furthermore, the experiment for closing the plug is carried out.

Several foundings can be drived from the results of the present research. First, the requirements for the size of the throat plug are determined as: for freestream Mach numbers above 5, the throat plug that has a 20 \% blockage is considered to be useful; for freestream Mach numbers from 4 to 5, 30 \% throat plug is considered to be proper. Second, a 6.2 \% stationary throat plug, in this experimental and numerical study, is found to be have a negligible effect on the shock tunnel flow; however, a 19.4 \% stationary throat plug shows a perceptible influcence by generating a bump in the nozzle reservoir pressure for a finite time period regardless of the nozzle throat area studied. Although it retards the establishment time of the nozzle flow, after the tranisent period, it does not cause deviation of the pressure from that for the clean nozzle configuration. It is also found that the reduction of the cross...