Shock tunnels and expansion tubes are used to generate high-energy, hypersonic flows for the ground testing of hypervelocity vehicles. Flow in each facility is usually initiated by the rupture of a diaphragm that separates high and low pressure gas. In this seminar, two different types of diaphragm rupture are examined.
Simulations of the relatively slow rupture of the primary diaphragm initially separating the driver and the driven (test) gases will be presented. The structure of the resulting flow will be examined. From these simulations, the speed of the developing shock was recorded. The maximum shock speed was greater than that predicted by one-dimensional models and closer to experimental results.Simulations of the fast rupture of the light secondary diaphragm in an expansion tube are presented. The secondary diaphragm has a smaller mass than a typical primary diaphragm and is ruptured when struck by the incident shock. The fate of the diaphragm material and its influence on the test gas are examined.
The simulations were performed with a finite-volume code solving the Euler equations for compressible, inviscid flow. The flow domains were discretised with unstructured grids of triangular elements and a solution-adaptive remeshing scheme was used to focus computatution effort in regions where the flow field gradients are high. This allowed the capture of shock waves and shear layers with greater resolution than possible with fixed grid simulations at the same (or similar) computational expense.