The Influence of Finite Rupture Times on Flow Dynamics within Micro-Shock Tubes

The importance of micro-shock tubes is growing in line with recent developments of microscale technology for products like micro-heat engines and micro-propulsion systems. The flow dynamics within a micro-shock tube are different from those found in a macro shock tube, and knowledge of these dynamics is not as yet well established, as the flow within these tubes includes extra physics namely rarefaction and complex effects due to viscosity. Studies have recently been made with assumed initial condition of instantaneous diaphragm rupture producing centred shock and expansion waves. However, for a real case, the diaphragm ruptures over a finite time causing a period of partial rupture and this will change the shock characteristics. The work here reports on a series of axisymmetric numerical simulations carried out to calculate the influence of an initial finite-time diaphragm rupture. Rarefaction effects were taken into account by the use of Maxwell’s slip velocity and temperature conditions. Use of an initial finite-time diaphragm rupture boundary condition causes the forming of a non-centred shock wave downstream of the diaphragm, and, the shock propagation distance is considerably reduced by use of the finite-time rupture process.