Phase 0: Driver based expansions.

Back to Phase 0

In the idealized case, the diaphragm rupture in the shocktube is a Riemann problem: the driver gas (generally He) and the driven gas (N2 for the Phase 0 experiments) are initially at rest but with different presures (and perhaps temps). This leads to the creation of a shock traveling down the shocktube in the driven gas and an expansion fan propagating back into the driver section of the tube. This expansion fan reflects off the driver end wall and then travels down the shock tube following the shock wave. In the initial Phase 0 experiments with modest shock mach numbers ( on the order of M=1.5) the expansion wave (traveling at u+c) overtakes the shock before the experiment is complete.

Here is a simple diagram in the x-t plane of the shock expansion in the situation where the expasion fan overtakes the shock.

Chris Bond suggested the idea of slowing the expansion fan in the driver gas to extend the flight time of the shock before being overtaken by the expansion. This is done by using a different mixture of gases in the driver to lower the speed of sound in the driver.

Here are several one-dimensional simuations using different mixtures of gases in the driver. In these animations the driver gas is blue and the driven gas is red.

• PureHe.avi: Pure HE driver

• FifteenPercentAir.avi: Fifteen percent Air driver

• TwentyPercentAir.avi: Twenty percent Air driver