Shock wave propagation in non-uniform gas mixtures

We consider a classical shock tube with Helium-filled driver section, and a driven section filled with a He– Ar gaseous mixture of continuously varying composition. We simulate a shock tube experiment, where the driven section composition starts out with pure Ar and ends with pure He (denoted ‘ − ’), or vice versa (denoted ‘+’). The initial pressures are 2 and 0.01 MPa. Two alternate initial species compositions are assumed: ‘Molar fraction’ – a linear distribution of the molar fraction; ‘Mass Fraction’ – a linear distribution of the mass fraction. Wave patterns arising in every case are presented and discussed.