This is an unsteady viscous computation of a shock tube problem in a closed 1x1 box. The initial conditions are set with two gases at rest, same temperature but pressure and density ratio of 100 (left over right values). The Reynolds number (200) is based on the initial speed of sound and the box length. This test case has been proposed by Daru and Tenaud.
Due to the initial pressure discontinuity, a shock wave travels from left to right while accelerating the flow and creating a boundary layer on the bottom wall. Then the shock hits the right wall, crosses the initial gas interface and travels back to the left. The shock wave makes the boundary layer separate into a complex vortical flow.