Fig 8. The planarity of the shock front is largely lost at the shock tube exit.

The edge of the shock front at each time step (Δt = 38.5 μs) from t = 0–13.5 ms in the moderate strength shock in a mid-wall cut. As the shock exits the shock tube, denoted by a grey bar, the shock front loses its planar nature and expands, becoming non-planar.