Figure 4.

Schematic of the second buffer region where the non-centred of rarefaction waves exiting the first buffer region interact with the contact discontinuity. Only five incoming rarefaction waves travelling along right-going characteristics of Riemann invariant r_i are considered. The blue rarefaction wave is the head wave, whereas the green one is the tail wave. Rarefaction waves reflected off the contact interface travel along left-going characteristics of Riemann invariant s^L_i. Because the sound speed is different on each side of the contact discontinuity, these Riemann invariants are discontinuous across the interface. On the right side, they all have the same value s^R due to the initial uniformity of the region between the contact discontinuity and the shock front. (Online version in colour.)