Figure 2.

The interaction of waves in a shock tube in the x–t space of characteristics. The shock wave is represented by the red characteristic, whereas the blue and the green ones are the head and the tail rarefaction waves, respectively. The contact interface is the thick black characteristic curve. The point P shows the position of the diaphragm and the point O shows the closed end of the shock tube. The points a, a₁ and a₂ indicate the locations where the head rarefaction wave and subsequent rarefaction waves reflect of the closed end of the tube. The points b, b₁, b₂ and b₃ mark the moment where the rarefaction waves exit the first buffer region. The points c_ij describe the intersections between right-going rarefaction waves interacts with rarefaction waves reflected the contact interface in the second buffer region. The point d designates where the head rarefaction wave meets the shock wave, which corresponds to the onset of the Friedlander wave inside the shock tube. The points d₁, d₂ and d₃ tag the time at which the trailing rarefaction waves reach the onset location of coordinate: x_d. (Online version in colour.)