The von Neumann Mach Reflection (vNR) resembles to the Simple Mach Reflection (SMR) but can not be described by simple two- or three-shock theories.

In this case according to Ben-Dor, the reflected shock is a smooth band of compression waves of finite thickness near the 'triple point' and as the compression waves radiate from the triple point they converge and steepen into a shock wave. 'The distance over which this happens is too small to be resolved experimentally.' Also, Ben-Dor says that "a comparison between the SMR and vNR reveals that, while in a SMR there is a slope discontinuity between the incident shock wave and the Mach stem, in a vNR the incident shock wave and the Mach stem appear to be a single wave with a smoothly turing tangent near the triple point. Furthermore the slipstream has quite a sharp appearance in SMR-photographs, where as it has a fuzzy appearance in vNR-photographs. As a matter of fact, the slipstream of a vNR resembles a distributed shear layer rahter than a shear discontinuity. Finally the so called 'triple point' of a vNR is not a well defined single point as in the case of a MR."

Only recently (Skews and Ashworth JFM 2005) has the region of the tripple point in a vNR been well captured in experiment. Here the authors argue that their results are consistent with the predictions of Guderley (1947) for the structure in the area of the triple point.

Our experiments do, I believe, a much better job of capturing this vNR with the optics Paul D designed.

* The full Run 42 - two vNR can be seen:

• Closeup from Run 42. 14degree wedge:
  

• Simulation overlay on experiment. Density contours shown: