Experimental and numerical study of shock wave interactions near axis of symmetry

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Courant and Friedrics has shown in 1948 that only the irregular reflection (Mach reflection) is possible as a shock wave reflection pattern in an axi-symmetric flow. This drew much attention in the shock wave research community since regular and irregular shock reflections are both possible in shock tube experiments. Extensive investigations were carried out by many researchers and quite a few experimentally obtained images that seem to present regular reflections were reported. However, it is claimed that those images are due to insufficient resolution of the experiments and the decisive conclusions on this subject is not yet made.Under this research project, a shock capturing numerical scheme with unstructured solution-adaptive grids was developed and applied to the subject of shock wave reflection on the axis of axi-symmetric flow. The numerical simulations were done with the high spatial resolution that is difficult to achieve experimentally. And it is found out that the reflection pattern is indeed irregular even when an experimental image showed it to be the regular reflection. This is one of the indications that the numerical simulations are quite important for this research subject.In 1992 Sokolov proposed a gasdynamic mechanism that a shock wave strengthens as it approaches to the axis of symmetry and, as a result, its incident angle always exceeds the transition angle. On the other hand, the non-stationary nature of shock reflections in that a irregular shock reflection always starts as a regular reflection due to viscosity, heat conduction and other non-equilibrium phenomena has been reported. It is now necessary to extend this research subject including such physical phenomena.