When a supersonic flow, M 0 > 1, encounters a straight compressive wedge a straight and attached to the leading edge of the reflecting wedge shock wave is formed provided the reflecting wedge angle is smaller than the maximum flow deflection angle appropriate to flow-Mach number, M 0 .If the reflecting wedge is positioned over a straight surface the oblique shock wave will be reflected from the surface resulting in either a regular reflection, RR, or a Mach reflection, MR. Schematic illustrations of an RR and an MR are shown in Figure 1. While passing through the incident shock wave, i, the oncoming flow is deflected by an angle of θ 1 = θ w , to become parallel to the reflecting wedge surface. The supersonic deflected flow obliquely approaches the bottom surface with an incident angle equal to θ w . The supersonic flow can negotiate this obstacle only with the aids of either an RR or an MR as shown in Figure 1. Two out of a variety of conditions, which were proposed by various investigators, for the RR↔MR transition, in the past 125 years, are extreme. They are the detachment condition beyond which an RR is impossible and the von Neumann condition beyond which an MR is impossible. Von Neumann [1] was the first to introduce these two conditions as possible RR↔MR transition criteria.Hornung & Robinson [2] showed that the RR↔MR transition criterion in steady flows depends upon whether M 0 is smaller or larger than M 0C , which is the value