An Interferometric Investigation of the Regular to Mach Reflection Transition Boundary in Pseudostationary Flow in Air.

Abstract

Abstract : The regular (RR) to Mach reflection (MR) transition boundary in pseudostationary flow in air was investigated, with emphasis on the influence of the shock induced boundary layer. Nearly 100 experiments were conducted in the RR to MR transition line over a range of incident shock wave Mach number 1.1 M Ms 6.5 by conducting experiments in hypervelocity shock tube. The wedge angles used were 42, 45, 47, and 48 deg. Initial pressures were kept as low to maximize viscous effects and ranged from 0.4 kPa to 100 kPa. A comparison was made between the boundary layer thickness, and the deviation of the transition boundary from inviscid theory. This difference is called the von Neumann paradox. The von Neumann paradox is due to viscous effects. The deviation of the RR to MR transition line from the detachment criterion boundary was found to increase with a drop in initial pressure, in a manner consistent with boundary layer theory. The effect of the end was boundary layer on the RR to MR transition line was more pronounced at low Mach number (Ms 2), and a model is proposed to explain this behavior. Initial pressure was also found to influence the height of the Mach stem in MR. Lower initial pressure (with greater viscous effects) reduced the height of the Mach stem, which was found to be smaller than the inviscid prediction in all MR experiments. An explanation for the reduction in Mach stem height is suggested, but the causes was not thoroughly investigated. (Canada)