Different aspects of the transition between regular and Mach re ections of strong shock waves in steady ows are numerically studied. Two approaches-kinetic (the direct simulation Monte Carlo method) and continuum (Euler equations)-are used to investigate the hysteresis phenomenon in the ow about two symmetrical wedges in two-and three-dimensional statements. The dependence of the nal shock wave con guration on initial conditions, the transition from regular to Mach re ection by means of ow perturbations, and three-dimensional effects are examined. The three-dimensionality of the ow is shown to increase the angles of transition from regular to Mach re ection and back and to decrease the Mach stem height.
IntroductionT HE hypothesis that a hysteresis phenomenon may exist in the transition between regular re ections (RR) and Mach re ections (MR) of strong shock waves in steady ows was rst put forward by Hornung et al. 1 They assumed that, when the angle of incidence ® changes smoothly, the transition from RR to MR and the reverse transition occur at different ® values. An attempt to assess this hypothesis was performed experimentally by Hornung and Robinson 2 and gave a negative result: No hysteresis was observed. They concluded that a possible reason might be the disturbances present in wind-tunnel ow. 2 Recently, though, the hysteresis was obtained experimentally by Chpoun et al. 3; 4 and numerically by Ivanov et al. 5 using the direct simulation Monte Carlo (DSMC) method. In later papers by Ivanov et al. 6 -9 the hysteresis phenomenon was examined carefully using two numerical approaches: kinetic and continuum. These numerical studies proved the existence of the hysteresis in accordance with the prediction of Hornung et al. 1 As for the experimental results of Chpoun et al., 3 ;4 some details of this work, such as the angle of transition from RR to MR, ® tr , do not correspond to what comes from the hypothesis of Hornung et al. 1 (® tr was 37.2 deg instead of ® D D 39:3 deg for M D 4:96). This was probably caused by three-dimensionaleffects, which were fairly signi cant in these experiments, where a wedge model with a small spanwise size was used. The contradiction motivated conducting new experiments 10 where different aspect ratios, i.e., ratios of spanwise to streamwisesize, from 0.66 up to 3.75, were used. The existence of hysteresis was con rmed there, but the total agreement of experimental and numerical data was not obtained.The dif culties of experimental studies of the hysteresis phenomenon are caused by acoustic and other perturbations inherent in any aerodynamic wind tunnel and also the problem of obtaining results with no in uence of three-dimensionality.These dif culties may be easily avoided if a numerical simulation is performed. The numerical approach gives an opportunity of not only assessing the impact of different perturbations and three-dimensionality but also elaborating a strategy for future experimental work. This paper is aimed at continuing the numerical study of various aspects of the pr...