The control and characterization of jet interactions have been central issues in high-altitude aerodynamics and vacuum system design, where the flow behavior is strongly influenced by rarefaction effects. This study employs the direct simulation Monte Carlo method to investigate the flow properties of hypersonic rarefied impinging jets over wide ranges of the Knudsen number (Kn), Mach number (Ma), and aspect ratio (AR). The results demonstrate that the flow exhibits three distinct regimes: deflection, symmetry, and penetration. At low Kn, the flow undergoes deflection accompanied by imbalanced recirculation zones. As Kn increases, the flow transitions to the symmetry regime with balanced vortical recirculation zones. When the flow becomes sufficiently rarefied, a penetration regime emerges in which some gas molecules pass through the impingement region and reach the opposite jet inlet and the adjacent wall surface. Moreover, the results show that higher Ma and AR lower the critical Knudsen number (Knc) for the transition to the penetration regime. Comprehensive regime maps are constructed to determine Knc for transitions among the three regimes. Finally, a theoretical model is developed based on the comparison between the mean collision time and the characteristic flow time to explain the dependence of Knc on Ma and AR. This study advances the understanding of rarefied gas dynamics and provides guidance for the design and operation of systems operating in high-altitude and vacuum environments.
Liu et al. (Wed,) studied this question.