Investigation of coupling effect on the evolution of Richtmyer-Meshkov instability at double heavy square bubbles

This study investigates numerically the coupling effect on the evolution of Richtmyer-Meshkov instability at double heavy square bubbles.Five scenarios are considered,each with varying initial separations S/L(where L demotes the side length of the square)ranging from 0.125 to 1.0.Squares are filled with SF6gas,and are enclosed by N2gas.The simulations of shock-induced multispecies flow are performed by solving the two-dimensional compressible Euler equations with a higher-order explicit modal discontinuous Galerkin solver.The simulations demonstrate that the flow morphology resulting from the coupling effect is highly dependent on the separation between two squares.When the separation is large,the squares experience a weaker coupling effect and evolve independently.While,as the separation reduces,the coupling effect manifests earlier in the interaction and becomes more substantial.As a result,this phenomenon greatly intensifies the motion of inner upstream/downstream vortex rings towards the symmetry axis,leading to the emergence of multiple jets such as the twisted downward,upward,and coupled jets.A thorough exploration of the coupling effect of double squares is conducted by analyzing the vorticity production.Notably,a significant quantity of vorticity is produced along the squares interface for smaller separation.Further,these coupling effects result in various interface features(upstream/downstream movement,and height/width evolution),and temporal variations of various spatially integrated fields.Finally,the analysis of the flow structure also considers the interaction between two more flow parameters,the Mach and Atwood numbers,in order to evaluate the coupling effects.