Interaction Effect of Two Ellipse Richtmyer-Meshkov Flows

The dynamic evolution process and velocity field of two elliptic heavy-gas (SF₆) cylinders accelerated by a planar shock wave are studied by laser-sheet high-speed photograph and PIV (particle image velocimetry) diagnostics techniques, respectively.The minor axes (b) of the elliptic cross-sections are aligned perpendicular to the shock direction.While the cylinder dimensions are fixed, we adjust the center-to-center separation (d) between the cylinders.The flow morphologies are visualized and the interaction effect between cylinders is analyzed.When d/b equals 4.0 or 3.0, the two elliptical cylinders roll up into 2 counter-rotating vortex pairs and the interaction is weak.The maximal velocity appears at 2 positions and its magnitude is close to 30 m/s, while the minimal velocity is close to zero and arises at 4 positions.Whend/b decreases to 2.0 or 1.2, due to the strong interaction of the two inner vortices, the inner structure completely disappears and the flow morphology evolves into a counter-vortex pair.The maximal velocity occurs at 4 locations, while the minimal velocity only appears at 2 positions.For the d/b =2.0 case, the evolving images assemble those of the single circular cylinder except for the small gap in the middle.Compared with the d/b =2.0 case, larger amount of baroclinic vorticity is produced in the d/b =1.2 case, and the morphology is similar to the single elliptic cylinder case, with a second vortex phenomenon and bifurcation structure occurring at later times.Actually, we observe a nonlinear, threshold-type behavior of inner vortex formation when d/b varies from 2.0 to 3.0.Finally, we outline and discuss 4 possible mechanisms which may lead to the obvious weakening phenomenon of inner vortices.