Effects of wave configuration parameters on the evolution of non-standard Richtmyer–Meshkov instability

The instability of a flat interface driven by Mach-reflection wave configurations is numerically investigated. These configurations are generated by diffracting a planar shock around rigid cylinders. Independent control of the triple-shock parameters (shock strength and incidence angle) and Mach stem length is achieved by varying the spacing ratio η=l/d (l: cylinder-interface distance; d: cylinder diameter) together with d, enabling a decoupled analysis of their effects. The complete evolution from cavity to a Λ-shaped interface with a jet-like bubble is captured for the first time. Three growth phases are identified: rapid start-up, a linear stage with nearly constant growth rate, and a nonlinear stage with a secondary increase. Triple-point impingement creates spikes curling inward, colliding on the axis, and driving a jet into the cavity, pushing a central spike backward. Slip line curling generates a counter-rotating vortex pair impinging on the cavity bottom, forming a bulge and enhancing growth. This curling also drives spike curling, initially suppressing growth, whereas collision provides the final acceleration. The growth rate decreases markedly with η, reflecting the dominant influence of the triple-shock parameters. Furthermore, the Mach stem length controls the timing of spike curling and collision, introducing an independent timescale; a smaller stem length yields an earlier nonlinear transition but a lower growth rate. Existing models fail to predict the perturbation growth because they neglect reflected shock effects and the start-up phase. These findings provide a comprehensive description of this non-standard Richtmyer–Meshkov instability and a benchmark for future modeling.