Revisiting the initial-amplitude effect on Richtmyer-Meshkov instability

The effect of initial perturbation amplitude has been a focus of research on Richtmyer-Meshkov instability (RMI) for decades.Three principal mechanisms have been advanced as potential explanations: interface geometry, secondary compression, and shock proximity.Nevertheless, disparate interpretations across prior studies have left the dominant mechanisms unresolved.Here, we revisit this long-standing issue through a carefully designed and systematic experimental campaign, providing, to our knowledge, the first direct mechanistic delineation.We demonstrate that secondary compression exerts no influence on linear evolution, whereas interface geometry and shock proximity play differing roles. Moreover, a previously unrecognised mechanism, termed vorticity deposition, is identified.Reduction factors quantifying the interface-geometric mechanism are validated under conditions satisfying their underlying assumption.We further find that the shock-proximity and vorticity-deposition mechanisms are strongly sensitive to shock intensity for Mach numbers below 1.5, but exhibit only weak sensitivity at higher values.Moreover, we reveal that the non-monotonic dependence of growth rate on initial amplitude arises from the coupled action of interface-geometric, shock-proximity, and vorticity-deposition mechanisms, rather than from interface geometry alone.This revisitation resolves a long-standing ambiguity and yields new insight into RMI dynamics.