The Richtmyer–Meshkov instability of heavy/light single-mode (SM), trapezoid (TR) and sawtooth (ST) interfaces is studied experimentally by considering the reshock. The TR and ST interfaces can be expanded into Fourier series with a dominant fundamental mode and more high-order modes, recognized as quasi-single-mode ones. In experiments, the distorted interfaces at the time of first reshock arrival develop in the weakly nonlinear stage, ensuring an approximate single-scale function of evolving interface. The results show an evident memory of initial interface shapes: the bubbles and spikes of ST interface after reshock mainly develop in the streamwise direction with sharp heads, while the counterparts of TR interface tend to grow in the spanwise direction. The influences of high-order modes are amplified by the reshock, resulting in significant interface shape dependence of mixing width growths. The amplitude superposition of major odd-order modes promotes the growth rates of mixing widths for the SM and ST cases, different from the TR one. The ST interface has larger mixing width growth rates in comparison with the SM interface, since high-order modes play a great role in promoting the increase of ST amplitudes, while the TR interface has a relatively small one. The linear and nonlinear mixing width growths of SM, TR and ST interfaces before and after reshock are further analysed theoretically, indicating that the fundamental mode still has a predominant influence on the interface evolution after reshock, and the growth behaviours exhibit strong similarities to those for the singly shocked cases.

The Richtmyer-Meshkov instability of a heavy fluid layer with reshock is investigated experimentally and theoretically, to reveal the mechanisms of the interfacial instabilities and motions of waves and interfaces under reshock conditions. Three kinds of heavy fluid layers with different thicknesses in unperturbed and perturbed cases are considered, highlighting the effects of initial layer thickness on the interface evolution. A general one-dimensional theory for describing the interaction between unperturbed interfaces and waves under reshock conditions is constructed, which supports the instability analysis and theoretical modeling in the perturbed cases. The perturbed fluid-layer results indicate that as the fluid-layer thickness decreases, the inhibition of squeezing effects on perturbation growth is gradually stronger than the promotion of rarefaction-wave effects on perturbation growth. The whole mixing width of fluid layers after reshock acceleration exhibits an approximately linear growth feature, and the reshocked mixing width growth rate is weakly dependent on the initial layer thickness, which is different from the finding before reshock. The linear amplitude growth of the right interface after reshock is promoted by the interface coupling effects but is still smaller than the prediction of the empirical linear model. When the squeezing effects are weak, the nonlinear model which considers the modification of rarefaction-wave effects can well predict the perturbation growth during and after the acceleration stage of rarefaction waves.

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