Study on Shock-Induced Gas/Water Interface Instability Based on Fourier Analysis

Shock-induced gas/water interfacial instability is important in multiphase flow processes involving rapid deformation, mixing, and breakup. In this study, the evolution of shock-impacted gas/water interfaces was investigated using high-speed images from previously conducted shock-tube experiments and two-phase numerical simulations. Interface contours were extracted through digital image processing, and spatial Fourier analysis was used to describe the modal evolution of interfacial perturbations. A numerical model based on the VOSET interface-capturing method and the SST k − ω turbulence model was established, with the compressibility of both phases considered. A mode number–amplitude–time (K-L-t) diagnostic framework was proposed. The results show that this framework can distinguish the dominant stages associated with Richtmyer–Meshkov (RM), Rayleigh–Taylor (RT), and Kelvin–Helmholtz (KH) instabilities. In the double-liquid-column case, the downstream interface exhibits a delayed transition, which may be associated with shielding and wake interference. Increasing the shock Mach number accelerates modal growth and advances the transition times, whereas increasing the liquid-column diameter delays the instability evolution because of larger inertia. A modified RM dispersion equation incorporating compressibility and finite-thickness effects was further proposed, showing improved agreement with the CFD-extracted initial growth rates.