Computational investigation of the Kelvin–Helmholtz instability: from Thorpe’s experiment to reactive flows

Abstract A computational study of the Kelvin–Helmholtz instability is presented, combining classical experimental configurations with multiphase flow simulations and extending the analysis to prototype reactive systems. Thorpe’s benchmark experiment is reproduced numerically using the Volume of Fluid (VOF) method, enabling accurate prediction of onset time, critical wavelength, and velocity thresholds. The simulations agree with theoretical and experimental results while revealing the influence of viscosity and geometry on instability development. Beyond the non-reactive case, the framework is extended to chemically reactive shear flows by introducing a simple reaction A + B → C. Viscosity stratification induced by the reaction product is shown to alter the velocity profile, generating inflection points that trigger or suppress instability depending on viscosity contrast. Specifically, lower-viscosity products accelerate the growth of interfacial waves, whereas higher-viscosity products stabilize the flow. The results underline the importance of coupling hydrodynamic and physicochemical effects in multiphase instability mechanisms, with implications for chemical processing, energy systems, and natural flows.