Impact of infinitely fast reaction on the dynamics of Marangoni flows

Marangoni flows driven by chemical reactions arise when interfacial tension is modified by reactants or products at an air–liquid interface. We investigate the flow generated by an infinitely fast A+B→C reaction front using direct numerical simulations, with particular emphasis on the origin and structure of the temporal oscillations frequently observed in such systems. Two nondimensional groups are introduced: a physical Marangoni number, MPhys, capturing hydrodynamic interfacial forcing, and a chemical Marangoni number, MChem, representing surface-tension sensitivity to reaction progress. These parameters enable a unified parametric map from which distinct flow regimes are identified. The results show that the lateral displacement of the reaction front depends primarily on MPhys, whereas temporal oscillations are governed by MChem, which exhibits a well-defined critical value marking their onset. While the reactant concentration ratio strongly influences the dynamics, the reactor aspect ratio affects the flow only during the initial transient. The physical Marangoni effect plays a non-monotonic role, enhancing oscillations at low MPhys but suppressing them at high values. Finally, asymmetric reactivity (β≠1) substantially lowers the oscillation threshold, whereas symmetric systems remain the most stable. These findings clarify the coupled hydrodynamic–chemical mechanisms underlying chemically driven Marangoni flows and provide a predictive framework for their control.