Investigation of a buoyancy-driven instability during horizontal miscible displacement*

Hydrodynamic instabilities in miscible reactive systems have significant impact on applications such as: CO₂ sequestration, soil reparation, or particle formation in precipitation systems. A buoyancy-induced instability has been observed when a fluid horizontally displaces another miscible fluid of different density, resulting in a complex flow field. With this study, we intended to characterize the flow patterns in such systems and to investigate their dependence on parameters such as the injection flow rate and the fluids density difference. We performed reactive and non-reactive experiments in a microscale geometry and explored the intricate 3D flow conditions of the system, using micro-Particle Image Velocimetry. The results evidence the existence of flow structures present in equivalent numerical studies and reveal the dependency of the instability on the direction of the displacement.