Abstract Two-dimensional direct numerical simulations (DNS) were conducted to investigate the effect of a reversible reaction of a type A⇌ B on the dynamics of viscous fingering (VF) instability in a Hele-Shaw cell containing two partially miscible fluids. We demonstrate that the reaction evolves the whole system to a transient state having concentration 0.5 and that the reaction completely suppresses the finger fragmentation resulting in droplets during spinodal decomposition in partially miscible fluids. Furthermore, through linear stability analysis (LSA), we show that for Damköhler numbers Da5×10−3 the whole system sitting at the transient state 0.5 phase separates into the two-coexisting phases having equilibrium concentrations, and the phase-separated domains evolve into viscous fingers and align with the flow direction. For Da5×10−3, we do not observe any fingers, and the whole system remains at the uniform concentration 0.5 as its final stable state without undergoing phase separation. We find that the reaction selects a specific wavelength for the phase-separated fingers for Da≤5×10−3. Furthermore, space-time maps show that the reaction also reduces the width of the mixing zone caused by the VF instability. These findings support the effectiveness of the reaction as a mechanism for controlling VF in partially miscible fluid pairs. We hence believe that the morphology of the system can be used to fabricate a functional material, and it will play a crucial role in determining the material’s performance. We can employ this mechanism to enhance sweeping efficiency in polymer flooding, where suppressing VF leads to enhanced oil recovery.
Tiwari et al. (2026) studied this question.