Interfacial-dominated torque response in liquid-liquid Taylor-Couette flows

Immiscible and incompressible liquid-liquid flows are considered in a Taylor-Couette geometry and analysed by direct numerical simulations coupled with the volume-of-fluid method and a continuum surface force model. The system Reynolds number Re -riwid/nu is fixed to 960, where the single-phase flow is in the steady Taylor vortex regime, whereas the secondary-phase volume fraction q) and the system Weber number We- (p)r(i)(2) w(i)(2)d/sigma are varied to study the interactions between the interface and the Taylor vortices. We show that different Weber numbers lead to two distinctive flow regimes, namely an advection-dominated regime and an interface-dominated regime. When We is high, the interface is easily deformed because of its low surface tension. The flow patterns are then similar to the single-phase flow, and the system is dominated mainly by advection (advection-dominated regime). However, when We is low, the surface tension is so large that stable interfacial structures with sizes comparable to the cylinder gap can exist. The background velocity field is modulated largely by these persistent structures, thus the overall flow dynamics is governed by the interface (interface-dominated regime). The effect of the interface on the global system response is assessed by evaluating the Nusselt number N-uw based on the non-dimensional angular velocity transport. It shows non-monotonic trends as functions of the volume fraction phi for both low and high W-e. We explain how these dependencies are closely linked to the velocity and interfacial structures.

Automated summary

This study investigates the behavior of immiscible and incompressible liquid-liquid flows in a Taylor-Couette geometry using direct numerical simulations coupled with the volume-of-fluid method and a continuum surface force model. The interactions between the interface and the Taylor vortices are studied by varying the secondary-phase volume fraction and the system Weber number. The results reveal two different flow regimes depending on the Weber number, namely an advection-dominated regime and an interface-dominated regime.