The interface between fluid-like and solid-like behavior for drops suspended in two-phase Couette flow

The flow of two-dimensional buoyant drops in a horizontal channel is studied by numerical simulations at finite Reynolds numbers. A linear shear flow is assumed inside the channel. The study is similar to that performed by Zhang and Campbell in granular flow regime (Zhang and Campbell in J Mech 237:541-568, 1992). The areal fraction is relatively large (0.72), and the flow is studied as a function of the bulk Reynolds number, a Reynolds number defined based on the acceleration due to gravity, and the capillary number. It is found that for a single drop motion the drop obtains an equilibrium position inside the channel. The equilibrium position is validated by comparing with other efforts. Results at a high areal fraction are compared to the work by Zhang and Campbell. The average velocity profile across the channel is relatively different compared to granular flow regime. The average fluctuation energy shows similar trends across the channel. The fluctuation energy is significantly lower on the average in the present study. The average normal stress (load) is also lower compared to granular flow regime. It is expected that this is due to the effect of interstitial fluid present in the present study.