Numerical study on droplet deformation in periodic pulsatile shear flow and effects of inertia

Abstract

Abstract Single droplet deformation in pulsatile shear flow is numerically studied by using meso-scopic dissipative particle dynamics method. Numerical model and simulation method are fully validated with three typical cases in which transient flow behaviors are well captured. Cases in quasi-Stokes regime are first investigated with flow Reynolds number to be less than O ( 1 0 − 2 ) . In early stage, droplet deforms gradually in the manner of periodic oscillation but irreversible. Later, droplet deformation gets into a stable state of oscillation and becomes reversible. The mean deformation parameter in stable state is frequency independent and its relationship to mean Capillary number is close to the trend in steady shear. Cases with finite inertia are studied with flow Reynolds number to be approximately to 1. In contrast, the inertial effects make the mean deformation parameters have a strong frequency dependence. The shear and relax tests are conducted to explain above dynamic behavior of droplet deformation. It is found that the droplet deformations in shear and relax are antisymmetric in quasi-Stokes regime while in finite inertia regime droplet deforms slower in shear process than it is in relax process. The frequency dependent behavior of droplet in pulsatile shear might provide a reliable strategy in the control of droplet deformation.