Electrohydrodynamic migration of a spherical drop in a general quadratic flow

TL;DR

This paper analytically studies the electrohydrodynamic migration of a spherical drop in a quadratic flow under an external electric field, revealing electric field-induced cross-stream migration in a leaky dielectric medium.

Contribution

It provides a coupled electrohydrodynamic model for a spherical drop in quadratic flow with an external electric field, including analytical solutions for small electric Reynolds number.

Findings

Electric field can induce cross-stream migration of the drop.

Migration direction depends on electric field orientation and electrical properties.

Analytical solutions for electric potential and flow field are derived.

Abstract

We investigate the motion of a spherical drop in a general quadratic flow acted upon by an arbitrarily oriented externally applied uniform electric field. The drop and media are considered to be leaky dielectrics. The flow field affects the distribution of charges on the drop surface, which leads to alteration in the electric field, thereby affecting the velocity field through the Maxwell stress on the fluid-fluid interface. The two-way coupled electrohydrodynamics is central towards dictating the motion of the drop in the flow field. We analytically address the electric potential distribution and Stokesian flow field in and around the drop in a general quadratic flow for small electric Reynolds number (which is the ratio of the charge relaxation time scale to the convective time scale). As a special case, we consider a drop in an unbounded cylindrical Poiseuille flow and show that, an otherwise absent, cross-stream drop migration may be obtained in the presence of a uniform electric field. Depending on the direction of the applied electric field and the relative electrical properties of the drop and media, the drop may migrate towards or away from the centreline of the imposed Poiseuille flow.