Electrokinetic Manipulation of the von Kármán Vortex Street in the Wake of a Confined Cylinder. I. DC Electric Field

Abstract

The present study is concerned with the numerical simulation of the pressure-driven flow around a confined cylinder subjected to a DC electric field. The flow situation differs from the conventional von Karm´ an vortex street flow in terms of confinement. Additionally, the DC electric field induces a very small but finite electrokinetic velocity at the cylinder surface in contrast to the no-slip velocity in the conventional case. Various numerical simulations are performed in the Laminar Vortex Shedding Regime to investigate the influence of the confinement and the direction and strength of the electric field. For flows without electrokinetic manipulation, the blockage ratio shifts the critical Reynolds number to higher values. Likewise, the dimensionless shedding frequency (Strouhal number) at a given Reynolds number increases with increasing blockage ratio. For flows with electrokinetic manipulation, the time that is required to obtain a steady Laminar Vortex Shedding Regime is reduced compared to the corresponding pure pressure-driven flow. Steady electrokinetic manipulation does not influence the dimensionless shedding frequency. The reduction of the transient is related to differences in the flow topologies around the cylinder. The electrokinetic velocity breaks the axial flow symmetry of the Laminar Steady Regime and therefore accelerates the onset of the Laminar Vortex Shedding Regime.