Electroconvective instability in a fluid layer

Abstract

Steady flows of a fluid of slight electrical conductivity under the influence of an applied electric field intensity are often unstable. A study is described to illustrate with experiments and an analytical model the fundamental aspects of a wide range of instabilities that are characterized by the incipience of steady cellular convection as the electric Hartmann number H a e = ∈ E /√(μσ) is of the order of unity (∈ is the permittivity, E the imposed electric field intensity, μ the viscosity, and σ the electrical conductivity). A non-uniform electric field is used to induce an unstable configuration of surface charge and electric field intensity at a planar interface. The resulting instability leads to cellular convection in the plane of the interface. Predictions of the electric Hartmann number and wavelength for incipience of instability compare favourably to measurements. The dependence of the measured cellular convection velocity, resulting from the instability, on electric Hartmann number and electric Reynolds number are also in satisfactory agreement with the predictions from the simple model.