Published online by Cambridge University Press: 20 April 2006
Electrohydrodynamic instability is described in a planar region of gas, with unipolar injection through a linear temperature gradient, with corresponding mobility, viscosity, and density gradients. The role of charge-relaxation instability, which is incipient at a critical value of electric Rayleigh number in a uniform mobility layer, is distinguished from the mobility-gradient-driven mechanism, which can produce instability at much smaller voltage thresholds. Relative values of electroviscous time, viscous diffusion time and ion transit time determine the nature of the instability process. The instability is stationary or dynamic for wavenumbers respectively below or above a critical value. The fastest-growing wavenumber and corresponding growth rate are determined as functions of time constants and temperature gradient.