Finite-amplitude traveling-wave convection in binary fluid mixtures

Abstract

We have performed flow-visualization and heat-transport measurements of convection in ethanol-water mixtures. For experimental parameters in the range studied, the Soret effect suppresses the onset of convection relative to that in a pure fluid. A simplified model predicts that flow will begin via a forward bifurcation to an oscillatory state of spatially fixed rolls in which the direction of circulation periodically reverses. For larger values of the Rayleigh number (i.e., the temperature difference applied across the fluid layer), nonlinear theory predicts a hysteretic transition to steady convection. Contrary to the expectations based on this model, we find no forward bifurcation at onset, but rather, an exponentially growing oscillatory transient which triggers a finite-amplitude convective state. The nonlinear state is not steady but instead consists of convective rolls which move laterally in the plane of the fluid layer, as traveling waves. In this paper, we describe the behavior of these traveling-wave states as a function of fluid properties and of the Rayleigh number.