Convection in Viscoelastic Fluids

Abstract

Nonequilibrium systems like Rayleigh-Benard convection in external temperature gradient or Taylor instability between rotating cylinders, have been much studied, theoretically and experimentally in recent years. Of particular interest are systems like Rayleigh-Benard convection in binary mixtures [1–5], or Taylor instability in counterrotating cylinders [6,7], which display, depending on external parameters, two types of instabilities at threshold: stationary and oscillatory. Consequently their phase diagrams contain codimension 2 points, which are often accompanied by tricritical points on the instability branches. In the past much attention has been focused on studying binary mixtures in thermal convection. It would be interesting, however, to study another system exhibiting codimension 2 point in a convection experiment. A possible candidate for such a system are viscoelastic fluids. It has been predicted [8], that in thermal convection viscoelastic fluids should exhibit an oscillatory instability at threshold and a codimension 2 point of a different type than the binary mixtures [9]. It was also suggested, that due to this different properties new and interesting nonlinear behavior should be expected in the neighborhood of the codimension 2 point [9, 10].