BINARY-FLUID CONVECTION IN A ROTATING CYLINDER

The onset of convection in binary fluid mixtures in a rotating vertica l cylinder is considered. Parameter values and boundary conditions rel evant to experiments on He-3-He-4 mixtures with negative separation ra tio are used. The eigenfunctions take the form of rigidly precessing s pirals. The azimuthal wavenumber of the first unstable mode as the Ray leigh number increases is calculated as a function of the rotation rat e and the separation ratio, as are the critical Rayleigh numbers and p recession frequencies. Depending on the parameters the spirals may tak e the form of spatially extended body modes which fill the container, or of wall modes confined to its boundary. The former typically preces s in the retrograde direction,while the latter are prograde. Under app ropriate circumstances the binary system with a negative separation ra tio becomes unstable for lower Rayleigh numbers than a pure fluid. Thi s property of the system is enhanced by the wall modes. (C) 1995 Ameri can Institute of Physics.