EARLY BIFURCATION IN ROTATING FLUID-FLOW WITH FREE-SURFACE STUDIED BYAXISYMMETRICAL NUMERICAL SIMULATIONS

Simulations of a fluid rotating inside a partially open cylindrical ca vity, performed by numerical solution of the unsteady axisymmetric Nav ier-Stokes equations, are presented. The configuration consists of a c ylindrical vessel holding the fluid, which is entrained into motion by a rotating lid. This one is a coaxial disk in contact with the fluid surface but without covering it entirely. The study focuses on the occ urrence of time-dependent flow, more specifically, the first transitio n to unsteadiness, by considering cavity cases with different amounts of free surface, for a fixed aspect ratio. By following the time evolu tion of a few arbitrarily chosen dynamical variables as a function of the Reynolds number, the location of this first Hopf bifurcation is ob tained for a collection of cavity cases. Results show a rather strong influence of the free surface both on the onset of the unsteadiness an d on the dynamical features of the flow. (C) 1996 American Institute o f Physics.