On the CFD Analysis of a Stratified Taylor-Couette System Dedicated to the Fabrication of Nanosensors (original) (raw)

An Experimental Investigation of Flow Mode Selection in a Conical Taylor-Couette System

2001

Transitions of viscous flow between coaxial conical cylinders with the inner one rotating and the outer one at rest were investigated to reveal mode selection of the first instabilities with the aid of flow visualization and spectral analysis. The rotational velocity of the inner conical cylinder was linearly accelerated from rest until reaching its final speed. The different observed states were successfully distinguished by their dependency on the acceleration rate β in the investigated range of Taylor number Ta. Transitions between states were determined as functions of β and Ta by fixing the Taylor number and varying the acceleration rate in the range 0.01-1.5 rad/s2. Observed states were classified into: first toroidal vortices (FTV), helical motion (HMV), upward travelling vortices (UTV), steady Taylor vortices (TVF) and wavy vortices (WVF). Modes of six pairs of Taylor vortices (6TVF), seven pairs (7TVF) and eight pairs (8TVF) were observed at the same Ta and different β. Steady Taylor vortices and wavy vortices were also observed when β increased at the same Ta. The spectral analysis indicated that the states HMV and WVF have constant ratios between the characteristic frequencies and the frequency of rotation of the inner conical cylinder, while in UTV the ratio decreases with increasing Ta. The mode selection diagram in the (Ta,β) plane has no regular form with regard to the zones delimiting the different observed states.

Direct Numerical Simulations of Taylor-Couette Flow using a Hybrid Spectral/Finite Element Approach

We perform simulations of the flow between two co-axial cylinders, where the inner cylinder is rotating and periodicity is assumed in the axial direction (Taylor-Couette flow). The computations are performed using two different approaches: (1) the solution unknowns are discretized by means of a truncated Fourier series in the axial direction and using linear finite elements in planes perpendicular to the axis of rotation or (2) a truncated Fourier series is used in the azimuthal direction, combined with linear finite elements in planes containing the axis of rotation. We concentrate on flows in the laminar and transitional regime. The computed flow fields contain the well-known families of Taylor vortices, that are either axisymmetric or spiralling, depending on the considered Reynolds and Taylor numbers. Results obtained using both numerical approaches are found to be in reasonable agreement. In addition, our computed values for the mean kinetic energy, angular momentum, en-strophy...