| Popis: |
We have conducted a flow-visualization and spectral survey of the flow patterns in a circular Couette system with both cylinders rotating [1]. The ranges of occurrence of previously reported flows and some newly observed flows have been determined as functions of the inner- and outer-cylinder Reynolds numbers (Ri and Ro, respectively) for a system with radius ratio 0.883 and aspect ratio 30 (the upper and lower boundaries were attached to the outer cylinder). The flow transitions were located by fixing Ro and slowly increasing Ri; by decreasing Ri several of these transitions were found to have hysteresis. Pattern velocities have been measured for some cases for flows between both counter- and co-rotating cylinders. For example, the turbulent spiral found between counter-rotating cylinders was found to move at an angular velocity of about 0.5Ωο, independent of Ri, for low outer cylinder speeds (Ωο is the angular velocity of the outer cylinder). The following new flows were found with counter-rotating cylinders: (1) wavy spirals (waves on laminar spiral vortices), (2) modulated wavy vortices (two waves on Taylor vortices) at very low Ri, and (3) V-shaped turbulence (a sometimes long- lived transient state of competing right- and left-handed spiral turbulence). We have also characterized several previously reported flows including spiral turbulence, intermittency, and laminar spiral vortices. The time-dependent flows found for co-rotating cylinders consist of periodic, multiply periodic or nonperiodic waves on Taylor vortices [2]. These flows include wavy-inflow and outflow boundary states, wavelets (both boundaries have waves, but they move at different velocities), twists (rope-like patterns internal to the vortices), and combinations of these. Interestingly, the wavy-inflow and outflow boundary states were found to have an axial periodicity extending over two Taylor vortex pairs, twice the axial wavelength of the usual wavy vortex flow. |
