Effect of acceleration on transition properties in a conical cylinder system

Visualization and spectral studies of the flow between two conical cylinders, with the inner one rotating, revealed different flow modes that were sensitive to the way in which the inner conical cylinder was accelerated until a specified angular velocity was attained. Control of the inner conical body rotation using a computer permitted the quantification and classification of the different flow modes obtained with regard to the non-dimensional acceleration rate dRedt imposed, where Re is the Reynolds number. In the range of Reynolds numbers between 0 and 1000, a transition branch was observed during the transition from the laminar state, according to the acceleration rate dRedt. For very slow acceleration of the inner conical cylinder speed, i.e. dRedt<6.8, a helical downward motion settled in the flow system, while for higher acceleration rates, dRedt⩾6.8, the first observed toroidal vortices were followed by an upward vortical motion. This motion stopped when the Reynolds number was increased, and steady Taylor vortices became established in the fluid column. These Taylor vortices became wavy for higher Reynolds numbers and acceleration. A study of the time dependence of these flow modes showed in particular that only a single periodic wavy mode exists in the range of Reynolds numbers investigated.