Thermodynamics and Energetic Systems Laboratory, Faculty of Physics. University of Sciences and Technology Houari Boumediene, B.P.32 El Alia 16111 Bab Ezzouar. Algiers, Algeria.
The aim of this work is to highlight the critical thresholds corresponding to the onset of different instabilities considered in the flow between two vertical coaxial cones with and without free surface. The inner cone is rotating and the outer one is maintained at rest. Both cones have the same apex angle Φ =12° giving a constant annular gap δ =d/R1max. The height of the fluid column is H=155mm and It can be progressively decreased for each studied case of the flow system. Two kinds of configurations are studied, small and large gap. The working fluid is assumed as Newtonian and having constant properties like density and viscosity within the range of the required experimental conditions. By means of visualization technique of the flow we have been able to show the different transition modes occurring in the conical flow system according to the aspect ratio and then the induced action of the free surface which introduces a delay in the onset of different instability modes. The obtained results in term of features and stability of the flow are compared to those of Wimmer and Noui-Mehidi.