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Ecoulements de type rotor-stator soumis à un flux axial: de Batchelor à Stewartson

Abstract : This experimental and numerical study deals with the characterization of rotor-stator flows when an axial throughflow is superimposed according to two aspects: turbulence and stability.

New velocity measurements are compared to the predictions of an advanced Reynolds Stress Model essentially for turbulent flows with separated boundary layers. In a closed cavity or when a
centripetal throughflow is superimposed, the flow structure is of Batchelor type: the boundary layer on the rotor and the one on the stator are separated by a central rotating core. The tangential velocity in the core is proportional to the local disk speed with the proportionality coefficient $K$. This coefficient can be determined by using a local flowrate coefficient according to a simple analytical law with two coefficients depending only on the prerotation level of the fluid. This law is independent on the interdisk space and on the geometry of the cavity. For strong centrifugal throughflows, the flow structure switches to Stewartson type with only one boundary layer on the rotating disk. The transition between these two flow structures can be characterized by a Rossby number based on the radial gap between the rotor and the shroud. This transition is continuous and does not depend on the geometry. Turbulence is concentrated in the two boundary layers and increases towards the periphery of the cavity. When a throughflow is superimposed, the relaminarized area close to the axis disappears and the turbulence intensity is maximum in the outlet and inlet areas.

The influence of a throughflow on the stability of torsional Couette flows, mixed flows and Batchelor flows has been investigated from flow visualizations. The circle and spiral networks as well as the solitary waves and the turbulent spots observed in the case of a closed cavity subsist when a throughflow is superimposed but the appearance thresholds are moved. Some new instabilities appear also. A ``crossflow'' instability, generic of these type of flows, has been observed. These are positive spirals, denoted RSJ2, located at the periphery of the cavity closed to the stator boundary layer. It is due to the inflexion point in the axial profil of the radial velocity component.
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Contributor : Sébastien Poncet <>
Submitted on : Friday, November 25, 2005 - 10:40:17 AM
Last modification on : Thursday, January 23, 2020 - 6:22:06 PM
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  • HAL Id : tel-00010993, version 3



Sébastien Poncet. Ecoulements de type rotor-stator soumis à un flux axial: de Batchelor à Stewartson. Mécanique []. Université de Provence - Aix-Marseille I, 2005. Français. ⟨tel-00010993v3⟩



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