Three-dimensional centrifugal instabilities development inside a parallelepipedic open cavity of various shape |
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Authors: | Thierry M Faure Luc Pastur François Lusseyran Yann Fraigneau Danièle Bisch |
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Institution: | (1) Laboratoire d’Informatique pour la Mécanique et les Sciences de l’Ingénieur, Unité Propre de Recherche 3251, Centre National de la Recherche Scientifique, B.P. 133, 91403 Orsay Cedex, France;(2) Université Pierre et Marie Curie, Paris 6, 4 Place Jussieu, 75252 Paris Cedex 05, France;(3) Université Paris-Sud, Paris 11, 91405 Orsay Cedex, France |
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Abstract: | This experimental study reports flow developments inside a parallelepipedic cavity of variable shape and dimensions. That
flow is generated by the interaction between a laminar boundary layer and the cavity, which creates shear-layer oscillations.
The aim is to understand the three-dimensional flow morphology varying the Reynolds number and the cavity shape. Flow visualizations
are obtained in a plane situated inside the cavity in order to get the dynamical structures. Dimensional analysis of the cavity
flow teaches that three dimensionless numbers are necessary for the flow reduction. This is confirmed by experimental results
pointing thresholds of appearance of instabilities identified for some combinations of Reynolds number and geometric parameters.
The key mechanisms for their existence are centrifugal effects induced by a vortex of spanwise axis with sufficient intensity,
and viscous effects due to the wall confinement of the cavity. Their destruction is linked to flow transition to turbulence
above a limiting convective velocity generated by the vortex of spanwise axis. These instabilities are generally present in
a spanwise row of counter-rotating pairs of vortices, but for some cases, isolated pairs are also identified. Secondary modulations
of primary instabilities are also present for particular parameters. Results permit to discriminate the relevant scales associated
with the shear layer and the inner cavity flow. |
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