Méthodes analytiques de caractérisation des structures cohérentes contribuant aux efforts aérodynamiques

Abstract : The link between the fluid force applied on a body and the coherent structures is obvious ; however there is no direct relationship between each structures and their contribution to the force. This issue is divided into two main parts : first the definition of a force density, and then a definition of coherent structures adapted to the force density definition. We show that the force formulation must not include any pressure term in order to characterize the coherent structures in a fluid domain ; moreover the contribution on the domain boundary must be negligible. We study two formulations of the force in details and show that the diffusive formulation, using an impulse of vorticity laplacian, is the only one able to give a real volume definition of the force. Using this formulation on a 2D flow around a cylinder in the von Kármán regime, we study the contributions to the force of two flow parts defined with the vorticity laplacian : the vortex layers and the back-flow region. The first are found to capture the viscous force, while the latter captures the interaction effects between the cylinder, the vortex layers and the roll-up. It is interesting to observe that the domain used to calculate the force does not include the wake ; the force density captures their influence through the induced vorticity near the base of the cylinder. The 3D application of the diffusive formulation needs a very accurate calculation of the vorticity laplacian, especially near the wall. We show that this method cannot be easily applied on complex flows with the current numerical solvers.
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Submitted on : Thursday, January 6, 2011 - 3:15:08 PM
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Lionel Fiabane. Méthodes analytiques de caractérisation des structures cohérentes contribuant aux efforts aérodynamiques. Mécanique des fluides [physics.class-ph]. Ecole Polytechnique X, 2010. Français. ⟨pastel-00553103⟩

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