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REGENERATION CYCLE OF VORTICAL STRUCTURES AND INTERMITTENCY IN HOMOGENEOUS SHEAR FLOW

Paolo Gualtieri
Dipartimento di Ingegneria Meccanica e Aerospaziale, 'Sapienza' University, Via Eudossiana 18, 00184 Roma, Italy

Carlo M. Casciola
Department of Mechanics and Aeronautics, 'Sapienza' University of Rome, Via Eudossiana 18, 00184 Rome, Italy

Renzo Piva
Department of Mechanics and Aeronautics, "Sapienza" University of Rome, Via Eudossiana 18, 00184 Rome, Italy,

Résumé

We consider a homogeneous shear flow in a confined box in order to analyze under simplified conditions the interaction of a mean velocity gradient with the turbulent fluctuations. Despite its geometrical simplicity, the evolution of this system is characterized by a cyclic behavior associated with the regeneration of the vortical structures which, in turn, by the Reynolds stresses, induce bursts in the kinetic energy. Purpose of the work is to discuss the statistical properties of the velocity fluctuations, here analyzed in terms of the extended self similarity, to understand to role of the mean shear on the scaling laws of the structure functions. When the effect of the shear is prevailing, i.e during the phases of Reynolds stress activity, the structure functions clearly manifest a double scaling regime. Theoretical considerations are discussed to link the double scaling and the increased intermittency found in shear dominated flows with respect to homogeneous isotropic turbulence.