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COHERENCE AND REYNOLDS STRESSES IN THE TURBULENT WAKE BEHIND A CURVED CIRCULAR CYLINDER

Jose P. Gallardo
Department of Marine Technology Norwegian University of Science and Technology NO-7491 Trondheim, Norway

Bjornar Pettersen
Department of Marine Technology, Norwegian University of Science and Technology,NO-7491 Trondheim, Norway

Helge I. Andersson
Department of Energy and Process Engineering, Norwegian University of Science and Technology, Trondheim, Norway

Résumé

The turbulent wake behind a curved circular cylinder is investigated based on data from a direct numerical simulation. A second-order finite-volume solver with an immersed boundary method was used to solve the incompressible Navier−Stokes equations. In this paper we analyse the instantaneous vortical structures, the proper orthogonal decomposition (POD) of the flow, and relevant Reynolds stress components. Despite the complexity of the instantaneous vortical structures, the wake dynamics are governed by the quasi-periodic shedding of primary vortices. Between 24% and 50% of the kinetic energy in the POD is captured by the two most energetic modes, and about 200 modes are needed to capture 90% of the kinetic energy. These findings suggest that the present case is suited for a low-dimensional representation. The magnitude of the Reynolds stresses varied considerably depending on the depth at which they where sampled. This dependence is likely related to the strength of the vortex shedding and the intensity of the secondary flows induced by the curvature of the cylinder. As a consequence of the combination of these two effects, the correlation between streamwise and vertical velocity fluctuations is highest at around half the depth of the curved cylinder.