Influence of confinement on obstacle-free turbulent wakes

Large-eddy simulations (LESs) of obstacle-free wakes, in a channel like geometry with an homogeneous transverse direction, are carried out in order to investigate the influence of confinement on turbulent wakes. The numerical solver makes use of a multi-domain Fourier-Chebyshev spectral method and the LES capability is implemented through a spectral vanishing viscosity technique. A top hat like velocity profile is imposed at the inlet and both no slip and free slip conditions are considered at the confining walls. Prescribing the velocity ratio, defined as the ratio of the velocity gap to the mean velocity, we study the influence of confinement on such flows at the Reynolds number Re = 5000. Several quantities are analyzed, as one-dimensional velocity spectra, third order-velocity structure function, turbulent kinetic energy and its dissipation rate. It turns out that for obstacle-free wakes confinement increases the intensity of turbulence and its three-dimensional feature, as e.g. pointed out by Lumley diagrams, in agreement with numerical and experimental results obtained for confined cylinder wake flows. Finally, comparing no slip simulation results with free slip ones, we also point out the role of boundary layers. (C) 2011 Elsevier Ltd. All rights reserved.