SPATIAL DISTRIBUTION OF ENERGY DISSIPATION IN A TURBULENT CYLINDER WAKEJiangang Chen SinopsisThis work aims to improve our understanding of the turbulent energy dissipation rate in the turbulent wake of a circular cylinder. Ten of the twelve velocity derivative terms which make up the energy dissipation rate are simultaneously obtained with a probe composed of four Xwires. Measurements are made in the plane of mean shear at x/d = 10, 20 and 40, where x is the streamwise distance from the cylinder axis and d is the cylinder diameter, at a Reynolds number of 2.5×10^{3} based on d and free-stream velocity. A phase-averaging technique is used to separate the coherent and remaining structures of the velocity derivatives and the energy dissipation rate ε, approximated by a surrogate based on the assumption of homogeneity in the transverse plane. It is found that the velocity derivatives (∂u/∂y) and (∂v/∂x) play an important role in the interaction between large- and small- scale turbulent structures. The phase-averaged data indicate that energy dissipation occurs spatially mostly within the coherent spanwise vortices, rather than in the regions of turbulent mixing as described by in the widely accepted flow structure model (Hussain and Hayakawa, 1986, 1987). A revised model is proposed to reflect the present finding on the spatial distribution of the energy dissipation rate. |
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