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Three-dimensional unsteady flow in the intake channel of a small-scale hydroelectric power facility has been simulated numerically using a large eddy simulation technique. The basic numerical method is the highly simplified MAC iteration method modified for the free-surface flow. The standard Smagorinsky model with near-wall damping and correction for irrotational strain was used to evaluate the sub-grid scale stresses. Using the numerical grid that marginally resolves the near-wall flow of laboratory-scale Reynolds number, the complex and unsteady nature of the vortical flow can be reproduced well. The free-surface depression associated with the formation of a free-surface vortex and its time development, which have so far been difficult to be reproduced numerically, are particularly well captured. The present study shows that this method is relevant for predicting the intake flows with possible air entrainment. [ABSTRACT FROM AUTHOR]

A new method of introducing the free-surface effects in the calculation of turbulent open-channel flows using the amplitude of the free-surface fluctuation is proposed along with a modeling method of the equation for the free-surface fluctuation. It can be incorporated in two-equation models like k-εor k-ωtype models by introducing the damping factor to represent the interaction of the eddies with the fluctuating free-surface. Test calculations for fully developed flows and those over backward-facing step indicate good agreement with direct numerical simulation results as well as experimental results. [ABSTRACT FROM AUTHOR]

The mean-velocity and turbulence quantities in a few qualitatively different types of asymmetric two-dimensional turbulent near wakes in nearly zero-pressure gradient have been experimentally studied. In all cases, the log-law similarity of the boundary layers was found to continue into the initial part of the wake, with the same similarity variables as in the boundary layers on the same side, provided the origin of the normal distance is taken at the smooth extension of the respective surfaces. The Reynolds stress profiles show sharp peaks just downstream of the trailing edge, and the magnitudes of the peaks are found to be related to the values of the surface friction at the trailing edge. These peaks grow into the full width of the wake to form the far wake profiles. In this process, the turbulent diffusions of the Reynolds stresses are very important, and when the size asymmetry is severe, is not clearly of the gradient-transport type [ABSTRACT FROM AUTHOR]