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Log-Wake Law in Time-Dependent and Depth-Varying Open-Channel Flow

Author(s): Michio Sanjou; Iehisa Nezu

Linked Author(s): Michio Sanjou

Keywords: Unsteady depth-varying open channel flow; Numerical calculation; Unsteadiness effect; Wake-strength parameter

Abstract: Unsteady depth-varying open-channel flows are really observed in flood rivers. We can use some valuable experimental database of flood-simulated open-channel flows which were measured accurately by laser Doppler anemometers (LDA). However, these LDA measurements are comparatively difficult to be conducted in flood-simulated open-channel flows with strong unsteadiness because of various limitations of experimental instruments and flumes. So, in the present study, a low-Reynolds-number type k −ε model involved with a function of unsteadiness effect was developed and some numerical calculations were conducted using the Volume of Fluid (VOF) method as a free-surface condition of flood. The present calculated values were in good agreement with the existing LDA data in the whole flow depth from the bed to free surface, which is described by the log-wake low. This calculation model could predict the phase-averaged of velocity distributions and the time- variations of wall shear stress and flow depth reasonably. In particular, these calculations are able to explain well the log-wake law, in which the wake-strength parameter Π varies with time more significantly, as the unsteadiness becomes larger.


Year: 2005

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