BED-SUCTION EFFECTS ON STRUCTURE OF TURBULENT OPEN-CHANNEL FLOW

The effects of bed suction on the structure of turbulent open-channel flow are studied numerically by solving the Reynolds-averaged Navier-Stokes equations. Two low-R turbulence models of the k-epsilon type are used for ''closing'' the system of equations. The models of Nagano and Hishida and of Launder and Sharma give similar predictions for suction rates up to 9% against experimental measurements performed by Maclean. The bed-suction effects on the mean flow characteristics are found to be significant within the suction region. The near-bed velocities are increased with increasing suction rate, as well as the bed shear stress. The law of the wall with suction, developed by Stevenson, is found to be applicable for low rates of bed suction up to 0.3%. The excess bed shear stress, resulting from suction, is calculated in the order of three to eight times the respective one with no suction. The turbulence levels are greatly reduced with increasing suction rate and a new normalization of the turbulence characteristics is satisfactory for suction rates up to 0.3%.