Author(s): Hin-Fatt Cheong; Soe Thein
Linked Author(s):
Keywords: Open channel bend; Turbulence model; Dredged fines; Dispersion
Abstract: This paper describes the experiments and the numerical computations for the dispersion of dredged fines in (a) a straight channel and (b) a 900 bend which has a straight upstream portion of 14m and a straight downstream portion of 7m. The bend has a mean radius to width ratio of 2. 75 which corresponds to the reported ratio of about 33 of 50 rivers by Leopold et. al. (1964). The hydrodynamic model represents the full Navier-Stokes equations based on the cylindrical coordinate system and the turbulent stresses in the momentum equations are based on the Boussinesq assumption which relates the stresses to velocity gradients through a turbulent viscosity. Theκ-εturbulence closure model is also adopted. The resulting hydrodynamics of the flow around the bend, along with the turbulent coefficient Γ s derived from the turbulent viscosity ν t and the turbulent Schmidt numberσ c, are used to predict the dispersion of a steady supply of a slurry of dredged fines. It is assumed that the sediment concentrations are not significant enough to influence the turbulence structure of the flow. Fairly comprehensive measurements of the tangential, radial and vertical components of the flow velocity and the sediment concentration are made at selected cross sections in both the straight channel and the channel with the 900 bend. A dimensionally homogeneous relationship for the settling speed of the dredged fines is derived from the measurements in the straight flume by selecting the combination of the Schmidt number and the parameter b is the proposed relationship that gives the best fit of the predicted concentration profiles to the measured profiles. This relationship is used for predicting the concentration profiles of the dredged fines in the channel with the bend. The resulting profiles showed reasonable agreement with the measured sediment profiles with the departures being more significant nearer the inner and outer walls.
Year: 1999