A 3D modeling of water-sediment two-phase movement in flat-bed channel bends

Sediment flow and transport in natural rivers are ofconsiderable interest in the field of river engineering. Generally, thereare many channel bends in natural rivers. The flow characteristics andsediment movement are much more complex in channel bends than in straightchannels. In order to study the development of water-sediment movement inchannel bend, a three-dimensional k-ε-kp solid-liquidtwo-phase two-fluid turbulence (STTT) model in curvilinear coordinatesis solved numerically with a finite-volume method on an adaptive grid.The k-ε-kp STTT model wasintroduced by Zhou and it consists of a Boussinesq expression with scalarviscosity coefficients to model STTT Reynolds stresses and particleturbulence flux. The water flow in an S-shaped flume was first used toverify liquid-phase model and the velocities of water flow were wellreproduced by the model. The secondary flow has different magnitude alongthe S-shaped flume. Then the model was used to calculate the movements ofwater and sediment in a 120°channel bend. From both experimental dataand numerical results, it was shown that the sediment shares the samestreamlines of water in the straight zone and deviates from the streamlinesof water at the channel bend. The deviation increases with the increase ofsediment particle diameters. The numerical results of solid-liquid two-phaseflow in an S-shaped flume have shown that the longitudinal velocities ofsolid-phase are bigger than those of liquid-phase near walls and smallerthan those of liquid-phase in other zones, while the transverse velocitiesof solid-phase are smaller than those of liquid-phase, and the verticalvelocities are almost equal to fall velocities of sediments in straightsections and change much in the bends under the action of helical flows. Inaddition, the concentration of sediment is bigger in the bottom than that inthe surface and also bigger in the inner bank of the S-shaped flume thanthat in the outer bank.