Three-dimensional computations of flow and morphology change in a curved open-channel.

Sung-Uk Choi, Seonmin Lee

Tuesday 30 june 2015

15:05 - 15:20h at Europe 1 & 2 (level 0)

Themes: (T) Water engineering, (ST) Computational methods

Parallel session: 6E. Engineering - Computational

This study presents a three-dimensional numerical model that is capable of computing turbulent flow and morphological change in a curved stream. The Reynolds-Averaged Navier-Stokes equations were solved by the finite volume method with the non-staggered curvilinear grid. The standard k-_ model was used for the turbulence closure. The hybrid scheme and the SIMPLER algorithm were used for differencing the convection and diffusion terms and velocity-pressure coupling, respectively. The momentum interpolation method proposed by Rhie and Chow (1983) was to eliminate numerical oscillations, known as checkerboard, caused by the use of the non-staggered grid. The Engelund-Hansen’s formula was used to estimate the bedload. The Exner’s equation was solved to account for the morphology change. The proposed model was applied to both fixed- and mobile bed laboratory experiments. First, the numerical model was applied to laboratory experiments by Rozovskii (1957). The experimental channel consists of two straight channels connected by 180 degree channel bend. The channel width is 0.8 m, and the inner and outer radii of the channel bend are 0.4 m and 1.2 m, respectively. The discharge is 0.0123 m3/s and the flow depth at the inlet is 0.06 m. The law of the wall was used for the channel bed and sidewalls, and the symmetric condition was imposed at the free surface. It was found that the distributions of computed velocity are in good agreement with measured data. Flow acceleration was observed to occur along the inner side of the bend near the entrance and along the outside of the wall after the bend due to the centrifugal force. The flow pattern of the secondary currents in the curved channel appeared to be consistent with that in the literature. Then, numerical the model was applied to LFM (the Laboratory Fluid Mechanics at Delft University of Technology) 180 degree curved channel experiments. The configuration of the experimental channel is similar to the previous one. The median size of particle at the bed is 0.78 mm. Simulated results indicated that the bed shear stress at the inner side of the bend is larger at the initial stage, however, the secondary currents transport bed sediment from the outer to inner side of the channel bend near the apex. Bed elevation change simulated by the proposed model compared favorably to the measured data.