Author(s): Hasan Zobeyer; Peter M. Steffler
Linked Author(s): Peter Steffler
Keywords: No Keywords
Abstract: The application of a full 3D computational fluid dynamic (CFD) model over a long river reach is often not practical due to the large computational effort required to solve the full Reynolds Averaged Navier-Stokes (RANS) equations. On the other hand the vertical distribution of horizontal velocities is probably the most useful output from a 3D river modeling. Therefore a quasi 3D model has been developed to simulate the vertical distribution of horizontal velocities in the open channel flow. The water surface elevation and depth averaged velocity are obtained from the Saint Venant equations or the Vertically Averaged and Moment (VAM) Equations if nonhydrostatic pressure and vertical velocity distributions are significant. These distributions are used as input to the horizontal momentum RANS equations that are then solved for the vertical distribution of horizontal velocities. This avoids the complicated pressure-velocity coupling of a full 3D model. A technique is developed to force the mean of horizontal velocity profile to be equal to the depth averaged velocity in order to maintain the continuity of the mean flow. The equations are discretized and solved in a nonorthogonal bodyfitted coordinate system by the finite difference method with a zero equation turbulence model. The method is tested for2D plane flows. The flow of a free overfall is modeled considering the vertical velocity and nonhydrostatic pressure obtained from the VAM model. The results show very good agreement with the experiment. The flow over a sill is modeled neglecting the vertical velocity and nonhydrostatic pressure. The model can simulate the converging flow very well. In the diverging section the results are reasonable although a better turbulence model may improve the results. Overall the model showed promising results.
Year: 2009