IAHR, founded in 1935, is a worldwide independent memberbased organisation of engineers and water specialists working in fields related to the hydroenvironmental sciences and their practical application. Activities range from river and maritime hydraulics to water resources development and ecohydraulics, through to ice engineering, hydroinformatics, and hydraulic machinery.





A quasi 3d numerical model for open channel flow 
Author : 
Hasan Zobeyer and Peter M. Steffler 
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 NavierStokes (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 pressurevelocity 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 for 2D 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.

File Size : 
115,721 bytes 
File Type : 
Adobe Acrobat Document 
Chapter : 
IAHR World Congress Proceedings

Category : 
33rd Congress  Vancouver (2009)

Article : 
Topic A: Advances in the Fundamentals of Water Science and Engineering

Date Published : 
09/08/2009 







