Rapidly varying flow over oblique weirs

Proceedings of the Seventh International Conference on Hydroscience and Engineering, Philadelphia, PA, September 2006. http://hdl.handle.net/1860/732Many obstacles in river floodplains can be considered as weirs; the flow over the obstacle varies rapidly and gives rise to energy losses. The weir-like structure can have any angle with respect to approach flow direction. In order to estimate the maximum conveyance capacity of a river, the energy losses need to be known for various conditions, but in particular for submerged conditions. In this study analytical and experimental data are compared with the results of a 3D numerical model. The non-hydrostatic finite element model FinLab, allows for a moving free surface and has a straightforward k −ε turbulence closure. The numerical model reproduces the experimental data very well and allows for a more extensive evaluation of the 3D flow structure. The analytical model reveals that the combination of energy conservation at the upstream side of the weir and momentum conservation at the downstream side explains most of the energy losses. For the oblique weir the assumption is verified that the velocity component parallel to the weir is not affected while the perpendicular component can be characterized by the standard weir formulations. The simulated separating flow downstream of the weir has interesting features with a clear relation with the energy losses. More detailed experimental data are needed however to validate the model on these aspects