Free-surface response to large-scale bed roughness

Proceedings of the Seventh International Conference on Hydroscience and Engineering, Philadelphia, PA, September 2006. http://hdl.handle.net/1860/732The state of the free-surface in open-channel flows over large-scale roughness elements is examined experimentally and numerically. Large Eddy Simulation (LES) of the incompressible fully developed turbulent flow in a rectangular channel bounded above by a rigid-wall is performed. The results of the computations are compared with Large Scale Image Velocimetry (LSPIV) measurements. Two roughness types, namely, square cavities and two-dimensional dunes, are tested with a range of flow depth (h) and roughness height (k) to obtain submergence ratios (h/k) of 4 to 8.5. The pressure, vorticity and velocity fields are used to identify the turbulent structures at the free-surface and their relationship with the channel roughness. It is found that the free-surface deformations and the velocity distributions are related to the geometry and relative submergence of the bed roughness elements. The results are used to support ongoing efforts for development of remote discharge measurements techniques