Analysis of flow structure over ogee-spillway in consideration of scale and roughness effects by using CFD model

In this study, flow characteristics such as flowrate, water surfaces, crest pressures on the ogee-spillway, and vertical distributions of velocity and pressure in consideration of model scale and surface roughness effects are investigated in detail by using the commercial CFD model, FLOW-3D, which is widely verified and used in the field of spillway flow analysis. Numerical errors in the discharge flowrate, water surfaces, and crest pressures due to the surface roughness are insignificant if we just use a general roughnessheight of construction materials, and the scale effects of the model are in an acceptable error range if the length scale ratio is less than 100 or 200. The roughness and scale effects are more severe belowhm, where the maximum velocity occurs in perpendicular coordinate to the weir crest. The velocity of the prototype is larger than that of the scaled model below but the phenomena are contrary abov ehm. Maximum velocity at any section slightly decreases as the surface roughness and the length scale ratio increase. The vertical location where maximum velocity occurs is located on a lower position as the upstream water head increases and the location almost linearly increases with the distance from the front of the spillway.