Spillway flow, a classical problem of hydraulics, is generally a gravitydriven free surface flow. Spillway flows are essentially rapidly varying flows near the crest with pronounced curvature of the streamlines in the vertical direction. Two processes simultaneously occur in the flow over the crest, that is, formation and gradual thickening of the turbulent boundary layer along the profile, and gradual increase in the velocity and decrease in the depth of main flow. Spillway hydrodynamics can be obtained through physical modelling or numerical modelling. Physical modelling of spillways is expensive, cumbersome and time-consuming. The main difficulties in solving the spillway problem numerically are: rapidly varying flow, existence of both subcritical and supercritical flows, development of turbulent boundary layers, unknown free surface and air entrainment. Numerical simulation of such flows over spillways in all flow regimes is a challenging task. This paper describes a numerical model and its application to a case study to investigate the hydraulic characteristics of flow over spillway crest profiles by simulating the velocity distribution, pressure distribution and discharge characteristics. Results of the numerical modelling are compared with those from the physical modelling and found to be satisfactory.

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SUMMARYNumerical simulation of rapidly varied, free surface turbulent flow over spillway with the existence of both sub-critical and super-critical flow regimes is a challenging task. Vertical acceleration plays a dominant role in the spillway flows. This paper describes the formulation and development of a numerical model for flow over the spillway. The computer model is developed using the finite volume method based on weakly compressible flow equations and large Eddy simulation (LES)-based turbulence model. The model is applied to a real world case study of partial gate operation of sluice spillway to investigate the hydraulic characteristics by simulating the velocity distribution, pressure distribution and discharge characteristics. Numerical modelling of sluice spillway is complicated because both moving free surface region and fixed conduit pressure flow in the sluice barrel are present. The numerical model results are compared with the physical model study. The simulated results are in close agreement with the measured values.