2019 CSCE Annual Conference - Laval (Greater Montreal)

2019 CSCE Annual Conference - Laval (Greater Montreal) Conference


Title
Characteristics of Flow over the Crest of a Siphon Spillway

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Author(s)
Ms. Warda Ahmed, Concordia University (Presenter)
Dr. S. Samuel Li, Concordia University
Dr. Amruthur Ramamurthy, Concordia University
Abstract

Abstract: Siphon spillways provide a highly efficient control of flow with a small increase in the reservoir water level. Flow over the circular crest of a siphon is highly curvilinear. In fact, curved flows are common in hydraulic engineering applications. It is important to achieve a good understanding of curved flows. The purpose of this paper is to study the characteristics of curvilinear flow over a siphon spillway in the regain of a rounded-crest. The siphon structure has fixed upstream and downstream slopes. To investigate the curvilinear flow over the crest, theoretical analysis and numerical modelling were performed. The theoretical analysis was conducted to determine distributions of streamlines and the radii of curvature of the streamlines. The theoretical analysis uses curvilinear coordinates. The Dressler equation was used to mathematically study the flow at the crest regain. The Dressler equation is significant in flow analysis. It has been used to solve many hydraulic problems involving curved surfaces. Furthermore, we obtained discharge coefficient values for the siphon spillway from the theoretical analysis and compared them with existent experimental results. The flow field was obtained using Computational Fluid Dynamics (CFD) model for the case of submerged flow. The model results give flow velocities in three dimensions covering the geometry of the siphon spillway. For computations of multiphase flow velocity and pressure distributions, a range of Reynolds number values are considered. The computations use the RNG k-? model for turbulence closure. The RNG k?? model is proven to have high accuracy for simulations of turbulent flow, especially in domains with curved boundaries and wall boundary layers. The CFD model predictions are validated with using results obtained from momentum analysis and theoretical siphon model. The results from the current study shed light on such characteristics of the flow past the siphon crest as the discharge coefficient, velocity distributions, and pressure distributions. It is shown that the pressure on the siphon crest’s low surface is negative and therefore could lead to the occurrence of cavitation. The results show that the flow field computed by using the RNG k-? model matches well with the data from the momentum analysis. There is a reasonable agreement between the computed and theoretical values of distributed pressures and velocities.