CFD MODELING TO DETERMINE THE OUTLET WATER JET FORMATIONS AND HYDRODYNAMIC CHARACTERISTICS OF A DAM BOTTOM OUTLET GATE

Abstract

Multiphase flow modeling using numerical simulation approach is by no means a simple task, especially when defining flow conditions in non-closed domain (such as outflows, spillways and open channel flows), compared to mixing of fluids in tanks or vessels. The task which was done was part of a refurbishment project of a regulating fixed-wheel bonneted gate of a dam bottom outlet works, so to obtain precise values of the hydrodynamic forces acting on the gate, to see if down-pull effect occurs in every gate position. The outflow conditions are in open atmosphere, so the formation of the water jet plays a crucial part to estimate the discharge rate of the bottom outlet. The numerical modeling was made via CFD simulations using the Volume of Fluid model, to gain phase fractions of water and ambient air and to see the water jet formation behind the gate. The obtained results are compared in several ways. The numerically obtained discharge rates for a given reservoir level were compared with the available model test data, dating from the origin of the dam. The numerically obtained hydrodynamic forces, hydraulic cylinder pressures and gate casing cover pressures are compared with physical measured data on site during the wet test of the gate functionality. The obtained jet formations behind the gate were examined through a drone footage taken at the same time when the wet test was made, to evaluate the CFD multiphase modelling approach visually with the real outflow conditions. All the mentioned result comparisons showed remarkable exactness and similarity with the available data, on-site measurements and drone footage, showing that all the steps taken to perform CFD evaluation give great prediction of the overall hydrodynamic conditions occurring on-site.