Comparison of the VOF and the Two-Fluid Models for the Numerical Simulation of Aeration and non Aeration Stepped Spillway

A spillway is a hydraulic structure that is provided at storage and detention dams to release surplus or flood water that cannot be safely stored in the reservoir. In this paper, two-dimensional simulation of gas-liquid two-phase flow on stepped spillway in different discharge rate is studied. The VOF model and the two-fluid model are used in order to simulate numerically and then the results of the two models are compared. In order to study the influence of aeration in stepped spillway, two different physics are proposed. In the first geometry it is assumed that there is no air intake via stairs and in second geometry air intake and its effect on the flow over the spillway is studied by embedding hole in the top edge of stair. The air pressure is assumed to be atmospheric. The results showed that VOF model provide more accurate result than that of two-fluid model in low discharge rate. However, in cases where aeration is studied, because of mixing phases, this model is not able to simulate fluid flow as well as two-fluid model. The two-fluid model is more accurate due to solving equations for both phases (air and water). For verification, numerical results have been compared with experimental values and determined that numerical models are able to predict the total energy loss within an error range of %10 compared with the measured experimental data.