418 / 2024-03-15 10:59:27

Evaluation of two multi-phase CFD models for air-water two-phase flow in spillway tunnels

spillway tunnel,aerated flow,air discharge,two-fluid models,numerical simulation

Subtheme 1: Water-related Hazard and Risk Reduction > Topic 6: Safety Risk Prevention and Control of Water Engineering

Spillway tunnels are frequently utilized in large dam projects, particularly in narrow valley regions. The high-velocity water flow results in significant air entrainment and transportation. This causes flow bulking and additional air discharge, which has to be carefully managed in engineering practice. In order to investigate the accuracy of multiphase Computational Fluid Dynamics (CFD) models for calculating the induced air discharge in high-velocity spillway tunnels, two different models were comparatively tested by comparing the simulated air concentration, mixture flow velocity and air discharge under six different Froude numbers with experiment data in literature. It is discovered that in the area where the air concentration Ca is between 0.2 and 0.9, the vertical air concentration profile obtained from both models overlapped well with the experiment data, whereas each model exhibited certain advantages at the tunnel bottom (Ca<0.2) and water surface (Ca>0.9), respectively. The mixture velocities and air vent discharge calculated using the two-fluid model in Ansys Fluent agrees significantly better than those given by the air entrainment model in Flow-3D. The former showed an average relative air vent discharge error of -3.82%, while the later returns average error as high as 66.35%. Therefore, the two-fluid model in Ansys Fluent is recommended for the simulation of air-water two-phase flow in spillway tunnels.