Experimental and Numerical Modeling of Free-Surface Turbulent Flows in Full Air Core Water Vortices

Résumé En

The results of experimental and numerical simulations implemented on free-surface turbulent flows in air core vortices are presented. Free water vortex flow is induced in a gravity driven, open channel vortex chamber. The two-phase, airwater fluid system is stratified at the inlet channel and vortex far field but transfers to annular flow at the vortex air core. Experiments are conducted in a scaled physical model of the chamber which permits the investigation of the airwater interface shape and relevant flow variables. In order to quantify the flow field for various boundary conditions, measurements of the tangential and radial velocity profile are determined using single particle tracking velocimetry (PTV). The fully segregated fluid system is numerically modelled using ANSYS CFX 14.5. A homogenous Eulerian-Eulerian multiphase flow model coupled with the volume-of-fluid (VOF) method is used to resolve the free water surface and to compute the turbulent flow field. The RANS turbulence model of shear-stress transport (SST) k-mode is employed. Predictions obtained using ANSYS CFX are validated using time averaged images of the vortex water surface profile and the measured velocity distributions using PTV. The predicted shape of the air core is in agreement with the physical model ; however, the location of the free water surface is under predicted. Concerning the velocity field, the k-model presents significant discrepancy in both the near and far field of the vortex to both the radial and tangential velocity profile. It is concluded that the fluid system is unsteady and extensive transient analysis is required to accurately analyse and resolve the flow field variables and water surfaces.