An experimental model was set up to investigate the formation and evolution of the free surface vortex. A Particle Image Velocimetry （PIV） was used to measure the free surface vortex flow field at different development stages. Flow visualization was used to locate the vortex position and find its structure. Empirical formulas about the critical submergence and the whole field structure were obtained. It is found that the tangential velocity distribution is similar to that of the Rankine vortex and the radial velocity changes little in the vortex functional scope. Vortex starts from the free surface and gradually intensifies to air entrainment vortex. The vortex core moves during the formation and evolution of the free surface vortex. Based on the experimental model, the vortex position and structure were predicted by numerical simulation combined with a vortex model and compared with that of the experiments, which shows satisfactory agreement.
Based on the Navier-Stokes equations with considering the effect of the Coriolis force, the finite volume method was employed to discretize the governing equations, the SIMPLE method was adopted to solve the discretized equations, and the flow field in a barrel with an outlet at the center of the bottom was simulated. The numerical results agree well with the experimental data. From the Lagrangian, the relations among the acceleration, the Coriolis force and the viscosity force were analyzed. The results show that the Coriolis force is the major factor that causes the formation of the vortex. The flow fields in the flume under different incoming flow conditions were numerically simulated using the software Fluent. The numerical simulations show good agreement with the experiments for the shape and position of the vortex.
