Air-core vortex formation in a draining reservoir using smoothed-particle hydrodynamics (SPH)

Vortex formation under unsteady flow conditions in a draining reservoir is studied. Considering the capabilities of mesh-free Lagrangian numerical methods in the simulation of highly deformed free surfaces, the smoothed-particle hydrodynamics approach is employed. The results of this numerical model are validated with the experimental data of the current study, including the depth over the intake at which vortex forms (critical submergence) and the velocity field. Experiments were also conducted in a rotating cylinder while water was draining from an outlet at its bottom center. The particle image velocimetry technique was used for measuring the velocity field in planes perpendicular to the vortex axis. The numerical results including the velocity distribution and water level variations as well as the depth at which an air-core forms were in acceptable agreement with the experimental data. In addition, vortex formation and the corresponding velocity and pressure distribution as well as the streamlines are analyzed based on the numerical results. The results indicate that as the flow depth decreases, high values of vorticity and low pressures are generated at the vicinity of the outlet, and over time, the generated vorticity develops in depth toward the free surface, and an air-core vortex forms.