The present study focuses on the effect of vortex formation on plane velocities in a reservoir. Velocity measurements are performed in the hydraulic model of Karun III dam and hydropower plant. Different vortices were produced at the horizontal intake by changing the submerged depth. Tangential velocities were measured on a rectangular mesh in the reservoir. The results were then processed to plot the contour lines of the plane velocities and study the effect of vortex formation on the flow condition in the reservoir. Contour lines in different submerged depths show that circulation zones are formed in different potential locations over the intakes causing vortex formation. These results were correlated with the location of the appearing vortices observed in the experiments. Experimental data of this study could be useful for numerical modelling of vortex in the reservoirs.
The problematic consequences regarding formation of air-core vortices at the intakes and the drastic necessity of a thorough investigation into the phenomenon has resulted in particular attention being placed on Computational Fluid Dynamics (CFD) as an economically viable method. Two main approaches could be taken using CFD, namely the Eulerian and Lagrangian methods each of which is characterized by specific advantages and disadvantages. Whereas many researchers have used the Eulerian approach for vortex simulation, the Lagrangian approach has not been found in the literature. The present study dealt with the comparison of the Lagrangian and Eulerian approaches in the simulation of vortex flow. Simulations based on both approaches were carried out by solving the Navier–Stokes equations accompanied by the LES turbulence model. The results of the numerical model were evaluated in accordance with a physical model for steady vortex flow using particle image velocimetry (PIV), revealing that both approaches are sufficiently capable of simulating the vortex flow but with the difference that the Lagrangian method has greater computational cost with less accuracy.
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.
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