چكيده به لاتين
Vortex can be mentioned as one of the unknown phenomena in the field of dewatering of dam reservoirs, which can cause problems in the dewatering process. The presence of eddy currents or more precisely eddies, reduces the efficiency of turbines, introduces vibration in the system, increases the hydraulic drop in the catchment of the power plant, increases operational problems such as blockage of exhaust ducts due to suction of air and floating materials on the water surface and Eventually the life of the turbines will be reduced.
The latest classification of vortices based on power was presented in 2010 by the Sarkardeh and colleagues. In this classification, vortices are classified into three different classes. Class C vortices are limited to rotations on the surface of the water, and sometimes small depressions are observed on the surface of the water, and they can be called harmless vortices. In Class B vortices, by pouring the dye into the stream, a rotating cone of dye is observed and the floating particles are drawn into the vortex and thus the intake duct. In Class A vortices, which are the strongest type of vortices formed, in addition to floating objects, air bubbles are drawn into the duct and an air core is observed from the free surface of the water to the intake duct.
In this study, by considering the appropriate length for the power plant tunnel in terms of computational capabilities of available systems, the effect of vortex on flow velocity along the tunnel under the conditions of surface vortex flow at the tunnel entrance has been investigated. STAR-CCM + software was used to simulate the numerical model in this study. LES (Large Eddy Simulation) was used to account for turbulence and VOF (Volume Of Fluids) was used to detect free water levels. Polyhedral meshing was used because it was optimal in terms of the number of cells available. Finally, after examining the simulation, the results showed that the vortex reduced the velocity components inside the tube and changed the maximum and minimum velocity, and in addition, the symmetry of the profile affected the flow velocity. Velocity magnitude and Axial velocity are decreased and on the other hand tangential and radial velocities increased at the location of the air core along the tube, which is the upper half of the tube. Due to this alterations along the tube and the existing rotation, the vortex-induced air core is more effective in the second half of the pipe length and leans to the left half of the pipe section. The minimum and maximum velocity components together after vortex formation, approach to the left of the tube and the intensity of the effects of air and rotational flow in the final quarter of the tube fades and the flow characteristics become more stable. In the area oriented to the presence of air along the pipe, the air has reduced the amount of velocity magnitude and axial velocity in the section, compared to other areas of the sections where there is no air, by 24.5% and 27%, respectively. In the case of tangential velocity and radial velocity, the opposite was true, increasing 2.37 times and 1.79 times, respectively.
