Evaluation of Critical Sink Surface in Vertical Intake Branched out from Reservoir

Intakes are the most significant hydraulic structures, which are also used as inlet structures in outlets to supply water for hydro-electric power, irrigation, and drinking. A major problem for vertical circular spillways is that vortexes are formed on their inlet with several negative effects: reducing discharge coefficient, excessive head formation on spillway inlet, structure vibration, increasing of cavitation formation probability, suction of floating bodies into conduit, excessive oscillations on flow surface, unsteady flow formation, and increasing energy losses are the major consequences. Vortex flows result from flow direction variation, viscosity and surface tension. The flow type causes negative effects in operation of structures such as vertical circular spillway (Kabiri Samani and Borghei, 2001).Taştan and Yildirim (2010) indicated that critical submerged depth for intake in canal with uniform flow equals radius of spherical sink surface, which was finally named critical spherical sink surface. Rankine (1858) represented a model of vortex, namely Rankine compound vortex. In this model, it is assumed fluid particles, which are in the vicinity of vortex center, are solid bodies with high viscosity and rotational motion around their axes (Forced Vortex). The area is located inside nonviscous zone at a distance from vortex center. This research investigates geometric and hydraulic properties of critical sink surface by simulating flow in the environs of vertical intake inlet.