Surface vortex prevention at power intakes by horizontal plates

The efficiency of horizontal perforated and solid plates, installed on top of an intake for prevention of surface vortex formation, was experimentally investigated. The experiments were conducted on a horizontal intake of a reservoir. By changing the angle of the approach flow, submergence of the intake and the discharge, 36 air-core surface vortices with different strengths were generated. The strengths of these vortices were evaluated by measuring tangential velocities using an acoustic Doppler velocimeter. A relationship between the strength of the surface vortex and the necessary percentage of uniform opening of the perforated plate is presented. It was found that a perforated plate of width 1D and 1·5D length normal to the intake (D is the tunnel diameter) with 50% uniform opening and a solid plate of 1·5D width and 2D length eliminated all surface vortices at the intake. Pressure was also measured in a section immediately downstream of the intake by means of four transducers. By using the measured pressure values, the effect of anti-vortex plates on local loss at the intake was determined.