Effect of Dimension and Position of Horizontal Stationary Rafts on Critical Submergence of Vertical Intakes

Agricultural, urban and industrial zones demand for water can be supplied by withdrawing water through reservoirs or conveying channels using vertical intakes. This method usually faces with some problems such as vortex flow formation in inlet. This causes entrainment of air and swirling flow into the intake, which followed by some other difficulties such as reduction of intake capacity and stimulation of vibrations and cavitation inception. In this study, the effect of dimensions, position and type of the horizontal stationary rafts on required submergence to suppress surface vortex (with air core) were examined experimentally. First some tests were carried out to determine discharge-critical submergence relation for a condition in which no anti-vortex device is used. Then, a dimensionless equation was fitted between relative submergence and intake Froude number. After that, the effect of each raft with a specified dimension and position were examined for five different flow rates. The performance of rafts to reduce required submergence is calculated for each setup. Based on the results, the 2d×2d raft at the position of 1d has the best performance of 29.85%. Finally, a regression equation is fitted to predict relative submergence in the presence of anti-vortex rafts, with respect to dimensionless parameters of Froude number, relative plate dimensions and relative installation position.