Critical Submergence for Horizontal Dual Water Intakes under Perpendicular Uniform Approach Flow

The present paper discusses an experimental study on the critical submergence for lateral dual horizontal intakes that are placed in a row and perpendicular to a uniform approach flow. The effect of clear spacing between the dual square intakes extracting the same flow discharge on the critical submergence is critically studied and found that the dual intakes show mutual influence on the flow withdrawal and critical submergence, which decreases with an increase in the clear spacing. The intakes behaved as isolated intakes in the same flow condition with separate vortices causing multiple vortices at a limiting clear spacing of twice the intake size. The downstream intake of the dual intakes is first affected by the air entrainment from surface vortex formation when both intakes operated under the same discharge condition for spacing less than twice the intake size. The effects of other significant parameters like sill height and intake size under various approach flow and intake flow conditions on the vortex formations at critical submergence of dual intakes are also studied. The intake flow Reynolds number and Weber number significantly affect the critical submergence of the lateral dual intakes, indicating the relevance of viscosity and surface tension effects on surface vortex formations. An empirical relationship for the prediction of critical submergence for dual side intakes has been developed and found to be in good agreement with the observed data with an error of less than $\pm 15\%$. The developed equation is also applicable for the computation of critical submergence for single-side horizontal square intakes under uniform approach flow. The outcomes of the study shall be helpful for the field engineers in fixing the invert level of the single and dual intake for avoiding the air-entraining vortex.