Effect of intake geometry on the velocity distribution upstream of intakes

Structures used to receive water from stagnant water environments such as reservoirs and seas, or the flow environments such as rivers and canals are called intake structures. Small-scale intake structures are generally pipes having a circular cross-section. There are two important issues to be considered in the design of intake structures. These are air entrainment to the intake through free surface air-core vortices occurring above the intakes, and entrainment of bed or suspended sediment to intakes. Both events prevent the efficient operation of the intake structures. To investigate these phenomena, it is necessary to know the velocity distributions near the intake structures. In this study, the effect of intake geometry on the velocity distributions upstream of intakes receiving water from a dead-end channel was compared both theoretically and numerically. In theoretical analysis, the available potential flow solution was used to find the velocity distribution in the vicinity of the intake structures. For numerical investigation, the computational fluid dynamics model was first calibrated with available experimental data related to circular cross-section pipe intake, and then the analyses of various intake types (rectangles with a width to height ratio of 4, 2, 1/4, 1/2, square, 45⁰ rotated square, equilateral triangle, 180⁰ rotated equilateral triangle, rhombus and 90⁰ rotated rhombus) were performed with and without flow boundary effects due to channel bottom and sidewalls. Theoretical and CFD results showed that the effect of the intake geometry on the velocity distribution in the vicinity of the intakes is large, but this effect disappears as the distance from the intake increases. For rectangular intakes with high width/height ratios, iso-velocity contours became different than that of the pipe intake while the behaviors of the square, rhombus, and triangular intakes were similar to the pipe intake. It was also shown that the flow boundary effects spoil the shape of the iso-velocity contours and generate larger velocities in the region away from the boundaries compared to the case with no boundary effects. Moreover, the agreement between numerical and theoretical results was found to be satisfactory.