Influence of the bottom slab upward angle of elbow-type suction box on pumping system performance

Elbow-type suction box is widely applied to China´s large and medium-scale vertical pumping systems. The bottom slab of elbow-type suction box in the inlet segment can be horizontal or has an upward angle, the cross-sectional area of which is gradually contracted along the way from the inlet section to the outlet section and the flowing water is gradually accelerated. Characteristic of small hydraulic loss and better flow pattern that can generate better flow conditions for pump. One of the shortcomings of elbow-type suction box lies in that its height is larger compared with other type ones, resulting in deeper foundation excavation of pump house and greater civil construction investment. In pump station engineering practice, the bottom slab of elbow-type suction box is often designed to have an upward angle in the inlet segment in order to raise the bottom elevations of both forbay and sump, so that the height of their wing walls can be reduced and the quantity of earth excavation and concrete works of the pump house foundation can be lessened. Based on a design case of a certain pump station in China, three optimized design schemes of an elbow-type suction box with different bottom slab upward angles were put forward, and the method of computational fluid dynamics was adopted to simulate the internal flow of pumping systems with different suction boxes to analyze the influence of bottom slab upward angle on flow conditions of pump in terms of internal flow patterns, hydraulic loss, distribution uniformity of outlet axial velocity and bias angle of outlet flow field. The numerical simulation results indicate that the upward angle of bottom slab can be regulated within a certain range, which mainly affects the average velocity of inlet section and the hydraulic loss of inlet segment, and slightly affects the distribution uniformity of outlet axial velocity, bias angle of outlet flow field and pumping system efficiency.