Simulation and validation of hydraulic performance of closed-style pump sump with different bell-mouth shapes

Closed-style pump sump is a kind of inlet structures of pump station. Bell-mouth, a part of axial-flow pump system, is used to adjust the velocity distribution on the inlet section of pump. The shape of bell-mouth is an important factor that can affect the hydraulic performance of pump system. In order to investigate the hydraulic performance of different shapes of bell-mouth,the three-dimensional fluid flow inside an axial-flow pumping system was simulated based on the Reynolds time-averaged Navier-Stokes equations, the RNG k-ε turbulent flow model, the SIMPLEC algorithm and the law of the wall. The parameters values of closed-style pump sump were from literature including sump length, sump width, bottom clearance, back wall distance, and submergence depth. In order to exclude the possible influence from closed-style parameters, these parameters values were fixed based on design standard of sump. Seven schemes with different bell-mouth shapes were designed with that without bell-mouth as control(scheme 1). The drawing line of bell-mouth shape in scheme 2-5 was 1/4-shaped arc with different radius, while the drawing line was 1/4 ellipse line with different axis lengths in scheme 6 and 7. The results illustrated that excessively small bell-mouth may lead to one-way inflow trend in the suction pipes. As the radius of bell-mouth gradually increased, the axial velocity of the suction pipe became more uniform and the hydraulic loss became smaller. Overlarge bell-mouths would lead to more hydraulic loss, larger width of the inlet sump and more investment of civil construction. When the size of bell-mouth were of same dimensions, the flow velocity distribution into the 1/4-shaped arc flare tubes mouths were more uniform and better than that of the 1/4-shaped elliptical flare tubes and had less hydraulic loss. The result of numerical simulation was consistent with the experimental results. The maximum relative error between the simulated value and experimental value in head was 9.8%, and that in efficiency was 13.6%. The relative error of head between the simulation and experiment was 1.7% in the design point with discharge of 0.035 m³/s, which was less than 5%. The relative error of efficiency between the simulation and experiment was 1.1%, which was also less than 5%. It indicated that the results were credible and the results here could be applied to engineering practice. The recommended drawing line of bell-mouth was 1/4-shaped circle and the recommended radius was 1/3～1/2 of impeller radius.