Performance simulation and experiment of different leading edge back-swept angle on double blade sewage pump

Abstract

The back-swept double blade sewage pump studied in the paper belongs to the new high efficiency non-clogging pump. It has a self-cleaning ability, and can effectively solve the problem of fiber winding and congestion. This research study designed to probe the effect of the leading edge back-swept angle on a forward-extended double blade sewage pump. By changing the leading edge shape to get different degrees of back-swept blade, four models of impellers with different back-swept angles of 60°, 100°, 140°, and 180° were created by BladeGen. According to the structure of the pump, we divided the fluid domain into six parts, namely entrance region, impeller, volute, front chamber, back chamber, and outlet section, which were modeled by Unigraphics NX. ICEM CFD software was used for dividing the structured mesh of each part, and the numerical simulation of the whole flow field was performed based on a standard k-E turbulence model and scalable wall function. The total pressure inlet condition and mass flow rate outlet condition were adopted in the computational domains. The impeller was defined as rotating domain with a speed of 1 450 r/min. Both front and back of the pump cover plate walls were set to the rotating walls with the speed of 1 450 r/min. Other domains and walls were defined as static fields or walls. The discrete control equations were based on the finite element of finite volume method. The convective term was a high resolution format and convergence precision was set to 10-4. At the same time, the trend of the pump head, efficiency, and power curves were leveling out to ensure the credibility of the calculation results. To further ensure the accuracy of the simulation results, a sewage pump of 100° back-swept angle was produced and tested. Comparison between the numerical simulation and experimental results was presented to prove the accuracy of the numerical simulation. Comparing performance curves concluded from the simulation, we found that the best efficiency point of pump shifts to the high flow condition and the required shaft power increases when the back-swept angle increases from 60° to 140°, and the best efficiency point of the pump apparently decreased when the back-swept angle increased from 140° to 180°. To probe the cause of the efficiency decrease, we did an analysis of the internal flow field when the flow ratio Q/Qn was 1.2, and found that, with the back-swept angle β increases, the value and range of turbulent kinetic energy had a sharp increase in the impeller inlet, namely, the hydraulic loss appeared in the inlet. Therefore, by further analysis of the leading edge in axial velocity distribution, it can be known that there are refluxes at the leading edge near the front shroud, which causes large hydraulic losses. And with the back-swept angle increasing, the flow passage near the outer periphery was much narrower, causing the region of reflux to become larger. So it was suggested that the back-swept angle of the leading edge should not more than 140°, otherwise the efficiency of the pump would apparently decrease. The results are instructive for the design and optimization of a forward-extended double blade sewage pump.