Numerical Simulation of Inlet Flow Characteristics of Mixed Flow Pumps during Start-up

Based on an established three-dimensional closed-loop model including impeller, guide vane, volute, valve, surge tank and pipeline, the numerical simulation for the start-up of mixed flow pumps was carried out. The generation reasons for form of reverse flow were analysed. The disributions of the axial length, axial and circumferential velocities of reverse flow, the variations of reverse flow rates and reverse flow areas at different axial positions were studied. The results show that the numerical computation results are reliable according to the comparison between test and numerical results. The separation flow of suction surfaces and leakage flow of tip clearances are mainly as the reasons for reverse flows. The each reverse parameter increases first and then decreases with time, the axial velocities of main flow and reverse flow present symmetrical distribution in the early stage of the start-up. After 0.8 s, the axial velocities of the reverse flow appear asymmetric distribution. Additional, the farther away from the impeller inlet, the more obvious the asymmetric distribution is. The axial velocity distribution of the main flow presents different changing tendency at different sections. The circumferential velocity gradually presents asymmetric distribution and the velocity direction at the circular section of the inlet pipe gradually deviates from the tangential direction of the circumference. The tendency of reverse flow rate and area at each axial section are basically consistent, and each section gradually presents a maximum return area. © 2021, China Mechanical Engineering Magazine Office. All right reserved.