STUDY ON THE HYDRAULIC PERFORMANCE OF LARGE AXIAL-FLOW PUMPING STATIONS

摘要

In order to investigate the influence of velocity circulation on the hydraulic performance of large axial-flow pumping stations, an accurate prediction method is necessary to be built. In this paper, vortex flows of pumps with internal cavitation and non-cavitation are firstly described by the velocity circulation theory. And then a CFD model, i.e., SST k-omega turbulence model is used to calculate the two different working conditions of the pump system with cavitation and non-cavitation. In addition, experiment is conducted to investigate the external characteristic curve of the real machine model pumps, which verifies the simulation results. The influence of velocity circulation on hydraulic characteristics is revealed. The research shows that under the optimal condition, the error of head of the pump between numerical calculation and experimental measurement is 3.58%, while the error of efficiency of pump is 3.31%, which indicate the accuracy of SST k-omega turbulence model. Furthermore, the external characteristics and cavitation characteristics of pumps are predicted, and the critical cavitation pressure (Pc) and fracture cavitation pressure (Pf) are obtained. By comparing the liquid flow deviation angle (γ) of the two conditions, it is shown that the angle (γ) velocity circulation and hydraulic loss of the pump internal passage increase as the pumps cavitation occurs. And by comparing the angle (γ)under different flow coefficient, Δ, which is defined as the ratio of operating flowrate (Q) and design flowrate (Q), it is shown that the values of γ increase rapidly as the operating conditions of the pump deviate from the design one, and the maximum of γ appears when the pump operates under small flow coefficient; and when cavitation occurs in the pump, the values of γ increase, which changes the velocity circulation and increases the pump internal passage hydraulic loss.