Numerical Investigation on Hydraulic Performance at Low Flow Rates of a Mixed-flow Pump with Impeller Inlet Diameter Effects

Abstract

A mixed-flow pump has a characteristic in which the pressure (P) decreases as the flow rate (Q) increases on the performance curve. Hence, the Q-P curve generally has a negative slope, which has been understood as an ideal and stable case. However, a complex recirculating flow may occur due to the increase in incidence angle at the low flow rates compared to the design flow rate. This phenomenon accompanies noise and vibration along with the deterioration of performance and causes a positive slope in the form of a saddle on the performance curve. In this study, the effect of the impeller inlet (eye) diameter of a mixed-flow pump on the saddle characteristics was confirmed through numerical simulation. The focus was on the internal flow field and performance of a pump, which could be solved with the steady-state analysis. Here, the impeller inlet diameter was adjusted with the leading edge (LE) vertex on the shroud line of the meridional plane. The blade angle was adjusted accordingly to maintain the previously optimized degree of the incidence angle. From this novel design method, the saddle characteristics were significantly improved. The performance in the saddle range was directly related to the recirculating flow near the shroud. The numerical results were validated with the experimental tests.