LAUSR

Abstract Large Eddy Simulations (LES) were carried out on a centrifugal pump in order to investigate the effect on pressure fluctuations through rotating and stationary channels by both flow-rate conditions and orientation of the diffuser blades. Computations were performed for Reynolds numbers, based on the inflow velocity and outer impeller radius, equal to R e = 1.5 × 10 5 (design flow-rate) and R e = 6 × 10 4 (off-design flow-rate, equivalent to 40% of the nominal one). Results show that sensitivity to both working conditions and setting angle of the diffuser blades is much stronger for the stationary vanes, compared to the rotating channels. At reduced flow-rates pressure fluctuations are higher, with more energy at frequencies lower than that of passage of the impeller blades. However, rotating stall phenomena were not observed. A reduction of the geometric inlet angle of the diffuser vanes produces an increase of the incidence angle on the diffuser blades at the nominal flow-rate and a decrease at the lower flow-rate. Pressure rise is negatively impacted in the former case, while the effect is beneficial in the latter one. In contrast, pressure fluctuations decrease for both flow-rates, mainly due to the wider gap between trailing edge of impeller blades and leading edge of diffuser blades. With the modified diffuser geometry, at the design flow-rate the role of the low frequencies keeps negligible and at the reduced flow-rate they become also less energetic, thanks to improved diffuser inflow and weaker separation phenomena.