Influence of the diffuser vane setting angle on the flow field in a radial pump

Particle image velocimetry (2D-PIV) has been used for the investigation of the time averaged flow field inside the vaned diffuser of a centrifugal pump operating at best efficiency point. Pump performances and the diffuser flow field were analysed for three different vane setting angles. It was evidenced that the best efficiency point flow coefficient decreases with the diffuser setting angle reduction. A boundary layer thickness growth on the pressure side, which increases as the flow coefficient decreases, was also shown. No evident separation was ever seen on the diffuser vane suction side even with a sharp diffuser vane LE, used in a previous investigation. The total pressure loss coefficient, obtained from the classical expression proposed by Lieblein for linear cascades, was found to decrease as the setting angle increases. It was evidenced an influence of the diffuser vane setting angle on the impeller slip and an over-turning of the diffuser flow field, at mid-span, with an under-turning at the hub and the shroud, suggesting the occurrence of significant secondary flows.