Modifying unstable headcurves of swept and unswept pump bladings by means of casing treatment

Abstract

Casing treatment was applied to three blade geometries for axial flow pumps to investigate its influence on their hydraulic characteristics and the well-known typical head curve instability. The geometries were a conventional blade with a radial leading edge and two blades with 45° forward and backward sweeps, respectively. The measurements were performed to show whether the effect of casing treatment does always remove the head curve instability and whether its smoothing effect on the head curve exists also in case of forward and backward sweeps, both of which geometries are known to differ considerably in stall inception. The head curves were measured in a standard way in cavitation-free flow, and additionally the pump head as function of net pressure suction head was measured to record the cavitational behaviour of the different set-ups. It was found that casing treatment strongly reduces the head curve instability though it does not always fully remove it and seems to have no distinct effect on the cavitation characteristics. All three impeller geometries are characterized by critical stall region near the tip.

Keywords

axial flow pumps rotating stall head curve instability blade sweep cavitation casing treatment

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