Abstract
In the range of very low specific-speed (ns≤100 [m, m3/min, rpm]), performance of a centrifugal pump is much different from that of a normal ns pump. In order to obtain a basic knowledge of pump performance, the internal flow in a semi-open impeller is measured by PIV method and calculated by a commercial CFD code. The results show that strong reverse flow at an impeller outlet is formed and reduces tangential velocity of the absolute flow at an impeller outlet. In the case of β2=90° impeller, a large vortex is formed in the impeller passage at partial flow rate and causes a performance instability. The reverse flow at an impeller outlet brings low angular momentum into an impeller and causes a sharp drop of tangential velocity just before the impeller outlet, which results in a increase of slip factor in the case of β2=30° impeller.
