Influence of forward rake and skew blade angle on positive slope characteristics of mixed flow pumps

In many of the mixed flow pumps that have been studied in the past, the impeller has a sweepback wing. Especially, the positive slope characteristics have been studied to operate pump in a stable regime. The cause of the positive slope in the characteristic curve of the mixed flow pump is the reverse flow, with the turning becomes stronger, at the leading edge of the blade tip side in the flow rate range. Also, at the flow rate at which the slope of the characteristic curve becomes positive, the angular momentum becomes negative at the leading edge of the impeller, and the work amount sharply decreases at the leading edge more than the work amount increase at the trailing edge so the angular momentum decreases. However, the influence of the forward rake and skew blade on the performance, the positive slope characteristics, and the internal flow have not been studied much. In this study, we designed and analysed a forward rake and skew blade mixed flow pump. About the forward rake and skew blade, we found the cause of the positive slope characteristics is the same reason as the sweepback wing, but the flow rate range of occurrence of the positive slope characteristics was lower in the forward rake and skew pump than in the sweepback pump.