Effect of blade thickness on rotating stall of mixed-flow pump using entropy generation analysis

Abstract

In a mixed-flow pump, the energy performance curve always appears as an unsteady region under rotating stall condition. In this paper, computational fluid dynamics (CFD) technology is employed to study the effect of variation in blade thickness of the impeller for the purpose of improving the stall characteristics of the mixed-flow pump. The local loss caused by the turbulent flow is investigated using the entropy generation method that considers the wall effects. The results show that the stall region of mixed-flow pump is closely related to the blade thickness, and the total entropy generation (TEG) in impeller and guide vane are affected. At design flow rate, the tip leakage vortex (TLV) accounts for most of the hydraulic loss in the impeller and the change in the blade thickness does not influence the pump head or efficiency significantly. Whereas, within stall region, the stall vortex and TLV determine the high TEG region in the impeller, the backflow and secondary flow are the source of major hydraulic loss in the guide vane. A small increase in the blade thickness reduces the loss caused by the stall vortex which delays the stall point. However, once the blade thickness increases significantly, the stall vortex becomes bigger which deteriorates the flow fields in the impeller and guide vane resulting in rotating stall. Thus, the blade thickness can be considered as a key parameter to minimize the occurrence of rotating stall in a mixed-flow pump for improving its efficiency and safety.