Numerical and Experimental Investigation of the Performance of Tandem Vanes for a Centrifugal Pump

Abstract

Conventional vane designs come with the disadvantage of flow detachment for high deflection. For axial machines, often tandem vanes are prevalent which combines two vanes for redirection of the flow and thus effectively prevents detachment. However, their application for radial machines has hardly been investigated so far. This study investigates the influence of tandem vanes on the performance in terms of head and efficiency of a centrifugal pump. First, different tandem designs were numerically investigated based on computational fluid dynamics (CFD). For a selected tandem variant, the numerical results were validated by experimental investigations. The preceding numerical investigations were done stationary by using a single passage model to compare the performance of different tandem impellers with a conventional impeller (unsplit vane). Therefore, a method was developed to design tandem vanes from given undivided vanes. In this way, the influence of the offset in the circumferential direction and the angle of attack of the rear blade profile were systematically investigated. Transient CFD simulations have been done for a complete single-stage volute pump. In the experiments, the performance curves for both the conventional and tandem impeller were determined. The results of this study show that tandem blades can increase the pressure rise of a centrifugal pump while maintaining almost the same efficiency if a suitable combination of blade angle and offset in the circumferential direction of the rear blade has been selected. Furthermore, the CFD results show that the detachment can be prevented inside the impeller passage.