Comparative study on stator corner separation vortex characteristics in axial-flow pump and tubular pump: To understand the effects of guide-vane cone diffusion on horn-like vortices

Abstract

The guide-vane cone diffusion is a typical structural difference between an axial-flow pump and a tubular pump, which is shown as low diffusivity and high diffusivity respectively, but it is still unclear how this structural difference affects the vortex characteristics in stator corner separation flows. In this paper, a comparative study of stator corner separation flows in an axial-flow pump and a tubular pump was conducted, and the effects of guide-vane cone diffusion on vortical structures were clarified. Firstly, for the apparent vortical features, compared with the guide-vane of axial-flow pump with low diffusivity, the horn-like vortex in the guide-vane of tubular pump with high diffusivity has the features of smaller scale, weaker swirling strength, shorter evolution cycle and lower pressure fluctuations. Secondly, for the vortex dynamics mechanism, the guide-vane cone diffusion of tubular pump can cause additional pressure energy recovery, which leads to higher adverse pressure gradients, so it is easier to induce additional shroud backflow near the suction surface. In this coupled flow field of main flow, namely hub corner separation flow and shroud backflow, the streamwise periodic oscillation of the pressure function gradient ωS ·▽(▽p/ρ) is found, and it induces the unique vortex-street-like distributions of the deformational vorticity ωS and the rigid vorticity ωR . This physical effect causes a mutual competition between the horn-like vortex near the hub corner and the opposite backflow vortex near the shroud side. It is this competition effect originating from the guide-vane cone diffusion that greatly suppresses the development of the horn-like vortex in a tubular pump.