Unsteady flow characteristics of an AFP based on energy loss and vortex identification under rotating stall condition

Rotating stall, as a typical unsteady flow phenomenon in the axial flow pump (AFP), might easily result in a sharp decline in the performance of the AFP, thereby affecting the safe and stable operation of the pump. To better understand the loss mechanism of flow in the AFP, this paper numerically computes the unsteady flow of an AFP with guide vanes under a variety of working conditions. Unstable flow characteristics such as flow separation, typical vortex structure and flow loss of the pump under varied working conditions are analyzed using energy loss and vortex identification methods. The analysis of boundary vorticity flow (BVF) of the pump flow field shows that unstable flow can be observed in the BVF positive peak area on the blade surface, affecting the work of the impeller. Meanwhile, there is also unsteady flow from the trailing edge of the blade to the pressure surface of the adjacent blade near the impeller hub. It is gradually enlarged to block the impeller channel as the stall aggravates, causing the formation of a ‘saddle zone’ in the AFP. The guide vane and the impeller are core areas of energy loss within the AFP. On this basis, large numbers of vortex inside the impeller and the impact of unstable flow on the blades are the main contributors to the energy loss of the impeller.