Unsteady Flow Field Analysis in an Axial Flow Pump at Design Flow Rate and Partial Flow Rate

Understanding the unsteady flow structure of axial pumps is crucial for pump design to reduce losses and increase efficiency. This paper analyzes both the steady and unsteady flow structures in the diffuser at design and partial flow rates. The unsteady flow field in the axial pump is examined using URANS numerical analysis, and changes according to the flow rate are described based on the flow field at 70 % span. The results shows that the impeller wake, which exhibits dominant unsteady flow characteristics, mixes with the main flow during transportation, becomes deformed due to the flow structure in the diffuser, and plays a role in reducing mixing losses. This is attributed to the increase in passage blockage area at the diffuser blade pressure surface as the flow rate decreases. Therefore, a diffuser design that maximizes the effect of reducing mixing losses even at partial load points is required.