Investigation and optimization into flow dynamics for an axial flow pump as turbine (PAT) with ultra-low water head

Abstract

When the water downstream is abundant, axial flow pumps are often used as turbines (PAT) for reverse power generation to obtain additional benefits. However, due to the actual water level difference, PAT usually operates at off-design conditions. The CFD technology and entropy production theory were used to study the working performance, flow characteristics, and energy loss mechanism of the blade adjustable axial-flow PAT under a low water head. The results indicate that the strength of the tubular vortex at the pressure surface and the separation position of the tip-leakage-vortex at the suction surface depend on the inlet angle of the blade. The energy loss in the draft tube is influenced by the velocity circulation at the runner’s outlet, which depends on the blade’s outlet angle. Subsequently, the blade inlet and outlet angles in the runner were optimized. In turbine mode, the overall efficiency of the optimized runner increased by an average of 0.99 %. The blade pressure load distribution of the optimized runner has improved, and the pressure fluctuation in the draft tube is also under control. In pump mode, due to the increasing of the inlet angle within the same demand pump head range, the optimized runner’s pumping flow increases by an average of 2 m3/s.