Study on the impact of blades curving degree on the performance of pumps as turbines used in water supply system of high rise buildings

The use of pumps as turbines (PATs) in different applications has attracted increasing attention in recent years. Based on our previous research, the PAT could be used in the water supply system of high rise buildings for water head reduction and hydropower generation, but the efficiency is relatively low. Due to the high water head and low flow rate, PATs used in water pipelines are usually low specific speed turbines. According to the impeller inlet and outlet velocity triangles, the blades curving degree of a centrifugal pump is not optimal for low specific speed turbines, so the impact of blades curving degree on the performance of PATs should be studied. In this paper, the impact is investigated by numerical and experimental methods. Firstly, a 3D model of the original PAT was developed in CAD software, and then the model was imported into the ICEM to generate grids for simulation in Fluent. After simulation, a PAT prototype was tested in a lab test rig to validate the simulation results. The comparison between simulation and experimental results indicates that although some deviations exist, the simulation could provide an acceptable prediction of the PAT performance. Finally, four PAT models with different curving blades (100%, 50%, -50% and -100%) were built and simulated to compare their performance in both power output and water head reduction. The results show that the blades curving degree does have effects on the PAT performance. To achieve a good balance between water head reduction and power output, the 50% curving degree has the best performance.