Study on the impact of blades wrap angle 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 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 wrap angle of a centrifugal pump is not optimal for low specific speed turbines, so the impact of blades wrap angle on the PAT performance should be studied. In this paper, the impact is investigated by numerical and experimental methods. Firstly, a 3D model of an original PAT was built in CAD software, then the model was imported into the ICEM to generate grids and then imported into Ansys CFX for simulation. After simulation, a PAT prototype was tested in the 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’s performance. Finally, four PAT models with different blades wrap angles were developed to compare their performance in terms of both power output and water head reduction. The results show that the blades wrap angle does have effects on the PAT’s efficiency and hydraulic loss, to achieve a good balance between water head reduction and power output. The model with −60° wrap angle has the best performance.