Studying the impact of impeller geometrical parameters on the high-efficiency working range of pump as turbine (PAT) installed in the water distribution network

Abstract

The development plan for micro hydropower is expanding with an increasing focus on renewable energy sources. There is increasing attention to using PATs to recover extra hydraulic energy in the water distribution network (WDN) pipelines. In this paper, the performance curves of PAT installed instead of pressure-reducing valves in WDN were investigated. The quality and reliability of numerical simulations were validated compared to the experimental results. Investigating hourly flow rate variations in WDN shows that the PAT working conditions change frequently and operate for a long time under off-design conditions. Since there are no tools to control and guide the fluid to the impeller, there is no proper conformance between the inlet flow and the blade profile, and in this condition loss increases and efficiency decreases. In order to improve the PAT performance in the working range, the effect of modifying parameters of blade thickness, blade number, and blade inlet width is numerically investigated. Optimal geometric parameters for designing a special impeller were determined by considering the flow rate changes of the PRS over 4 working months. Analyzing the PAT performance with a special impeller indicates that losses caused by the flow separation at the leading and trailing edges of the blade as well as the formation of vortices are significantly reduced. Moreover, the fluid's tendency to follow the blade profile is improved due to the flow field form in impeller passages, and the PAT's high-efficiency working range is extended. The greatest increase in efficiency occurs in the overload flow rate (1.2QBEP) and is improved by 6.48%. In this case study, the power generation capacity of the soft pressure regulating system (SPRS) will increase by 5.1% using the special impeller.