Study on the energy loss characteristics of ultra-low specific speed PAT under different short blade lengths based on entropy production method

With the increasing attention to micro-hydro power, the PAT has a broad prospect in micro-hydro power generation because of its low cost and simple structure. The ultra-low specific speed pump as turbine (USSPAT) is widely used in remote areas to realize micro-hydro power generation because of its advantages, such as high output power under a small flow rate. However, the output power of USSPAT is closely related to the length of the short blade. Therefore, this paper optimizes the design of USSPAT and selects four groups of short blades for the numerical simulation of energy loss characteristics of the USSPAT based on entropy production theory. Unlike other fluid machinery, the entropy production of USSPAT increases with the flow rate increase, so it has certain limitations to measure the energy loss of USSPAT under different flow rates simply by entropy production method. Therefore, the power loss number is defined in this paper to characterize the energy loss characteristics of PAT at different flow rates. The energy loss in the impeller is always the largest under all flow rate conditions, but at 0.4Qdes, the energy loss in the chamber is the largest. The length of the short blade mainly causes the change of entropy production in the downstream region at large flow rates. In contrast, at small flow rates, the entropy production in the upstream region changes the most. In addition, it is also found that the determination of the optimal Rs can effectively suppress the incident loss in the impeller inlet and the high wall shear in the local regions. As a result, to improve the performance of the USSPAT, it is necessary to consider the length of short the blade as an essential parameter. This study not only reveals the energy loss characteristics of the USSPAT, but also provides a new perspective for optimizing the USSPAT structure.