Numerical Investigation of Cavitation Improvement for a Francis Turbine

9th International Symposium on Cavitation

Yao, Zhifeng^1,2 ; Xiao, Ruofu^1,2 ; Wang, Fujun^1,2 ; Yang, Wei^1,2

College of Water Resources and Civil Engineering, China Agricultural University, Beijing

100083, China^1

Beijing Eng. Research Center of Safety and Energy Saving Technology for Water Supply Network System, Beijing

100083, China^2

关键词: Best efficiency point;    Cavitation performance;    Geometry optimization;    Hydraulic machines;    Internal flow field;    Numerical investigations;    Outlet diameters;    Pressure surface;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/656/1/012075/pdf
DOI  :  10.1088/1742-6596/656/1/012075

来源: IOP

【 摘 要 】

Cavitation in hydraulic machine is undesired due to its negative effects on performances. To improve cavitation performance of a Francis turbine without the change of the best efficiency point, a model runner geometry optimization was carried out. Firstly, the runner outlet diameter was appropriately increased to reduce the flow velocity at runner outlet region. Then, to avoid the change of the flow rate at the best efficiency point, the blade shapes were carefully adjusted by decreasing the blade outlet angles and increasing the blade wrap angles. A large number of the modified runners were tested by computational fluid dynamic (CFD) method. Finally the most appropriate one was selected, which has the runner outlet diameter 10% larger, the blade outlet angles 3 degrees smaller and the blade wrap angles 5 degrees larger. The results showed that the critical cavitation coefficient of the model runner decreased at every unit rotational speed after the optimization, and the effect was much remarkable at relative high flow rate. Besides, by analysing the internal flow field, it was found that the zone of the low pressure on pressure surface of the optimized turbine blades was reduced, the backflow and vortex rope in draft tube were reduced, and the cavitation zone was reduced obviously.