Experimental study of the influence of Thoma number and model testing head on pressure fluctuation in draft tube of a Francis turbine

28th IAHR symposium on Hydraulic Machinery and Systems

Qin, Daqing^1,2 ; Xu, Yongliang^1,2 ; Liu, Wenjie^1,2 ; Wei, Xianzhu^1,2 ; Zhao, Yue^1,2 ; Meng, Xiaochao^3

State Key Laboratory of Hydro-power Equipment, Harbin

150040, China^1

Harbin Electrical Machinery Company Limited, Harbin

150040, China^2

China Institute of Water Resources and Hydropower Research, Beijing

100038, China^3

关键词: Experimental methods;    Frequency components;    Head;    Load condition;    Pressure fluctuation;    Reference levels;    Thoma number;    Typical operating conditions;   

Others  :  https://iopscience.iop.org/article/10.1088/1755-1315/49/8/082017/pdf
DOI  :  10.1088/1755-1315/49/8/082017

来源: IOP

【 摘 要 】

In this paper, the influence of Thoma number and model testing head on pressure fluctuation of Francis turbines was studied through experimental method. Firstly, the influence of model testing head on pressure fluctuation in the draft tube was carried out by varying model testing head at 6 typical operating conditions including no load, deep part load, part load, optimum, rated and overload points. It is found that model testing head has little influence on amplitudes of the pressure fluctuation in the draft tube of Francis turbine within the test range, which represented the influence of similitude number such as Reynolds number, Froude number, Weber number and so on. Then, analysis of the influence of Thoma number on pressure fluctuation amplitudes in the draft tube as well as frequency was performed at the part load and rated load conditions. It shows that the Thoma number not only influences pressure fluctuation amplitude but also the distribution of the frequency components in the draft tube. Finally, comparison of pressure fluctuation with two different cavitation levels was carried out. It is reasonable that selection of guide vane centerline is as cavitation reference level in the pressure fluctuation tests for France turbines. Hence, when pressure fluctuation similarity is studied, apart from load condition, the influence of the difference of Thoma number and the selection of cavitation reference level should be considered.