Pressure fluctuation test and vortex observation in Francis turbines draft tube

29th IAHR Symposium on Hydraulic Machinery and Systems

Zhu, L.^1 ; Meng, X.C.^1 ; Zhang, J.G.^1 ; Chen, Y.^1 ; Zhang, H.P.^1 ; Wang, W.P.^1 ; Lu, L.^1

Laboratory of Hydraulic Machinery, China Institute of Water Resources and Hydropower Research, Beijing

100038, China^1

关键词: Experimental research;    High-speed photography technique;    Operating condition;    Peak to peak amplitudes;    Pressure fluctuation;    Pressure fluctuation measurements;    Resonance frequencies;    Resonant condition;   

Others  :  https://iopscience.iop.org/article/10.1088/1755-1315/240/2/022029/pdf
DOI  :  10.1088/1755-1315/240/2/022029

来源: IOP

【 摘 要 】

The pressure fluctuations in draft tube causes serious vibration and instability, which may affect the safe operation of turbines. In this paper, the pressure fluctuation of hydraulic turbine is studied by means of model test. Two model turbines with specific speed NQE0 of 0.1221 and 0.1178 are selected for experimental research, and pressure fluctuation measurement and vortex observation are carried out on the universal hydraulic machinery test stand under typical part-load and overload operating conditions. The influence of Reynolds number and Thoma number on the draft tube vortex was verified by adjusting the test head HM and tail water pressure pDT on the model test stand. The high-speed photography technique was applied to observe the vortex in the draft tube, meanwhile, the pressure fluctuation signal of the vortex was acquired and analysed. The peak-to-peak amplitude and the frequency of the pressure fluctuation are analysed and compared with the vortex zone morphology. The results show that, 1) the influence of Reynolds number on pressure fluctuation can generally be neglected in the range of Reynolds number Re>4×106; 2) pressure fluctuation may decrease with the Thoma number before critical cavitation in special overload conditions, indicating that the impact of cavitation on fluctuation is related to the shape of vortex rope; 3) resonance frequency is obtained at special part-load point, the resonant condition should be confirmed accurately due to the risk of system resonance.