Experimental and numerical investigation of unsteady behavior of cavitating vortices in draft tube of low specific speed Francis turbine

27th IAHR Symposium on Hydraulic Machinery and Systems

Tamura, Y.^1 ; Tani, K.^1 ; Okamoto, N.^2

Hitachi Mitsubishi Hydro Co., Japan^1

Shikoku Electric Power Co., Inc., Japan^2

关键词: Expansion and contraction;    Experimental research;    Low specific speed;    Numerical approaches;    Numerical investigations;    Numerical research;    Pressure pulsation;    Unsteady behaviors;   

Others  :  https://iopscience.iop.org/article/10.1088/1755-1315/22/3/032011/pdf
DOI  :  10.1088/1755-1315/22/3/032011

来源: IOP

【 摘 要 】

At both partial and full load of Francis turbines, the unsteady behavior of cavitating draft tube vortices occurs and leads to undesirable matters such as power house vibration, noise and power swing in some cases. This paper presents the investigation of the interaction between the flow pattern at runner outlet and the unsteady behavior of cavitating vortices in draft tube with experimental and numerical approaches. On the experimental research, the pressure pulsation in the draft tube is measured and the unsteady behavior of cavitating vortices is taken pictures with a high speed camera in the model test. On the numerical research, by Computational Fluid Dynamics (CFD) adopting a two-phase unsteady analysis, the analysis domain from the guide vane to the draft tube is carried out for investigating the interaction between the runner outlet flow and the vortex pattern. The pressure pulsation at the upper draft tube and the unsteady behavior of cavitating vortices obtained from CFD results are similar to those obtained in the model test. Detailed analysis of CFD results at overload indicates the repeat of expansion and contraction of cavitating vortices, which were shaped helical vortices with opposite direction of runner rotation, and the corresponding flow pattern in every time step of the pressure pulsations.