Investigation on internal flow of draft tube at overload condition in low specific speed Francis turbine

28th IAHR symposium on Hydraulic Machinery and Systems

Tamura, Yuta^1 ; Tani, Kiyohito^1

Hitachi Mitsubishi Hydro Co., 2-1, Saiwaicho, 3-Chome, Hitachi

317-0073, Japan^1

关键词: Experimental approaches;    Low specific speed;    Numerical approaches;    Overload condition;    Pressure fluctuation;    Pressure pulsation;    Unsteady behaviors;    Unsteady phenomena;   

Others  :  https://iopscience.iop.org/article/10.1088/1755-1315/49/8/082016/pdf
DOI  :  10.1088/1755-1315/49/8/082016

来源: IOP

【 摘 要 】

The cavitating vortices causes the unsteady phenomena like the pressure fluctuation, the noise and the vibration in the draft tube at the overload condition which is the far operating point from the design point. Because the full load was normally near the design point, there were few troubles due to cavitating vortices at the full load. Today, however, the design point is sometimes set to lower load to achieve the high efficiency from the partial load to the full load in low specific speed Francis turbines, which have good performance to a change in a discharge. Then, the full load is relatively further from the design point. As the result, the potential for the cavitating vortices at the full load is increased. To control of the unsteady phenomena at the full load, the study focused on the cavitating vortices at the overload condition is important. This paper presents the unsteady behavior of the cavitating vortices at the overload condition with the scaled model of specific speed NQE=0.083. On the experimental approach, the pressure pulsation in the upper draft tube was measured and the unsteady behavior of cavitating vortices was taken movies with a high speed camera. On the numerical approach, Computational Fluid Dynamics (CFD) adopting a two-phase unsteady analysis was carried out. The pressure fluctuation and the velocity distribution of two runners, an original and a newly designed, were compared.