Air injection test on a Kaplan turbine: prototype - model comparison

28th IAHR symposium on Hydraulic Machinery and Systems

Angulo, M.^1 ; Rivetti, A.^1 ; Díaz, L.^1 ; Liscia, S.^1

Laboratory of Hydromechanics, UNLP, 47 street No 200, La Plata

1900, Argentina^1

关键词: Air injection tests;    Beneficial effects;    Cavitation intensity;    Pressure fluctuation;    Pressure pulsation;    Reducing vibrations;    Structural vibrations;    Tip vortex cavitations;   

Others  :  https://iopscience.iop.org/article/10.1088/1755-1315/49/2/022006/pdf
DOI  :  10.1088/1755-1315/49/2/022006

来源: IOP

【 摘 要 】

Air injection is a very well-known resource to reduce pressure pulsation magnitude in turbines, especially on Francis type. In the case of large Kaplan designs, even when not so usual, it could be a solution to mitigate vibrations arising when tip vortex cavitation phenomenon becomes erosive and induces structural vibrations. In order to study this alternative, aeration tests were performed on a Kaplan turbine at model and prototype scales. The research was focused on efficiency of different air flow rates injected in reducing vibrations, especially at the draft tube and the discharge ring and also in the efficiency drop magnitude. It was found that results on both scales presents the same trend in particular for vibration levels at the discharge ring. The efficiency drop was overestimated on model tests while on prototype were less than 0.2 % for all power output. On prototype, air has a beneficial effect in reducing pressure fluctuations up to 0.2 ‰ of air flow rate. On model high speed image computing helped to quantify the volume of tip vortex cavitation that is strongly correlated with the vibration level. The hydrophone measurements did not capture the cavitation intensity when air is injected, however on prototype, it was detected by a sonometer installed at the draft tube access gallery.