Numerical investigation of tip clearance cavitation in Kaplan runners

28th IAHR symposium on Hydraulic Machinery and Systems

Nikiforova, K.^1 ; Semenov, G.^2 ; Kuznetsov, I.^3 ; Spiridonov, E.^2

Polytechnical State University, St.Petersburg, Russia^1

PJSC Power Machines, LMZ, St.Petersburg, Russia^2

Head of Department, PJSC Power Machines, LMZ, St.Petersburg, Russia^3

关键词: Continuous distribution;    Engineering techniques;    Homogeneous mixtures;    Numerical computations;    Numerical investigations;    Streamline curvature;    Tip vortex cavitations;    Vortex structures;   

Others  :  https://iopscience.iop.org/article/10.1088/1755-1315/49/9/092008/pdf
DOI  :  10.1088/1755-1315/49/9/092008

来源: IOP

【 摘 要 】

There is a gap between the Kaplan runner blade and the shroud that makes for a special kind of cavitation: cavitation in the tip leakage flow. Two types of cavitation caused by the presence of clearance gap are known: tip vortex cavitation that appears at the core of the rolled up vortex on the blade suction side and tip clearance cavitation that appears precisely in the gap between the blade tip edge and the shroud. In the context of this work numerical investigation of the model Kaplan runner has been performed taking into account variable tip clearance for several cavitation regimes. The focus is put on investigation of structure and origination of mechanism of cavitation in the tip leakage flow. Calculations have been performed with the help of 3-D unsteady numerical model for two-phase medium. Modeling of turbulent flow in this work has been carried out using full equations of Navier-Stokes averaged by Reynolds with correction for streamline curvature and system rotation. For description of this medium (liquid-vapor) simplification of Euler approach is used; it is based on the model of interpenetrating continuums, within the bounds of this two- phase medium considered as a quasi-homogeneous mixture with the common velocity field and continuous distribution of density for both phases. As a result, engineering techniques for calculation of cavitation conditioned by existence of tip clearance in model turbine runner have been developed. The detailed visualization of the flow was carried out and vortex structure on the suction side of the blade was reproduced. The range of frequency with maximum value of pulsation was assigned and maximum energy frequency was defined; it is based on spectral analysis of the obtained data. Comparison between numerical computation results and experimental data has been also performed. The location of cavitation zone has a good agreement with experiment for all analyzed regimes.