Experimental and numerical analysis of turbulent velocity fluctuations in a Francis turbine draft tube in part load operation

29th IAHR Symposium on Hydraulic Machinery and Systems

Frey, A.^1 ; Kirschner, O.^1 ; Riedelbauch, S.^1 ; Jester-Zuerker, R.^2 ; Jung, A.^2

Institute of Fluid Mechanics and Hydraulic Machinery, University of Stuttgart, Pfaffenwaldring 10, Stuttgart

70569, Germany^1

Voith Hydro Holding GmbH and Co. KG, Alexanderstraße 11, Heidenheim

89522, Germany^2

关键词: CFD simulations;    Experimental and numerical analysis;    High resolution;    Hybrid RANS-LES;    Part load operation;    Rotating vortex;    Turbulent velocity fluctuations;    Velocity fluctuations;   

Others  :  https://iopscience.iop.org/article/10.1088/1755-1315/240/2/022032/pdf
DOI  :  10.1088/1755-1315/240/2/022032

来源: IOP

【 摘 要 】

The part load operation of turbines with non-regulated runner blades is often associated with the occurrence of a rotating corkscrew-shaped vortex rope in the draft tube. Due to its negative influence on power plants, this phenomenon is an important factor in the design process of a water turbine. Investigations using CFD aim to predict the draft tube flow, especially regarding the efficiency and the losses of the turbine. As there are still discrepancies between CFD simulations and experimentally gained data, a research project on this subject was initiated, including extensive measurements with 2D-Laser-Doppler-Anemometry. CFD simulations were carried out using high-resolution hybrid RANS-LES turbulence models. In this paper, the interrelation of the turbulent velocity fluctuations and the periodic vortex rope movement is being examined. Therefore, the measured data is provided time averaged and phase resolved. The specialities of the swirling flow influenced by the periodic vortex concerning the turbulence are illustrated on two planes, one downstream the runner in the cone and one at the lowest position of the draft tube. The results show good conformity with the CFD data including periodic part of the velocity fluctuations. The dependence of the velocity field on the rotating vortex rope is significantly higher in the cone than at the end of the draft tube bend.