Influence of the Runner Gap on the Flow Field in the Draft Tube of a Low Head Turbine

28th IAHR symposium on Hydraulic Machinery and Systems

Junginger, Bernd^1 ; Riedelbauch, Stefan^1

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

70550, Germany^1

关键词: Experimental modeling;    Flow field simulation;    Hydraulic machines;    Integral quantity;    Operating points;    Pressure signal;    Propeller turbines;    Velocity profiles;   

Others  :  https://iopscience.iop.org/article/10.1088/1755-1315/49/2/022011/pdf
DOI  :  10.1088/1755-1315/49/2/022011

来源: IOP

【 摘 要 】

The gap flow of axial turbines is usually neglected in the design process of hydraulic machines, although it can lead to a stabilization of the draft tube flow. Though, this negligence of the gap can falsify the flow field in the draft tube. Presented in this paper are simulations of an axial propeller turbine operated at Δγ= ΔγBEPwith Q > Qbep. Simulations of four gap sizes, using a mesh with about 15 million elements for the entire machine, are performed. Additionally, two turbulence models are applied, the k-ω-SST and the SAS-SST model. At the evaluated operating point a full load vortex develops. Depending on the turbulence model the developing vortex rope can either arise from the hub in a straight shape or in a shape resembling a corkscrew. Integral quantities such as head and torque are compared with experimental model test results performed in the laboratory of the Institute. Flow field simulation results are evaluated for different gap widths. Furthermore, the impact of the gap flow respectively the gap size can be observed in velocity profiles evaluated at different positions downstream the runner until to the end of the draft tube cone. Moreover, the pressure signals recorded at the beginning of the draft tube cone are also affected by the gap flow.