Numerical Investigation of the Flow Structure in a Kaplan Draft Tube at Part Load

28th IAHR symposium on Hydraulic Machinery and Systems

Maddahian, R.^1 ; Cervantes, M.J.^2 ; Sotoudeh, N.^1

Faculty of Mechanical Engineering, Tarbiat Modares University, Tehran, Iran^1

Division of Fluid and Experimental Mechanics, Lulea University of Technology, Lulea

SE 971 87, Sweden^2

关键词: Flow features;    Numerical investigations;    Part load conditions;    Pressure fluctuation;    Shear-stress transport;    Turbulent stress;    Velocity gradients;    Vortex identifications;   

Others  :  https://iopscience.iop.org/article/10.1088/1755-1315/49/2/022008/pdf
DOI  :  10.1088/1755-1315/49/2/022008

来源: IOP

【 摘 要 】

This research presents numerical simulation of the unsteady flow field inside the draft tube of a Kaplan turbine at part load condition. Due to curvature of streamlines, the ordinary two-equations turbulence models fail to predict the flow features. Therefore, a modification of the Shear Stress Transport (SST-SAS) model is utilized to approximate the turbulent stresses. A guide vane, complete runner and draft tube are considered to insure the real boundary conditions at the draft tube inlet. The outlet boundary is assumed to discharge into the atmosphere. The obtained pressure fluctuations inside the draft tube are in good agreement with available experimental data. In order to further investigate the RVR formation and its movement, the λ2criterion, relating the position of the vortex core and strength to the second largest Eigen value of the velocity gradient tensor, is employed. The method used for vortex identification shows the flow structure and vortex motion inside the draft tube accurately.