Numerical Prediction of Non-Cavitating and Cavitating Vortex Rope in a Francis Turbine Draft Tube

Abstract

The paper presents a prediction of vortex rope in a draft tube obtained by the numerical flow analysis. The main goal of the research was to numerically predict pressure pulsation amplitude versus different guide vanes openings and compare the results with experimental ones. Three turbulent models (SAS-SST, ω-RSM and LES) were used. Also the effect of different domain configurations, grid density and time step size on results was examined. At first analysis was done without cavitation, while later at one operating point the cavitation model was included.

On the Flow Instabilities and Turbulent Kinetic Energy of Large-Scale Francis Hydroturbine Model at Low Flow Rate Conditions

“…With the aid of particle image velocimetry (PIV), the velocity fields of a model pump-turbine with a straight cone draft tube were also measured, which validated the former numerical findings [10] and identified the correlation between the vortex rope rotation and the pressure fluctuations [11]. Meanwhile, with various numerical results for the draft tube vortex prediction, the scale-adaptive simulation (SAS), Reynolds stress model (RSM), and large eddy simulation (LES) were suggested to be suitable for this cavitation flow [12]. Kuibin et al (2010) presented a mathematical model which could reproduce the vortex rope geometry, precessing frequency, and associated pressure fluctuations.…”

Experimental Investigation on the Characteristics of Hydrodynamic Stabilities in Francis Hydroturbine Models

“…It was found that the flow field simulation needs to include the entire flow passage to model the runner vane surface 2 Advances in Mechanical Engineering pressure distribution so that stresses in the runner vane can be accurately calculated. Jošt and Lipej [6] numerically predicted the patterns of vortex rope in the draft tube, and they concluded that pressure fluctuations were usually a result of the strong vortex created in the center of flow at the outlet of the runner. Their simulations also showed that the results based on the improved Reynolds averaged Navier Stokes model (RANS) rather than the multiphase cavitation model agreed better to the experimental results.…”

Minimizing the Principle Stresses of Powerhoused Rock-Fill Dams Using Control Turbine Running Units: Application of Finite Element Method

“…Jošt and Lipej built a three-dimensional (3D) numerical model for a Francis turbine unit to predict the vortex rope in the draft tube based on numerical flow analyses by performing two analyses, both with and without cavitation effects [8]. Another study reported a numerical analysis of the cavitation turbulent flow in a Francis turbine under partial load operation using the k-ω shear stress transport turbulence model in the Reynolds-averaged Navier-Stokes equations [9].…”

“…The vibrational effect produced by the hydraulic turbines was studied by mechanical engineering researchers to assess their hydraulic performance due to powerhouse operation. Mechanical researchers [3,8,[10][11][12][13][14][15][16][17][41][42][43][44][45] focused on modeling and analysis of pressure distribution on the turbine draft tube. There is no comprehensive study connecting the vibration effect on the dam body, including the powerhouse and the vibration effect generated by operating the turbines inside the powerhouse.…”