Abstract
The aim of this study is to develop a reliable numerical model that provides additional information to experimental measurements and contributes to a better exploitation of hydraulic turbines during transient operation. The paper presents a numerical analysis of the flow inside a Kaplan turbine model operated at a fixed runner blade angle during load variation from the best efficiency point (BEP) to part load (PL) operation. A mesh displacement is defined in order to model the closure of the guide vanes. Two different types of inlet boundary conditions are tested for the transient numerical simulations: linear flow rate variation (InletFlow) and constant total pressure (InletTotalPressure). A time step analysis is performed and the influence of the time discretization over the fluctuating quantities is discussed. Velocity measurements at the corresponding operating points are available to validate the simulation. Spectrogram plots of the pressure signals show the times of appearance of the plunging and rotating modes of the rotating vortex rope (RVR) and the stagnation region developed around the centerline of the draft tube is captured.
Highlights
Nowadays, hydropower plants are experiencing frequent off-design operation regimes and load variations because of the fluctuating energy production requirements
Concerning the modelling of transient load variations of hydraulic turbines, the inlet boundary conditions may be provided as velocity or pressure
In order to analyse the rotating vortex rope (RVR) formation and decomposition, spectrogram plots of the pressure fl3u.3c.t2u.aStpioencstrianl tAhneadlyrasifst tube and on the runner blade recorded during the transient operation of the Kaplan turbine model are presented
Summary
Hydropower plants are experiencing frequent off-design operation regimes and load variations because of the fluctuating energy production requirements. The formation and mitigation of the RVR in the draft tubes of hydraulic machines were investigated experimentally during part load (PL) operation [7,8]. 33 ooff 2201 capture the RVR movement and showed that the turbulence model provides results in good uangrseteeamdeynstiwmiuthlatthioenesxopfetrhime eflnotwal ivnasliudeest.he draft tube of a Kaplan turbine during PL operation [28].
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