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Numerical simulations of tip vortex responsible for drag, vibration and cavitation in Kaplan turbines


The HydroNET 2 project focuses on the improvement of hydraulic plants in several domains as project management, monitoring, hydropower design, real time simulation… The project is support by the CCEM, SwissElectricResearch, Canton du Valais and involves several partnerships as: EPFL, EMPA, EAWAG, Hochschule Luzern, ETH Zürich…

The HES-SO Valais-Wallis takes part to the project through the task 3, which deals with the numerical simulations of the tip vortex responsible for drag, vibration and cavitation in Kaplan turbines. The tip vortex takes place at approximately 30 % of the blade chord due to the pressure difference between the pressure side and the suction side. The vortex rolls up from the pressure side and evolves downstream the blade. The risk of erosion and the increase in loss charge lead to a large amount of studies to better understand the mechanisms that drive the vortex formation. Nevertheless, no model is sufficiently accurate to describe entirely the vortex generation and evolution particularly in the case of cavitation.

To improve our knowledge of these mechanisms, a research plan has been scheduled combining numerical computations and experimental measurements through a collaboration between the EPFL for the experimental part and the HES-SO Valais-Wallis for the computational one.

Concerning the numerical part of the task, three solvers are used:

  • the CFX commercial solver developed by Ansys,
  • the OpenFOAM open source solver distributed by OpenCFD Ltd and ESI Group,
  • the Yales 2 research solver developed by a group of research team, which leads by the Coria.

From the different capacities provide by these three solvers, we perform various computations:

  • applying RANS or LES model for the turbulence,
  • applying cavitation models available in the literature,
  • developing our own model to better take into account the interaction between turbulence and cavitation.

Comparing our results with the experimental data base provided by the EPFL, we try to develop new physical modelling and provide accurate design solution to inhibit or reduce the negative influence of the cavitating tip vortex in the hydraulic turbines.