FAVREL, Arthur Tristan Researcher
Research Institute for Science and Engineering
Hydraulic turbines operating in off-design conditions may experience two types of draft tube flow instabilities:
- Cavitation surge at full load, characterized by self-excited oscillations of a axisymmetric cavitation vortex inducing severe pressure pulsations;
- Vortex-induced pressure source, inducing pressure pulsations and resonance in certains conditions.
The latter is induced by a precessing vortex core occurring in swirling flows after vortex breakdown. This phenomenon is encountered in a wide range of engineering applications involving swirling flows and the results of the proposed research might attract attention of researchers in the fields of fundamental swirling flow dynamics.
Following my backgroung and previous researches, this research plan proposes to investigate both phenomena from an experimental and theoretical point of view. It is proposed to take advantage of the experimental facilities of Waseda University (i.e. simple air draft tube with swirlers, Venturi water draft tube with swirlers and Francis turbine reduced scale model) and to upgrade them to enable advanced optical flow measurements, such as stereo Particle Image Velocimetry and Laser Doppler Velcometry, and a new type of cavitation visualization based on two cameras, which will be developped in the present research. The final objective is to gain a better understanding of the underlying physical mechanisms involved in both phenomena, to develop more accurate models enabling the prediction of flow instabilities dynamics and the induced effects, i.e. pressure and flow rate fluctuations, and finally to propose counter-measures mitigating these instabilities, based on a precise understanding of the underlying physical mechanisms.