Open AccessNumerical Investigation of flow instabilities in Speed No-Load operation of a Bulb turbine
Author(s) -
Ken Yamamoto,
M Roubaty,
M Morisod,
Maxime Coulaud,
Sébastien Houde
Publication year - 2021
Publication title -
iop conference series. earth and environmental science
Language(s) - English
Resource type - Journals
eISSN - 1755-1307
pISSN - 1755-1315
DOI - 10.1088/1755-1315/774/1/012115
Subject(s) - turbine , torque , vortex , stall (fluid mechanics) , rotational speed , mechanics , flow (mathematics) , physics , control theory (sociology) , engineering , aerospace engineering , mechanical engineering , computer science , artificial intelligence , thermodynamics , control (management)
When operating in Speed-No-Load (SNL), turbines function at their synchronous rotating speed with a fraction of discharge at best efficiency point, ready for electrical grid connection. The flow in SNL condition is characterized by high swirling component leading to complex flow structures inside the runner, which generate wide-band pressure fluctuations. When operating in SNL condition, high specific speed turbines, such as axial turbines, can be damaged by significant pressure oscillations attributed to rotating vortex phenomena, alike rotating stall. However, understanding the fundamental flow dynamics behind the phenomena in SNL condition remains challenging due to the stochastic nature of flow. The present research highlights unsteady flow characteristics and flow instabilities in SNL condition of a bulb turbine by URANS simulations based on scale-resolving techniques. The simulation results provide evidence that the development of a rotating vortex array in precession with the runner is a major source of pressure oscillations and torque fluctuations in SNL operation of this bulb turbine.