Publications de Keita Yamamoto

Control of spin currents by magnon interference in a canted antiferromagnet

Jean-Philippe Ansermet, Dirk Grundler, Keita Yamamoto, Peng Chen, Junfeng Hu

Controlling the spin current lies at the heart of spintronics and its applications. In ferromagnets, the sign of spin currents is fixed once the current direction is determined. However, spin currents in antiferromagnets can possess opposite polarizations, ...

Springer Science and Business Media LLC2025

Evaluation of a Dynamic Transfer Matrix for a Hydraulic Turbine

François Avellan, Andres Müller, Keita Yamamoto

It is well known that hydraulic machines experience various types of flow instabilities causing a negative influence on the system under off-design operations. The transfer matrix method correlating the flow properties in upstream and downstream of hydraul ...

2020

Swirl number based transposition of flow-induced mechanical stresses from reduced scale to full-size Francis turbine runners

François Avellan, Christian Landry, Arthur Tristan Favrel, Keita Yamamoto, Joao Gomes Pereira Junior

At part load conditions, Francis turbines are subject to the emergence of a hydrodynamic instability in their draft tube, referred to as precessing vortex rope. It induces pressure pulsations in the water passages at the precession frequency of the vortex, ...

2020

Physical Mechanism of Interblade Vortex Development at Deep Part Load Operation of a Francis Turbine

François Avellan, Arthur Tristan Favrel, Keita Yamamoto

For seamless integration of growing electricity production from intermittent renewable energy sources, Francis turbines are under increasing demand to extend their operating range. This requires Francis turbines to operate under off-design conditions, wher ...

ASME2019

Experimental evidence of inter-blade cavitation vortex development in Francis turbines at deep part load condition

François Avellan, Arthur Tristan Favrel, Keita Yamamoto

Francis turbines are subject to various types of cavitation flow depending on the operating condition. To enable a smooth integration of the renewable energy sources, hydraulic machines are now increasingly required to extend their operating range, especia ...

Springer Verlag2017

Experimental investigation of the mass flow gain factor in a draft tube with cavitation vortex rope

François Avellan, Arthur Tristan Favrel, Christian Landry, Andres Müller, Sébastien Alligné, Keita Yamamoto

At off-design operating operations, cavitating flow is often observed in hydraulic machines. The presence of a cavitation vortex rope may induce draft tube surge and electrical power swings at part load and full load operations. The stability analysis of t ...

2017

Dynamics of the precessing vortex rope and its interaction with the system at Francis turbines part load operating conditions

François Avellan, Arthur Tristan Favrel, Christian Landry, Andres Müller, Keita Yamamoto, Joao Gomes Pereira Junior

At part load conditions, Francis turbines experience the formation of a cavitation vortex rope at the runner outlet whose precession acts as a pressure excitation source for the hydraulic circuit. This can lead to hydro-acoustic resonances characterized by ...

2017

Experimental Hydro-Mechanical Characterization of Full Load Pressure Surge in Francis Turbines

François Avellan, Arthur Tristan Favrel, Christian Landry, Andres Müller, Keita Yamamoto

Full load pressure surge limits the operating range of hydro-electric generating units by causing significant power output swings and by compromising the safety of the plant. It appears during the off-design operation of hydraulic machines, which is increa ...

2017

Flow characteristics and influence associated with inter-blade cavitation vortices at deep part load operations of a Francis turbine

François Avellan, Arthur Tristan Favrel, Christian Landry, Keita Yamamoto

At a deep part load operation, Francis turbines are subject to the formation of inter-blade cavitation vortices inside blade channels, however its characteristics are not fully understood yet. The present study aims to investigate the development of the in ...

2017

Hydrodynamics of Francis turbine operation at deep part load condition

Keita Yamamoto

The electrical energy production from New and Renewable Energy (NRE) sources have become increasingly important in the past decades. However, intermittent electrical generation from NRE sources due to their stochastic nature often prevents stable power out ...

EPFL2017