Publications by Keita Yamamoto

Control of spin currents by magnon interference in a canted antiferromagnet

Jean-Philippe Ansermet, Peng Chen, Dirk Grundler, Keita Yamamoto, 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, Joao Gomes Pereira Junior, Arthur Tristan Favrel, Keita Yamamoto

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, Andres Müller, Christian Landry, Sébastien Alligné, Arthur Tristan Favrel, 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, Andres Müller, Christian Landry, Joao Gomes Pereira Junior, Arthur Tristan Favrel, Keita Yamamoto

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, Andres Müller, Christian Landry, Arthur Tristan Favrel, 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, Christian Landry, Arthur Tristan Favrel, 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

LDV survey of cavitation and resonance effect on the precessing vortex rope dynamics in the draft tube of Francis turbines

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

The large-scale penetration of the electrical grid by intermittent renewable energy sources requires a continuous operating range extension of hydropower plants. This causes the formation of unfavourable flow patterns in the draft tube of turbines and pump ...

Springer Verlag2016

Numerical and experimental evidence of the inter-blade cavitation vortex development at deep part load operation of a Francis turbine

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

Francis turbines are subject to various types of the cavitation flow depending on the operating condition s. In order to compensate for the stochastic nature of renewable energy sources, it is more and more required to extend the operating range of the gen ...

International Association For Hydraulic Research2016

Space and time reconstruction of the precessing vortex core in Francis turbine draft tube by 2D-PIV

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

Francis turbines operating at part load conditions experience the development of a high swirling flow at the runner outlet, giving rise to the development of a cavitation precessing vortex rope in the draft tube. The latter acts as an excitation source for ...

International Association For Hydraulic Research2016

Measurement of the Self-Oscillating Vortex Rope Dynamics for Hydroacoustic Stability Analysis

François Avellan, Sébastien Alligné, Keita Yamamoto

Flow instabilities in hydraulic machines often feature oscillating cavitation volumes, which locally introduce compliance and mass flow gain effects. These unsteady characteristics play a crucial role in one-dimensional stability models and can be determin ...

American Society of Mechanical Engineers2016

Study of the vortex-induced pressure excitation source in a Francis turbine draft tube by particle image velocimetry

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

changes and loses its coherence, leading to a drastic reduction in the intensity of the induced excitation source. Francis turbines operating at part-load experience the development of a precessing cavitation vortex rope at the runner outlet, which acts as ...

Springer Verlag2015

Analysis of the part load helical vortex rope of a Francis turbine using on-board sensors

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

The cavitation helical vortex rope arising at Francis turbine partial load induces pressure fluctuations at the rope precession frequency, which can be decomposed into two components; the convective one and the synchronous one. The latter acts as an excita ...

Iop Publishing Ltd2015

Experimental method for the evaluation of the dynamic transfer matrix using pressure transducers

François Avellan, Andres Müller, Keita Yamamoto

This paper introduces an experimental method for the evaluation of dynamic transfer matrices using only pressure transducers. The discharge fluctuations are evaluated from the fluctuation of the pressure difference at different streamwise locations. The tr ...

Taylor & Francis Ltd2015

On the physical mechanisms governing self-excited pressure surge in Francis turbines

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

The required operating range for hydraulic machines is continually extended in an effort to integrate renewable energy sources with unsteady power outputs into the existing electrical grid. The off-design operation however brings forth unfavorable flow pat ...

IOP Publishing Ltd2014

Experimental investigation of the local wave speed in a draft tube with cavitation vortex rope

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

Hydraulic machines operating in a wider range are subjected to cavitation developments inducing undesirable pressure pulsations which could lead to potential instability of the power plant. The occurrence of pulsating cavitation volumes in the runner and t ...

IOP Publishing Ltd2014

Hydro-acoustic resonance behavior in presence of a precessing vortex rope: observation of a lock-in phenomenon at part load Francis turbine operation

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

Francis turbines operating at part load condition experience the development of a cavitating helical vortex rope in the draft tube cone at the runner outlet. The precession movement of this vortex rope induces local convective pressure fluctuations and a s ...

Iop Publishing Ltd2014