Publications de Steven Roth | EPFL Graph Search

Photocarrier-induced band-gap renormalization and ultrafast charge dynamics in black phosphorus

Majed Chergui, Marco Grioni, Michele Puppin, Alberto Crepaldi, Steven Roth, Gianmarco Gatti

With its tunable band-gap and its unique optical and electronic properties black phosphorus (BP) opens exciting opportunities for optoelectronic nanotechnology. The band-gap extends from the visible to the mid-infrared spectral range, as a function of samp ...

2019

Interaction of a pulsating vortex rope with the local velocity field in a Francis turbine draft tube

François Avellan, Arthur Tristan Favrel, Christian Landry, Andres Müller, Matthieu Dreyer, Steven Roth, Alberto Bullani

Acoustic resonances in Francis turbines often define undesirable limitations to their operating ranges at high load. The knowledge of the mechanisms governing the onset and the sustenance of these instabilities in the swirling flow leaving the runner is es ...

IOP science2013

Fluid-Structure Coupling Effects on the Dynamic Response of Pump-Turbine Guide Vanes

Steven Roth

Hydraulic pump-turbines are subject to a high periodic excitation due to the Rotor-Stator Interaction, RSI. Basically, the RSI is caused by the impeller blade passage in the wake of the guide vanes in generating mode, or upstream from the guide vanes in pu ...

EPFL2012

Influence of the Pump-Turbine Guide Vanes Vibrations on the Pressure Fluctuations in the Rotor-Stator Vaneless Gap

François Avellan, Mohamed Farhat, Vlad Hasmatuchi, Steven Roth, Francisco Botero

We investigate the Rotor-Stator Interaction in a pump-turbine reduced scale model by considering fluid-structure coupling. The pressure fluctuations amplitude in the rotor-stator vaneless gap has generally been shown to increase linearly with the operating ...

2011

Experimental Evidence of Rotating Stall in a Pump-Turbine at Off-Design Conditions in Generating Mode

François Avellan, Mohamed Farhat, Vlad Hasmatuchi, Steven Roth, Francisco Botero

An experimental investigation of the rotating stall in reduced scale model of a low specific speed radial pump-turbine at runaway and turbine brake conditions in generating mode is achieved. Measurements of wall pressure in the stator are performed along w ...

American Society of Mechanical Engineers2011

Non-Linear Stability Analysis of a Reduced Scale Model Pump-Turbine at Off-Design Operation

François Avellan, Christian Landry, Andres Müller, Sébastien Alligné, Vlad Hasmatuchi, Steven Roth

Nowadays, the pump-storage power plants are a proven solution for storing electricity at large scale and offering flexibility to the power management. Therefore, the hydraulic machines are increasingly subject to off-design operation, start-up and shutdown ...

2011

Hydrodynamics of a Pump-Turbine at Off-Design Operating Conditions: Numerical Simulation

François Avellan, Mohamed Farhat, Vlad Hasmatuchi, Steven Roth, Francisco Botero

Flow numerical simulations in a low specific speed radial pump-turbine scale model are performed to investigate off-design operating conditions in generating mode. The Best Efficiency Point (BEP) and the runaway operating conditions at 10° guide vanes open ...

2011

Fluid-Structure Coupling in the Guide Vanes Cascade of a Pump-Turbine Scale Model

François Avellan, Mohamed Farhat, Vlad Hasmatuchi, Steven Roth, Francisco Botero

The present study concerns fluid-structure coupling phenomena occurring in a guide vane cascade of a pump-turbine scale model placed in the EPFL PF3 test rig. An advanced instrument set is used to monitor both vibrating structures and the surrounding flow. ...

International Association For Hydraulic Research2010

High-speed flow visualization in a pump-turbine under off-design operating conditions

François Avellan, Mohamed Farhat, Vlad Hasmatuchi, Steven Roth, Francisco Botero

The flow hydrodynamics in a low specific speed radial pump-turbine reduced scale model is experimentally investigated under off-design operating conditions in generating mode. Wall pressure measurements, in the stator, synchronized with high-speed flow vis ...

International Association For Hydraulic Research2010

Advanced Instrumentation for Measuring Fluid-Structure Coupling Phenomena in the Guide Vanes Cascade of a Pump-Turbine Scale Model

François Avellan, Mohamed Farhat, Vlad Hasmatuchi, Steven Roth, Francisco Botero

In the present study, the fluid-structure coupling is investigated in the guide vanes of a pump-turbine scale model placed in one of the test rigs of the Laboratory for Hydraulic Machines (EPFL) in Lausanne. The paper focuses on the advanced instrumentatio ...

American Soc Mechanical Engineers, Three Park Avenue, New York, Ny 10016-5990 Usa2010