Rechercher

Paramétrage

Thèmes

Accessibility

Accessibility

Benjamin Luce

Maître de conférences CNU : SECTION 60 - MECANIQUE, GENIE MECANIQUE, GENIE CIVIL

Research topics

Geophysical flows

My current research (LMFL) is on the study of turbulence in geophysical flows, mainly in the atmospheric boundary layer.

Numerical tools: ERF and OpenFOAM

Two simulation tools are used:

  • ERF (Energy Research Forecast) is a massively parallel code (MPI+X, including GPU) with adaptive meshing capable of simulating atmospheric equations.
  • OpenFOAM is a simulation toolkit, mainly for fluid mechanics, adapted for industrial applications.

Atmospheric boundary layer

This topic was related to my postdoctoral research (LHEEA, 2021-2023) on simulating and understanding the atmospheric boundary layer under realistic conditions. Two topics were studied:

  • the transport of marine aerosols (land-sea interface in the bay of Le Croisic)
  • low-level jets

Numerical tools: WRF and ARPS

Altitude and nesting WRF - ARPS
Visualisation of altitude through successive nesting of WRF - ARPS simulations. The smaller the domain in horizontal extension, the finer the mesh (adapted from hal-04808282).

Depending on our needs, two free and open source codes were used:

  • WRF (Weather Research and Forecasting) is a numerical weather prediction model. It allows realistic large-scale simulations to be carried out at very fine resolutions using a nesting method.
  • ARPS is the precursor to WRF and was also used for multi-scale (and multi-code) nesting

Sea-spray simulations in coastal transition

2D corss-section of sea-spray concentration
2D cross-section of sea-spray concentrations as a function of altitude (y) and distance (x). The coast is on the right, the Atlantic Ocean on the left.
These three successive simulations over Le Croisic show a parametric situation at the top (turbulence is purely modelled, not resolved), then mesh refinement and the use of LES bring out the turbulent structures that considerably change the observation of the aerosol concentration (adapted from hal-04808282).

The nested LES WRF - ARPS simulations make it possible to deal with complex terrains and a micro-meteorology that is absent from the meso-scale codes. These delicate simulations reflect the complexity of capturing all the scales in the atmosphere: the large scales give the global trend and the micro-scales that develop under the effect of local constraints change the phenomena considerably.

Low-level jet simulations

The WRF-ARPS coupling also allows realistic simulations of low-layer jets. Jets generally originate on land and extend far out to sea. The presence of a ridge is sufficient to generate gravity waves over several tens of kilometers, with a potential impact on wind resources.

Plasma of nuclear fusion

This topic was the subject of my PhD and a post-doc (M2P2/CEA Cadarache, 2017-2021). I studied turbulence in tokamak edge plasmas under the effect of three-dimensional magnetic perturbations. I performed direct numerical simulations by adding the magnetic perturbation component to the equations. This allowed me to study turbulence and how it changes as a result of these perturbations, which are necessary for controlling plasma in a tokamak configuration designed to reach an operating point capable of producing more energy than it consumes.

Numerical tools: TOKAM3X et MHDG

Limiter vs divertor design
Possible tokamak design : limiter et divertor with some geometrical elements

Two simulation tools were used:

  • TOKAM3X (currently SOLEDGE3X-HDG), which performs direct 3D numerical simulations of tokamak edge plasma (limiter or divertor configuration) using a fluid approach (finite volumes).
  • MHDG which also performs 3D numerical simulations of edge plasma transport (without turbulence) but on realistic geometries using an original hybrid Galerkin scheme (finite elements), again using a fluid approach.

TOKAM3X limiter simulations

Image 3D densité température avec perturbations magnétiques
Modélisation 3D configuration limiteur avec TOKAM3X. La densité du plasma est à gauche, la température à droite. Les perturbations magnétiques sont symbolisées par les bobines rectangulaires. Les lignes de champs magnétiques sont également tracées.

TOKAM3X allows you to choose fluid equation models:

  1. An N-Gamma model (conservation of mass and momentum). Turbulence is ensured by an equation on the electric potential between ions and electrons.
  2. An N-Gamma-T model (conservation of mass, momentum, and energy). The equation on ionic and electronic temperatures adds complex physics whose influence has led to major differences in conclusions.

MHDG divertor (WEST) simulations

Maillage du tokamak WEST avec MHDG
Maillage pour un calcul en éléments finis du tokamak WEST pour MHDG

MHDG simulations also allow two equation models to be selected, with the option of including or excluding energy conservation in the equations relating to ion and electron temperatures. This code has been used to study various magnetic perturbations:

  • RMPs (resonant magnetic perturbations), also studied with TOKAM3X.
  • Ripple (field undulations due to coil spacing).