# Laboratoire de Mécanique des Fluides et d’Acoustique - UMR 5509

LMFA - UMR 5509
Laboratoire de Mécanique des Fluides et d’Acoustique
Lyon
France

## Wouter Bos

Équipe de Recherche : Turbulence & Instabilités
tél : 04.72.18.62.04
email

Current PhD Students
Wesley Agoua (with Benjamin Favier, IRPHE)
Ryo Araki (with Susumu Goto, Osaka)
Tong Wu

### Research Activities

Birth of helicity

Article dans Phys. Rev. E (2021)

### Spontaneous generation and reversal of helicity in anisotropic turbulence

Wesley Agoua, Benjamin Favier, Alexandre Delache, Antoine Briard & Wouter Bos

Helicity plays an important role in spectacular geophysical phenomena such as hurricanes or the generation of the terrestrial magnetic field. The present investigation shows how helicity can be (...)

Lire la suite

Modeling the epidemic

Article dans Comput. Mech. (2021)

### Modeling the role of clusters and diffusion in the evolution of COVID-19 infections during lock-down

Wouter Bos, Jean-Pierre Bertoglio & Louis Gostiaux

The dynamics of the spread of epidemics, such as the recent outbreak of the SARS-CoV-2 virus, is highly nonlinear and therefore difficult to predict. As time evolves in the present pandemic, it (...)

Lire la suite

Turbulence without vortex-stretching

Article dans J. Fluid Mech. (2021)

### Three-dimensional turbulence without vortex stretching

Wouter Bos

We consider three-dimensional turbulence from which vortex stretching is removed. The resulting system conserves enstrophy, but does not conserve kinetic energy. Using spectral closure, it is (...)

Lire la suite

ANR project CM2E

ANR Project 2021-2025

### CM2E

Characteristic Mapping Method for the Euler Equations

Project Partners Kai Schneider (PI, Aix-Marseille University), Jean-Christophe Nave (McGill University, Canada), Benjamin Kadoch (Aix-Marseille University), Wouter Bos
Even though (...)

Lire la suite

Grid-turbulence

Article dans Phys. Rev. Fluids (2020)

### Production and dissipation of kinetic energy in grid turbulence

Wouter Bos

In grid turbulence, not so far behind the grid, an average flow can be observed with a close to sinusoidal velocity profile, corresponding to the wakes behind the grid bars. The kinetic energy of (...)

Lire la suite

Article dans Phys. Rev. Letters (2020)

### Generation of Atmospheric Turbulence with Unprecedentedly Large Reynolds Number in a Wind Tunnel

Lars Neuhaus, Michael Hölling, Wouter Bos & Joachim Peinke

Generating laboratory flows resembling atmospheric turbulence is of prime importance to study the effect of wind fluctuations on objects such as buildings, vehicles, or wind turbines. A novel (...)

Lire la suite

Article dans Phys. Rev. Fluids (2017)

Wouter J.T. Bos, Robert Rubinstein

Recent experiments and simulations have shown that unsteady turbulent flows display a universal behavior at short and intermediate times, different from classical scaling relations. The origin of (...)

Lire la suite

Critical transitions in turbulent flows

Article dans J. Turbulence (2021)

### Transition from axisymmetric to three-dimensional turbulence

Zecong Qin, Aurore Naso & Wouter Bos

In purely axisymmetric turbulence sustained by a linear forcing mechanism, a stable, entirely poloidal flow is observed when the toroidal component of the forcing is below a threshold. We (...)

Lire la suite

Article dans Phys. Rev. E (2020)

### Linearly forced isotropic turbulence at low Reynolds numbers

Wouter Bos, Faouzi Laadhari & Wesley Agoua

The forcing strength needed to sustain a flow using linear forcing is investigated. A critical Reynolds number $R_c$ is determined, based on the longest wavelength allowed by the system, the (...)

Lire la suite

Article dans Phys. Rev. Fluids (2020)

### Transition from non-swirling to swirling axisymmetric turbulence

Zecong Qin, Hugues Faller, Bérengère Dubrulle, Aurore Naso & Wouter Bos

Strictly axisymmetric turbulence, i.e., turbulence governed by the Navier-Stokes equations modified such that the flow is invariant in the azimuthal direction, is a system intermediate between (...)

Lire la suite

Physics of sports

Article dans Phys. Rev. Fluids (2017)

### Directional change of fluid particles in two-dimensional turbulence and of football players

Benjamin Kadoch, Wouter J. T. Bos, and Kai Schneider

Multiscale directional statistics are investigated in two-dimensional incompressible turbulence. It is shown that the short-time behavior of the mean angle of directional change of fluid (...)

Lire la suite

with Gabin Rolland, Nathan Rivière et Romain Vuillemot (LIRIS)

Characterization of Space and Time-Dependence of 3-Point Shots in Basketball.
Work presented at the MIT Sloan Sports Analytics Conference.

Lire la suite

In the media

### Turbulence and footbal-players

with B. Kadoch and K. Schneider

(...) Indeed, even though a football match does not seem to be ergodic, and some may argue that the trajectories of football players are not completely random, the long-time PDF of the (...)

Lire la suite

Mixing of passive scalars and viscous heating

Article dans Phys. Rev. E (2020)

### Efficiency of laminar and turbulent mixing in wall-bounded flows

Benjamin Kadoch, Wouter Bos & Kai Schneider

A turbulent flow mixes in general more rapidly a passive scalar than a laminar flow does. From an energetic point of view, for statistically homogeneous or periodic flows, the laminar regime is (...)

Lire la suite

Article dans Fluid Dyn. Res. (2019)

### Passive scalar mixing in modulated turbulence

Yuyao Yang, Robert Chahine, Robert Rubinstein & Wouter JT Bos

We investigate the mixing of a passive scalar in an isotropic turbulent flow in the presence of a time-periodic forcing. The results corroborate recent analytical predictions on the frequency (...)

Lire la suite

Article dans J. Fluid Mech. (2014)

### The temperature spectrum generated by frictional heating in isotropic turbulence

Wouter J. T. Bos

In every turbulent flow with non-zero viscosity, heat is generated by viscous friction. This heat is then mixed by the velocity field. We consider how heat fluctuations generated in this way are (...)

Lire la suite

Article dans J. Fluid Mech. (2014)

### On the anisotropy of the turbulent passive scalar in the presence of a mean scalar gradient

Wouter J. T. Bos

We investigate the origin of the scalar gradient skewness in isotropic turbulence on which a mean scalar gradient is imposed. The problem of the advection of an anisotropic scalar field is (...)

Lire la suite

Article dans Phys. Rev. E (2015)

### Dependence of turbulent advection on the Lagrangian correlation time

Wouter J. T. Bos & Le Fang

In turbulent scalar mixing, starting from random initial conditions, the root-mean-square advection term rapidly drops as the flow and the scalar field organize. We show first analytically, for (...)

Lire la suite

Article dans Phys. Fluids (2015)

### On the scaling of temperature fluctuations induced by frictional heating

Wouter J. T. Bos, Robert Chahine & Andrey V. Pushkarev

The temperature fluctuations generated by viscous dissipation in an isotropic turbulent flow are studied using direct numerical simulation. It is shown that their scaling with Reynolds number is (...)

Lire la suite

Article dans Comput. Fluids (2017)

### Mixing in modulated turbulence. Analytical results

Wouter J.T. Bos, Robert Rubinstein

Recent numerical results show that if a scalar is mixed by periodically forced turbulence, the average mixing rate is directly affected for forcing frequencies small compared to the integral (...)

Lire la suite

Article dans Phys. Rev. Fluids (2017)

### Reynolds and Prandtl number scaling of viscous heating in isotropic turbulence

Andrey Pushkarev, Guillaume Balarac, and Wouter J. T. Bos

Viscous heating is investigated using high-resolution direct numerical simulations. Scaling relations are derived and verified for different values of the Reynolds and Prandtl numbers. The (...)

Lire la suite

Power fluctuations

Article dans Phys. Rev. letters (2019)

### Power fluctuations in turbulence

Wouter J. T. Bos & Rémi Zamansky

To generate or maintain a turbulent flow, one needs to introduce kinetic energy. This energy injection necessarily fluctuates and these power fluctuations act on all turbulent excited length (...)

Lire la suite

### Un article LMFA en couverture de PRL

Power fluctuations in turbulence [with Rémi Zamansky (IMFT)]

How universal are the power-fluctuations measured in the electricity output of a windmill ? Indeed, the power fluctuation experienced by a windmill blade are determined by the power absorbed by (...)

Lire la suite

Lagrangian dynamics of turbulence

Article dans Phys. Rev. letters (2015)

### Angular statistics of Lagrangian trajectories in turbulence

Wouter J. T. Bos, Benjamin Kadoch & Kai Schneider

The angle between subsequent particle displacement increments is evaluated as a function of the time lag in isotropic turbulence. It is shown that the evolution of this angle contains two (...)

Lire la suite

Article dans Phys. Fluids (2015)

### Short-time evolution of Lagrangian velocity gradient correlations in isotropic turbulence

Le Fang, Wouter J. T. Bos & Guodong D. Jin

We show by direct numerical simulation (DNS) that the Lagrangian cross correlation of velocity gradients in homogeneous isotropic turbulence increases at short times, whereas its auto-correlation (...)

Lire la suite

Axisymmetric Turbulence

Article dans Phys. Rev. Fluids (2018)

### Cascades of energy and helicity in axisymmetric turbulence

Bo Qu, Aurore Naso, & Wouter J. T. Bos

A spectral analysis of strictly axisymmetric turbulence is performed. Both freely decaying and statistically steady flows are considered. In helical flows we identify a dual cascade, where energy (...)

Lire la suite

Article dans Phys. Rev. Fluids (2017)

### Direct numerical simulation of axisymmetric turbulence

Bo Qu, Wouter J. T. Bos, and Aurore Naso

The dynamics of decaying, strictly axisymmetric, incompressible turbulence is investigated using direct numerical simulations. It is found that the angular momentum is a robust invariant of the (...)

Lire la suite

MHD and The Fluid Mechanics of Fusion Plasmas

### Wouter Bos raconte ITER à RCF

15 septembre 2020

Wouter Bos a été interviewé par la radio lyonnaise RCF pour parler du projet ITER, International Thermonuclear Experimental Reactor. Ce programme a l’ambition de construire le plus grand tokamak (...)

Lire la suite

Article dans Phys. Rev. Fluids (2020)

### Scaling laws in axisymmetric magnetohydrodynamic duct flows

Alexandre Poyé, Olivier Agullo, Nicolas Plihon, Wouter Bos, Victor Desangles & Guillaume Bousselin

We report on a numerical study of axisymmetric flow of liquid metal in a circular duct with a rectangular cross section. The flow is forced through the combination of an axial magnetic field and (...)

Lire la suite

Article dans Fluid Dyn. Res. (2014)

### Self-organization of helically forced MHD flow in confined cylindrical geometries

Malcolm Roberts, Matthieu Leroy, Jorge Morales, Wouter Bos & Kai Schneider

The dynamics of a magnetically forced conducting fluid in confined geometries is studied. A pseudospectral method with volume penalisation is used to solve the resistive magnetohydrodynamic (...)

Lire la suite

Article dans Plasma Phys. Control. Fusion (2014)

### The effect of toroidicity on reversed field pinch dynamics

Jorge A. Morales, Wouter J. T. Bos, Kai Schneider & David C. Montgomery

The influence of the curvature of the imposed magnetic field on reversed field pinch dynamics is investigated by comparing the flow of a magnetofluid in a torus with aspect ratio 1.83, with the (...)

Lire la suite

Article dans J. Comput. Phys. (2014)

### Simulation of confined magnetohydrodynamic flows with Dirichlet boundary conditions using a pseudo-spectral method with volume penalization

Jorge A.Morales, Matthieu Leroy, Wouter J. T. Bos & Kai Schneider

A volume penalization approach to simulate magnetohydrodynamic (MHD) flows in confined domains is presented. Here the incompressible visco-resistive MHD equations are solved using parallel (...)

Lire la suite

Article dans J. Plasma Phys. (2015)

### Flow dynamics and magnetic induction in the von-Kármán plasma experiment

N. Plihon, G. Bousselin, F. Palermo, J. Morales, W. J. T. Bos, F. Godeferd, M. Bourgoin, J.-F. Pinton, M. Moulin & A. Aanesland

The von-Kármán plasma experiment is a novel versatile experimental device designed to explore the dynamics of basic magnetic induction processes and the dynamics of flows driven in weakly (...)

Lire la suite

Article dans Phys. Plasmas (2015)

### Magnetohydrodynamically generated velocities in confined plasma

Jorge A. Morales, Wouter J. T. Bos, Kai Schneider & David C. Montgomery

We investigate by numerical simulation the rotational flows in a toroid confining a conducting magnetofluid in which a current is driven by the application of externally supported electric and (...)

Lire la suite

Article dans Phys. Plasmas (2015)

### Dynamic equilibria and magnetohydrodynamic instabilities in toroidal plasmas with non-uniform transport coefficients

Shimpei Futatani, Jorge A. Morales & Wouter J. T. Bos

It can be shown that in the presence of a toroidal magnetic field induced by poloidal coils, combined with the electromagnetic field induced by a central solenoid, no static equilibrium is (...)

Lire la suite

Article dans Phys. Plasmas (2018)

### On the role and value of $\beta$ in incompressible MHD simulations

Robert Chahine & Wouter J. T. Bos

The parameter $\beta$, defined as the ratio of the pressure to the square of the magnetic field, is widely used to characterize astrophysical and fusion plasmas. However, in the dynamics of a (...)

Lire la suite

Active Turbulence

Article dans Phys. Rev. Fluids (2018)

### Turbulence and turbulent pattern formation in a minimal model for active fluids

Martin James, Wouter J. T. Bos, and Michael Wilczek

Active matter systems display a fascinating range of dynamical states, including stationary patterns and turbulent phases. While the former can be tackled with methods from the field of pattern (...)

Lire la suite

Depletion of nonlinearity

Article dans Phys. Fluids (2014)

### Depletion of nonlinearity in two-dimensional turbulence

Andrey V. Pushkarev & Wouter J. T. Bos

The strength of the nonlinearity is measured in decaying two-dimensional turbulence, by comparing its value to that found in a Gaussian field. It is shown how the nonlinearity drops following a (...)

Lire la suite

Visco-elastic turbulence

Article dans Phys. Rev. Fluids (2016)

### Small scale dynamics of isotropic viscoelastic turbulence

Min Quan Nguyen, Alexandre Delache, Serge Simoëns, Wouter J. T. Bos & Mamoud El Hajem

The comparison of the results of direct numerical simulations of isotropic turbulence of Newtonian and viscoelastic fluid provides evidence that viscoelasticity modifies qualitatively the (...)

Lire la suite