Aim:

The aim of our new ASTROFLU VI workshop is to once again gather, mainly in presence, the fluid mechanics specialists from the physics, engineering, astrophysics, and mathematics communities in order to exchange ideas and collaborate on our common interests. The workshop will be an opportunity to compare the tools, theoretical and numerical, used in the different SIG’s, SIG14 for rotating stratified flows, SIG39 for aeroacoustics, SIG42 for synthetic models of turbulence, SIG50 for geophysics and astrophysics, in addition to the leading SIG35 for multipoint turbulence structure and modelling.

One of the main themes will be the dynamics and structure of rotating stratified flows, possibly magnetized, for environment and engineering, upper atmosphere and astrophysics (e.g. accretion discs).

New mathematical and numerical approaches will be presented, for asymptotic `weak’ turbulence, especially when non-propagating modes coexist with dispersive wave modes, the latter being only considered in classical wave turbulence theory.

Prospective studies towards weakly compressible flows will be presented and discussed. It is expected to include aeroacoustics (SIG 39) beyond classical approximations, such as the Boussinesq hypothesis for density-stratified flows and the anelastic approximation in astrophysics.

A list of speakers taking part:

• Tomas Bodnar (Prague,SIG 14 and Czech PC) - Compressible flows with diffusivity
• Mickaël Bourgoin (ENS-Lyon) - Settling of magnetic rods at low Reynolds number
• Léa Cherry (Université de Perpignan et Promes) with Françoise Bataille - EDQNM for solar energy
• Claude Cambon (LMFA, ECL, ERCOFTAC SIG 35) - Short opening, wave turbulence and beyond
• Bruno Chaouat (ONERA, Palaiseau) - Scale analysis of non-homogeneous turbulent flow using direct numerical simulation database
• Natalia Dimitrieva (Institute of Hydromechanics of NASU, Ukraina) - Numerical Simulation of Stratified Flows near Obstacles
• Benjamin Favier (IRPHE, Marseille) - Asymptotic structure of inertial wave singularities in spherical shells
• Jeremy Fench (ENS-Lyon) - Turbulence compressible du milieu interstellaire et ondes stellaires topologiques
• Philippe Fraunié (Pythéas, Toulon) - Some turbulent mechanisms at air/sea interface
• Sébastien Galtier (LPP Polytechnique Palaiseau) - Compressible wave turbulence in the solar wind at sub-MHD scales: theory, DNS and observation
• Sebastian Gallon (ENS-Lyon) with Javier Sierra and Alain Pumir - Lagrangian irreversibility in rotating-stratified turbulent flows
• Laurent Jacquin (ONERA, Palaiseau,) Contact in progress - Recent challenges in modelling rotating flows and systems
• Andrzej Nowakowski (Université de Sheffield, UK, ERCOFTAC SIG 42) - Variational formulation for recovering pressure field from velocity-vorticity formulation of Navier-Stokes equations
• Abdelaziz Salhi (Université de Tunis, Tunisie) - Rotating stratified flows in magnetized turbulence
• Daniel Schertzer (Ecole Nationale des Ponts et Chaussées, near Paris) - What’s new in intermittency?
• Julian Scott (LMFA, ECL) - Weak turbulence theory and DNS, with non-propagating modes
• Eric Serre (M2P2, Marseille) - Recent results of modelling turbulent transport in the tokamak WEST
• Ilias Sibgatulin (ENS-Lyon) - Internal wave instabilities and transition to turbulence in large aspect ratio wave attractors
• Rolf Walder (Zurich, and ENS-Lyon) - Accretion by a black hole in a binary system
• Ying Zhu (UNICE, Nice) - Acoustic systems with weak dispersion

General context:

Meetings around the DFGA theme (Dynamics of Geophysical and Astrophysical Fluids) have shown promising and truly multidisciplinary perspectives, in particular from the meeting co-organized by Philippe Fraunié in Paris in 2017, with the CNRS and the University. These themes are found in ERCOFTAC's pan-European `SIG's (Special Interest Groups). Our event will therefore bring together the heads of four SIG's: Tomas Bodnar (SIG 14 Stably-Stratified & Rotating Flows), Claude Cambon, CC (SIG 35 Multipoint Turbulence Structure & Modelling), Raffaele Marino (SIG 50 Geophysical & Astrophysical Flows), and Andrzej Nowakowski (SIG 42 Synthetic Models in Turbulence). Recent work has illustrated the rapprochement of modal projection techniques for deterministic and statistical equations, and those of stochastic modeling for the internal intermittency of turbulence (e.g. last ERCOFTAC workshop at CIRM, near Marseille.)

Modal projection is essential to describe the complex dynamics of turbulence in the presence of waves, which help structure in atmospheric and oceanic flows, such as inertia (rotation) and gravity (stratification) waves. These waves can be combined with Alfvén waves in MHD flows. As far as possible, compressibility will be addressed, first in considering acoustic waves (e.g. magnetosonic waves) and acoustic systems in weak turbulence.

The first two local events "ASTROFLU" were principally organised by the Henri Bénard PC in Lyon, 12-13/11/2008 and 15/12/2011. The third one, which took place on November 20-21, 2013, attracted an European audience and was supported by ERCOFTAC with label and scholarships. The "ASTROFLU IV" was supported by ERCOFTAC and took place at Ecole Centrale de Lyon, January 24-25, 2019. "ASTROFLU V" took place in December 7-8, 2021 and was also supported by ERCOFTAC.