New Directions in Turbulence

 

Date :	From 2012-03-12 To 2012-04-20
Advisory committee :
Local coordinators :	Shiyi Chen(Chair), Guowei He, Cunbiao Lee, Zhensu She, Keqing Xia
International coordinators :	Luca Biferale, Shiyi Chen(Chair), Gregory Eyink, Itamar Procaccia, Federico Toschi(Contact Person)

SCIENTIFIC CONTENT

 

This six-week program (12 March 2012 to 20 April 2012) will focus on recent development in the understanding of fluid dynamics turbulence  with the goal to identify promising breakthrough directions.

 

From the point of view of theoretical physics, turbulence is a classical field theory, out of equilibrium and in a strong coupling  regime.

 

Turbulence is one of the great problems of classical physics still mainly unsolved. With turbulence we mean a physical state of a flow with many  dynamically active variables and far from equilibrium. The first  difficulty in theoretical approaches to turbulence consists in the large number of active degrees of freedoms. The scales where energy is  injected is typically  strongly separated from the scales where energy  is dissipated. Non-linear interactions lead to a strong coupling  between all degrees of freedoms. Energy transfer may be in average  positive, leading to formation of small-scales fluctuations superposed  to large scale structures or in average  negative, leading to  an  accumulation of energy at larger and larger scales. Moreover, fluctuations around the mean can be Gaussian or strongly intermittent, depending on the direction of the energy cascade and on the  dimensionality of the system.  The situation is complicated in  presence of active scalar fields, like for the case of thermal convection, active vector fields, as in magnetohydrodynamics and/or by  the presence of boundaries, where also a net transfer of momentum is established in the system. The Lagrangian point of view, measuring  underlying fluid velocity riding tracers or inertial particles,  point-like or with a finite size, is also crucial to control statistical properties at different frequencies.

 

Among the questions that will be address during the program we cite: is the energy cascade in isotropic turbulence  universal?  What are  the corrections expected in presence of large scale anisotropy? What  happens if external or internal mechanism breaks parity invariance?  What happens at changing the embedding dimensionality? Can we improve　 sub grid modeling by a better understanding of the energy cascade  mechanism? What are the effects of strong active fields, like in thermal  convection and MHD? Are large scale structures universal in these  latter cases? What are the statistical connections between Eulerian  and Lagrangian descriptions. Can 2d and 3d physics coexist? Can we  smoothly change from a 2d to a 3d systems?　 What about turbulence in  1d turbulence (Burgers equations) in 0d (Shell Models) in larger and  larger dimension  or even in non-integer dimensions?

 

A partial answer to even only a small sub-set of these questions will require important synergies between scientists from theory, numerics  and experiments and would qualify the program as big success.

The program will be organised in "focused" weeks concerning one or two of  the above topics.

TENTATIVE PROGRAM 

12/03-18/03 : sub-grid modeling, wall bounded flows, Non Newtonian flows.

19/03-25/03 : 2d and 3d systems. Turbulence in rotating systems; Geophysical flows.

26/03-01/04 : Lagrangian and Eulerian turbulence.

02/04-06/04 : INTERNATIONAL CONFERENCE.

07/04-13/04 : Thermal convection & Magnetohydrodynamics.

14/04-20/04 : Turbulence modeling and theory.

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