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Statistical approach of Turbulence
R. Monchaux
N. Leprovost, F. Ravelet, P-H. Chavanis*, B. Dubrulle, F. Daviaud and A. Chiffaudel
GIT-SPEC, Gif sur Yvette France*Laboratoire de Physique Théorique, Toulouse France
Out-of-equilibrium systems vs. Classical equilibrium systems
Degrees of freedom: N L
3
Re9
4
Statistical approach of turbulence: Steady states, equation of state, distributions
• 2D: Robert and Sommeria 91’, Chavanis 03’• Quasi-2D: shallow water, β-plane Bouchet 02’’• 3D: still unanswered question (vortex stretching)
Axisymmetric flows: intermediate situation• 2D and vortex stretching• Theoretical developments by Leprovost, Dubrulle and
Chavanis 05’
2D and quasi-2D resultsStatistical equilibrium state of 2D Euler equation (Chavanis):- Classification of isolated vortices: monopoles and dipoles- Stability diagram of these structures: dependence on a single control parameter
Quasi 2D statistical mechanics (Bouchet):– Intense jets– Great Red Spot
Approach Principle
• Basic equation: Euler equation
– Forcing is neglected
– Viscosity is neglected
• Variable of interest:
Probability to observe the conserved quantity at
• Maximization of a mixing entropy at conserved
quantities constraints
2D vs axisymmetric (1)2D axisymmetric
Vorticity conservation Angular momentum conservation
No vortex stretching Vortex stretching
2D experiment
Coherentstructures
Bracco et al. Torino
2D versus axisymmetric (2)
Von KarmanTaylor-Couette
610Re Re 105
Presentation of Laboratory experiments
2D turbulence in a Ferro Magnetic fluid
Re 103
Jullien et al., LPS, ENS Paris
Daviaud et al. GIT, Saclay, France
2D versus axisymmetric (3)Basic equations
Vertical vorticity:2D:
Azimuthal vorticity:AXI:
azimuthal vorticity:
angular momentum:
poloidal velocity:
Variables of interest:
2D versus axisymmetric (4)
Inviscid stationary states
Inviscid Conservation laws
(Casimirs)
F and G are arbitraryfunctions in infinite number
infinite number of steady states
Casimirs (F)
Generalized helicity(G)
Statistical description (1)
• Mixing occurs at smaller and smaller scalesMore and more degrees of freedom
• Meta-equilibrium at a coarse-grained scaleUse of coarse-grained fields
• Coarse-graining affects some constraintsCasimirs are fragile invariant
Statistical description (2)Probability distribution to observe
at point r
Mixing Entropy:
Coarse-grained A. M.
Coarse-grained constraints:
Robust constraints
Fragile constraints
Statistical description (3bis)Maximisation of S under conservation constraints
Equilibrium state
Equation for mostprobable fields
The Gibbs State
Steady solutions of Euler equation
Steady States (1)
What happens when the flow is mechanically stirred and viscous?
T1 T2
Two thermostats T1>T2
F
Working hypothesis (Leprovost et al. 05’):
NS:
Steady States (2)
Steady states of turbulent axisymmetric flow
F and G are arbitraryfunctions in infinite number
infinite number of steady states
- How are F and G selected?
- Role of dissipation and forcing in this selection?
Steady States (3)
Von Kármán Flow - LDV measurement
Data Processing (1)
Data Processing (2)
Time-averaged
fmpv
Test: Beltrami Flow with 60% noise
A steady solution of Euler equation:
Data Processing (3)
• F is fitted from the windowed plot• F is used to fit G
Whole flow 50% of the flow
Distance to center
<0.7
>0.85
intermediate
Flow Bulk
Comparison to numerical study
Simulation: Piotr Boronski (Limsi, Orsay, France)
Re=3000“inertial” stirring
Re=5000viscous stirring
Dependence on viscosity (1)
(+)(-)
F function:
Legend
Dependence on viscosity (2)
(+) (-)
G function:
Legend
(+)
92.5mm
Re = 190 000Re = 250 000Re = 500 000
50mm
Dependence on forcing
Conclusions
Perspectives