Yves Pomeau - French National Centre for Scientific Research
Wednesday, March 30, 10:45AM (Zoom meeting starts at 10:30)
“Turbulence: from the basics to slightly beyond”
In the landscape of physics, turbulence stands in a rather unique place. The problems it attempts to solve can be traced back to Newton's Principia with slow progress afterwards even though
1) the equations to be solved are well-known (Euler eq. for inviscid fluids, Navier-Stokes with viscosity)
2) The range of applications is huge, from moving objects to weather and climate studies
Over the last forty years, big progress in the understanding of the transition from laminar (not time dependent) to turbulent flows. Dynamical system theory yields a fair understanding of transition in small boxes (the "routes to chaos").In systems with many degrees of freedom (like parallel flows or pipe flows) the transition is continuous and follows the directed percolation scenario, which explains observations made in 1888 by Osborne Reynolds.
There remains to understand the regime of very large Reynolds numbers, very far from the onset of stability. I'll discuss the modeling of this regime, namely the way momentum is exchanged by interaction between turbulent fluctuations, the so-called closure problem, in a concrete situation.