Turbulence measurements under extreme conditions : the example of cryogenic flows

Christophe Baudet, Laboratoire des Ecoulements Géophysiques et Industriels (LEGI), Grenoble, France

The realization and characterization of very high Reynolds number flows is still a challenging problem either for experimentalists or numericians. I will discuss some of the reasons which motivate such a quest for very large Reynolds turbulence as well as the need for well controled experimental situations (ruling out, in some way, geophysical flows). A very promising route to the production of highly turbulent laboratory flows is the resort to cryogenic helium, due to several unique physical properties of this fluid. I will describe two recent experiments performed in Helium at very low temperatures (a jet flow around 4 K and a grid flow below the critical temperature where helium is in the superfluid state), as well as the dedicated instrumentation necessary to the probing of the turbulent fluctuations in such extreme conditions. I will end with a presentation of the statistical results obtained at Taylor microscale Reynold numbers flows up to 6000.