INTERMITTENCY OF VELOCITY FLUCTUATIONS IN

Among the most important questions about turbulence, is the origin of intermittency in a flow. Another, closely related, is whether there is an ultimate, high Reynolds number regime, and if so, how it ari ses and how to characterize it. The main difficulty in studying these questions is that an experiment usually gives access only to a limited range of Reynolds numbers. Physicists have to compare results from different experimental configurations, such as grid, jet and tunnel flow wi th the hope that the Taylor based Reynolds number $\mathrm{R}_{\Theta} $ is the unique and universal parameter for turbulence [1]. With cryogenic experiments using gaseous $4\mathrm{H}\mathrm{e}[2] $ it becomes possible to cover a large range of $\mathrm{R}_{\Theta} $ with the same geometry. Close to its critical point (2.2 bar, 5.2 K), gaseous Helium has the smallest known kinematic viscosity $(\mathrm{V}=210- 8\mathrm{m}2/\mathrm{s}) $ , but can be an appreciably viscous fluid at low pressure $\mathrm{P}(\mathrm{v}\mathrm{P}=\mathrm{c}\mathrm{o}\cap \mathrm{S}\iota.)[3] $. We have built the first open flow working under such conditions, an axisymetric jet. We have developed the correspondin