Superfluid high REynolds von Kármán experiment

Abstract

The Superfluid High REynolds von Kármán experiment facility exploits the capacities of a high cooling power refrigerator (400 W at 1.8 K) for a large dimension von Kármán flow (inner diameter 0.78 m), which can work with gaseous or subcooled liquid (He-I or He-II) from room temperature down to 1.6 K. The flow is produced between two counter-rotating or co-rotating disks. The large size of the experiment allows exploration of ultra high Reynolds numbers based on Taylor microscale and rms velocity [S. B. Pope, Turbulent Flows (Cambridge University Press, 2000)] (Rλ > 10000) or resolution of the dissipative scale for lower Re. This article presents the design and first performance of this apparatus. Measurements carried out in the first runs of the facility address the global flow behavior: calorimetric measurement of the dissipation, torque and velocity measurements on the two turbines. Moreover first local measurements (micro-Pitot, hot wire,…) have been installed and are presented.

Experimental characterization of extreme events of inertial dissipation in a turbulent swirling flow

“…This has been checked in a scale 4:1 version of our experiment in Helium, using precise calorimetric measurements18. Previous global dissipation measurements have shown that the dimensionless energy dissipation rate saturates at large Re towards a value that depends on the impellers and the mean flow geometry19 (more details in Supplementary Note 1).…”

Extreme velocity gradients in turbulent flows

“…While α≈0.275 for the current range of l R , we anticipate newer simulations at higher l R would progressively update α and also quantify its dependence on l R (though given the slow growth of α with l R , a very substantial range of l R might be required). The result provided by equation (17) should also apply to experimental investigations, which are currently capable of providing data at much higher l R compared to DNS [40,48]. A simple estimate suggests that  h h 3 ext corresponding to these laboratory experiments at » l -R 6000 10 000.…”

“…A simple estimate suggests that  h h 3 ext corresponding to these laboratory experiments at » l -R 6000 10 000. While this correction is unlikely to affect the dynamics in wind tunnel experiments [40], it might enhance the quantum effects in liquid-He experiments at [48]. However, more quantitative studies, even at relatively lower l R , would be useful, since currently resolving even η in such high l R experiments is an outstanding technical challenge.…”

Probing quantum and classical turbulence analogy in von Kármán liquid helium, nitrogen, and water experiments

“…4) as was done in Ref. 20, knowing the non-dimensional dissipation K p . The inter-vortex distance is estimated to be δ ≈ 1.0 × 10 −6 m. This distance is therefore of the same order as the Kolmogorov dissipative scale η.…”