Turbulent spin-down flow of liquid sodium in a thick torus

P. Frick^1,2 - V. Noskov¹ - S. Denisov¹ - R. Stepanov^1,2

¹ Institute of Continuous Media Mechanics, 1 Korolyov str., Perm, 614013, Russia
² National Research Polytechnical University of Perm, 29 Komsomolsky ave., 614990 Perm, Russia

Abstract
Spin-down flow of liquid sodium generated in a toroidal channel by fast rotation followed by abrupt brake is studied experimentally. The channel is made of titanium and has the aspect ratio Γ = R/r=2.25 (R is the radius of the torus and r is the radius of the cross-section). For the free channel, we show that the decrease of Γ leads to a stronger mean poloidal motion, while the toroidal motion (the throughflow) becomes weaker. For the screw flow initiated by two diverters installed at the opposite cross-sections of the channel, we observe a flow, which is completely different from all the spin-down flows found before in toroidal channels. All previous experiments were performed in tori with Γ ≥ 2.75 and showed that diverters provided a pronounced screw flow in the whole channel. Our measurements of velocity and induced magnetic field show that the screw flow behind the diverters collapses. The flow in this thick torus breaks up into separated vortices, which keep the angular momentum. These vortices reach the opposite diverter rotating in a direction inconsistent with the screw of the diverter, which results in an extremely fast decay of the flow. Tables 1, Figs 7, Refs 23.