Large-scale turbulent flow around a cylinder in counterflow superfluid4He (He (II))

The detailed nature of fluid flow over a cylinder is one of the fundamental topics in classical fluid dynamics as it demonstrates flow separation and vortex shedding 1 . In superfluid helium, either He ( II ) or the B phase of 3 He, an important question has been to what extent these quantum fluids show classical fluid turbulent states 2 , 3 , 4 . Although the existence of turbulent structures can be inferred using precise instrumentation 5 , 6 , direct visualization of the flow field can provide unequivocal evidence of these phenomena. Here we show the existence of large turbulent structures in He ( II ) counterflow across a cylinder as obtained by the particle image velocimetry technique. Compared with classical fluid flow, the particle motion driven by He ( II ) counterflow shows macroscopic eddies downstream of the cylinder but also similar structures are observed in front of the cylinder, behaviour not seen in classical fluids. As Landau’s two-fluid model 7 for He ( II ) describes counterflow as the relative motion of the superfluid and normal fluid components, the current results indicate that both components may be undergoing a kind of flow separation as they pass over the cylinder.