Nonlinear dynamics are not easy !!

This review [http://www.nature.com/nature/journal/v470/n7335/full/470475a.html?WT.ec_id=NATURE-20110224#/references] explains why I claim that !

The formal problem of the stability of rotating flow was first addressed by Lord Rayleigh in the late nineteenth century⁷. Rayleigh found that if the rotational velocity of a fluid decreases more rapidly with radius than the reciprocal of the distance from the axis of rotation, such a system is unstable to infinitesimal perturbations. Astrophysical disks, by this criterion, should be stable. But Rayleigh's analysis was restricted to vanishingly small disturbances, and the geometrical shape of the perturbations was in the form of rings with cylindrical symmetry. It is still not known what types of flow that are formally stable by this Rayleigh criterion might still be unstable to more general forms of disturbance; it is known, however, that some types of Rayleigh-stable flow certainly can be destabilized^{4, 8}. The issue of interest is whether the rotation of an astrophysical gas disk about a central mass falls into this unstable category.

This problem can be investigated in the laboratory by studying what is known as Couette flow. In a Couette apparatus, water is confined to flow in the space between two coaxial cylinders. There should be no motion along the central axis, only rotational flow about the axis. The cylinders rotate independently of one another, so that small frictional viscous forces near the cylindrical walls will set up a hydrodynamical flow in which the rotational velocity depends on the distance from the rotation axis. By choosing the rotational velocities of the rotating cylinders appropriately, a small section of an astrophysical disk can be mimicked in the laboratory. In such a disk, the flow velocity is inversely proportional to the square root of the distance from the centre, a pattern known as Keplerian flow. The question to be answered is whether Keplerian flow, formally stable by the Rayleigh criterion, actually breaks down into turbulence.
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It is this question that Paoletti and Lathrop¹ have sought to address. When a Couette flow becomes turbulent, one of the consequences is a greatly enhanced outward flux of angular momentum, which is imparted to the outer cylinder in the form of a torque. In their experiment, the authors measure this torque directly. An earlier investigation⁹ had claimed to detect this torque, but the new experiment¹ was conducted under conditions in which (undesirable) viscous effects were more effectively minimized.

Close on the heels of Paoletti and Lathrop's claim, however, comes a report by Schartman et al.¹⁰ on a related experiment. These investigators found no transition to turbulence for Keplerian flow with the same controlled level of viscosity. This null result was first reported³ in 2006, and the most recent paper maintains its original conclusion that there is no evidence of a turbulent breakdown of Keplerian-like laminar flow for very small values of the viscosity.