How Noise Affects the Vortices in a Spherical Flow

13:01, August 21, 2018

The discovery will help to build more accurate models of such natural currents as the circulation of the Earth's atmosphere

A team of Russian and foreign scientists, including Maria Gritsevich, a senior researcher at the Laboratory of Extra Terra Consortium, Ural Federal University, found that random fluctuations in velocity in a spherical fluid flow affect the flow velocity .

The experiment revealed there is a rather complicated relationship between the noise (random fluctuations in the rotation speed) and the flow regime of the fluid. At small noises or absolutely without noise there were three vortices in current. If the noise is increased, then in the course of the formation four whirlwinds were formed. But the most interesting was the effect of noise of medium strength. In this case, the number of vortices depends on both the acceleration and the magnitude of the noise, and this dependence is nonlinear.

‘We believe that studying the effect of noise on the state of the flow is extremely important not only for astrophysical objects, such as pulsars, but also for the circulation regime in the atmosphere. In the work of colleagues, for example, it was suggested that in order to better understand the choice of the atmospheric circulation regime, such as interaction with Rossby waves and transitions between them, it is necessary to take into account the dependence on the noise state,’ the article concludes. ‘Theoretical models were used to estimate the effect of noise in phase transitions of condensed media for which it was found that the noise intensity is a control parameter: a low intensity induces a phase transition to an ordered state, while strong noise plays a destructive role. This behavior can also be expected when a structure is formed in a fluid flow.’

Discovery can be useful in the construction of more accurate models of natural currents, for example, the circulation of the Earth's atmosphere. The answer to the question of what influences the stability or instability of the current will help to predict climate change more accurately.

‘We still have to find out exactly how the noise of medium amplitude affects the current,’ says Dmitry Zhilenko, a senior researcher at Moscow State University. This will help assess the impact of noise on processes in natural objects: in pulsars, in the Earth's atmosphere and other planets. For example, random fluctuations in the influx of solar heat into the atmosphere, as some researchers believe, can change the elements of atmospheric circulation: the Hadley, Ferrel and the polar cells. Such cells are "rings" with a closed circulation of air, and the climate on the whole planet depends directly on the circulation of the atmosphere in them.’

We will explain that the flow of Couette is called the steady flow of fluid caused by the displacement of the walls of the vessel. In the laboratory, Couette flow is studied in an installation of two transparent spheres, one of which is external, usually immobile, and the inner one can be rotated at a given speed. Such a model describes the motion of the atmosphere, oceans and mantle of the Earth. The regime of the Couette flow and the formation of vortices depend on how much the rotation speed of the inner sphere varies.

The reserchers’ team included scientists from Moscow State University (Dmitry Zhilenko, Olga Krivonosova), Ural Federal University (Maria Gritsevich, who is also an employee of the University of Helsinki) and Oxford University (Peter Reed).

 

• The results of the experiment are published in the journal Chaos