Flow reversals in thermally driven turbulence
Researchers from the Foundation for Fundamental Research on Matter (FOM), the University of Twente, the Chinese University of Hong Kong (China), the University of Tokyo (Japan), and the Philipps University of Marburg (Germany) have demonstrated with the help of experiments and numerical simulations (partly performed on the Huygens cluster of SARA) that the flow in two-dimensional Rayleigh-Bénard convection can spontaneously reverse under the influence of the flow in the corners of the tank. The researcher's findings will be published in the renowned journal Physical Review Letters on 16 July 2010.
A fluid between two horizontal walls, in which the lower wall is kept at a higher temperature than the upper wall, exhibits convection behaviour in the case of a sufficiently large temperature difference. Fluid near the lower wall becomes warmer and therefore lighter than the fluid above, and under gravitational effects moves upwards and vice versa. This effect is called Rayleigh-Bénard convection. This system is relevant for many astrophysical and geophysical phenomena, such as convection in the oceans, the earth’s mantle, on the inside of the large gas planets, and in the outermost layer of the sun. In these systems, spontaneous reversals of the flow are observed, which are associated with the reversal of the earth's magnetic field.
FOM PhD researcher Richard Stevens, Kazuyasu Sugiyama from the University of Tokyo (Japan), Tak Shing Chan, Sheng-Qi Zhou, Heng-Dong Xim, and Ke-Qing Xia from the Chinese University of Hong Kong (China), Siegfried Grossmann from the Philipps University of Marburg (Germany), and Chao Sun and Detlef Lohse from the University of Twente demonstrated that the flow in two-dimensional Rayleigh-Bénard can spontaneously reverse under the influence of the flow that develops in the corners of the tank. The flow in the corners is found to slowly increase in energy until it is strong enough to ensure that the main flow in the tank is disrupted and subsequently reverses. The frequency of the reversals depends on the rate at which the flow in the corners can gain energy and this is determined by the properties of the liquid (the Prandtl (Pr) number) and the temperature difference between the plates (the Rayleigh (Ra) number). It was also found that for certain combinations of Ra and Pr there are no flow reversals, because the flow in the corners can not gain enough energy.
Reference
Flow reversals in thermally driven turbulence, Kazuyasu Sugiyama1,3, Rui Ni2, Richard J.A.M. Stevens1, Tak Shing Chan1,2, Sheng-Qi Zhou2, Heng-Dong Xi2, Chao Sun1,2, Siegfried Grossmann4, Ke-Qing Xia2, and Detlef Lohse1, Phys. Rev. Lett. Lett. 105, 034503 (2010): http://prl.aps.org/abstract/PRL/v105/i3/e034503.
1 Physics of Fluids, University of Twente, the Netherlands
2 Department of Physics, Chinese University of Hong Kong, China
3 Department of Mechanical Engineering, School of Engineering, University of Tokyo, Japan
4 Faculty of Physics, Philipps University of Marburg, Germany
Information
For further information please contact:
Richard Stevens, University of Twente, telephone +31 (0)53 489 24 87
Detlef Lohse, University of Twente, telephone +31 (0)53 489 80 76