Turbulent thermal convection in the ultimate regime
Researchers of the Foundation for Fundamental Research on Matter and the University of Twente have shown in collaboration with an international research team with experiments and computer simulations that the vertical temperature profile close to sidewall in Rayleigh-Bénard convection varies logarithmically with the distance from the plate in the classical and in the ultimate regime. This is major news as it had generally been assumed that the temperature in the sample interior is either constant or varying linearly and slowly in space in the classical regime. These new findings contribute to the understanding of convection in natural systems, such as the atmosphere and oceans. The researchers publish their latest findings in the renowned journal Physical Review Letters on 3 September 2012.
Convection
Fluids between two horizontal plates, with the lower plate at a higher temperature than the top plate, show convection behavior when there is a large enough temperature difference between the plates. The fluid near the lower plate is warmer and therefore lighter than the fluid above, which results in it flowing upwards. The reverse happens near the top plate. This phenomenon is called Rayleigh-Bénard convection. When the Rayleigh number (the dimensionless temperature difference between the horizontal plates) is very high one can reach the so-called ultimate Rayleigh-Bénard regime in which the boundary layers at the horizontal plates are turbulent. Fully understanding the physics of this ultimate regime is relevant to better comprehend natural phenomena such as convection in the atmosphere and oceans.
Temperature profiles
In the 'ultimate regime' the heat transfer as function of the Rayleigh number increases faster than in the 'classical regime', where the temperature difference between the horizontal plates is lower. Theoretically it has been argued that the ultimate regime should start when the boundary layers at the horizontal plates become turbulent, whereas in the classical regime (thus for lower Rayleigh) the boundary layers are considered to behave laminar. Therefore a transition towards the ultimate regime should be visible in the vertical temperature profiles. Recent state of the art large-scale experiments performed in Gottingen have now confirmed the presence of logarithmic temperature profiles, which are typical for turbulent boundary layers, close to the sidewalls in the ultimate regime. However, interestingly enough the experiments and very large computer simulations have revealed a similar logarithmic sidewall temperature profile in the classical regime, although it is less pronounced than in the ultimate regime. Further research on this observation will be necessary to fully understand this phenomenon and its possible implications on current theories.
EUROTHERM Young Scientist Prize 2012
Recently, former FOM-oio dr. Richard Stevens received the EUROTHERM Young Scientist Prize 2012. EUROTHERM promotes and fosters European cooperation in Thermal Sciences and Heat Transfer by gathering together scientists and engineers working in these specialized areas. Stevens obtained his PhD degree on June 30, 2011 with FOM at the University of Twente with his thesis 'Rayleigh-Bénard turbulence ' and now works at the Johns Hopkins University in Baltimore with a YES! Fellowship from FOM.
Since 1992 the EUROTHERM Young Scientist Prize is awarded once every four years to the best PhD thesis in the field of Thermal Sciences and Heat Transfer and is intended to stimulate young scientists towards the research work in the field of thermal sciences. The 2012 EUROTHERM Young Scientist Prize will be presented at the 6th European Thermal Sciences Conference to be held in Futuroscope, Poitiers on 3-8 September 2012.
Further information
For further information you can contact Richard Stevens or Detlef Lohse.
About the research of Richard Stevens:
PRL 1
PRL 2 + FOM press release (Only Dutch)
PRL 3 + FOM press release
PRL 4 + FOM press release (Only Dutch)
FOM press release about YES! fellowship
FOM press release about Da Vinci Prize 2011
Press release about second prize DSM Science & Technology Awards (North) 2012
Reference
Logarithmic temperature profiles in turbulent Rayleigh-Bénard convection, Guenter Ahlers, Eberhard Bodenschatz, Denis Funfschilling, Siegfried Grossmann, Xiaozhou He, Detlef Lohse, Richard J.A.M. Stevens en Roberto Verzicco, Phys. Rev. Lett. (2012).