Thermal boundary layer near roughnesses in turbulent Rayleigh-Bénard convection: Flow structure and multistability

We present global heat-transfer and local temperature measurements, in an asymmetric parallelepiped Rayleigh-Bénard cell, in which controlled square-studs roughnesses have been added. A global heat transfer enhancement arises when the thickness of the boundary layer matches the height of the roughne...

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Bibliographic Details
Published in:Physics of fluids (1994) 2014-01, Vol.26 (1)
Main Authors: Salort, J., Liot, O., Rusaouen, E., Seychelles, F., Tisserand, J.-C., Creyssels, M., Castaing, B., Chillà, F.
Format: Article
Language:English
Subjects:
Engineering Sciences
Fluid dynamics
Fluid mechanics
Fluids mechanics
Heat transfer
Mechanics
Parallelepipeds
Physics
Plates (structural members)
Studs
Temperature
Thermal boundary layer
Thickness
Turbulent boundary layer
Turbulent flow
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Summary:We present global heat-transfer and local temperature measurements, in an asymmetric parallelepiped Rayleigh-Bénard cell, in which controlled square-studs roughnesses have been added. A global heat transfer enhancement arises when the thickness of the boundary layer matches the height of the roughnesses. The enhanced regime exhibits an increase of the heat transfer scaling. Local temperature measurements have been carried out in the range of parameters where the enhancement of the global heat transfer is observed. They show that the boundary layer at the top of the square-stub roughness is thinner than the boundary layer of a smooth plate, which accounts for most of the heat-transfer enhancement. We also report multistability at long time scales between two enhanced heat-transfer regimes. The flow structure of both regimes is imaged with background-oriented synthetic Schlieren and reveals intermittent bursts of coherent plumes.
ISSN:1070-6631
1089-7666
DOI:10.1063/1.4862487