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Onset of thermal convection and influence of rotation in wide spherical gap flow
Author(s) -
Brucks A.,
Sitte B.,
Egbers C.
Publication year - 2002
Publication title -
pamm
Language(s) - English
Resource type - Journals
ISSN - 1617-7061
DOI - 10.1002/1617-7061(200203)1:1<286::aid-pamm286>3.0.co;2-s
Subject(s) - taylor number , prandtl number , mechanics , vortex , physics , reynolds number , instability , convection , rotation (mathematics) , particle image velocimetry , flow visualization , rayleigh number , thermal , stratification (seeds) , boundary layer , classical mechanics , optics , flow (mathematics) , natural convection , geometry , turbulence , meteorology , mathematics , seed dormancy , germination , botany , dormancy , biology
The onset of thermal convection and the effect of rotation in a high Prandtl number fluid in a wide gap between two concentric spheres with an axial force field are investigated experimentally. Both spheres rotate along the vertical axis with the same angular velocity Ω while the inner one (r 1 ) is cooled and the outer one (r 2 ) is heated. The velocity field is investigated by different visualization techniques and Particle Image Velocimetry (PIV). The axisymmetric basic flow is disturbed by local instabilities. At a Rayleigh number of Ra = 6.97 · 10 6 , a pulsing vortex develops in the south polar region. A different, coexisting instability in the outer boundary layer appears at Ra = 1.79 · 10 7 . Rotating with Taylor numbers Ta > 1.4 · 10 5 , this instability vanishes. The instabilities occur mainly in the southern hemisphere where the thermal stratification is unstable.