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Mahendra K. Verma
Physics Department, Indian Institute of Technology, Kanpur

October 11, 2010
Mesa Laboratory, Chapman Room
Lecture 3:00pm

Field Reversals in Rayleigh Benard Convection

In many convection experiments the vertical velocity measured near the lateral wall switches sign randomly as a function of time.  This phenomena has been observed typically for large Rayleigh numbers.  We present numerical simulations for cylindrical geometry that reproduce these reversals. We observe that the reversals of the large scale circulations are induced by its reorientation along the azimuthal direction, which is quantified using the phase of the first Fourier mode of the vertical velocity measured near the lateral surface in the mid plane. Numerically we observe rotation-led and cessation-led reorientations, in agreement with earlier experimental results. The ratio of the amplitude of the second Fourier mode and the first Fourier mode rises sharply during the cessation-led reorientations. This observation is consistent with the quadrupolar dominant temperature profile observed during the cessations.
      We also present reversals in box geometry, and show that the reversals in the box geometry is very similar to those observed for the cylinder.