Rayleighnumber evolution of largescale coherent motion in turbulent convection
Abstract
At least up to Rayleigh numbers of the order 10^{13}, a feature of turbulent convection in confined containers is a selforganized and coherent largescale motion ("mean wind"). For aspect ratio unity, the mean wind is comparable in scale to the container size. Its magnitude is measured here using shorttime temperature correlations in a cylindrical container of aspect ratio unity; the working fluid is cryogenic helium and the Rayleigh numbers span from 10^{6} to 10^{15}. The selforganizing advection of "plumes" by the mean wind leads to periodic temperature oscillations near the sidewall. Comparisons of the observed oscillation frequency to the rotational rate of the mean wind, however, have differed by a factor of 2 in the recent literature. It is argued here that this apparent discrepancy is the result of the evolution of the shape of the mean wind, from a tilted and nearly elliptical shape at low Rayleigh numbers to a squarish shape at high Rayleigh numbers, thereby altering the effective path length from which the rotational rate of the mean wind is deduced.
 Publication:

EPL (Europhysics Letters)
 Pub Date:
 June 2003
 DOI:
 10.1209/epl/i2003004473
 Bibcode:
 2003EL.....62..829N
 Keywords:

 47.27.Te;
 47.27.Jv;
 HighReynoldsnumber turbulence