EXPERIMENTS ON CONVECTION AT VERY HIGH RAYLEIGH NUMBERS

Experiments in which a thick layer of fluid was heated from below at a constant rate were conducted at flux Rayleigh numbers in the range of 10**9 to 10**1**2. The resulting convection was investigated by statistical analysis of the temperature signals from a pair of thermistor probes at different horizontal spacings. Power spectra showed that the temperature variance was distributed over a broad band of periods but that the centroid of this band, the characteristic period, depended very nearly on the minus one-half power of the heat flux. Measurements of the coherency between the probe signals at varying distances were interpreted as defining a characteristic horizontal length scale that depended approximately upon the minus one quarter power of the heat flux. These results tend to substantiate the boundary layer instability model of convection at very high Rayleigh numbers.