Affiliations: Division of Energy and Environment Systems, Graduate
School of Engineering, Hokkaido University, N13W8, Sapporo, 060-8628, Japan.
E-mail: tasaka@eng.hokudai.ac.jp | Nissan Motor Co., Ltd., 6-1 Tsurumi-ku, Yokohama,
230-0053, Japan | Institute for Research on Earth Evolution, Japan
Agency for Marine-Earth Science and Technology, 2-15 Natsushima, Yokosuka,
237-0061, Japan
Abstract: The dilatation and the pattern formation of convection cells in
natural convection driven by internal heat generation, first investigated
during the 1970s, are reexamined in this paper using an improved experimental
apparatus in order to reduce uncertainties as much as possible. The convective
motion in the fluid layer was visualized using reflecting particles
(Kalliroscope). Cell dilatation was confirmed in the improved experimental
apparatus and then investigated quantitatively by extracting the pattern
wavenumber from Fourier analysis of the images recorded by a digital camera.
The pattern wavenumber was found to decrease with increasing Rayleigh number.
We compare our results with earlier investigations and discuss the influence of
the thermal boundary condition at the bottom of the fluid layer on the
variation of the wavenumber. Two different structures were observed in the same
fluid layer at a relatively high Rayleigh number; an additional cell appears in
the original cell (Double cell structure) and the descending flow region around
the center of the cell expands laterally like a spoke of wheels (Spoke-like
structure). Factors for the formation of such complex structures are discussed.
