Hexagonal and roll flow patterns in temporally modulated Rayleigh-Benard convection

Journal Article · Mon Jun 15 00:00:00 EDT 1992 · Physical Review A. General Physics; (United States)

DOI:https://doi.org/10.1103/PhysRevA.45.8583· OSTI ID:7286038

Meyer, C W; Cannell, D S; Ahlers, G ^[1]

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1. Department of Physics, University of California, Santa Barbara, California 93106 (United States) Center for Nonlinear Science, University of California, Santa Barbara, California 93106 (United States)

We present experimental results for pattern formation in a thin fluid layer heated time periodically from below. They were obtained with computer-enhanced shadowgraph flow visualization and with heat-flux measurements. The experimental cell was cylindrical, with a radius-to-height ratio of 11.0. The temperature of the top plate was held constant while that of the bottom plate was modulated sinusoidally so that the reduced Rayleigh number {epsilon}{equivalent to}{Delta}{ital T}/{Delta}{ital T}{sub {ital c}}{minus}1 had the form {epsilon}({ital t})={epsilon}{sub 0}+{delta} sin({omega}{ital t}). Here the time {ital t} and frequency {omega} are scaled by the vertical thermal diffusion time. Experiments were performed within the ranges 8.0{le}{omega}{le}18.0, 0.4{le}{delta}{le}3.3, and {minus}0.2{le}{epsilon}{sub 0}{le}0.6. Measurements of the convective threshold shift {epsilon}{sub {ital c}}({delta},{omega}) were in good agreement with theoretical predictions. Comparisons were made with theoretical predictions of a range {epsilon}{sub {ital A}}({delta},{omega}){le}{epsilon}{sub 0}{lt}{epsilon}{sub {ital R}}({delta},{omega}) ({epsilon}{sub {ital A}}{lt}{epsilon}{sub {ital c}},{epsilon}{sub {ital R}}{gt}{epsilon}{sub {ital c}}) where only a hexagonal pattern with downflow at the cell centers is predicted to be stable, a range {epsilon}{sub {ital R}}{le}{epsilon}{sub 0}{lt}{epsilon}{sub {ital B}}({delta},{omega}) where both hexagonal and roll patterns are expected to be stable, and a range {epsilon}{sub 0}{ge}{epsilon}{sub {ital B}} where only a roll pattern should be stable.

• DOE Contract Number: FG03-87ER13738
• OSTI ID: 7286038
• Journal Information: Physical Review A. General Physics; (United States), Journal Name: Physical Review A. General Physics; (United States) Vol. 45:12; ISSN 1050-2947; ISSN PLRAA
• Country of Publication: United States
• Language: English

Related Subjects

665000* -- Physics of Condensed Matter-- (1992-)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
BOUNDARY LAYERS
CONVECTION
CONVECTIVE INSTABILITIES
ENERGY TRANSFER
FLOW VISUALIZATION
FLUIDS
HEAT TRANSFER
HEATING
INSTABILITY
LAYERS
MASS TRANSFER
MODULATION
PATTERN RECOGNITION
PHOTOGRAPHY
PLASMA INSTABILITY
PLATES
TEMPERATURE DISTRIBUTION
TIME DEPENDENCE