Patterns in time-dependent Rayleigh-Benard convection experiments

Thesis/Dissertation · Sun Jan 01 04:00:00 EST 1989

OSTI ID:6069489

Meyer, C W

In this dissertation, the author reports on studies involving computer enhanced shadowgraph flow-visualization and heat-flux measurements on patterns in convective flows within a thin fluid layer of depth d that is heated from below. The experiments were conducted in a cylindrical container of radius r and aspect ratio L {equivalent to} r/d. In one study, the effects of stochastic perturbations on pattern formation and survival were examined. Two sets of experiments were performed in a cell with L = 10. In one set, the temperature of the top plate of the container was held constant while the heat current through the fluid was linearly ramped in time, resulting in a temperature difference {Delta}T between the bottom and top plates. After initial transients ended, the reduced Rayleigh number {epsilon} {equivalent to} {Delta}T/{Delta}{Tc}, - 1, where {Delta}{Tc}, is the critical temperature difference for the onset of convection, increased linearly with ramp rate {beta} such that near the onset {epsilon}(t) = {beta}t, where the time t is in units of the vertical thermal diffusion time t{sub v} {equivalent to} d{sup 2}/{kappa}({kappa} is the thermal diffusivity of the fluid). The ramp rates were in the range 0.01 {le} {beta} {le} 0.30. Two novel sidewall designs were used to allow pattern formation to occur independent of cell geometry. In the second set of experiments the heat current was modulated sinusoidally with dimensionless frequency {omega} = 1, where {omega} is scaled by t{sub v}, resulting in {epsilon}(t) = {epsilon}{sub o} + {sigma} sin({omega}t). The second study was concerned with the competition between reproducible cellular and roll-like flow patterns when {epsilon} is modulated as described above, but with higher values of {omega} and {delta}. The experiments were performed in a cell with L = 11.

• Research Organization: California Univ., Santa Barbara, CA (USA)
• OSTI ID: 6069489
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
420400* -- Engineering-- Heat Transfer & Fluid Flow
CONVECTION
CYLINDERS
DATA
DIFFUSION
ENERGY TRANSFER
EXPERIMENTAL DATA
FLOW VISUALIZATION
FLUID FLOW
FLUIDS
HEAT FLUX
HEAT TRANSFER
HEATING
INFORMATION
LAYERS
MASS TRANSFER
MEASURING METHODS
NUMERICAL DATA
STOCHASTIC PROCESSES
TEMPERATURE GRADIENTS
TIME DEPENDENCE