arXiv subjects

David S. Cannell

Publications and source records attributed to David S. Cannell.

4 recordsLinked to original sources

arXiv1997

Competition between Spiral-Defect Chaos and Rolls in Rayleigh-Benard Convection

We present experimental results for pattern formation in Rayleigh-Benard convection of a fluid with a Prandtl number, Pr~ 4. We find that the spiral-defect-chaos (SDC) attractor which exists for Pr~1 has become unstable. Gradually increasing the temperature difference from below to well above its critical value no longer leads to SDC. A sudden jump of temperature difference from below to above onset causes convection to grow from thermal fluctuations and does yield SDC. However, the SDC is a transient; it coarsens and forms a single cell-filling spiral which then drifts toward the cell wall and disappears.

patt-sol↗

arXiv1996

The Spatio-Temporal Structure of Spiral-Defect Chaos

We present a study of the recently discovered spatially-extended chaotic state known as spiral-defect chaos, which occurs in low-Prandtl-number, large-aspect-ratio Rayleigh-Benard convection. We employ the modulus squared of the space-time Fourier transform of time series of two-dimensional shadowgraph images to construct the structure factor ${S}({\vec k},ω)$. This analysis is used to characterize the average spatial and temporal scales of the chaotic state. We find that the correlation length and time can be described by power-law dependences on the reduced Rayleigh number $ε$. These power laws have as yet no theoretical explanation.

chao-dyn↗

arXiv1995

Thermally Induced Fluctuations Below the Onset of Rayleigh-Bénard Convection

We report quantitative experimental results for the intensity of noise-induced fluctuations below the critical temperature difference $ΔT_c$ for Rayleigh-Bénard convection. The structure factor of the fluctuating convection rolls is consistent with the expected rotational invariance of the system. In agreement with predictions based on stochastic hydrodynamic equations, the fluctuation intensity is found to be proportional to $1/\sqrt{-ε}$ where $ε\equiv ΔT / ΔT_c -1$. The noise power necessary to explain the measurements agrees with the prediction for thermal noise. (WAC95-1)

patt-sol↗

arXiv1993

Spiral Defect Chaos in Large Aspect Ratio Rayleigh-Benard Convection

We report experiments on convection patterns in a cylindrical cell with a large aspect ratio. The fluid had a Prandtl number of approximately 1. We observed a chaotic pattern consisting of many rotating spirals and other defects in the parameter range where theory predicts that steady straight rolls should be stable. The correlation length of the pattern decreased rapidly with increasing control parameter so that the size of a correlated area became much smaller than the area of the cell. This suggests that the chaotic behavior is intrinsic to large aspect ratio geometries.

patt-sol↗