dorsal/arxiv
View SchemaRotations and cessations of the large-scale circulation in turbulent Rayleigh-Benard convection
| Authors | Eric Brown, Guenter Ahlers |
|---|---|
| Categories | |
| ArXiv ID | physics/0603088 |
| URL | https://arxiv.org/abs/physics/0603088 |
| DOI | 10.1017/S0022112006002540 |
Abstract
We present a broad range of measurements of the angular orientation theta_0(t) of the large-scale circulation (LSC) of turbulent Rayleigh-Benard convection as a function of time. We used two cylindrical samples of different overall sizes, but each with its diameter nearly equal to its height. The fluid was water with a Prandtl number of 4.38. The time series theta_0(t) consisted of meanderings similar to a diffusive process, but in addition contained large and irregular spontaneous reorientation events through angles Delta theta. We found that reorientations can occur by two distinct mechanisms. One consists of a rotation of the circulation plane without any major reduction of the circulation strength. The other involves a cessation of the circulation, followed by a restart in a randomly chosen new direction. Rotations occurred an order of magnitude more frequently than cessations. Rotations occurred with a monotonically decreasing probability distribution p(Delta theta), i.e. there was no dominant value of Delta theta and small Delta theta were more common than large ones. For cessations p(Delta theta) was uniform, suggesting that information of theta_0(t) before the cessation is lost. Both rotations and cessations have Poissonian statistics in time, and can occur at any theta_0. The average azimuthal rotation rate increased as the circulation strength of the LSC decreased. Tilting the sample relative to gravity significantly reduced the frequency of occurrence of both rotations and cessations.
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"abstract": "We present a broad range of measurements of the angular orientation\ntheta_0(t) of the large-scale circulation (LSC) of turbulent Rayleigh-Benard\nconvection as a function of time. We used two cylindrical samples of different\noverall sizes, but each with its diameter nearly equal to its height. The fluid\nwas water with a Prandtl number of 4.38. The time series theta_0(t) consisted\nof meanderings similar to a diffusive process, but in addition contained large\nand irregular spontaneous reorientation events through angles Delta theta. We\nfound that reorientations can occur by two distinct mechanisms. One consists of\na rotation of the circulation plane without any major reduction of the\ncirculation strength. The other involves a cessation of the circulation,\nfollowed by a restart in a randomly chosen new direction. Rotations occurred an\norder of magnitude more frequently than cessations. Rotations occurred with a\nmonotonically decreasing probability distribution p(Delta theta), i.e. there\nwas no dominant value of Delta theta and small Delta theta were more common\nthan large ones. For cessations p(Delta theta) was uniform, suggesting that\ninformation of theta_0(t) before the cessation is lost. Both rotations and\ncessations have Poissonian statistics in time, and can occur at any theta_0.\nThe average azimuthal rotation rate increased as the circulation strength of\nthe LSC decreased. Tilting the sample relative to gravity significantly reduced\nthe frequency of occurrence of both rotations and cessations.",
"arxiv_id": "physics/0603088",
"authors": [
"Eric Brown",
"Guenter Ahlers"
],
"categories": [
"physics.flu-dyn"
],
"doi": "10.1017/S0022112006002540",
"title": "Rotations and cessations of the large-scale circulation in turbulent Rayleigh-Benard convection",
"url": "https://arxiv.org/abs/physics/0603088"
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