Large-scale thermal motions of turbulent Rayleigh-Bénard convection in a wide aspect-ratio cylindrical domain

P. J. Sakievich, Yulia Peet, Ronald Adrian

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11 Citations (Scopus)

Abstract

The large-scale structures that occur in turbulent Rayleigh-Bénard convection in a wide-aspect-ratio cylindrical domain are studied by means of direct numerical simulation. The simulation is performed in a 6.3 aspect-ratio cylindrical cell with a Rayleigh number of 9.6 × 107 and Prandtl number equal to 6.7. Single-point and double-point statistics compare well against experimental results under nearly identical conditions. Large-scale thermal motions with coherence times exceeding 20 eddy-turnovers (∼600 free-fall time units) are seen in the instantaneous fields. Temporally filtering them by integrating over approximately one eddy-turnover time scale reveals a clear pattern consisting of seven discrete thermal structures: three warm, rising sectors, three cool, falling sectors and a single plume of warm, rising fluid that wanders around the center of the cylindrical cell. Smoothing over still longer times (10 and 20 eddy turn-over time scales) yields a clear hub-and-spoke pattern of warm and cool sectors in a dominantly 120° periodic pattern separated by concentrations of radial vortex lines (the spokes) plus a nearly circular plume at the center of the test section (the hub). The similarity of the patterns in the instantaneous fields and the long-time smoothed fields demonstrates long persistence of these structures, a defining characteristic of coherent structures in turbulence. The warm and cool sectors are intimately linked with conical roll-cells rotating about the spokes, and these circulations are likely the analogs of the 'wind of turbulence' found in low-aspect-ratio RBC experiments.

Original languageEnglish (US)
JournalInternational Journal of Heat and Fluid Flow
DOIs
StateAccepted/In press - Nov 9 2015

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aspect ratio
Aspect ratio
convection
spokes
Turbulence
sectors
vortices
hubs
Prandtl number
Direct numerical simulation
plumes
Vortex flow
cells
turbulence
Statistics
low aspect ratio
free fall
Fluids
Rayleigh number
direct numerical simulation

Keywords

  • Coherent structures
  • Rayleigh-Bénard
  • Thermal convection
  • Turbulence
  • Wide aspect ratio

ASJC Scopus subject areas

  • Mechanical Engineering
  • Condensed Matter Physics
  • Fluid Flow and Transfer Processes

Cite this

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title = "Large-scale thermal motions of turbulent Rayleigh-B{\'e}nard convection in a wide aspect-ratio cylindrical domain",
abstract = "The large-scale structures that occur in turbulent Rayleigh-B{\'e}nard convection in a wide-aspect-ratio cylindrical domain are studied by means of direct numerical simulation. The simulation is performed in a 6.3 aspect-ratio cylindrical cell with a Rayleigh number of 9.6 × 107 and Prandtl number equal to 6.7. Single-point and double-point statistics compare well against experimental results under nearly identical conditions. Large-scale thermal motions with coherence times exceeding 20 eddy-turnovers (∼600 free-fall time units) are seen in the instantaneous fields. Temporally filtering them by integrating over approximately one eddy-turnover time scale reveals a clear pattern consisting of seven discrete thermal structures: three warm, rising sectors, three cool, falling sectors and a single plume of warm, rising fluid that wanders around the center of the cylindrical cell. Smoothing over still longer times (10 and 20 eddy turn-over time scales) yields a clear hub-and-spoke pattern of warm and cool sectors in a dominantly 120° periodic pattern separated by concentrations of radial vortex lines (the spokes) plus a nearly circular plume at the center of the test section (the hub). The similarity of the patterns in the instantaneous fields and the long-time smoothed fields demonstrates long persistence of these structures, a defining characteristic of coherent structures in turbulence. The warm and cool sectors are intimately linked with conical roll-cells rotating about the spokes, and these circulations are likely the analogs of the 'wind of turbulence' found in low-aspect-ratio RBC experiments.",
keywords = "Coherent structures, Rayleigh-B{\'e}nard, Thermal convection, Turbulence, Wide aspect ratio",
author = "Sakievich, {P. J.} and Yulia Peet and Ronald Adrian",
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AU - Sakievich, P. J.

AU - Peet, Yulia

AU - Adrian, Ronald

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Y1 - 2015/11/9

N2 - The large-scale structures that occur in turbulent Rayleigh-Bénard convection in a wide-aspect-ratio cylindrical domain are studied by means of direct numerical simulation. The simulation is performed in a 6.3 aspect-ratio cylindrical cell with a Rayleigh number of 9.6 × 107 and Prandtl number equal to 6.7. Single-point and double-point statistics compare well against experimental results under nearly identical conditions. Large-scale thermal motions with coherence times exceeding 20 eddy-turnovers (∼600 free-fall time units) are seen in the instantaneous fields. Temporally filtering them by integrating over approximately one eddy-turnover time scale reveals a clear pattern consisting of seven discrete thermal structures: three warm, rising sectors, three cool, falling sectors and a single plume of warm, rising fluid that wanders around the center of the cylindrical cell. Smoothing over still longer times (10 and 20 eddy turn-over time scales) yields a clear hub-and-spoke pattern of warm and cool sectors in a dominantly 120° periodic pattern separated by concentrations of radial vortex lines (the spokes) plus a nearly circular plume at the center of the test section (the hub). The similarity of the patterns in the instantaneous fields and the long-time smoothed fields demonstrates long persistence of these structures, a defining characteristic of coherent structures in turbulence. The warm and cool sectors are intimately linked with conical roll-cells rotating about the spokes, and these circulations are likely the analogs of the 'wind of turbulence' found in low-aspect-ratio RBC experiments.

AB - The large-scale structures that occur in turbulent Rayleigh-Bénard convection in a wide-aspect-ratio cylindrical domain are studied by means of direct numerical simulation. The simulation is performed in a 6.3 aspect-ratio cylindrical cell with a Rayleigh number of 9.6 × 107 and Prandtl number equal to 6.7. Single-point and double-point statistics compare well against experimental results under nearly identical conditions. Large-scale thermal motions with coherence times exceeding 20 eddy-turnovers (∼600 free-fall time units) are seen in the instantaneous fields. Temporally filtering them by integrating over approximately one eddy-turnover time scale reveals a clear pattern consisting of seven discrete thermal structures: three warm, rising sectors, three cool, falling sectors and a single plume of warm, rising fluid that wanders around the center of the cylindrical cell. Smoothing over still longer times (10 and 20 eddy turn-over time scales) yields a clear hub-and-spoke pattern of warm and cool sectors in a dominantly 120° periodic pattern separated by concentrations of radial vortex lines (the spokes) plus a nearly circular plume at the center of the test section (the hub). The similarity of the patterns in the instantaneous fields and the long-time smoothed fields demonstrates long persistence of these structures, a defining characteristic of coherent structures in turbulence. The warm and cool sectors are intimately linked with conical roll-cells rotating about the spokes, and these circulations are likely the analogs of the 'wind of turbulence' found in low-aspect-ratio RBC experiments.

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