Large-scale mean patterns in turbulent convection

Abstract

Large-scale patterns, which are well-known from the spiral defect chaos regime of thermal convection at Rayleigh numbers $Ra<10^4$, continue to exist in three-dimensional numerical simulations of turbulent Rayleigh-Bénard convection in extended cylindrical cells with an aspect ratio $\Gamma =50$ and $Ra>10^5$. They are uncovered when the turbulent fields are averaged in time and turbulent fluctuations are thus removed. We apply the Boussinesq closure to estimate turbulent viscosities and diffusivities, respectively. The resulting turbulent Rayleigh number $R{a}_{\ast }$, that describes the convection of the mean patterns, is indeed in the spiral defect chaos range. The turbulent Prandtl numbers are smaller than one with $0.2\le P{r}_{\ast }\le 0.4$ for Prandtl numbers $0.7\le Pr\le 10$. Finally, we demonstrate that these mean flow patterns are robust to an additional finite-amplitude side wall-forcing when the level of turbulent fluctuations in the flow is sufficiently high.

13 pages, 7 figures

References in corpus (5)

• Computational Study of Turbulent-Laminar Patterns in Couette Flow
• Aspect ratio dependence of heat transfer and large-scale flow in turbulent convection
• Large-scale mean patterns in turbulent convection
• Symmetry related dynamics in parallel shear flows
• Lagrangian tracer dynamics in a closed cylindrical turbulent convection cell

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