Enhanced Vertical Inhomogeneity in Turbulent Rotating Convection

Kunnen, Rudie; Clercx, Hjh Herman; Geurts, BJ Bernard

doi:10.1103/physrevlett.101.174501

Cited by 24 publications

(31 citation statements)

References 21 publications

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“…This is however not the case in the turbulent flows studied here, since the PDFs of vertical velocity are shown to have wider tails, compared to the Gaussian distribution, in both electromagnetically forced turbulence (EFT) and Rayleigh-Bénard convection (RBC) [22,23]. Moreover, anisotropy and inhomogeneity play a role, especially in the flow close to the horizontal top and bottom plates [22][23][24][25]. Even though the scaling laws, derived in HIT, are shown to be robust [20], it is not clear how anisotropy, inhomogeneity and non-Gaussian velocity statistics influence the curvature and torsion PDFs and whether one recovers these scaling laws in different turbulent flows like, for example, the ones studied here.…”

Section: Introductionmentioning

confidence: 99%

“…First, rotation does influence the level of anisotropy and inhomogeneity in RBC and EFT [22][23][24][25]. Second, it changes the length scales of the typical coherent structures in both types of turbulence systems.…”

Section: Introductionmentioning

confidence: 99%

“…This can be studied by comparing scaling laws, measured in the bulk, to scaling laws measured in the boundary layer at different rotation rates. In the bulk we will moreover consider a measurement volume in the center of the cell and one closer to the top plate, to include effects of anisotropy and inhomogeneity [22][23][24][25]. In this way, we aim at finding a general effect of rotation on the geometry of particle trajectories, not only in different types of turbulent flows, but also closer to, or even inside, the boundary layer.…”

Section: Introductionmentioning

confidence: 99%

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Geometry of tracer trajectories in rotating turbulent flows

et al. 2017

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The geometry of passive tracer trajectories is studied in two different types of rotating turbulent flows; rotating Rayleigh-Bénard convection (RBC; experiments and direct numerical simulations) and rotating electromagnetically forced turbulence (EFT; experiments). This geometry is fully described by the curvature and torsion of trajectories and from these geometrical quantities we can subtract information on the typical flow structures at different rotation rates. Previous studies, focusing on non-rotating homogeneous isotropic turbulence (HIT), show that the probability density functions (PDFs) of curvature and torsion reveal pronounced power laws. However, the set-ups studied here involve inhomogeneous turbulence and in RBC the flow near the horizontal plates is definitely anisotropic. We want to investigate how the typical shapes of the curvature and torsion PDFs, including the pronounced scaling laws, are influenced by this level of anisotropy and inhomogeneity and how this effect changes with rotation. A first effect of rotation is observed as a shift of the curvature and torsion PDFs towards higher values in the case of RBC and towards lower values in the case of EFT. This shift is related to the length scale of typical vortical structures that decreases with rotation in RBC, but increases with rotation in EFT, explaining the opposite shifts of the curvature (and torsion) PDFs. A second remarkable observation is that in RBC the HIT scaling laws are always recovered, as long as the boundary layer (BL) is excluded. This suggests that these scaling laws are very robust and hold as long as we measure in the turbulent bulk. In the BL of the RBC cell, however, the scaling deviates from the HIT prediction for lower rotation rates. This scaling behavior is found to be consistent with the coupling between the boundary layer dynamics and the bulk flow, that changes under rotation. In particular, it is found that the active coupling of the Ekman-type boundary layer with the bulk flow suppresses anisotropy in the BL region for increasing rotation rates.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Geometry of tracer trajectories in rotating turbulent flows

et al. 2017

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“…Most practical flows however involve external fields and walls, hence they could have significant anisotropy, and their behaviour could differ from Kolmogorov's theory. Some of the examples of anisotropic turbulent flows are magnetohydrodynamic (MHD) turbulence [4], rotating turbulence ( [5] and references their in), quasi-static liquid-metal flows [6][7][8][9], turbulent convection [10], and rotating convection [11]. In this paper we will study anisotropy in turbulent convection.…”

Section: Introductionmentioning

confidence: 99%

Near isotropic behavior of turbulent thermal convection

et al. 2016

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We investigate the anisotropy in turbulent convection in a 3D box using direct numerical simulation. We compute the anisotropic parameter A = u 2 ⊥ /(2u 2 ), where u ⊥ and u are the components of velocity perpendicular and parallel to the buoyancy direction, the shell and ring spectra, and shell-to-shell energy transfers. We observe that the flow is nearly isotropic for the Prandtl number Pr ≈ 1, but the anisotropy increases with the Prandtl number. For Pr = ∞, A ≈ 0.3, thus anisotropy is not very significant even in extreme cases. We also observe that u feeds energy to u ⊥ via pressure. The computation of shell-to-shell energy transfers reveals that the energy transfer in turbulent convection is local and forward, similar to hydrodynamic turbulence. These results are consistent with the Kolmogorov's spectrum observed by Kumar et al. [Phys. Rev. E 90, 023016 (2014)] for turbulent convection.

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“…At larger rotation rates, an irregular, rapidly changing array of vertically oriented vortices is found. The turbulence intensity is reduced by strong rotation, compared to the non-rotating case, and the vertical inhomogeneity increases, reflecting the consequences of the thermal wind balance [16,25].…”

Section: Qualitative Flow-structure Changes Under Modulated Rotation mentioning

confidence: 99%

Rotating turbulent Rayleigh–Bénard convection subject to harmonically forced flow reversals

Geurts

Kunnen

2014

Journal of Turbulence

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The characteristics of turbulent flow in a cylindrical Rayleigh-Bénard convection cell which can be modified considerably in case rotation is included in the dynamics. By incorporating the additional effects of an Euler force, i.e., effects induced by nonconstant rotation rates, a remarkably strong intensification of the heat transfer efficiency can be achieved. We consider turbulent convection at Rayleigh number Ra = 10 9 and Prandtl number σ = 6.4 under a harmonically varying rotation, allowing complete reversals of the direction of the externally imposed rotation in the course of time. The dimensionless amplitude of the oscillation is taken as 1/Ro * = 1 while various modulation frequencies 0.1 ≤ Ro ω ≤ 1 are applied. Both slow and fast flow-structuring and heat transfer intensification are induced due to the forced flow reversals. Depending on the magnitude of the Euler force, increases in the Nusselt number of up to 400% were observed, compared to the case of constant or no rotation. It is shown that a large thermal flow structure accumulates all along the centreline of the cylinder, which is responsible for the strongly increased heat transfer. This dynamic thermal flow structure develops quite gradually, requiring many periods of modulated flow reversals. In the course of time, the Nusselt number increases in an oscillatory fashion up to a point of global instability, after which a very rapid and striking collapse of the thermal columnar structure is seen. Following such a collapse is another, quite similar episode of gradual accumulation of the next thermal column. We perform direct numerical simulation of the incompressible Navier-Stokes equations to study this system. Both the flow structures and the corresponding heat transfer characteristics are discussed at a range of modulation frequencies. We give an overview of typical time scales of the system response.

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Enhanced Vertical Inhomogeneity in Turbulent Rotating Convection

Cited by 24 publications

References 21 publications

Geometry of tracer trajectories in rotating turbulent flows

Geometry of tracer trajectories in rotating turbulent flows

Near isotropic behavior of turbulent thermal convection

Rotating turbulent Rayleigh–Bénard convection subject to harmonically forced flow reversals

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