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Sharp transitions in rotating turbulent convection

Authors :
Federico Toschi
Richard J. A. M. Stevens
Rudie Kunnen
Detlef Lohse
Herman Clercx
Kim M. J. Alards
Physics of Fluids
Fluids and Flows
Computational Multiscale Transport Phenomena (Toschi)
Turbulent and Multiphase Flows (Kunnen)
Transport in Turbulent Flows (Clercx)
Source :
Physical Review Fluids, Physical review fluids, 4(7):074601. American Physical Society, Physical Review Fluids, 4(7):074601, 1-19. American Physical Society, Physical review fluids (Online) 4 (2019). doi:10.1103/PhysRevFluids.4.074601, info:cnr-pdr/source/autori:Alards K.M.J.; Kunnen R.P.J.; Stevens R.J.A.M.; Lohse D.; Toschi F.; Clercx H.J.H./titolo:Sharp transitions in rotating turbulent convection: Lagrangian acceleration statistics reveal a second critical Rossby number/doi:10.1103%2FPhysRevFluids.4.074601/rivista:Physical review fluids (Online)/anno:2019/pagina_da:/pagina_a:/intervallo_pagine:/volume:4
Publication Year :
2019
Publisher :
American Physical Society, 2019.

Abstract

In RB convection for fluids with Prandtl number $Pr\gtrsim 1$, rotation beyond a critical (small) rotation rate is known to cause a sudden enhancement of heat transfer which can be explained by a change in the character of the BL dynamics near the top and bottom plates of the convection cell. Namely, with increasing rotation rate, the BL signature suddenly changes from Prandtl--Blasius type to Ekman type. The transition from a constant heat transfer to an almost linearly increasing heat transfer with increasing rotation rate is known to be sharp and the critical Rossby number $Ro_{c}$ occurs typically in the range $2.3\lesssim Ro_{c}\lesssim 2.9$ (for Rayleigh number $Ra=1.3\times 10^9$, $Pr=6.7$, and a convection cell with aspect ratio $\Gamma=\frac{D}{H}=1$, with $D$ the diameter and $H$ the height of the cell). The explanation of the sharp transition in the heat transfer points to the change in the dominant flow structure. At $1/Ro\lesssim 1/Ro_c$ (slow rotation), the well-known LSC is found: a single domain-filling convection roll made up of many individual thermal plumes. At $1/Ro\gtrsim 1/Ro_c$ (rapid rotation), the LSC vanishes and is replaced with a collection of swirling plumes that align with the rotation axis. In this paper, by numerically studying Lagrangian acceleration statistics, related to the small-scale properties of the flow structures, we reveal that this transition between these different dominant flow structures happens at a second critical Rossby number, $Ro_{c_2}\approx 2.25$ (different from $Ro_{c_1}\approx 2.7$ for the sharp transition in the Nusselt number $Nu$; both values for the parameter settings of our present numerical study). When statistical data of Lagrangian tracers near the top plate are collected, it is found that the root-mean-square (rms) values and the kurtosis of the horizontal acceleration of these tracers show a sudden increase at $Ro_{c_2}$.<br />Comment: 16 pages, 9 Figures

Details

Language :
English
ISSN :
2469990X
Volume :
4
Issue :
7
Database :
OpenAIRE
Journal :
Physical Review Fluids
Accession number :
edsair.doi.dedup.....d3c3709390a1f42c80ebeafbc9e5054b