Length of near-wall plumes in turbulent convection

Puthenveettil, Baburaj A and Gunasegarane, GS and Agrawal, Yogesh K and Schmeling, Daniel and Bosbach, Johannes and Arakeri, Jaywant H (2011) Length of near-wall plumes in turbulent convection. In: Journal of Fluid Mechanics, 685 . pp. 335-364.

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Abstract

We present planforms of line plumes formed on horizontal surfaces in turbulent convection, along with the length of line plumes measured from these planforms, in a six decade range of Rayleigh numbers (10(5) < Ra < 10(11)) and at three Prandtl numbers (Pr = 0.7, 5.2, 602). Using geometric constraints on the relations for the mean plume spacings, we obtain expressions for the total length of near-wall plumes on horizontal surfaces in turbulent convection. The plume length per unit area (L(p)/A), made dimensionless by the near-wall length scale in turbulent convection (Z(w)), remains constant for a given fluid. The Nusselt number is shown to be directly proportional to L(p)H/A for a given fluid layer of height H. The increase in Pr has a weak influence in decreasing L(p)/A. These expressions match the measurements, thereby showing that the assumption of laminar natural convection boundary layers in turbulent convection is consistent with the observed total length of line plumes. We then show that similar relationships are obtained based on the assumption that the line plumes are the outcome of the instability of laminar natural convection boundary layers on the horizontal surfaces.

Item Type:	Journal Article
Publication:	Journal of Fluid Mechanics
Publisher:	Cambridge University Press
Additional Information:	Copyright of this article belongs to Cambridge University Press.
Keywords:	buoyant boundary layers;plumes/thermals;turbulent convection
Department/Centre:	Division of Mechanical Sciences > Mechanical Engineering
Date Deposited:	21 Dec 2011 09:53
Last Modified:	21 Dec 2011 09:53
URI:	http://eprints.iisc.ac.in/id/eprint/42628

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