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Bluff bodies in deep turbulent boundary layers: Reynolds-number issues

Published online by Cambridge University Press:  04 January 2007

HEE CHANG LIM ,
IAN P. CASTRO  and
ROGER P. HOXEY
HEE CHANG LIM
Affiliation:
School of Engineering Sciences, University of Southampton, Highfield, Southampton, SO17 1BJ, UK
IAN P. CASTRO*
Affiliation:
School of Engineering Sciences, University of Southampton, Highfield, Southampton, SO17 1BJ, UK
ROGER P. HOXEY
Affiliation:
Department of Civil Engineering, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
*
†Author to whom correspondence should be addressed: i.castro@soton.ac.uk
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Abstract

It is generally assumed that flows around wall-mounted sharp-edged bluff bodies submerged in thick turbulent boundary layers are essentially independent of the Reynolds number Re, provided that this exceeds some (2–3) × 104. (Re is based on the body height and upstream velocity at that height.) This is a particularization of the general principle of Reynolds-number similarity and it has important implications, most notably that it allows model scale testing in wind tunnels of, for example, atmospheric flows around buildings. A significant part of the literature on wind engineering thus describes work which implicitly rests on the validity of this assumption. This paper presents new wind-tunnel data obtained in the ‘classical’ case of thick fully turbulent boundary-layer flow over a surface-mounted cube, covering an Re range of well over an order of magnitude (that is, a factor of 22). The results are also compared with new field data, providing a further order of magnitude increase in Re. It is demonstrated that if on the one hand the flow around the obstacle does not contain strong concentrated-vortex motions (like the delta-wing-type motions present for a cube oriented at 45° to the oncoming flow), Re effects only appear on fluctuating quantities such as the r.m.s. fluctuating surface pressures. If, on the other hand, the flow is characterized by the presence of such vortex motions, Re effects are significant even on mean-flow quantities such as the mean surface pressures or the mean velocities near the surfaces. It is thus concluded that although, in certain circumstances and for some quantities, the Reynolds-number-independency assumption is valid, there are other important quantities and circumstances for which it is not.

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Type
Papers
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Journal of Fluid Mechanics , Volume 571 , 25 January 2007 , pp. 97 - 118
Copyright
Copyright © Cambridge University Press 2007

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