It is generally assumed that flows around wall-mounted sharp-edged bluff bodiessubmerged in thick turbulent boundary layers are essentially independent of theReynolds number Re, provided that this exceeds some (2–3) × 104. (Re is based onthe body height and upstream velocity at that height.) This is a particularization ofthe 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 windengineering thus describes work which implicitly rests on the validity of thisassumption. This paper presents new wind-tunnel data obtained in the ‘classical’ caseof thick fully turbulent boundary-layer flow over a surface-mounted cube, covering anRe range of well over an order of magnitude (that is, a factor of 22). The results arealso compared with new field data, providing a further order of magnitude increase inRe. It is demonstrated that if on the one hand the flow around the obstacle does notcontain strong concentrated-vortex motions (like the delta-wing-type motions presentfor a cube oriented at 45? to the oncoming flow), Re effects only appear on fluctuatingquantities such as the r.m.s. fluctuating surface pressures. If, on the other hand, theflow is characterized by the presence of such vortex motions, Re effects are significanteven on mean-flow quantities such as the mean surface pressures or the mean velocitiesnear the surfaces. It is thus concluded that although, in certain circumstances and forsome quantities, the Reynolds-number-independency assumption is valid, there areother important quantities and circumstances for which it is not.
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