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2 Acta Geophysica

2 2008

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Spatially-averaged flow statistics within a canopy of large bluff bodies: Results from direct numerical simulations

Coceal O., Thomas T. G., Belcher S.

Acta Geophysica

2008

Vol. 56, no. 3

862-875

The flow within a canopy of large bluff bodies is highly turbulent and spatially heterogeneous. Results from direct numerical simulations over groups of cubical obstacles are analysed using the double-averaging methodology. The obstacles occupy a significant fraction of the canopy space; this gives rise to substantial dispersive stresses within the canopy. The underlying bluff-body turbulent dynamics is different from typical canopy turbulence, and this is reflected in the double-averaged statistics. The spatially-averaged velocities, stresses and drag force depend significantly upon the layout of the obstacles. An ongoing challenge is to parameterise these spatially-averaged quantities in terms of the obstacle geometry and layout.

On the significance of form-induced stress in rough wall turbulent boundary layers

Manes C., Pokrajac D., Coceal O., McEwan I.

Acta Geophysica

2008

Vol. 56, no. 3

845-861

This paper presents a review of recent experimental and numerical studies which deal with the analysis of form-induced stress in rough wall turbulent boundary layers. The aim of the paper is to assess the importance of this stress for various rough wall geometries and flow conditions. Analysis of the significance of form-induced stress is first performed by comparing its magnitude with the magnitude of Reynolds stress for each data set available in literature. Then, by selecting a special set of data, we analyze the comparison between the gradients of both stresses. We point out that the comparison of stress gradients gives a different perspective on the role of form-induced stress in rough wall boundary layers.