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dc.contributor.authorSharma, Aen
dc.contributor.authorGarcía-Mayoral, Ren
dc.date.accessioned2019-11-15T00:30:43Z
dc.date.available2019-11-15T00:30:43Z
dc.date.issued2020-01-01en
dc.identifier.issn0022-1120
dc.identifier.urihttps://www.repository.cam.ac.uk/handle/1810/298901
dc.description.abstractTurbulent flows within and over sparse canopies are investigated using direct numerical simulations at moderate friction Reynolds numbers Reτ ≈ 520 and 1000. The height of the canopies studied is h+ ≈ 110–200, which is typical of some engineering canopies but much lower than for most vegetation canopies. The analysis of the effect of Reynolds number in our simulations, however, suggests that the dynamics observed would be relevant for larger Reynolds numbers as well. In channel flows, the distribution of the total stress is linear with height. Over smooth walls, the total stress is the sum of the viscous and the Reynolds shear stresses, the `fluid stress' τf. In canopies, in turn, there is an additional contribution from the canopy drag, which can dominate within. Furthermore, the full Reynolds shear stress has contributions from the dispersive, element-induced flow and from the background turbulence, the part of the flow that remains once the element-induced flow is filtered out. For the present sparse canopies, we find that the ratio of the viscous stress and the background Reynolds shear stress to their sum, τf, is similar to that over smooth-walls at each height, even within the canopy. From this, a height-dependent scaling based on τf is proposed. Using this scaling, the background turbulence within the canopy shows similarities with turbulence over smooth walls. This suggests that the background turbulence scales with τf, rather than with the conventional scaling based on the total stress. This effect is essentially captured when the canopy is substituted by a drag force that acts on the mean velocity profile alone, aiming to produce the correct τf, without the discrete presence of the canopy elements acting directly on the fluctuations. The proposed mean-only forcing is shown to produce better estimates for the turbulent fluctuations compared to a conventional, homogeneous-drag model. These results suggest that a sparse canopy acts on the background turbulence primarily through the change it induces on the mean velocity profile, which in turn sets the scale for turbulence, rather than through a direct interaction of the canopy elements with the fluctuations. The effect of the element-induced flow, however, requires the representation of the individual canopy elements.
dc.description.sponsorshipCambridge Commonwealth, European and International Trust PRACE DECI-15 European Research Council
dc.publisherCambridge University Press
dc.rightsAll rights reserved
dc.rights.uri
dc.titleScaling and dynamics of turbulence over sparseA canopiesen
dc.typeArticle
prism.publicationDate2020en
prism.publicationNameJournal of Fluid Mechanicsen
prism.volume888en
dc.identifier.doi10.17863/CAM.45958
dcterms.dateAccepted2019-11-12en
rioxxterms.versionofrecord10.1017/jfm.2019.999en
rioxxterms.versionAM
rioxxterms.licenseref.urihttp://www.rioxx.net/licenses/all-rights-reserveden
rioxxterms.licenseref.startdate2020-01-01en
dc.identifier.eissn1469-7645
rioxxterms.typeJournal Article/Reviewen
pubs.funder-project-idEPSRC (EP/P020259/1)
cam.orpheus.successTue Mar 31 10:38:49 BST 2020 - Embargo updated*
cam.orpheus.counter2*
rioxxterms.freetoread.startdate2020-07-01


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