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History effects and near equilibrium in adverse-pressure-gradient turbulent boundary layers
KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.ORCID-id: 0000-0001-9833-9560
KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.ORCID-id: 0000-0001-6570-5499
KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Centra, SeRC - Swedish e-Science Research Centre.ORCID-id: 0000-0002-1663-3553
KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.ORCID-id: 0000-0001-9627-5903
2017 (engelsk)Inngår i: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 820, s. 667-692Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Turbulent boundary layers under adverse pressure gradients are studied using well-resolved large-eddy simulations (LES) with the goal of assessing the influence of the streamwise pressure-gradient development. Near-equilibrium boundary layers were characterized through the Clauser pressure-gradient parameter β. In order to fulfil the near-equilibrium conditions, the free stream velocity was prescribed such that it followed a power-law distribution. The turbulence statistics pertaining to cases with a constant value of β (extending up to approximately 40 boundary-layer thicknesses) were compared with cases with non-constant β distributions at matched values of β and friction Reynolds number Reδ∗. An additional case at matched Reynolds number based on displacement thickness Reδ∗ was also considered. It was noticed that non-constant β cases appear to approach the conditions of equivalent constant β cases after long streamwise distances (approximately 7 boundary-layer thicknesses). The relevance of the constant β cases lies in the fact that they define a 'canonical' state of the boundary layer, uniquely characterized by β and Re. The investigations on the flat plate were extended to the flow around a wing section overlapping in terms of β and Re. Comparisons with the flat-plate cases at matched values of β and Re revealed that the different development history of the turbulent boundary layer on the wing section leads to a less pronounced wake in the mean velocity as well as a weaker second peak in the Reynolds stresses. This is due to the weaker accumulated effect of the β history. Furthermore, a scaling law suggested by Kitsios et al. (Intl J. Heat Fluid Flow, vol. 61, 2016, pp. 129-136), proposing the edge velocity and the displacement thickness as scaling parameters, was tested on two constant-pressure-gradient parameter cases. The mean velocity and Reynolds-stress profiles were found to be dependent on the downstream development. The present work is the first step towards assessing history effects in adverse-pressure-gradient turbulent boundary layers and highlights the fact that the values of the Clauser pressure-gradient parameter and the Reynolds number are not sufficient to characterize the state of the boundary layer.

sted, utgiver, år, opplag, sider
Cambridge University Press , 2017. Vol. 820, s. 667-692
Emneord [en]
turbulent boundary layers, turbulent flows, Atmospheric thermodynamics, Boundary layer flow, Flow of fluids, Large eddy simulation, Pressure gradient, Reynolds number, Turbulence, Turbulent flow, Velocity, Adverse pressure gradient, Constant pressure gradient, Displacement thickness, Equilibrium boundaries, Equilibrium conditions, Power law distribution, Pressure-gradient parameters, Boundary layers
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Identifikatorer
URN: urn:nbn:se:kth:diva-216464DOI: 10.1017/jfm.2017.236Scopus ID: 2-s2.0-85019182537OAI: oai:DiVA.org:kth-216464DiVA, id: diva2:1162973
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QC 20171205

Tilgjengelig fra: 2017-12-05 Laget: 2017-12-05 Sist oppdatert: 2017-12-05bibliografisk kontrollert

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