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Effect of adverse pressure gradients on turbulent wing boundary layers
KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.ORCID iD: 0000-0001-6570-5499
KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.ORCID iD: 0000-0001-9627-5903
2020 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 883, no A8, p. 1-28Article in journal (Refereed) Published
Abstract [en]

    The characteristics of turbulent boundary layers (TBLs) subjected to adverse pressure gradients are analysed through well-resolved large-eddy simulations. The geometries under study are the NACA0012 and NACA4412 wing sections, at 0 and 5 degrees angle of attack, respectively, both of them at a Reynolds number based on inflow velocity and chord length Rec = 400,000. The turbulence statistics show that adverse pressure gradients (APGs) have a significant effect on the mean velocity, velocity fluctuations and turbulent kinetic energy budget, and this effect is more prominent on the outer region of the boundary layer. Furthermore, the effect of flow history is assessed by means of an integrated Clauser pressure-gradient parameter, β, through the study of cases with matching local values of β and the friction Reynolds number, Reτ, to isolate this effect. Our results show a noticeable effect of the flow history on the outer region, however the differences in the near-wall peak of the tangential velocity fluctuations appear to be mostly produced by the local APG magnitude. The one-dimensional power-spectral density shows energetic small scales in the outer region of APG TBLs, whereas these energetic scales do not appear in zero-pressure-gradient (ZPG) TBLs, suggesting that small scales near the wall are advected towards the outer layer by the APG. Moreover, the linear coherence spectra show that the spectral outer peak of high-Reynolds-number ZPG TBLs is highly correlated with the near-wall region , unlike APG TBLs which do not show such a correlation. This result, together with the different two-dimensional spectra of APG and high-Reynolds-number ZPG TBLs, suggests different energisation mechanisms due to APG and increase in Reynolds number. To the authors' knowledge, this is the first in-depth analysis of the TBL characteristics over wings, including detailed single-point statistics, spectra and coherence.

Place, publisher, year, edition, pages
2020. Vol. 883, no A8, p. 1-28
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-267017DOI: 10.1017/jfm.2019.838ISI: 000508121500008OAI: oai:DiVA.org:kth-267017DiVA, id: diva2:1390043
Note

QC 20200203

Available from: 2020-01-31 Created: 2020-01-31 Last updated: 2020-02-17Bibliographically approved
In thesis
1. Studies on adverse-pressure-gradient turbulent boundary layers on wings
Open this publication in new window or tab >>Studies on adverse-pressure-gradient turbulent boundary layers on wings
2020 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The present licentiate thesis addresses the use of well-resolved simulations to simulate turbulent boundary layers (TBL) subjected to adverse pressure gradients. Within the thesis a wide variety of analyses are performed, and a method to improve the performance of the simulations is presented. The first aim of the thesis is to assess the effect of adverse pressure gradients and flow history on the development and fundamental characteristics of turbulent boundary layers. With this in mind, well-resolved large-eddy simulations (LES) of the turbulent boundary layers over two wing sections are performed using the spectral-element-method (SEM) code Nek5000. In order to assess the effects of the adverse pressure gradient on turbulent boundary layers, turbulence statistics are computed and time series are collected from the simulations. The turbulence statistics show a significant effect of the adverse pressure gradient on the mean velocity profiles, turbulent fluctuations and turbulent kinetic energy budgets. In addition, the time series are used to compute the power-spectral densities of the turbulent boundary layers and to analyse the effect of the adverse pressure gradient on the turbulent scales across the boundary layer. After having compared both wings at moderate Reynolds number Rec=400,000, the next goal is to perform high-resolution simulations of wings at higher Reynolds numbers in order to study conditions closer to those in reality, and to evaluate the effect of adverse pressure gradient with increasing Reynolds numbers. To achieve this, better and more efficient computational methods are required. In this thesis, the performance of the adaptive mesh refinement method recently implemented in Nek5000 is assessed for the first time on wing simulations. The obtained results show a large potential of this new method (which includes the use of non-conformal meshes) with respect to the previous simulations carried out with conformal meshes. Lastly, we performed a modal decomposition of the TBLs developing around both wing sections. To this end, we consider spectral proper orthogonal decomposition (SPOD), which can be used to identify the most energetic structures of the turbulent boundary layer.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2020. p. 38
Series
TRITA-SCI-FOU ; 02
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-267022 (URN)978-91-7873-436-8 (ISBN)
Presentation
2020-02-28, Seminarierum Faxén (rum 5316), KTH Mekanik, Teknikringen 8, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20200131

Available from: 2020-01-31 Created: 2020-01-31 Last updated: 2020-02-03Bibliographically approved

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Tanarro, AlvaroVinuesa, RicardoSchlatter, Philipp

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