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An explicit algebraic model for the subgrid-scale passive scalar flux
KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0002-3173-7502
KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0002-9819-2906
KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0002-2711-4687
2013 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 721, 541-577 p.Article in journal (Refereed) Published
Abstract [en]

In Marstorp et al. (J. Fluid Mech., vol. 639, 2009, pp. 403-432), an explicit algebraic subgrid stress model (EASSM) for large-eddy simulation (LES) was proposed, which was shown to considerably improve LES predictions of rotating and non-rotating turbulent channel flow. In this paper, we extend that work and present a new explicit algebraic subgrid scalar flux model (EASSFM) for LES, based on the modelled transport equation of the subgrid-scale (SGS) scalar flux. The new model is derived using the same kind of methodology that leads to the explicit algebraic scalar flux model of Wikstrom et al. (Phys. Fluids, vol. 12, 2000, pp. 688-702). The algebraic form is based on a weak equilibrium assumption and leads to a model that depends on the resolved strain-rate and rotation-rate tensors, the resolved scalar-gradient vector and, importantly, the SGS stress tensor. An accurate prediction of the SGS scalar flux is consequently strongly dependent on an accurate description of the SGS stresses. The new EASSFM is therefore primarily used in connection with the EASSM, since this model can accurately predict SGS stresses. The resulting SGS scalar flux is not necessarily aligned with the resolved scalar gradient, and the inherent dependence on the resolved rotation-rate tensor makes the model suitable for LES of rotating flow applications. The new EASSFM (together with the EASSM) is validated for the case of passive scalar transport in a fully developed turbulent channel flow with and without system rotation. LES results with the new model show good agreement with direct numerical simulation data for both cases. The new model predictions are also compared to those of the dynamic eddy diffusivity model (DEDM) and improvements are observed in the prediction of the resolved and SGS scalar quantities. In the non-rotating case, the model performance is studied at all relevant resolutions, showing that its predictions of the Nusselt number are much less dependent on the grid resolution and are more accurate. In channel flow with wall-normal rotation, where all the SGS stresses and fluxes are non-zero, the new model shows significant improvements over the DEDM predictions of the resolved and SGS quantities.

Place, publisher, year, edition, pages
Cambridge University Press, 2013. Vol. 721, 541-577 p.
Keyword [en]
rotating turbulence, turbulence modelling, turbulent flows
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-124303DOI: 10.1017/jfm.2013.81ISI: 000319160800007Scopus ID: 2-s2.0-84886241457OAI: oai:DiVA.org:kth-124303DiVA: diva2:634176
Note

QC 20130628. Updated from "Submmitted" to "Published"

QC 20160412 Fulltext updated

Available from: 2013-06-28 Created: 2013-06-28 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Modelling of subgrid-scale stress and passive scalar flux in large eddy simulations of wall bounded turbulent flows
Open this publication in new window or tab >>Modelling of subgrid-scale stress and passive scalar flux in large eddy simulations of wall bounded turbulent flows
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The aim of the thesis is to develop and validate subgrid-scale models that are relevant for large eddy simulations of complex flows including scalar mixing. A stochastic Smagorinsky model with adjustable variance and time scale is developed by adding a stochastic component to the Smagorinsky constant. The stochastic model is shown to provide for backscatter of both kinetic energy and scalar variance without causing numerical instabilities. In addition, new models for the subgrid-scale stress and passive scalar flux are derived from modelled subgrid scale transport equations. These models properly account for the anisotropy of the subgrid scales and have potentials wall bounded flows. The proposed models are validated in wall bounded flows with and without rotation and show potential or significantly improve predictions for such cases.      

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. iii, 22 p.
Series
Trita-MEK, ISSN 0348-467X ; 2008:06
Keyword
Turbulence, large-eddy simulation, subgrid-scale model
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-4809 (URN)
Public defence
2008-06-13, Sal D3, KTH, Lindstedtsvägen 5, Stockholm, 10:30
Opponent
Supervisors
Note

QC 20100826

Available from: 2008-06-05 Created: 2008-06-05 Last updated: 2013-10-30Bibliographically approved
2. Anisotropy-resolving subgrid-scale modelling using explicit algebraic closures for large eddy simulation
Open this publication in new window or tab >>Anisotropy-resolving subgrid-scale modelling using explicit algebraic closures for large eddy simulation
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The present thesis deals with the development and performance analysis ofanisotropy-resolving models for the small, unresolved scales (”sub-grid scales”,SGS) in large eddy simulation (LES). The models are characterised by a descriptionof anisotropy by use of explicit algebraic models for both the subgridscale(SGS) stress tensor (EASSM) and SGS scalar flux vector (EASSFM). Extensiveanalysis of the performance of the explicit algebraic SGS stress model(EASSM) has been performed and comparisons made with the conventionalisotropic dynamic eddy viscosity model (DEVM). The studies include LES ofplane channel flow at relatively high Reynolds numbers and a wide range ofresolutions and LES of separated flow in a channel with streamwise periodichill-shaped constrictions (periodic hill flow) at coarse resolutions. The formersimulations were carried out with a pseudo-spectral Navier–Stokes solver, whilethe latter simulations were computed with a second-order, finite-volume basedsolver for unstructured grids. The LESs of channel flow demonstrate that theEASSM gives a good description of the SGS anisotropy, which in turn gives ahigh degree of resolution independence, contrary to the behaviour of LES predictionsusing the DEVM. LESs of periodic hill flow showed that the EASSMalso for this case gives significantly better flow predictions than the DEVM.In particular, the reattachment point was much better predicted with the EASSMand reasonably well predicted even at very coarse resolutions, where theDEVM is unable to predict a proper flow separation.The explicit algebraic SGS scalar flux model (EASSFM) is developed toimprove LES predictions of complex anisotropic flows with turbulent heat ormass transfer, and can be described as a nonlinear tensor eddy diffusivity model.It was tested in combination with the EASSM for the SGS stresses, and itsperformance was compared to the conventional dynamic eddy diffusivity model(DEDM) in channel flow with and without system rotation in the wall-normaldirection. EASSM and EASSFM gave predictions of high accuracy for meanvelocity and mean scalar fields, as well as stresses and scalar flux components.An extension of the EASSM and EASSFM, based on stochastic differentialequations of Langevin type, gave further improvements. In contrast to conventionalmodels, these extended models are able to describe intermittent transferof energy from the small, unresolved scales, to the resolved large ones.The present study shows that the EASSM/EASSFM gives a clear improvementof LES of wall-bounded flows in simple, as well as in complex geometriesin comparison with simpler SGS models. This is also shown to hold for a widerange of resolutions and is particularly accentuated for coarse resolution. The advantages are also demonstrated both for high-order numerical schemes andfor solvers using low-order finite volume methods. The models therefore havea clear potential for more applied computational fluid mechanics.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. vii, 48 p.
Series
TRITA-MEK, ISSN 0348-467X ; 2014:07 2014:07
Keyword
Turbulence, large eddy simulation, explicit algebraic subgridscale model, passive scalar, stochastic modelling, periodic hill flow
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-142401 (URN)978-91-7595-038-9 (ISBN)
Public defence
2014-03-14, F3, Lindstedsvägen 26, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Projects
Explicit algebraic sub-grid scale modelling for large-eddy simulations
Funder
Swedish Research Council, 621-2010- 6965
Note

QC 20140304

Available from: 2014-03-04 Created: 2014-03-03 Last updated: 2014-03-04Bibliographically approved

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Rasam, AminBrethouwer, GeertJohansson, Arne V.

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