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Anisotropy-resolving subgrid-scale modelling using explicit algebraic closures for large eddy simulation
KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.ORCID iD: 0000-0002-3173-7502
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 [en]
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: urn:nbn:se:kth:diva-142401ISBN: 978-91-7595-038-9 (print)OAI: oai:DiVA.org:kth-142401DiVA: diva2:700132
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
List of papers
1. Effects of modelling, resolution and anisotropy of subgrid-scales on large eddy simulations of channel flow
Open this publication in new window or tab >>Effects of modelling, resolution and anisotropy of subgrid-scales on large eddy simulations of channel flow
Show others...
2011 (English)In: Journal of turbulence, ISSN 1468-5248, E-ISSN 1468-5248, Vol. 12, no 10, 1-20 p.Article in journal (Refereed) Published
Abstract [en]

In this paper, the effect of subgrid-scale (SGS) modelling, grid resolution and anisotropy of the subgrid-scales on large eddy simulation (LES) is investigated. LES of turbulent channel flow is performed at Re=934, based on friction velocity and channel half width, for a wide range of resolutions. The dynamic Smagorinsky model (DS), the high-pass filtered dynamic Smagorinsky model (HPF) based on the variational multiscale method and the recent explicit algebraic model (EA), which accounts for the anisotropy of the SGS stresses are considered. The first part of the paper is focused on the resolution effects on LES, where the performances of the three SGS models at different resolutions are compared to direct numerical simulation (DNS) results. The results show that LES using eddy viscosity SGS models is very sensitive to resolution. At coarse resolutions, LES with the DS and the HPF models deviate considerably from DNS, whereas LES with the EA model still gives reasonable results. Further analysis shows that the two former models do not accurately predict the SGS dissipation near the wall, while the latter does, even at coarse resolutions. In the second part, the effect of SGS modelling on LES predictions of near-wall and outer-layer turbulent structures is discussed. It is found that different models predict near-wall turbulent structures of different sizes. Analysis of the spectra shows that although near-wall scales are not resolved at coarse resolutions, large-scale motions can be reasonably captured in LES using all the tested models.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2011
Keyword
large eddy simulation, subgrid-scale modelling, resolution effects, subgrid-scale anisotropy, channel flow
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-31322 (URN)10.1080/14685248.2010.541920 (DOI)000287703700001 ()2-s2.0-83055170803 (Scopus ID)
Funder
Swedish Research Council, 621-2010-6965Swedish Research Council, 621-2007-4232Swedish e‐Science Research Center
Note

QC 20110318

Available from: 2011-03-18 Created: 2011-03-14 Last updated: 2016-04-12Bibliographically approved
2. Large eddy simulation of channel flow with andwithout periodic constrictions using the explicit algebraic subgrid-scale model
Open this publication in new window or tab >>Large eddy simulation of channel flow with andwithout periodic constrictions using the explicit algebraic subgrid-scale model
(English)In: Journal of turbulence, ISSN 1468-5248, E-ISSN 1468-5248Article in journal (Other academic) Submitted
Abstract [en]

We analyse the performance of the explicit algebraic subgrid-scale stress model(EASSM) of Marstorp et al. (J. Fluid Mech., vol. 639, 2009, pp. 403–432) inlarge eddy simulation (LES) of plane channel and the flow in a channel withstreamwise periodic hill-shaped constrictions (periodic hill flow) which induceseparation. The LESs are performed with Code Saturne which is an unstructuredcollocated finite volume solver with a second-order spatial discretisationsuitable for LES of incompressible flow in complex geometries. At first, performanceof the EASSM in LES of plane channel flow at two different resolutionsusing the Code Saturne and a pseudo-spectral method is analyzed. It is observedthat EASSM predictions of the mean velocity and Reynolds stresses aremore accurate than with the conventional dynamic Smagorinsky model (DSM).The results with the pseudo-spectral method were in general more accurate.In the second step, LES with the EASSM of flow separation in the periodichill flow is compared to LES with the DSM, no subgrid-scale model and thehighly resolved LES data of Breuer et al. (Computers & Fluids, vol. 38, 2009,pp. 433–457) using the DSM. Results show that the mean velocity profiles,the friction and pressure coefficients, the length and shape of the recirculationbubble, as well as the Reynolds stresses are considerably better predicted bythe EASSM than the DSM and the no subgrid-scale model simulations. It wasalso observed that in some parts of the domain the resolved strain-rate andsubgrid-scale shear stress have the same sign. The DSM cannot produce acorrect subgrid-scale stress in this case, in contrast to the EASSM.

National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-142398 (URN)
Funder
Swedish Research Council, 621-2010- 6965
Note

QS 2014

Available from: 2014-03-03 Created: 2014-03-03 Last updated: 2017-12-05Bibliographically approved
3. A comparison between isotropic and anisotropy-resolving closures in large eddy simulation of separated flow
Open this publication in new window or tab >>A comparison between isotropic and anisotropy-resolving closures in large eddy simulation of separated flow
2014 (English)Report (Other academic)
Abstract [en]

This study compares the conventional isotropic dynamic eddy viscosity model(DEVM) and anisotropy-resolving nonlinear explicit algebraic subgrid-scale(SGS) stress model (EASSM) of Marstorp et al. (J. Fluid Mech., vol. 639,2009, pp. 403–432) in large-eddy simulations (LESs) of flow separation in achannel with streamwise periodic hill-shaped constrictions and spanwise homogeneity(periodic hill flow). The results are validated with well-resolved LESdata of Breuer et al (Computers & Fluids, vol. 38, 2009, pp. 433-457). Threedifferent resolutions ranging from moderate to very coarse are used. LESs arecarried out with the Code Saturne, an unstructured collocated finite volumesolver for incompressible flows with a second-order central difference schemein space and a second-order discretisation in time. It has inherent numericaldissipation due to the low-order of the numerical method. LESs with no SGSmodel (NSM) are also carried out to analyse the influence of the SGS modelsin the presence of discretisation errors. LESs with the NSM show that the inherentnumerical dissipation is sufficient to give a reasonable prediction of themean velocity profiles at the finest resolution. The LES predictions of the meanvelocity and Reynolds stresses with the EASSM are found to be much moreaccurate than the ones with the DEVM at all resolutions. Although the SGSdissipation produced by the EASSM is found to be considerably lower than bythe DEVM, the EASSM predictions show appreciable improvements over theNSM, indicating the importance of the nonlinear part of the model. At thecoarsest resolution, where the SGS anisotropy is large, LES with the EASSMshows a reasonable prediction of the mean separation and reattachment points,whereas LES with the isotropic DEVM predicts a considerably delayed separationand early flow reattachment with a small separation bubble and the LESwith NSM does not display flow separation. At finer resolutions, the DEVMand NSM predict a shorter separation bubble than the EASSM, which has agood agreement with the well-resolved reference LES data. Hence, a correctprediction of the separation and reattachment by LES requires resolving the SGS anisotropy either by a fine grid or by an anisotropy-resolving SGS modelsuch as the EASSM.

National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-142399 (URN)
Funder
Swedish Research Council, 621-2010- 6965
Note

QC 20140304

Available from: 2014-03-03 Created: 2014-03-03 Last updated: 2014-03-04Bibliographically approved
4. An explicit algebraic model for the subgrid-scale passive scalar flux
Open this publication in new window or tab >>An explicit algebraic model for the subgrid-scale passive scalar flux
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
Keyword
rotating turbulence, turbulence modelling, turbulent flows
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-124303 (URN)10.1017/jfm.2013.81 (DOI)000319160800007 ()2-s2.0-84886241457 (Scopus ID)
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
5. A stochastic extension of the explicit algebraic subgrid-scales models
Open this publication in new window or tab >>A stochastic extension of the explicit algebraic subgrid-scales models
2014 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 26, no 5, 055113- p.Article in journal (Refereed) Published
Abstract [en]

The explicit algebraic subgrid-scale (SGS) stress model (EASM) of Marstorp et al. ["Explicit algebraic subgrid stress models with application to rotating channel flow," J. Fluid Mech. 639, 403-432 (2009)] and explicit algebraic SGS scalar flux model (EASFM) of Rasam et al. ["An explicit algebraic model for the subgrid-scale passive scalar flux,"J. Fluid Mech. 721, 541-577 (2013)] are extended with stochastic terms based on the Langevin equation formalism for the subgrid-scales by Marstorp et al. ["A stochastic subgrid model with application to turbulent flow and scalar mixing," Phys. Fluids 19, 035107 (2007)]. The EASM and EASFM are nonlinear mixed and tensor eddy-diffusivity models, which improve large eddy simulation (LES) predictions of the mean flow, Reynolds stresses, and scalar fluxes of wall-bounded flows compared to isotropic eddy-viscosity and eddy-diffusivity SGS models, especially at coarse resolutions. The purpose of the stochastic extension of the explicit algebraic SGS models is to further improve the characteristics of the kinetic energy and scalar variance SGS dissipation, which are key quantities that govern the small-scale mixing and dispersion dynamics. LES of turbulent channel flow with passive scalar transport shows that the stochastic terms enhance SGS dissipation statistics such as length scale, variance, and probability density functions and introduce a significant amount of backscatter of energy from the subgrid to the resolved scales without causing numerical stability problems. The improvements in the SGS dissipation predictions in turn enhances the predicted resolved statistics such as the mean scalar, scalar fluxes, Reynolds stresses, and correlation lengths. Moreover, the nonalignment between the SGS stress and resolved strain-rate tensors predicted by the EASM with stochastic extension is in much closer agreement with direct numerical simulation data.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2014
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-142389 (URN)10.1063/1.4879436 (DOI)000337103900045 ()2-s2.0-84905270384 (Scopus ID)
Funder
Swedish Research Council, 621-2010-6965
Note

QC 20140704

Available from: 2014-03-03 Created: 2014-03-03 Last updated: 2017-12-05Bibliographically approved

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