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Modelling of subgrid-scale stress and passive scalar flux in large eddy simulations of wall bounded turbulent flows
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
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 [en]
Turbulence, large-eddy simulation, subgrid-scale model
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-4809OAI: oai:DiVA.org:kth-4809DiVA: diva2:14088
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
List of papers
1. A stochastic subgrid model with application to turbulent flow and scalar mixing
Open this publication in new window or tab >>A stochastic subgrid model with application to turbulent flow and scalar mixing
2007 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 19, no 3, 035107- p.Article in journal (Refereed) Published
Abstract [en]

A new computationally cheap stochastic Smagorinsky model which allows for backscatter of subgrid scale energy is proposed. The new model is applied in the large eddy simulation of decaying isotropic turbulence, rotating homogeneous shear flow and turbulent channel flow at Re-tau=360. The results of the simulations are compared to direct numerical simulation data. The inclusion of stochastic backscatter has no significant influence on the development of the kinetic energy in homogeneous flows, but it improves the prediction of the fluctuation magnitudes as well as the anisotropy of the fluctuations in turbulent channel flow compared to the standard Smagorinsky model with wall damping of C-S. Moreover, the stochastic model improves the description of the energy transfer by reducing its length scale and increasing its variance. Some improvements were also found in isotropic turbulence where the stochastic contribution improved the shape of the enstrophy spectrum at the smallest resolved scales and reduced the time scale of the smallest resolved scales in better agreement with earlier observations.

Keyword
LARGE-EDDY SIMULATION; BACKSCATTER; VISCOSITY; ENERGY
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-8696 (URN)10.1063/1.2711477 (DOI)000245318500019 ()2-s2.0-34047223580 (Scopus ID)
Note
QC 20100825Available from: 2008-06-05 Created: 2008-06-05 Last updated: 2010-08-25Bibliographically approved
2. Explicit algebraic subgrid stress models with application to rotating channel flow
Open this publication in new window or tab >>Explicit algebraic subgrid stress models with application to rotating channel flow
2009 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 639, 403-432 p.Article in journal (Refereed) Published
Abstract [en]

New explicit subgrid stress models are proposed involving the strain rate and rotation rate tensor, which can account for rotation in a natural way. The new models are based on the same methodology that leads to the explicit algebraic Reynolds stress model formulation for Reynolds-averaged Navier-Stokes simulations. One dynamic model and one non-dynamic model are proposed. The non-dynamic model represents a computationally efficient subgrid scale (SGS) stress model, whereas the dynamic model is the most accurate. The models are validated through large eddy simulations (LESs) of spanwise and streamwise rotating channel flow and are compared with the standard and dynamic Smagorinsky models. The proposed explicit dependence on the system rotation improves the description of the mean velocity profiles and the turbulent kinetic energy at high rotation rates. Comparison with the dynamic Smagorinsky model shows that not using the eddy-viscosity assumption improves the description of both the Reynolds stress anisotropy and the SGS stress anisotropy. LESs of rotating channel flow at Re-tau = 950 have been carried out as well. These reveal some significant Reynolds number influences on the turbulence statistics. LESs of non-rotating turbulent channel flow at Re-tau = 950 show that the new explicit model especially at coarse resolutions significantly better predicts the mean velocity, wall shear and Reynolds stresses than the dynamic Smagorinsky model, which is probably the result of a better prediction of the anisotropy of the subgrid dissipation.

Keyword
LARGE-EDDY SIMULATION; DIRECT NUMERICAL-SIMULATION; TURBULENT FLOWS; SCALE STRESSES; CLOSURE METHOD; TRANSPORT
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-8697 (URN)10.1017/S0022112009991054 (DOI)000272521600015 ()2-s2.0-76349094920 (Scopus ID)
Note
QC 20100825. Uppdaterad från submitted till published (20100825).Available from: 2008-06-05 Created: 2008-06-05 Last updated: 2010-08-25Bibliographically approved
3. 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
4. Validation of SGS models in large eddy simulation of turbulent zero pressure gradient boundary layer flow
Open this publication in new window or tab >>Validation of SGS models in large eddy simulation of turbulent zero pressure gradient boundary layer flow
Show others...
2008 (English)Report (Other academic)
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-8699 (URN)
Note

QC 20100826

Available from: 2008-06-05 Created: 2008-06-05 Last updated: 2016-05-11Bibliographically approved

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Citation style
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