Counter-gradient diffusion in a slot-ventilated enclosure assessed by LES and RANS

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Abstract

In Computational Fluid Dynamics (CFD) studies for the prediction of room airflow the Reynolds-averaged Navier-Stokes (RANS) approach is often used, in which only the averaged quantities are computed, whereas the effect of turbulence is modeled. Since the RANS approach does not provide information on the velocity and concentration fluctuations, turbulent mass transport is often modeled using the standard gradient-diffusion hypothesis, which relates the turbulent mass flux to the mean concentration derivatives. This paper presents a CFD analysis of pollutant dispersion in an enclosure ventilated by a transitional wall jet (Re ˜ 2,500), using validated high-resolution RANS and Large Eddy Simulations (LES). The LES simulations show that a counter-gradient turbulent mass flux is present, indicating that the standard gradient-diffusion hypothesis used in RANS is not valid in the entire flow domain. However, it is shown that for this particular case, the convective mass fluxes dominate over the turbulent mass fluxes, and that the predicted pollutant concentrations by RANS will therefore not differ significantly from the results obtained with LES.
Original languageEnglish
Pages (from-to)63-75
Number of pages13
JournalComputers & Fluids
Volume96
DOIs
Publication statusPublished - 2014

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Large eddy simulation
Enclosures
Mass transfer
Computational fluid dynamics
Dynamic analysis
Turbulence
Derivatives

Cite this

@article{0094e029e1ee495bb5578de254e498c8,
title = "Counter-gradient diffusion in a slot-ventilated enclosure assessed by LES and RANS",
abstract = "In Computational Fluid Dynamics (CFD) studies for the prediction of room airflow the Reynolds-averaged Navier-Stokes (RANS) approach is often used, in which only the averaged quantities are computed, whereas the effect of turbulence is modeled. Since the RANS approach does not provide information on the velocity and concentration fluctuations, turbulent mass transport is often modeled using the standard gradient-diffusion hypothesis, which relates the turbulent mass flux to the mean concentration derivatives. This paper presents a CFD analysis of pollutant dispersion in an enclosure ventilated by a transitional wall jet (Re ˜ 2,500), using validated high-resolution RANS and Large Eddy Simulations (LES). The LES simulations show that a counter-gradient turbulent mass flux is present, indicating that the standard gradient-diffusion hypothesis used in RANS is not valid in the entire flow domain. However, it is shown that for this particular case, the convective mass fluxes dominate over the turbulent mass fluxes, and that the predicted pollutant concentrations by RANS will therefore not differ significantly from the results obtained with LES.",
author = "{van Hooff}, T. and B.J.E. Blocken and P. Gousseau and {Heijst, van}, G.J.F.",
year = "2014",
doi = "10.1016/j.compfluid.2014.02.020",
language = "English",
volume = "96",
pages = "63--75",
journal = "Computers & Fluids",
issn = "0045-7930",
publisher = "Elsevier",

}

Counter-gradient diffusion in a slot-ventilated enclosure assessed by LES and RANS. / van Hooff, T.; Blocken, B.J.E.; Gousseau, P.; Heijst, van, G.J.F.

In: Computers & Fluids, Vol. 96, 2014, p. 63-75.

Research output: Contribution to journalArticleAcademicpeer-review

TY - JOUR

T1 - Counter-gradient diffusion in a slot-ventilated enclosure assessed by LES and RANS

AU - van Hooff, T.

AU - Blocken, B.J.E.

AU - Gousseau, P.

AU - Heijst, van, G.J.F.

PY - 2014

Y1 - 2014

N2 - In Computational Fluid Dynamics (CFD) studies for the prediction of room airflow the Reynolds-averaged Navier-Stokes (RANS) approach is often used, in which only the averaged quantities are computed, whereas the effect of turbulence is modeled. Since the RANS approach does not provide information on the velocity and concentration fluctuations, turbulent mass transport is often modeled using the standard gradient-diffusion hypothesis, which relates the turbulent mass flux to the mean concentration derivatives. This paper presents a CFD analysis of pollutant dispersion in an enclosure ventilated by a transitional wall jet (Re ˜ 2,500), using validated high-resolution RANS and Large Eddy Simulations (LES). The LES simulations show that a counter-gradient turbulent mass flux is present, indicating that the standard gradient-diffusion hypothesis used in RANS is not valid in the entire flow domain. However, it is shown that for this particular case, the convective mass fluxes dominate over the turbulent mass fluxes, and that the predicted pollutant concentrations by RANS will therefore not differ significantly from the results obtained with LES.

AB - In Computational Fluid Dynamics (CFD) studies for the prediction of room airflow the Reynolds-averaged Navier-Stokes (RANS) approach is often used, in which only the averaged quantities are computed, whereas the effect of turbulence is modeled. Since the RANS approach does not provide information on the velocity and concentration fluctuations, turbulent mass transport is often modeled using the standard gradient-diffusion hypothesis, which relates the turbulent mass flux to the mean concentration derivatives. This paper presents a CFD analysis of pollutant dispersion in an enclosure ventilated by a transitional wall jet (Re ˜ 2,500), using validated high-resolution RANS and Large Eddy Simulations (LES). The LES simulations show that a counter-gradient turbulent mass flux is present, indicating that the standard gradient-diffusion hypothesis used in RANS is not valid in the entire flow domain. However, it is shown that for this particular case, the convective mass fluxes dominate over the turbulent mass fluxes, and that the predicted pollutant concentrations by RANS will therefore not differ significantly from the results obtained with LES.

U2 - 10.1016/j.compfluid.2014.02.020

DO - 10.1016/j.compfluid.2014.02.020

M3 - Article

VL - 96

SP - 63

EP - 75

JO - Computers & Fluids

JF - Computers & Fluids

SN - 0045-7930

ER -