Hybrid RANS/LES Method for High Reynolds Numbers, Applied to Atmospheric Flow over Complex Terrain

A. Bechmann, Niels Sørensen, J. Johansen, S. Vinther, B.S. Nielsen, P. Botha

Research output: Contribution to journalJournal articleResearchpeer-review

8 Citations (Scopus)

Abstract

 

The use of Large-Eddy Simulation (LES) to predict wall-bounded flows has presently been limited to low Reynolds number flows. Since the number of computational grid points required to resolve the near-wall turbulent structures increase rapidly with Reynolds number, LES has been unattainable for flows at high Reynolds numbers. To reduce the computational cost of traditional LES a hybrid method is proposed in which the near-wall eddies are modelled in a Reynolds-averaged sense. Close to walls the flow is treated with the RANS-equations and this layer act as wall model for the outer flow handled by LES. The wellknown high Reynolds number two-equation k - ǫ turbulence model is used in the RANS layer and the model automatically switches to a two-equation k - ǫ subgrid-scale stress model in the LES region. The approach can be used for flow over rough walls.
To demonstrate the ability of the proposed hybrid method, simulations of the wind flow over a complex terrain near Wellington in New Zealand are presented. Under certain conditions unsteady flow features have been measured at the site - flow features that could lead to high structural loads on a planned wind farm. These transient flow phenomena are reproduced with the new RANS/LES method. Additionally, the results from the hybrid method are compared with pure RANS results.

 
Original languageEnglish
Book seriesJournal of Physics - Conference Series
Volume75
Number of pages14
ISSN1742-6588
DOIs
Publication statusPublished - 2007

Fingerprint

high Reynolds number
large eddy simulation
computational grids
wall flow
unsteady flow
New Zealand
turbulence models
low Reynolds number
Reynolds number
switches
vortices
costs

Bibliographical note

Presented at the conference "The Science of Making Torque from Wind" 28-31 August 2007, Technical University of Denmark

Cite this

Bechmann, A. ; Sørensen, Niels ; Johansen, J. ; Vinther, S. ; Nielsen, B.S. ; Botha, P. / Hybrid RANS/LES Method for High Reynolds Numbers, Applied to Atmospheric Flow over Complex Terrain. In: Journal of Physics - Conference Series. 2007 ; Vol. 75.
@article{0f4504805c5111dc867f000ea68e967b,
title = "Hybrid RANS/LES Method for High Reynolds Numbers, Applied to Atmospheric Flow over Complex Terrain",
abstract = "  The use of Large-Eddy Simulation (LES) to predict wall-bounded flows has presently been limited to low Reynolds number flows. Since the number of computational grid points required to resolve the near-wall turbulent structures increase rapidly with Reynolds number, LES has been unattainable for flows at high Reynolds numbers. To reduce the computational cost of traditional LES a hybrid method is proposed in which the near-wall eddies are modelled in a Reynolds-averaged sense. Close to walls the flow is treated with the RANS-equations and this layer act as wall model for the outer flow handled by LES. The wellknown high Reynolds number two-equation k - ǫ turbulence model is used in the RANS layer and the model automatically switches to a two-equation k - ǫ subgrid-scale stress model in the LES region. The approach can be used for flow over rough walls. To demonstrate the ability of the proposed hybrid method, simulations of the wind flow over a complex terrain near Wellington in New Zealand are presented. Under certain conditions unsteady flow features have been measured at the site - flow features that could lead to high structural loads on a planned wind farm. These transient flow phenomena are reproduced with the new RANS/LES method. Additionally, the results from the hybrid method are compared with pure RANS results. ",
author = "A. Bechmann and Niels S{\o}rensen and J. Johansen and S. Vinther and B.S. Nielsen and P. Botha",
note = "Presented at the conference {"}The Science of Making Torque from Wind{"} 28-31 August 2007, Technical University of Denmark",
year = "2007",
doi = "doi:10.1088/1742-6596/75/1/012054",
language = "English",
volume = "75",
journal = "Journal of Physics: Conference Series (Online)",
issn = "1742-6596",
publisher = "IOP Publishing",

}

Hybrid RANS/LES Method for High Reynolds Numbers, Applied to Atmospheric Flow over Complex Terrain. / Bechmann, A.; Sørensen, Niels; Johansen, J.; Vinther, S.; Nielsen, B.S.; Botha, P.

In: Journal of Physics - Conference Series, Vol. 75, 2007.

Research output: Contribution to journalJournal articleResearchpeer-review

TY - JOUR

T1 - Hybrid RANS/LES Method for High Reynolds Numbers, Applied to Atmospheric Flow over Complex Terrain

AU - Bechmann, A.

AU - Sørensen, Niels

AU - Johansen, J.

AU - Vinther, S.

AU - Nielsen, B.S.

AU - Botha, P.

N1 - Presented at the conference "The Science of Making Torque from Wind" 28-31 August 2007, Technical University of Denmark

PY - 2007

Y1 - 2007

N2 -   The use of Large-Eddy Simulation (LES) to predict wall-bounded flows has presently been limited to low Reynolds number flows. Since the number of computational grid points required to resolve the near-wall turbulent structures increase rapidly with Reynolds number, LES has been unattainable for flows at high Reynolds numbers. To reduce the computational cost of traditional LES a hybrid method is proposed in which the near-wall eddies are modelled in a Reynolds-averaged sense. Close to walls the flow is treated with the RANS-equations and this layer act as wall model for the outer flow handled by LES. The wellknown high Reynolds number two-equation k - ǫ turbulence model is used in the RANS layer and the model automatically switches to a two-equation k - ǫ subgrid-scale stress model in the LES region. The approach can be used for flow over rough walls. To demonstrate the ability of the proposed hybrid method, simulations of the wind flow over a complex terrain near Wellington in New Zealand are presented. Under certain conditions unsteady flow features have been measured at the site - flow features that could lead to high structural loads on a planned wind farm. These transient flow phenomena are reproduced with the new RANS/LES method. Additionally, the results from the hybrid method are compared with pure RANS results. 

AB -   The use of Large-Eddy Simulation (LES) to predict wall-bounded flows has presently been limited to low Reynolds number flows. Since the number of computational grid points required to resolve the near-wall turbulent structures increase rapidly with Reynolds number, LES has been unattainable for flows at high Reynolds numbers. To reduce the computational cost of traditional LES a hybrid method is proposed in which the near-wall eddies are modelled in a Reynolds-averaged sense. Close to walls the flow is treated with the RANS-equations and this layer act as wall model for the outer flow handled by LES. The wellknown high Reynolds number two-equation k - ǫ turbulence model is used in the RANS layer and the model automatically switches to a two-equation k - ǫ subgrid-scale stress model in the LES region. The approach can be used for flow over rough walls. To demonstrate the ability of the proposed hybrid method, simulations of the wind flow over a complex terrain near Wellington in New Zealand are presented. Under certain conditions unsteady flow features have been measured at the site - flow features that could lead to high structural loads on a planned wind farm. These transient flow phenomena are reproduced with the new RANS/LES method. Additionally, the results from the hybrid method are compared with pure RANS results. 

U2 - doi:10.1088/1742-6596/75/1/012054

DO - doi:10.1088/1742-6596/75/1/012054

M3 - Journal article

VL - 75

JO - Journal of Physics: Conference Series (Online)

JF - Journal of Physics: Conference Series (Online)

SN - 1742-6596

ER -