# Hybrid LES-RANS: back scatter from a scale-similarity model used as forcing

**Lars Davidson
** (Institutionen för tillämpad mekanik, Strömningslära)
**Philosophical Transactions of the Royal Society A - Mathematical, Physical and Engineering Sciences** (1364-503X). Vol. 367 (2009), 1899, p. 2905-2915.

[Artikel, refereegranskad vetenskaplig]

A dissipative scale-similarity subgrid model was recently proposed in which only the dissipative part of the subgrid stresses was added to the momentum equations. This was achieved by adding the gradient of a subgrid stress only when its sign agreed with that of the corresponding viscous term. In the present work, this idea is used the other way around as forcing in hybrid large eddy simulation-Reynolds-averaged Navier-Stokes: only the part of a subgrid stress term that corresponds to back scatter is added to the momentum equations. The forcing triggers resolved turbulence in the transition region between the unsteady Reynolds-averaged Navier-Stokes and large eddy simulation regions. The new approach is evaluated for fully developed channel flow at Re(tau) = 4000. It is found that the forcing indeed does increase the resolved turbulence in the transition region. The magnitude of the production (i.e. back scatter) due to forcing in the equation for resolved kinetic energy is of the order of that due to the usual strain-rate production term. The present approach of using back scatter from a scale-similarity model can also probably be useful for triggering transition.

**Nyckelord: ** large eddy simulation; dissipative; forcing; back scatter; scale similar; transition

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Davidson, L. (2009) *Hybrid LES-RANS: back scatter from a scale-similarity model used as forcing*.

** BibTeX **

@article{

Davidson2009,

author={Davidson, Lars},

title={Hybrid LES-RANS: back scatter from a scale-similarity model used as forcing},

journal={Philosophical Transactions of the Royal Society A - Mathematical, Physical and Engineering Sciences},

issn={1364-503X},

volume={367},

issue={1899},

pages={2905-2915},

abstract={A dissipative scale-similarity subgrid model was recently proposed in which only the dissipative part of the subgrid stresses was added to the momentum equations. This was achieved by adding the gradient of a subgrid stress only when its sign agreed with that of the corresponding viscous term. In the present work, this idea is used the other way around as forcing in hybrid large eddy simulation-Reynolds-averaged Navier-Stokes: only the part of a subgrid stress term that corresponds to back scatter is added to the momentum equations. The forcing triggers resolved turbulence in the transition region between the unsteady Reynolds-averaged Navier-Stokes and large eddy simulation regions. The new approach is evaluated for fully developed channel flow at Re(tau) = 4000. It is found that the forcing indeed does increase the resolved turbulence in the transition region. The magnitude of the production (i.e. back scatter) due to forcing in the equation for resolved kinetic energy is of the order of that due to the usual strain-rate production term. The present approach of using back scatter from a scale-similarity model can also probably be useful for triggering transition.},

year={2009},

keywords={ large eddy simulation; dissipative; forcing; back scatter; scale similar; transition },

}

** RefWorks **

RT Journal Article

SR Electronic

ID 101976

A1 Davidson, Lars

T1 Hybrid LES-RANS: back scatter from a scale-similarity model used as forcing

YR 2009

JF Philosophical Transactions of the Royal Society A - Mathematical, Physical and Engineering Sciences

SN 1364-503X

VO 367

IS 1899

SP 2905

OP 2915

AB A dissipative scale-similarity subgrid model was recently proposed in which only the dissipative part of the subgrid stresses was added to the momentum equations. This was achieved by adding the gradient of a subgrid stress only when its sign agreed with that of the corresponding viscous term. In the present work, this idea is used the other way around as forcing in hybrid large eddy simulation-Reynolds-averaged Navier-Stokes: only the part of a subgrid stress term that corresponds to back scatter is added to the momentum equations. The forcing triggers resolved turbulence in the transition region between the unsteady Reynolds-averaged Navier-Stokes and large eddy simulation regions. The new approach is evaluated for fully developed channel flow at Re(tau) = 4000. It is found that the forcing indeed does increase the resolved turbulence in the transition region. The magnitude of the production (i.e. back scatter) due to forcing in the equation for resolved kinetic energy is of the order of that due to the usual strain-rate production term. The present approach of using back scatter from a scale-similarity model can also probably be useful for triggering transition.

LA eng

DO 10.1098/rsta.2008.0299

LK http://dx.doi.org/10.1098/rsta.2008.0299

OL 30

Denna post skapades 2009-11-21. Senast ändrad 2013-10-29.

CPL Pubid: 101976