1

* 2 conf. paper papers presented by Y. Addad (UoM) and R. Howard (EDF)

* Int. Symp on Convective Heat and Mass Transfer in Sustainable Energy, April 26 – April 26 – 1 May, 2009 Hammamet, Tunisia1 May, 2009 Hammamet, Tunisia

* France-Japan joint Seminar on Thermal fatigue, 5th to 6th October 2009, Tokyo, Japan

STURM4-progress meeting, Clamart 13 Oct 2009

EDF – U o Man collaborations on Unstructured meshes for DNS and LES

THE EFFECT OF DIFFERENTS GRIDS AND DIFFERENT LES MODELS

ON TURBULENCE STATISTICS IN CHANNEL

FLOWS

Richard Howard and Yacine Addad

International Symposium on International Symposium on Convective Heat and Mass Convective Heat and Mass Transfer in Sustainable EnergyTransfer in Sustainable Energy

April 26 – 1 May, 2009 Yasmine Hammamet, TunisiaApril 26 – 1 May, 2009 Yasmine Hammamet, Tunisia

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DIFFERENTS GRIDS AND DIFFERENT LES MODELSIN CHANNEL FLOWS

Stretched uniform

hybrid

Box

Reynolds (u tau) 180

Code Saturne http///www.code-saturne.org

Collocalised, Cell centered, 2nd order central differences

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DIFFERENTS GRIDS AND DIFFERENT LES MODELSIN CHANNEL FLOWS

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DIFFERENTS GRIDS AND DIFFERENT LES MODELSIN CHANNEL FLOWS

Stretched

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DIFFERENTS GRIDS AND DIFFERENT LES MODELSIN CHANNEL FLOWS

Stretched Term I (second derivatives) Term II (gradients of turbulent viscosity) Term III (products of gradients)

WALE Smagorinsky

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DIFFERENTS GRIDS AND DIFFERENT LES MODELSIN CHANNEL FLOWS

Uniform

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DIFFERENTS GRIDS AND DIFFERENT LES MODELSIN CHANNEL FLOWS

Hybrid

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DIFFERENTS GRIDS AND DIFFERENT LES MODELSIN CHANNEL FLOWS

• The dominant term is TermIII (products of velocity gradients which includes a kind subgrid dissipation term)

• The WALE model dissipates the resolved fluctuations in v and w more than the other models.

• The hybrid grid show numerical noise particularly at the channel centreline. The sloping faces of the non structured grid act to transfer the local mean velocity field between each velocity component.

Thermal mixing in T-Junction: Hexa Grid, STAR V4 LES

Grid Cells= 2.56 M.

LES RUNS:

SGS Model: Smago.PrSGS=0.9 (Default).

URANS RUNS:

Non-linear k- modelSuga et al. 2006.

Numerical schemes:

2nd order in space.2nd order in time.

3.1D

h

3Dc 13Dc

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- URANS model: - Fails to capture the complex features of the flow.

- Most information needed for thermal fatigue studies is lost. - Not able to capture high frequency events.

- Can this be improved or other approaches tested (example DES) ??

- LES with Unstructured grids and Professional Software: - Second order accuracy seems OK.- Mesh is extremely important, adapted to (1/10) large eddy scale ? => need unstructured mesh- Work in progress: How about tetrahedral and polyhedral cells, different SGS models??

Conclusions and future work

Acknowledgements:UK research council project “Keeping the Nuclear Option Open” (KNOO)FR ANR-CIS STURM4