LES and URANS predictions using Star-CD V&V for T-Junction test case

(Vattenfall Experiment)Part of UK’s “Keeping Nuclear Options Open” project

School of Mechanical, Aerospace & Civil Engineering (MACE)The University of Manchester

Presented by: Y. Addad

Collaborators: A. Keshmiri, S. Rolfo, M. Cotton, D. Laurence

France-Japan joint Seminar on Thermal fatigue, 5th to

6th October 2009, Tokyo, Japan.

The person to contact: www.cfd.mace.manchester.ac.uk/Main/StefanoRolfo

Rod Bundle arranged in a triangular array

Exp. f=13Hz

SFR fuel assembly

Re=11,000Liquid sodium

Thermal mixing in T-Junction:Previous work:

Author Study type Case Grid ObservationsKimura et al. 2002 Exp. •Dh=Dc

•V ratio 0.2 to 5.0

•Re=3105 to 6105

- •Thermocouple frequency 25Hz.

Pasutto et al. 2005 LES (Code_Saturne)

•Dh=Dc

•Vc=0.2 Vh

0.5M-1M •Wall functions used

•Trms over predicted.

Hu et al. 2006 LES (Fluent) Kimura (2002) 1.3 M • Trms over predicted.

Pasutto et al. 2007 LES (Code_Saturne)

As above 0.85M •Study upstream elbow effects.

Anderson 2006 Exp. •Qc/Dh=2 - Thermocouple 30Hz.

Westin et al. 2008 LES (Fluent) Anderson 2006 0.45-9.5M •Trms over predicted.

• 9M grid .

Kuczaj et al. 2008 LES (in-house code)

Anderson 2006 0.15M-7.2M

•No perturbations at inlet.

•Wall function used

•10 % order of error on Temp.

•At least 0.9 M grid.

•Trms over predicted.

Reference:Westin J. et al. “High-Cycle Thermal Fatigue in Mixing Tees. Large-Eddy Simulations Compared to a New Validation Experiment”, 16th Int. Conf. On Nuclear Engineering (ICONE-16).

Experiment of thermal mixing in T-Junction

Previous LES runs with Fluent (see reference)

Flow Ratio: Qc/Qh=2

T = 15°C

DC=0.14 m, Dh=0.1m

ReC=105 , Reh=105

Thermal mixing in T-Junction: Grid

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

Hot

Hot

Cold

Cold

Inlet Boundary conditions (cyclic RANS)

LES run

URANS run

Instantaneous Temperature variation

LES versus URANS

Experiment

URANS

Plan 2.6D Plan 6.6D

LES

Recirculation

Time-averaged V & Temp. in cross sections

2.6Dz

x

Velocity Profiles at the plan x=2.6D

Velocity fluctuations Profiles at the plan x=2.6D

2.6Dz

x

6.6Dz

x

Velocity Profiles at the plan x=6.6D

Resolved part only

6.6Dz

x

Temperature Profiles at the plan x=6.6D

R

B

L

TY

Z

T variation at 1mm from walls along the x axis.

URANS

LES

U

URANS

LES

W

R

B

L

TY

Z

Trms variation at 1 mm from walls along the x axis

CentreY

Z

Variation of the velocity fluctuations along the x axis in the centre.

1

4

3

2Y

Z

Probe1

Probe2 Probe4

Probe3

Time history of temperature near the walls

1

4

3

2Y

Z

Spectra of temperature near the walls

1

4

3

2Y

Z

Spectra of streamwise velocity near the walls.

- 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)