1. 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, 5 th to 6 th October 2009, Tokyo, Japan.

2. 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=11,000 Liquid sodium

3. Thermal mixing in T-Junction: Previous work : AuthorStudy typeCaseGridObservations Kimura et al. 2002Exp.D h =D c V ratio 0.2 to 5.0 Re=310 5 to 610 5 -Thermocouple frequency 25Hz. Pasutto et al. 2005LES (Code_Saturne) D h =D c V c =0.2 V h 0.5M-1MWall functions used T rms over predicted. Hu et al. 2006LES (Fluent)Kimura (2002)1.3 M T rms over predicted. Pasutto et al. 2007LES (Code_Saturne) As above0.85MStudy upstream elbow effects. Anderson 2006Exp.Q c /D h =2-Thermocouple 30Hz. Westin et al. 2008LES (Fluent)Anderson 20060.45- 9.5M T rms over predicted. 9M grid. Kuczaj et al. 2008LES (in-house code) Anderson 20060.15M- 7.2M No perturbations at inlet. Wall function used 10 % order of error on Temp. At least 0.9 M grid. T rms over predicted.

4. Reference: Westin J. et al. “High-Cycle Thermal Fatigue in Mixing Tees. Large-Eddy Simulations Compared to a New Validation Experiment”, 16 th Int. Conf. On Nuclear Engineering (ICONE-16). Experiment of thermal mixing in T-Junction Previous LES runs with Fluent (see reference) Flow Ratio: Q c /Q h =2  T = 15°C D C =0.14 m, D h =0.1m Re C =10 5, Re h =10 5

5. Thermal mixing in T-Junction: Grid Grid Cells= 2.56 M. LES RUNS: SGS Model: Smago. Pr SGS =0.9 (Default). URANS RUNS: Non-linear k-  model Suga et al. 2006. Numerical schemes: 2 nd order in space. 2 nd order in time. 3.1D h 3D c 13D c

6. Hot Cold Inlet Boundary conditions (cyclic RANS)

7. LES run URANS run Instantaneous Temperature variation LES versus URANS Experiment

8. URANS Plan 2.6DPlan 6.6D LES Recirculation Time-averaged V & Temp. in cross sections

9. 2.6D z x Velocity Profiles at the plan x=2.6D

10. Velocity fluctuations Profiles at the plan x=2.6D 2.6D z x

11. 6.6D z x Velocity Profiles at the plan x=6.6D Resolved part only

12. 6.6D z x Temperature Profiles at the plan x=6.6D

13. R B L T Y Z T variation at 1mm from walls along the x axis.

14. URANSLES U URANS LES W

15. R B L T Y Z T rms variation at 1 mm from walls along the x axis

16. Centre Y Z Variation of the velocity fluctuations along the x axis in the centre.

17. 1 4 3 2 Y Z Probe1 Probe2Probe4 Probe3 Time history of temperature near the walls

18. 1 4 3 2 Y Z Spectra of temperature near the walls

19. 1 4 3 2 Y Z Spectra of streamwise velocity near the walls.

20. - 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)