1. 1 KNOO Annual Meeting 2008 LES and URANS of Turbulent Flow parallel to PWR and AGR Fuel Rod Bundles S. Rolfo The University of Manchester, M60 1QD, UK School of Mechanical, Aerospace & Civil Engineering. CFD group The University of Manchester

2. 2 RNR-Na assembly (Super Phoenix Reactor).

3. 3 Scales separation and levels of approximation. DNS LES RANS Scales separation and levels of approximation. Fixed point at which the FFT is evaluated

4. 4 Code_Saturne Code developed by EdF and now open source downloadable from: http://rd.edf.com/the-edf-offers/research-and-development/softwares/code-saturne- 107008.html  Unstructured  Co-located, Finite Volume Formulation  Different turbulent models (both RANS and LES)  Incompressible or expandable flows with or without heat transfer  Different modules: radiative heat transfer, combustion, magneto-hydrodynamics, compressible flows, two-phase flows  Possible coupling with Code_Aster for structural analysis and with Syrthes for thermal analysis.  Parallel code coupling capabilities (awarded the Gold medal on HPCx) ‏

5. 5 Rod Bundle arranged in a triangular array Two different geometrical configuration 1. P/D = 1.06 2. P/D = 1.15 Three different Thermal Hydraulic regimes: 1.P/D = 1.06 @ Re = 6000 with heat transfer (LES) ‏ 2. P/D = 1.06 @ Re = 36000 with heat transfer (RSM-URANS) ‏ 3. P/D = 1.15 @ Re = 6000 with heat transfer (LES) ‏ A’ A

6. 6 Flow Pulsation in the mid-plane (P/D = 1.06)‏ LES @ Re = 6000 URANS @ Re = 39000

7. 7 Flow Pulsation in the mid-plane (P/D = 1.06)‏ URANS LES

8. 8 Power spectra P/D =1.06 LES @ Re = 6000 Point APoint B P/D =1.15 LES @ Re = 6000 Point B P/D =1.06 URANS @ Re = 36000 Point A

9. 9 Average Field (LES P/D = 1.06 Re = 6000)

10. 10 Reynolds Stress

11. 11 Conclusions and future work  Flow Fluctuations in the mid plane of the geometry were successfully detected for the configuration characterised by P/D = 1.06. However P/D = 1.15 did not show any significant behaviour from channel or pipe flows.  URANS is able to capture the flow fluctuations, however the Reynolds stresses are more similar to those observed at higher P/D.  LES, at low Re number, of larger geometry (two complete sub-channels) to be tested in order to verify the correct prediction of the dominant frequency.  Improved geometry with the addition of a wire, wrapped around the pin (SFR assembly), will be computed. Acknowledgements This work was carried out as part of the TSEC programme KNOO and as such we are grateful to the EPSRC for funding under grant EP/C549465/1.