1. WP4: Safety and Performance for Innovative Reactor Systems 3 rd Annual Meeting, Imperial College London, 9 th April 2008 Reynolds-Averaged Navier-Stokes (RANS) investigation of Advanced Gas-Cooled Reactors (AGRs) by Amir Keshmiri School of Mechanical, Aerospace & Civil Engineering (MACE) The University of Manchester Manchester M60 1QD

2. Outline Topic 1: Ascending Flow in a Heated Pipe under Post-trip Condition Topic 2: Modelling the Coolant in the AGR’s Fuel Elements Topic 3: Development of Wall Functions Future Work

3. Topic 1: Topic 1: Ascending Flow in a Heated Pipe under Post-trip Condition

4. Solution Methods Solution Methods In-House Code (CONVERT) In-House Code (CONVERT) Commercial CFD Package (STAR-CD) Commercial CFD Package (STAR-CD) Industrial Code (Code_Saturne) or Radius=0.1 m Ascending Flow Constant Heat Flux BC ‘Boussinesq’ Approximation Key Features of the Flow Problem

5. The analysis focuses on 4 cases: Gr/Re^2=0.000  Forced Convection Gr/Re^2=0.063  Early onset Mixed Convection Gr/Re^2=0.087  Laminarization Gr/Re^2=0.241  Recovery Test Cases

6. Models Tested Turbulence Models/Techniques Tested: Launder-Sharma k-ε model (CONVERT) Cotton-Ismael k-ε-S model (CONVERT) Chen k-ε model (STAR-CD) Suga NLEVM (CONVERT) k-ω-SST model (Code_Saturne and STAR-CD) Lien-Durbin v2f model (Code_Saturne and STAR-CD) Manchester v2f model (Code_Saturne) LES (STAR-CD) – presented by Dr. Yacine Addad The Results are validated against: DNS of You et al (2003)

13. Topic 2: Topic 2: Modelling the Coolant in the AGR’s Fuel Elements

14. Advanced Gas-Cooled Reactors (AGRs) 1. Charge tubes 2. Control rods 3. Graphite moderator 4. Fuel assemblies 5. Concrete pressure vessel and radiation shielding 6. Gas circulator 7. Water 8. Water circulator 9. Heat exchanger 10. Steam Fuel Element

21. Axis of symmetry

24. Transverse Ribs

30. Work in progress: Multi-Start Rib-Roughened Fuel Elements

31. Helical/Spiral Ribs

35. Topic 3: Development of Topic 3: Development of Wall Functions

37. Wall Functions  Standard Wall Function Assume ‘universal’ logarithmic velocity and temperature profiles in evaluation of wall shear stress, turbulent kinetic energy production and wall temperature. Inaccurate results when flow departs from a state of local equilibrium. Different versions of this WF are available in STAR-CD, Code_Saturne, TEAM and STREAM codes.  Analytical Wall Function Based on the analytical solution of the simplified Reynolds equations and takes into account such effects as convection and pressure gradients as well as the influence of buoyant forces and changes in the thickness of the viscous sublayer. Has proved to be successful in many flow problems e.g. Buoyant flows. Currently available in STREAM and TEAM codes.  Numerical Wall Function Based on an efficient one-dimensional numerical integration of the simplified LRN model equations across near-wall cells. Currently available in STREAM and TEAM codes.

38. AWF Results in Ascending Pipe Flow

39. Running STAR-CD for “Spiral Ribs” and measure the effects of CO 2 Particle deposition on the heat transfer. Running TEAM/STREAM codes for mixed convection and ribbed surfaces and evaluate the effectiveness and performance of AWF. Modify the AWF if needed to take into account different flow problems such as ribbed surfaces. Development of Code_Saturne by implementing AWF and validation against TEAM/STREAM Codes. Future Works

40. THE END THANK YOU