Thermal mixing around in-line tube banks

Experiments conducted in the Advanced Gas-cooled Reactor (AGRs) design stages indicate a three-dimensional flow swirl present in the in-line tube bank section of certain boilers (Jones et al., 1978). The boiler is located within the reactor pressure vessel where accessibility is severely limited therefore investigation of the flow and thermodynamic features need to be carried out using three-dimensional (3D) Computational Fluid Dynamics (CFD).Unsteady Reynolds Averaged Navier-Stokes (URANS) simulations of square in-line tube banks have been conducted and compared against Large Eddy Simulation (LES) (Afgan, 2007) and experimental data (Aiba et al., 1982) in order to determine the most effective turbulence models to pursue. A 2 × 2 periodic tube section is chosen to represent a tube bank deep within a boiler. 2D simulations show high Reynolds number and low Reynolds number approaches predict two significantly different flow patterns (constant asymmetry and alternating asymmetry). 3D simulations have shown high-Reynolds-number Reynolds Stress Models (RSMs) (Launder et al., 1975; Charles G Speziale et al., 1991) revert to an alternating asymmetric flow prediction as expected from experimental visualizations. Initial 2D simulations of the 4 × 7 tube bank used by Aiba et al. (1982) have also been conducted, where the flow and thermodynamic features following the fifth tube are seen to be similar to the periodic simulations.