GAS FLOW SIMULATIONS IN RANDOMLY DISTRIBUTED PEBBLES

In this paper, computational fluid dynamics (CFD) gas flow simulations are carried out. In CFD calculations, geometry modeling and physical modeling are crucial to CFD results. The effects of the treatments of the inter-pebble contacts on gas flow fields and heat transfer are examined; a sensitivity analysis for the gap size is conducted with two spherical pebbles, in which the inter-pebble region is modeled by means of two types of inter-pebble gaps and two kinds of direct contacts. On the other hand, both of large eddy simulation (LES) and Reynolds-averaged Navier-Stokes (RANS) models are employed to investigate the turbulent effects. It is found that the flow fields and relevant heat transfer are significantly dependent on the modeling of the inter-pebble regions. The calculations indicate the complex flow structures present within the voids between the fuel pebbles.