Modal Decomposition of the Flow in a Randomly Packed Pebble Bed with Direct Numerical Simulation

This paper presents a direct numerical simulation (DNS) and proper orthogonal decomposition (POD) of the flow in a randomly packed pebble bed. Nek5000, a spectral-element computational fluid dynamics code, was used to develop the DNS fluid flow data, including first- and second-order statistics for an experimental randomly packed pebble bed. Turbulence budgets were also produced. The flow domain consists of 147 pebbles enclosed by a bounding wall. In the present work, the Reynolds number is 1700 based on the hydraulic diameter and interstitial velocity. First- and second-order statistics were compared with the experimental data. The POD analysis was performed to identify dominant flow structures, especially in the wall channeling region.