  Recent interest for the development of high-temperature gas reactors has
increased the need for more advanced understanding of flow characteristics in
randomly packed pebble beds. A proper understanding of these flow
characteristics can provide a better idea of the cooling capabilities of the
system in both normal operation and accident scenarios. In order to enhance the
accuracy of computationally efficient, intermediate fidelity modeling,
high-fidelity simulation may be used to generate correlative data. For this
research, NekRS, a GPU-enabled spectral-element computational fluid dynamics
code, was used in order to produce the high-fidelity flow data for beds of
1,568 and 45,000 pebbles. Idaho National Lab's Pronghorn porous media code was
used as the intermediate fidelity code. The results of the high-fidelity model
were separated into multiple concentric regions in order to extract porosity
and velocity averages in each region. The porosity values were input into the
Pronghorn model and the resulting velocity profile was compared with that from
NekRS. Both cases were run with a Reynolds number of 20,000 based on pebble
diameter. The Pronghorn results were found to significantly overestimate the
velocity in the outermost region indicating that changes in the porosity alone
do not cause the difference in fluid velocity. We conclude that further work is
necessary to develop a more effective drag coefficient correlation for the
near-wall region and improve predictive capabilities of intermediate fidelity
models.
