Fluids flow in granular aggregate packings reconstructed by high-energy X-ray computed tomography and lattice Boltzmann method

TL;DR

This study combines high-energy X-ray computed tomography and lattice Boltzmann simulations to analyze fluid flow in granular packings, revealing effects of particle size, porosity, and pore structure on flow properties.

Contribution

It introduces a comprehensive method for reconstructing granular packings and simulating fluid flow, highlighting the impact of aggregate size and porosity on permeability and flow behavior.

Findings

Wall effects significantly influence porosity with increasing aggregate size.

Poisson and power laws fit coordination number and volume distributions.

Fluid mass flow rates vary with porosity and aggregate size.

Abstract

Properties of fluids flow in granular aggregates are important for the design of pervious infrastructures used to alleviate urban water-logging problems. Here in this work, five groups of aggregates packing with similar average porosities but varying particle sizes were scanned by a high-energy X-ray computed tomography (X-CT) facility. The structures of the packings were reconstructed. Porosities were calculated and compared with those measured by the volume and mass of infilled water in the packing. Then pore networks were extracted and analyzed. Simulations of fluids flow in the packings were performed by using a lattice Boltzmann method (LBM) with BGK (Bhatnagar-Gross-Krook) collision model in the pore-network domain of the packings. Results showed wall effect on the porosity of aggregates packing was significant and the influence increased with the aggregate sizes. In addition, Poisson law and power law can be used to fit the coordination number and coordination volume of the packing's pore network, respectively. Moreover, the mass flow rates of fluids in the aggregates were affected by the porosities. On the two-dimensional slices, the mass flow rate decreased when the slice porosity increased. But for the three-dimensional blocks, the average mass flow rate increased with the volume porosity. And the permeability of the aggregates packing showed correlating change trend with the average pore diameter and fitting parameters of coordination volumes, when the sizes of aggregates changed. Though the limitation of merging interfaces causing fluctuation and discontinuity on micro parameters of fluid flow existed, the methods and results here may provide knowledge and insights for numerical simulations and optimal design of aggregate-based materials.