Lattice Boltzmann modeling of two-phase flow in macroporous media with application to porous asphalt

Abstract

Porous asphalt (PA) is an open-graded porous material with a porosity of 20%, allowing fast drainage of rain and improving driving and acoustic conditions. However, the high porosity leads to significant contact with water resulting in a shorter life expectancy. To improve the durability and performance of PA, the distribution of water and its residence time have to be understood which entails capturing diverse multiphase phenomena. For these reasons, a numerical study is performed to analyze in detail the fluid transport mechanisms at play in PA, towards estimating the liquid distribution inside the nanometer- to millimeter-sized pore structure of PA. In this study, LBM is used for a detailed analysis of multiphase flow in complex porous domains. A multiphase single component LBM method, with parallel computing, has been developed different phase separation phenomena on surfaces and in porous media. The LBM is validated with Laplace law and dynamic capillary intrusion test and then the capillary uptake simulations are validated with analytical solutions, varying contact angles, tube shapes and sizes. Pore meniscus and corner arc menisci are studied in both square and triangular tubes. In order to address the behavior of rain droplets on a PA surface, run-off, wetting, pinning and evaporation of single droplet are considered in terms of effects of variation of contact angle, surface wetting heterogeneity and structure. Finally, gravity-driven drainage in PA is studied with LBM in accordance with temporal evolution of water distribution by comparing with experimental data, showing good agreement. This study allows a better understanding of the diverse multiphase flow phenomena occurring in complex porous media, namely PA, at pore scale in saturated and unsaturated states, providing information towards improving the durability and performance of PA.