Investigation of particle migration and drainage behavior in railway ballast induced by multiphase flow using a coupled VOF-DEM approach

Railway ballast is a crucial component of rail tracks and plays a vital role in various functions, with drainage being one of the most important for maintaining the track’s operation ability. Over time, ballast degradation and accumulation of foreign materials result in fouling, which blocks the interstitial spaces and flow passage between ballasts, thereby significantly reducing drainage efficiency. To investigate the interaction between fouling and fluid flow and its effect on fine particle migration and drainage, a coupled discrete element method (DEM) and computational fluid dynamics (CFD) model capable of solving multiphase fluid flow is developed, aiming to advance the understanding of the relevant transport behavior. The discrete (particle) and the continuous (water and air) phases are resolved using a Lagrangian and a Eulerian approach, respectively. Then, the model is employed to investigate multiphase fluid flow that washes away fouled materials through the ballast aggregate for different parameters, including fouling index, fouling profile, cohesive energy density (CED) between particles, and shoulder cleaning. This parametric simulation offers comprehensive insights into the interplay between the multiphase flow and fine particles within ballast at different conditions. Moreover, the particle distribution and their migrations over time are quantitatively evaluated using the Local Fouling Index. It is evident from the analysis that particle migration greatly depends on the parameters under consideration, with the CED value being the most important factor. Additionally, the comparison of the water table height demonstrates that shoulder cleaning is an effective means of improving drainage efficiency.