Computational fluid dynamics–discrete element method simulation of locomotive sanders

Locomotive sanders are used to optimize the traction between the train wheels and the railhead by spraying sand into the interface. It has been previously shown that a large fraction of sand sprayed by the sanders does not make it through the wheel–rail nip, leading to sand wastage and thereby increasing the cost and refilling effort. In this study, pneumatic conveying of sand through the wheel–rail nip is numerically modeled through coupled computational fluid dynamics and discrete element method simulations. The gas phase, discrete phase, and coupled two-phase flows are separately validated against the literature, and the parameters affecting the deposition of sand into the nip are analyzed to determine their impact on sander efficiency. The aerodynamics associated with the particle-laden jet play a critical role in optimizing the amount of sand going through the wheel–rail interface, with the particle velocities being directly correlated with the sander efficiency. Particle–geometry interactions (e.g. particle bouncing) are found to have a negligible effect on the deposition. In the absence of crosswinds, it is recommended to employ particles with a smaller Stokes number to enhance the sander efficiency. A larger airflow rate through the nozzle is also recommended. Crosswinds strongly and adversely affect sander efficiency. The effects of crosswinds can be mitigated by reducing the nip–nozzle distance and using coarser particles.