Numerical study of the aerodynamics of a full scale train under turbulent wind conditions, including surface roughness effects

A numerical simulation of the aerodynamic behavior of a full scale train under synthetic crosswind is presented. Both smooth and rough train surfaces are contemplated in this paper. The synthetic wind is defined based on the Kaimal spectrum, which is generated using Turbsim. The flow description is based on numerical simulations obtained using Large Eddy Simulation (LES) with the commercial code ANSYS-Fluent. Considering a very-high Reynolds number for our train model with LES requires the use of a wall function in the near-wall region. In this way, it is removed the need to resolve any turbulent eddies in the inner part of the wall layer, and the entire inner-layer dynamics are represented by a single value of the wall shear stress. The simulation gives a time history of the force and moments acting on the train; this includes averaged values, standard deviations and extreme values. Of particular interest are the spectra and admittances of the forces and moments. Comparisons are made with numerical and experimental results obtained for a small scale model fixed to the ground in a wind tunnel.