On the Aerodynamics of Freight Trains: Crosswind Stability, Slipstream Effects and Tunnel Overpressure

Freight train aerodynamics has received considerably less attention than passenger train aerodynamics, despite its growing importance for railway safety and infrastructure design. This paper presents recent research activities carried out at Politecnico di Milano on freight trains in three key aerodynamic topics: crosswind stability, slipstream effects and tunnel overpressure for freight trains. Crosswind stability represents a major safety concern, as demonstrated by recent rollover accidents involving freight vehicles. Wind tunnel experiments and multibody simulations are employed to assess the influence of wagon typology, loading arrangement and load dynamics. Results highlight the strong dependence of crosswind stability on loading configuration and show that simplified rigid-load assumptions may significantly overestimate the stability of intermodal freight vehicles. Slipstream experimental investigations indicate that freight trains can generate, both open-air and tunnel, slipstream velocities comparable to, or exceeding, regulatory thresholds despite operating at relatively low speeds and reveal significant differences between freight and passenger train flow development. Finally, a CFD methodology for analysing train-tunnel pressure signatures is applied to freight trains. Parametric studies demonstrate the role of train length and inter-wagon gaps on pressure peaks, highlighting that tunnel overpressure may become critical for very long freight convoys.