CFD analysis of exhaust flow for reducing soot stains on railcar body surfaces

Diesel railcars are widely used in rail transport, particularly in rural areas, because of their ability to operate without overhead power lines. However, the exhaust gas emitted by diesel railcars can cause soot stains on the car body surface, which requires regular cleaning. In this study, computational fluid dynamics (CFD) simulations were conducted to investigate the effects of roof equipment and exhaust pipe configurations on the exhaust flow around a car body. Unsteady flow analysis was performed using delayed detached eddy simulation. The exhaust flow from the exhaust pipe was simulated using a non-isothermal flow based on the Boussinesq approximation. The velocity profiles obtained by CFD were validated against wind tunnel test results. The CFD results showed that the exhaust gas emitted into a cavity consisting of roof equipment caused soot staining on the car body surface. This study proposes an appropriate location for the exhaust outlet, in which the flow velocity normalised to the train speed was higher than 0.7 to reduce soot stains on the surface. • Exhaust pipes near the roof equipment may cause soot stains on the train body. • The simulation visualised the exhaust flow on the train roof. • The exhaust flow interacts with a cavity flow formed by the roof equipment. • The flow velocity at the exhaust outlet position is related to the soot stains. • The results provide insights for preventing problems caused by exhaust.