Effect of surface roughness on the aerodynamics of a high-speed train subjected to crosswinds

Abstract: The irregularities on trains bodies are normally ignored or greatly simplified in studies concerned with aerodynamics. However, surface roughness is known to affect the flow characteristics in the boundary layer near the wall, hence potentially influencing the aerodynamic performance of a train. This work investigates the effects of roughness on the overall aerodynamic characteristics of a high-speed train subjected to crosswinds. Both experimental work and numerical work have been conducted to simulate a typical high-speed train with a 90^∘ yaw angle, with both a smooth and rough surface. Roughness is applied to the roof of the train surface in the form of longitudinal strips. Results reveal that the addition of roughness is able to reduce the surface pressure on the roof and leeside of the train. Numerical results agree well with experimental ones and confirm that an increase in the roughness relative size can effectively restrain flow separation and reduce surface pressure. Moreover, numerical simulation results show that side force coefficient and roll moment coefficient subjected to rough model significantly decreased compared with smooth model. The conclusions drawn in this study offer the chance to derive critical reference values for the optimization of the aerodynamic characteristics of high-speed trains. Graphic Abstract: [Figure not available: see fulltext.]