The influence of decreasing underbody clearance on surrounding flow of high-speed train within the yaw range of 45°–75°

This paper investigates the surrounding flow of a 1:10 scaled train model at Reynolds number 3.48 × 105, focusing on the yaw angle range from 45° to 75°, where the dominant flow structure transitions. The study employs an improved delayed detached eddy simulation method. A grid independence study and validation against experimental data were conducted prior to the investigation. The clearance does not alter the basic flow pattern around the train as the yaw angle changes. However, it has a significant local impact, modifying the surface pressure and the drag, lateral force, and lift. The underbody region is most affected, particularly the skirt area near the track, where the pressure decreases markedly due to changes in clearance. This reduction in pressure leads to a decrease in the lift of all cars at all yaw angles, with the lift reduction ranging from 5.1% to 29.6% in the studied cases. While the lift is the most significantly affected force due to the reduced clearance compared to drag and lateral forces, the impact on drags and lateral forces is also substantial. Turning points are observed in all three force components of the leading car. Additionally, a new turning point in the lateral force of the middle car is identified at a yaw angle of 60° in the reduced clearance scenario. This is attributed to the delayed switching of the dominant flow vortices on the leeward side of the train.