Numerical study on the effect of braking plates on flow structure and vehicle and enhanced braking of vehicles inside and outside tunnels

With the continuous improvement of train speeds, aerodynamic braking is a good choice to effectively reduce the braking distance. In this study, unsteady aerodynamic characteristics of vehicles with braking plates inside and outside the tunnel were evaluated by CFD using an improved delayed detached eddy simulation (IDDES). Mesh convergence studies were also performed, and results were compared with two wind tunnel tests to verify the numerical method. By comparing and analyzing the effect of plates on the force, braking distance, and flow field around vehicles inside and outside the tunnel, it is found that the aerodynamic braking force of vehicles inside and outside the tunnel increases nearly 1.5 times and 2.2 times due to the opened plates, respectively. The positive lift force of vehicles is also increased, especially inside the tunnel, which reduces the friction between the wheels and rail tracks. The opened plates also cause the formation of many vortices with excessive energy, which may aggravate the vehicle vibration and noise, especially inside the tunnel. By comparing the impact of the operating environment (inside or outside the tunnel) on the aerodynamic characteristics of each vehicle, it is also found that the closer the vehicle to the downstream, the more sensitive it is to the tunnel. The findings of this study can help to design the braking plate and guide the operation of rail vehicles.