Reducing the aerodynamic drag of high-speed trains by air blowing from the nose part: Effect of blowing speed

To reduce the aerodynamic drag of high-speed trains, this work proposes an air blowing configuration on the head and tail cars of high-speed trains. The variation in the aerodynamic drag and slipstream velocity is analyzed under different blowing velocities, and the flow mechanism for train aerodynamic performance alteration is explained. The results show that under the blowing speeds of U_b = 0.05U_t, 0.10U_t, 0.15U_t, and 0.20U_t, where U_t is the train speed, the total drag coefficient (C_d) decreases by 5.81%, 10.78%, 13.70%, and 15.43% compared to the without-blowing case, respectively. However, with the increase in the blowing speed, the reduction trend of C_d tends to be smoother; namely, the decrement ratio compared to the previous blowing speed for the head car is 9.08%, 0.11%, 0.60%, and 1.14% for U_b = 0.05U_t, 0.10U_t, 0.15U_t, and 0.20U_t, respectively. The blowing measure generates an air gap between the coming flow and train surface, consequently causing a reduction in the viscous and pressure drag. In addition, the structure size and strength of the wake flow under different blowing cases show a decreasing trend from U_b = 0.00U_t to 0.10U_t and then an increasing trend from U_b = 0.10U_t to 0.20U_t. Thus, considering the blowing cost, efficiency, and flow structure evolution comprehensively, the case of U_b = 0.10U_t is recommended. Under this blowing speed, the reduction ratio of the aerodynamic drag is 9.18%, 12.77%, 10.90%, and 10.78% for the head, middle, tail car, and total train, respectively.