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 = 0.05 U t , 0.10 U t , 0.15 U t , and 0.20 U 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 = 0.05 U t , 0.10 U t , 0.15 U t , and 0.20 U 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 = 0.00 U t to 0.10 U t and then an increasing trend from U b = 0.10 U t to 0.20 U t. Thus, considering the blowing cost, efficiency, and flow structure evolution comprehensively, the case of U b = 0.10 U 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. • A unique active air blowing design to reduce the aerodynamic drag of high-speed trains. • Significant reduction of the pressure drag on head middle, and tail cars by the proposed approach. • The obtained optimal blowing speed is 0.10 U t (U t is the train speed) with consideration of the blowing cost and efficiency. • Under the optimal blowing speed, the train's overall aerodynamic drag coefficient is reduced by 10.78%. [ABSTRACT FROM AUTHOR]