Alleviating tunnel aerodynamics through hybrid suction & blowing techniques applied to train nose sections

As high-speed railway lines upgrade speeds or develop ultra-high-speed trains, traditional passive measures may struggle to address tunnel aerodynamics and passenger comfort. This study employs numerical calculations to investigate the aerodynamic mitigation of an ultra-high-speed train traveling at U = 600 km/h through a tunnel, utilizing active suction & blowing techniques in its streamlined nose sections. The simulation employs three-dimensional, compressible, unsteady Reynolds-averaged Navier-Stokes (URANS) methods, validated against full-scale experiments. The effects of slot shapes, suction directions, activation periods, and the suction & blowing velocities (SB_v) are examined. Results show that the slit design, normal direction, along with continuous activation, outperforms the rectangular design, parallel direction, and partial activation in reducing pressure peaks. Notably, maximum pressure peaks on the train and tunnel surface exhibit an exponential decay pattern as SB_v increases. The micro-pressure wave 20 m from the tunnel exit decreases by 28% as SB_v increases from 0 to 0.27U. Additionally, maximum slipstream peaks decrease linearly with SB_v, with a more pronounced decline on the near side. While drag on the head and middle cars decreases linearly with increasing SB_v, the tail car experiences a quadratic increase in drag, leading to an overall reduction in total drag. Furthermore, the reduction in side force and the positive lift of the tail car enhances train safety during tunnel passage. Overall, the hybrid suction & blowing technique offer promising prospects for enhancing the aerodynamic performance of high-speed maglev trains in the future.