Reducing adverse tunnel aerodynamics via nose-based suction & blowing during ultra-high-speed trains meeting scenario

With the advancement of high-speed railway and the advent of ultra-high-speed maglev, conventional passive mitigation strategies are increasingly insufficient in addressing the tunnel aerodynamic challenges. This study numerically investigates the aerodynamic responses of two trains passing each other in a tunnel at 600 km/h, employing active flow control (AFC) via suction and blowing slots integrated into the train noses. Simulations were conducted using a validated 3D compressible URANS framework with sliding mesh techniques. The analysis explores the effects of two slot configurations, low-velocity large-area (LVLA) and high-velocity small-area (HVSA), under constant volumetric flow rate, along with the influence of suction/blowing velocities (SB_v). Results show that LVLA performs better, reducing tunnel wall pressure peaks by 3.4 %, drag by 2.4 %, and rolling moment by 6.7 % compared to HVSA design. As SB_v increases from 0 to 45 m/s, both tunnel and train surface pressure fluctuations are reduced, following a quadratic decay trend. Notably, the peak-to-peak pressure ΔP and micro-pressure waves (MPWs) are reduced by 27.2 % and 26.8 %, respectively. Moreover, AFC also improves aerodynamic load performance across all cars, with lateral force (ΔF_y) reduced by up to 31.5 % of the leading car, and rear-nose blowing lowering rear-car positive lift by 22.8 %, thereby enhancing tunnel operational stability. These findings highlight that AFC offers a flexible and effective strategy for alleviating tunnel aerodynamic issues in ultra-high-speed rail/maglev systems.