Mitigating inflow acceleration effects in twin mountains using air jets: Emphasis on anti-wind for high-speed railways

The twin mountains, a common terrain in mountainous areas, tend to induce the acceleration effect under crosswinds, which enhances the wind speed and the turbulence performance of the flow field. To mitigate the impact of the acceleration effect on high-speed trains, structures, and aircraft near the twin mountains, this study investigates the effectiveness of the jet strategies, which are realized on natural mountain slopes by mechanical ventilation, with different jet angles on the flow field and the train. Wind speed tests, flow visualization, wind field prediction, and research on the train's aerodynamic behavior are conducted in this paper using the wind tunnel and the improved delayed detached eddy simulation dynamic models. The results indicate that the wind velocity on the leeward side of the twin mountains increases up to 1.42 folds of the wind velocity of the incoming flow under crosswinds. The jet streams with 0° and 30° angles are the most effective in mitigating the acceleration effect among those tested (0°, 15°, 30°, and 45°), reducing the maximum wind speed by 11.87% and 16%, respectively. Compared with the mitigation effect of the jet stream with the 30° angle, the jet stream with the 0° angle has a better mitigation effect on the aerodynamic loads (4.0%–13.2%) and its fluctuation amplitude (24.4%–42.7%) of the train. These findings are valuable for studying the flow field characteristics of the twin mountains and the designing anti-wind measures for high-speed railways.