Optimization Of Structural Parameters Of The Single-line Tunnel Entrance Hood Based On Aerodynamic Performance

When the high-speed train suddenly enters into a tunnel,a compression wave will be generated at the entrance of the tunnel.And it will propagate along the direction of the tunnel at an approximate sound velocity.The energy will be released at the tunnel exit and form micro-pressure waves,which will cause noise pollution in the surrounding environment.In order to reduce the pressure fluctuations in the tunnel and the micro-pressure wave at the tunnel exit,the hood is built at the entrance of the tunnel,reducing the pressure and pressure gradient of the initial compression wave.In order to optimize structural parameters of the hood at the entrance of a single-line tunnel,the method of three-dimensional computational fluid dynamics was used to analyzes the effects of the length,the sectional area and the opening ratio of an entrance hood on the maximum pressure and the maximum pressure gradient of the initial compression wave in the tunnel,and the optimal structural parameters of the section enlarging opening hood and the flare hood were obtained when all factors are combined.Calculation and analysis results show that:(1)The interaction between the length,the sectional area,and the opening area ratio of the section enlarging opening hood is obvious.The maximum pressure gradient can be reduced effectively when the length is 80m,the sectional area is 120m~2 and the opening ratio is 40%.And the entrance hood with the length of 80m,the sectional area of 140m~2 and the opening ratio of 20%can effectively reduce the maximum pressure.Mainly considering the reduction effect of the pressure gradient,the optimized structural parameters of the section enlarging opening hood are the length of 80m,the sectional area of 120m~2 and the opening ratio of40%.(2)For the tunnel with a flare hood,the maximum pressure of the initial compression wave is mainly affected by the length of the hood,and the maximum pressure gradient is mainly affected by the sectional area of the hood.The maximum pressure and the maximum pressure gradient are most effectively reduced,when the length of the flare hood is 120m and the sectional area is 240m~2.Mainly considering the reduction effect of the pressure gradient and the construction cost,the optimized structural parameters of the flare hood are the length of 80m and the sectional area of 240m~2.