Numerical Simulation Study On Air-tightness Characteristics Of High Speed Trains In Mountainous Tunnel Conditions

Throughout the development of high-speed railway-related technologies in China and abroad,countries highlight their different characteristics of high-speed railways based on different national conditions,geo-economics,and technical reserves.Countries represented by Japan are pursuing the economics of railways.Representative European countries are pursuing technology and comfort more.China absorbs the development experience of high-speed railways from all over the world,and introduces advanced high-speed railway technology,forming an independent and innovative high-speed railway China model so far.In order to meet the different needs characteristics of the countries along the“Belt and Road”,and to improve the technical system of train design,manufacturing,testing,and evaluation,the Ministry of Science and Technology has released a national key research and advanced rail transit special project‘Research on key technology of high-speed passenger transport equipment with a speed of 400km/h.’In response to the above phenomena and problems,this article studies the following work:When the train pass through a tunnel,it is limited by the narrow space of the tunnel cross section.When the front and rear of the train enter the tunnel,they have the respectively effect of compressing and expanding the air.Vairous wave reciprocate in the tunnel causing a series fo pressure wave effects in high-speed railway tunnels.With the construction of high-speed railway technology and tunnel engineering,there is a higher demand for train speed and tunnel length,due to the large pressure fluctuations caused by the high-speed train passing through the tunnel,the transient pressure changes transmit from the exterior to interior caused the problem of uncomfortable feelings of the passengers.It has significant to improve the airtight performance and the pressure comfort standard inside of the train.In view of the above phenomena and problems,this article studies the following work:1)Summarize the pressure wave effects of high-speed railway tunnels at home and abroad,high-speed train aerodynamic issues,air tightness research methods,and domestic and international pressure comfort standards since the 1960s;2)Summarize the calculation method of the external pressure of the vehicle based on the one-dimensional unequal-entropy flow model and the calculation method of the internal pressure of the vehicle based on the time constant,leakage area,and deformation factor k,the method of calculating the airtightness threshold of the vehicle body,and systematically derive The definition of the dynamic time constant gives the formula for calculating the pressure inside of the train:（?）3)Select trains to pass through tunnels of different lengths in medium,long and very long tunnels to establish the dimensionless time history characteristics,the mechanism of pressure fluctuations inside and outside the high-speed train is analyzed.Based on the CR400BF Chinese standard EMU model,the effects of train speed,tunnel length,and time constant on the pressure wave inside the car were studied.The study found that:（1）The effect of speed on the pressure fluctuations in the car during the interval is linear;（2）The influence of the tunnel length on the pressure fluctuations in the car during the interval time is obviously non-linear;（3）As the coefficient to measure the airtight performance of the car body,the larger the time constant,the higher the airtight performance of the car body;（4）Under the conditions of long and large tunnels,based on the pressure comfort standards of the car in different organizations,its strictness:German standard>UIC standard>Chinese standard>ERRI standard.4)According to the non-linear characteristics of the fluctuation of the tunnel length with the pressure inside the vehicle,the most unfavorable tunnel length based on the comfort conditions of the pressure inside the vehicle is systematically proposed.According to the research results:when the tunnel length L_tu≤3km,the pressure inside the vehicle can be selected The comfort standard is evaluated;when the tunnel length L_tu≥10km,the composite interior pressure comfort standard should be considered for evaluation.5)The influence of the tunnel length is taken into the interior pressure comfort standard,and the mutual fitting relationship between the pressure threshold（35）P_max,the interval time（35）t and the most unfavorable tunnel length L_critrit is established,and a new type of interior pressure considering the tunnel length is proposed.Comfort criteria.This paper starts with the analysis of the internal and external pressure formation and influencing factors of high-speed trains,numerically simulates the most unfavorable tunnel length value based on the pressure comfort conditions inside the train,fitting and driving mathematical relations of related variables.Proposes a new composite interior pressure comfort criterion.Looking forward the criterion method provides important reference for the evaluation of interior pressure comfort and the manufacture of air-tightness of the trian body under the condition of very long tunnels.