Numerical Study On The Effect Of Pressure Wave Induced By High-speed Train Passing Through Tunnel

The effect of pressure wave as high-speed trains passing through tunnels,such as aerodynamic load on car body,pressure comfort,and air resistance et al.,must be concerned in the field of aerodynamic fatigue,passenger comfort,and energy saving and environmental protection.They are important to safety,comfort and energy conservation.With the increase of train speed,high-speed trains need to operate in mountainous areas with massive tunnels in western China and even diverse environments around the world.Therefore,it is necessary to systematically study the effect of pressure wave.This study can provide support for China's high-speed trains to meet the demand of domestic mountainous environment and“going out”strategy.Based on the one-dimensional?1D?flow model,this paper reveals the relationship among aerodynamic load on train body,pressure comfort,and air resistance.In addition,the main factors on the effect of pressure wave were studied.The research work is funded by the sub-task of the National Program on Key Basic Research Project?973 Project?,the sub-task of the National Key R&D Program of China in Advanced Rail Transit Key Project,and the Key Project of the China Railway Corporation Science and Technology R&D Program.The main research work carried out is as follows:1.Based on the one-dimensional,compressed,unsteady,and non-homentropic flow model and the method of characteristics of generalized Riemann variables,the numerical methods of pressure wave when a single train passes through a tunnel and two trains cross in the tunnel with same speed is improved firstly.Furthermore,two numerical methods and corresponding programs are developed.One is for the calculation of pressure waves in the tunnel caused by two trains crossing with different speed,and the other is for air resistance of high-speed trains when they cross in the tunnel with same speed.The verification show that the error of the 1D flow model is 10%and 8.5%in predicting the pressure wave and the air resistance,respectively.The calculation accuracy of the 1D flow model can meet the requirements of engineering design.By analyzing the space-time evolution process of pressure fluctuations in the tunnel and outside the train,it is found that,the pressure fluctuations in the tunnel,the pressure load on the car body,the internal pressure fluctuation,and the air resistance are all directly or indirectly related to the propagation,reflection,and superposition of the compression wave and the expansion wave.It is also the foundation in using a unified 1D flow model in the studying of such effect of pressure wave.2.In studying the influence of tunnel length on aerodynamic load on train body and air resistance,combined with the propagation,reflection and superposition process of compression wave and expansion wave,the formula of critical tunnel length of maximum air resistance of high-speed train is proposed for the first time.The work expanded and improved the theory of critical tunnel length in EN 14067-5.The difference between calculation by the 1D flow model and that from the formula is within±12%,for the critical tunnel length of maximum positive pressure change at train nose and that of maximum negative pressure change at train tail.When the 400 m train with speed between 250 to 380 km/h is considered,the critical tunnel length of maximum aerodynamic loads at car body is in the range of 0.6³.0 km.The critical tunnel length of maximum air resistance of high-speed train at the speed of 250⁵00 km/h is in the range of 0.5¹.5 km.In addition,the critical tunnel lengths of maximum peak-to-peak value of the aerodynamic loads at 1^st car and the tail car are obtained,which are also found to be close to the critical tunnel length of maximum positive pressure change at train nose and that of maximum negative pressure change at train tail,respectively.3.Based on the 1D flow model,the characteristics of the aerodynamic loads on car body when two trains crossing in the tunnel with different speeds are systematically studied for the first time.The case of two trains crossing with same speeds and that a single train passing through a tunnel are also carried out.The effects of tunnel length,blockage ratio,train speed,train length,and the time delay of train entries on aerodynamic loads on car body are studied.The calculation show that,from nose to tail,only the negative peak of the aerodynamic load when two trains crossing in tunnel with same speed almost keep constant.The other positive peak and negative peak of the aerodynamic load all decrease.The peak of the aerodynamic load is about 2.0 to 2.5 power of the train speed.When two trains crossing at the middle of the tunnel with same speed,the peak of the aerodynamic load is usually more than twice as many as when they crossing near the tunnel portal or at the one-third tunnel length position.And the maximum positive pressure change at train nose of high-speed train with 16 units is about 1.5².0 times as that of high-speed train with 8 units.While,for both the single train passing through and the two trains crossing case,the maximum negative pressure change of train tail of high-speed train with 16 units are both 1.1 times as that of high-speed train with 8 units.As there is the critical tunnel length,the peak load of the train subjected when they passing through or crossing at tunnel with length of 0.5³.0 km is relatively larger.4.The influence of tunnel length,blocking ratio,train length,and air-tightness time constant on the comfort of the passengers in the cabins is studied.The relationship between tunnel length and the minimum air-tightness time constant has obtained.Referring to UIC779-11,the trend of the maximum pressure change per 1 s,3 s,10 s and 60 s under the combined influence of tunnel length and blocking ratio is obtain,which is based on the CR400AF train.It is found that the error is less than 12.8%when the maximum pressure change in the tail car is used as the maximum pressure change of the train.This indicates that the method using air-tightness time constant still has merit in evaluating the pressure comfort.The calculation shows that,when the tunnel length,blocking ratio,and train length increases,and when the air-tightness time constant decreases,the pressure fluctuation inside the tunnel and in the cabins becomes more intense.Then the greater the pressure change,the worse the pressure comfort.In addition,the minimum air-tightness time constant required for each tunnel length is studied,in which UIC660 is adopted as datum.At speed between 350 to 400 km/h,the highest requirements of air-tightness is found at the tunnel with length of about 8.0 km.When the cross-sectional area of tunnel is 100 m²,the minimum air-tightness time constant at 350 km/h is 34 s,and which will increase to more than 50 s at 400 km/h.5.The effects of tunnel length,blockage ratio,train speed,train length,and the time delay of train entries on the air resistance is also carried out.The numerical results show that,the tunnel length,blocking ratio,and train speed is positively related to the air resistance.The time delay of train entries has little effect on air resistance.When the exponent form is used to fit the relationship between average air resistance of the high-speed train and tunnel length,blocking ratio and train speed,the exponent n is about±0.005?high-speed trains with 8 units,two trains crossing in the tunnel?^±0.1?single train passing through the tunnel?,1.0 and 2.0,respectively.When a single train passes through the tunnel,the maximum air resistance increases firstly with the increasement of tunnel length,and then remains almost unchanged.As two trains cross in the tunnel,the maximum air resistance increases and then decreases with tunnel length.The critical tunnel length can also be found.The ratio of the maximum air resistance in tunnel to that in the open air decreases as train speed increases.At 350 km/h,the maximum ratio is 68%and 55%for high-speed trains with 8 units and 16 units,respectively.And they will reach to135%and 125%at the crossing case,respectively.While,a maximum of 30%is used in our High-Speed Railway Design Specification.So it is recommended to conduct a study on the maximum air resistance and average air resistance in a wider range of tunnel length and train length,and modify and improve the related items if necessary.