Numerical Simulation Of Flow Field Of High-Speed Train Intersecting In Tunnel And Analysis Of Aerodynamic Fatigue Strength Of Carbody

At present,most of high-speed train lines that have been opened in China must pass through tunnels,tunnels such as Wuguang and Zhengxi line account for about 20% of the total length,so it is inevitable that two trains interscet in the tunnel.High-speed trains operate at high speeds in a small space,due to tunnel wall restriction and entry effect,the space will form a complex flow field.Moreover,the aerodynamic pressure changes are more complicated and intense than that of in the open air,so the aerodynamic loads acting on the carbody will be significantly enhanced.The wake of the tail will continuously fall off,and its frequency may affect vibration and fatigue reliability of carbody.Therefore,a reasonable numerical simulation method is used to study the flow field and aerodynamic characteristics,and then the method of vibration and fatigue strength is studied,it is significant to aerodynamic performance and fatigue reliability design of the high-speed train.This paper firstly compared and analyzed the numerical method of turbulence,selected the delayed DES to study the train tunnel aerodynamics,and used the finite volume method to calculate the three operating conditions and get the aerodynamic characteristics and surface pressure distribution;the finite element model of head car and middle car were established,and the modal analysis was carried out by using the finite element method.Then the pressure waves of three working conditions were analyzed in the frequency domain;Finally,fatigue strength method and the influence of pressure wave on the fatigue strength were calculated and analyzed.The main research contents are as follows:Firstly,a three-car model was established.The delayed DES was used to simulate and calculate the three operating conditions(one car pass through tunnel,two trains intersect in the short tunnel and the long tunnel),and the numerical results of the flow fields were obtained.By comparing the calculated data of the train passed through the tunnel with the measured data,the accuracy of the model and numerical calculation were verified.The variation of the flow field during the whole operation process was analyzed by the pressure curves of the measuring points,the curves of the aerodynamic coefficients of the train and the pressure cloud images of the typical times;the wake vortex was analyzed by the rotation intensity and the tail flow diagram.The numerical results show that negative pressure when two train intersct in the short tunnel is the largest,and pressure wave when two train intersct in the long tunnel is the smallest.The entry effect will affect the running resistance of the train,but the influence to lift and lateral is small.Finally,the difference between the RANS and the DDES was compared by the wake vortex and the pressure cloud maps.The RANS do not recognize the vortex at the tail,its result show two airflows separated and flows backwards.The DDES can capture the eddy component in the tail flow.It can be clearly seen that the tail vortex extends backward and falls off.Therefore,the DDES is better than the RANS for regenerating the flow field vortex and showing the actual flow field.The finite element model of the head car and the middle car were established and the model was tested for grid sensitivity.The existing standards were used to specify the first-order vertical bending frequency of the train.Then the modal was calculated by the Block Lanczos method,the results meeted the standard requirements;the mode shapes at different modal frequencies were compared and analyzed.The results shows that the vehicle chassis was prone to local vibration,and probability of local modal is small in the side wall area,which is generally accompanied by the overall mode.Then based on the fourier transform theory,a simple formula for calculating the power spectral density in engineering was cited.Then,the spectrum analysis of the aerodynamic pressure waves were carried out,and the tail vortex frequency and the main frequencies of different measuring points were summarized.The vortex frequency was consistent with the literature data;the results shows that main frequencies of the pressure waves were at low frequency.so the influence of the pressure wave on the fatigue strength of the vehicle body was continuously investigated.The time integral method was used to convert transient pressure wave into aerodynamic loads on the side wall,and simulated the dynamic process of the aerodynamic pressure wave.The inertial release method was used to eliminate the abnormal stress concentration of the constraint point.The Goodman fatigue strength curve of the aluminum alloy material was drawed,and the stress range was within the curve,which meeted the fatigue design requirements.The influence of the aerodynamic loads on the fatigue strength was analyzed.The impact of the aerodynamic loads on the fatigue strength was notable.Under entry effect,the aerodynamic loads maked the safety factors of the focus points decrease obviously.The numerical simulation method,the modal analysis and the frequency domain analysis method of the aerodynamic load,and the aerodynamic analysis method were used to provide a reference for the aerodynamic performance and the fatigue reliability design.