Investigation On Characteristics Of Underbody Wind-Snow Flow And Anti-Snow Accretion In Bogie Region Of High-Speed Train

When a high-speed train runs on a snow-covered track,a wind-snow flow will form around the train,resulting in a snow accumulation in the bogie region.In severe cases,the bogie region will be full of ice and snow.The accumulation of ice and snow will not only hinder the movement of the suspension and braking devices,but also affect the train dynamic and the braking system performances,which threats the train’s running safety.For high-speed trains operating in cold regions,improving their ability to prevent snow and icing holds some great significance for ensuring operation safety of high-speed railways in winter.Up to now,most of the researches on snow accretion on high-speed train bogies have focused on prevention measures.There are few researches on the mechanism of snow accretion and the factors that affect the snow accretion on the bogie region.It cannot effectively support the research on anti-snow technology for bogies.Therefore,a simulation analysis method for wind-snow flow and snow particle deposition of high-speed train are established in this thesis.The characteristics of airflow,snow movement,snow-wall collision and snow particle deposition in the bogie region are systematically studied.The main contents and conclusion are as follows.First,an aerodynamic calculation model of a high-speed train consisting of 3 vehicles with complex-shaped bogies is established.Based on the detached-eddy simulation(DES)method,the vortex characteristics underneath the train and around the bogie are studied.The influence of vortex characteristics on snow particle transport is analyzed,and the mapping relationship between vortex cores and snow particle transport characteristics is obtained.Long longitudinal vortices with a strong ability to transport snow particles along the flow direction are mostly distributed underneath the train.The rear bogie is mostly distributed with long vertical vortices with a strong ability to transport snow particles upwards.The front bogie is mostly distributed with long vertical vortices with a strong ability to transport snow particles downwards.Besides,the vortex strength in the rear is greater than that in the front,and the vortex transport shows the characteristics of "strong at the inlet and weak at the outlet".The orientation of the vortex cores around the internal components of bogie is rather chaos,which goes against the airflow to transport snow particles out of the bogie region,and it is easy to cause snow particle deposition.Secondly,a wind-snow flow calculational model of a high-speed train comprised of 3vehicles is established based on the DES method and the discrete phase model(DPM).The suspension movement process of snow particles underneath the train is simulated by arranging a snow ejector on the ground,and the process of snow particles sucked into the bogie region by the airflow is reconstructed.Based on the simulation model,the influences of the anti-snow spoiler on the transportation of snow particles underneath the train are studied.The spoiler can effectively reduce the snow particles hitting the front area of the bogie.At the same time,it will also increase the number of snow particles hitting the rear area of the bogie.The spoiler guides the airflow underneath the train flowing to the ground in the back of the bogie and forms a downward airflow,which causes more snow particles on the downward ground to be accumulated.Simultaneously,a drag vortex is formed at the end of the spoiler to transport snow particles to the side area of the train,increasing the number of snow particles captured by the downstream skirting board.Then,the characteristics of snow particles movement and the collision between snow particles and the bogie are studied by means of the DPM.By counting the average incidence angle and average normal incident velocity of snow particles on the bogie,the collision characteristics of snow particles on the wall are analyzed.The snow particles with smaller sizes are more likely to be carried by the airflow to the upper part of the bogie.The normal incident velocity of snow particles on most part of the bogie is rather extensive and higher than the natural sedimentation speed of snow particles.For snow particles with a low density,the sticky accretion due to collision is the main factor for the snow accumulation on the bogie.The incident angle of the snow particles on the surfaces impacted by the direct incoming flow and backflow underneath the vehicle are consistent with the incoming flow angle,and the incident velocity of the snow particles is relatively high.When the snow particles are sticky,the speed of snow accretion on these parts will be faster.By comparing the movement characteristics of snow particles in the region of the motor and the trailer bogie in the case of a uniform particle size,it can be seen that the backflow around the trailer bogie is stronger than that for the motor bogie,which leads to more snow particles captured on the inner walls of the trailer bogie than the motor bogie at the same time.Part of the airflow discharged by the traction motor will form a revolving air flow around the wheels,carrying more snow particles from the bottom into the inner region of the bogie cabin.It increases the number of snow particles that hit some components.The pumping air effect of the brake disc increases the intensity of the rotating airflow around the brake disc,which increases the effects of the rotating airflow to agitate and splash snow particles.In terms of snow deposition on the wall,according to the differences in properties of snow particles under different meteorological conditions,a wet snow deposition model based on the critical capture angle and the critical friction wind speed and a dry snow deposition model based on the critical capture velocity and the critical friction wind speed are established respectively.They are used to process the behavior of snow particles after hitting the components and study the initial snow deposition characteristics on the bogie.2D snow morphology dynamic simulation method of a cylinder is established based on the dynamic mesh technology,and it is verified for the wet snow deposition model.The results show that whether in dry or wet snow conditions,the snow deposit rate and average snow accretion mass on the brake rigging,traction rods,and suspension components of the bogie are larger than those of the other components.Finally,a method for estimating the flux of saltation snow particle caused by the airflow underneath the train is proposed based on the frictional wind speed of the snow bed on the track.A method used to predict in the snow accretion rate of a high-speed train is established by combining the non-dimensional snow accretion rate of each component.This method is used to estimate the real snow accretion rate of dry snow on the bogie of the high-speed train comprised of 3 vehicles.When the train speed is 300 km/h,the initial snow accretion rate of bogie is about 1893 kg/h.Based on the control of wind-snow flow,the anti-snow structure of the bogie is designed.The deposition model is used to analyze its anti-snow effects and mechanism on the high-speed train.When the anti-snow spoilers are installed on the bogie cavity,the initial snow accretion rate on the bogie can be reduced by over 25%.The anti-snow spoiler mainly reduces the snow accumulation by significantly reducing the number of snow particles entering into the bogie region,rather than reducing the snow deposition rate.The anti-snow spoilers intend to reduce the snow accretion rate and change the snow distribution.In all,the DES method and DPM are utilized to study the wind-snow flow around the high-speed train.A method for studying the wind-snow flow of high-speed trains and evaluating the amount of snow particles deposited on the surfaces of components is established,which directly obtains the deposition characteristics of snow particles on the complex-shaped bogie by tracking the trajectory of the typical snow particles and using the deposition model.The method can be used to evaluate the snow accretion rate of the bogies of the operation trains,and provide a reference basis for the operation organization of high-speed railway in winter.