Study On Crosswind Stability Of Medium Bus On Bridge Considering Body Attitude

With the continuous development of society,cars have become an important means of transportation for people to travel,and the driving safety of vehicles is getting more and more attention;Since entering the 21 st century,China’s bridge construction has developed rapidly,and the bridge driving conditions have increased significantly.Due to the influence of bridge section structure,the flow field environment is more complex when the vehicle is driving on the bridge,and the body will change its attitude under the action of aerodynamic force,which is harmful to the driving stability of the vehicle.However,in the current research of automobile aerodynamics,the whole vehicle is often regarded as a rigid body,and the influence of body attitude change on vehicle aerodynamic characteristics is ignored,which leads to the low precision of numerical simulation.In this paper,the simplified model of the medium-sized bus Coaster is taken as the research object,through the “Fluid-Structure” co-simulation,a more realistic numerical simulation of the vehicle aerodynamic characteristics is realized.The crosswind stability of medium-sized bus on bridge considering body attitude is studied,and the crosswind stability of the medium-sized bus is improved by setting bridge wind barrier.The main contents of this paper are as follows:Firstly,the reliability of the simulation method in this paper is verified by experimental benchmarking.On this basis,the influence of bridge structure on vehicle aerodynamic characteristics is explored;Using the proper orthogonal decomposition method,the order reduction analysis of the flow field structure is carried out to reveal the causes of the differences in the vehicle aerodynamic characteristics.The results show that: The vehicle is located on the bridge or not,the different forms of the bridge section and the relative position of the Vehicle-Bridge all affect the structure of the incoming flow and the flow field around the vehicle,thus changing the aerodynamic characteristics of the medium-sized bus;Compared with the ground,the vehicle has lower crosswind stability when it is located on the bridge without anti-collision wall;When the medium-sized bus is located on the bridge with different section forms,its crosswind stability from high to low is: anti-collision wall bridge >steel box bridge > concrete bridge;The crosswind stability of vehicles located on the leeward side lane of concrete bridge is higher than that on the windward side lane.Secondly,the numerical simulation interface between the fluid dynamics software STAR CCM+ and structural mechanics software ABAQUS was built to realize the “Fluid-Structure” co-simulation and explore the influence of body attitude on vehicle aerodynamic characteristics.The results show that: The fluid-structure coupling effect will lead to a height difference of up to 20 mm between the windward and leeward sides of the vehicle body;The change of body attitude mainly affects the flow field structure at the top and bottom of the vehicle,and has a great influence on the aerodynamic lift of the vehicle,with an increase of more than 20 %.The influence on the aerodynamic lateral force of the vehicle is small,except the condition of anti-collision wall bridge,the increase is less than 6%;The influence of body attitude change on vehicle aerodynamic characteristics is different under different bridge section forms.Thirdly,the influence of vehicle speed,crosswind speed and crosswind forms on vehicle aerodynamic characteristics under time-varying crosswind is analyzed by the“Fluid-Structure” co-simulation.The system dynamics model of medium-sized bus is constructed,and the system dynamics characteristics of vehicles under the action of aerodynamic forces are studied.The position of the vehicle center of mass and the road environment are changed to predict the dangerous conditions during the driving process of the vehicle.The results show that: The increase of vehicle speed and crosswind speed will increase the system dynamic response of the vehicle,and have a negative impact on the crosswind stability of the vehicle;Under the change of unit speed,the change of crosswind speed has a greater influence on the aerodynamic characteristics of the vehicle than the change of vehicle speed;The variation rate of vehicle aerodynamic characteristic parameters and system dynamic response under pseudo-step crosswind condition is higher than that of other time-varying crosswind types;The influence degree of different time-varying crosswind forms on vehicle crosswind stability is ranked from high to low as follows: Pseudo-step wind >Sinusoidal wind > Triangular wind;Increasing the longitudinal distance between the vehicle center of mass and the front axle is beneficial to the crosswind stability of the vehicle;Rainy and snowy road environment will lead to dangerous condition such as sideslip.Finally,the bridge wind barrier is set up to improve the crosswind stability of the vehicle.Taking the height and ventilation rate of the wind barrier as factors,the multi-objective optimization design of the bridge wind barrier is carried out to reduce the roll moment coefficient of the vehicle and aerodynamic lateral force of the bridge.After optimization,the absolute value of vehicle roll moment coefficient is reduced by 67.3%,and the aerodynamic lateral force of bridge is reduced by 14.1%.In conclusion,based on the methods of automotive aerodynamics,structural mechanics and system dynamics,this paper has carried out a more in-depth analysis of the crosswind stability of medium-sized buses on the bridge.The research conclusions have certain reference value for the design of vehicle crosswind stability.