| As rapid development of automobile industry and expressway construction come with economic development,various types of vehicles are increasingly widely used,and the gradual improvement of driving speed leads to the increasingly high sensitivity of vehicles to changes in external physical conditions.Especially,the aerodynamic lateral force has obvious influence on the running stability of freight cars.On the one hand,it is the influence on the vehicle cornering characteristics,that is,the existence of lateral force and yaw moment weaken the ability of the vehicle to maintain a straight line On the other hand,it is the impact on vehicle roll safety,that is,when the aerodynamic force value is too large,the direction of action change or its change rate is large,the high-speed vehicle presents a roll trend,and even the possibility of rollover is greatly increased.This kind of phenomenon needs to introduce the method of fluid structure interaction,while the previous researchers in the automotive field focused on the model test verification.Therefore,it is helpful for engineers to improve their understanding of aerodynamics problems and inspire the solution of related engineering problems to explore the influence of fluid structure interaction effect on the vibration frequency of force and torque in different directions under different wind directions and speeds.Aiming at the Ahmed car body model,based on the elastic mechanics and hydrodynamics,the flow-solid coupling method is used to study the variation law of the aerodynamic six component force in the time and frequency domain under the wind speed conditions by STAR-CCM+ and ABAQUS.The specific research content is divided into three parts:Firstly,the influence of fluid structure interaction on aerodynamic six component force in 90°Ahmed model without crosswind is studied.Firstly,the feasibility of the scheme is verified by non fluid structure coupling simulation.Through the natural mode analysis of the elastic model and the comparison of the flow field simulation results,the results are as follows : In the no side wind flow field,the fluid structure coupling effect changes the frequency of the peak frequency of each parameter spectrum of the aerodynamic six component force of the elastic support model,making the peak stable at 17 Hz of the second natural mode.The second natural mode of the model is front and back vibration,and the vibration direction is consistent with the incoming flow direction.The change of wind speed does not affect the elastic support Ahmed model vibration mode of the model.The change of wind speed only affects the amplitude of the model vibration;Secondly,the influence of steady crosswind at different speeds on the elastic support Ahmed model is studied.The results show that the curves of the aerodynamic six component force obtained by the two different simulation methods are different in time domain and frequency domain.The fluid structure coupling makes the fluctuation of the aerodynamic six component force increase,especially the lift and pitching moment.Under each working condition,the model is swaying under the action of the flow field,although the displacement amplitude has the size,the motion mode of each time period is the same;the model vibrates.Some small-scale vortices disappear,and some small-scale vortices merge into large-scale vortices;Thirdly,the influence of fluid structure interaction on the elastic support Ahmed model under linear and sinusoidal crosswind conditions is analyzed.The results show that the lift and pitching moment will change to 0 instantaneously under the condition of linear crosswind.This means that under the actual working conditions,the fluid structure coupling effect will lead to a sudden drop of downforce,which seriously affects the operation stability.Under the condition of sinusoidal fluctuating crosswind,the displacement of the model also fluctuates,and the maximum value does not change obviously,but the minimum value increases with time. |
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