Research Of Flow Field Characteristics And Aerodynamic Loads Of The High-Speed Train Under Turbulent Incoming Flow

At present,the research on the aerodynamic performance of high-speed trains in strong wind conditions uses uniform inflow as the boundary condition,but the natural wind field has turbulent and pulsating characteristics,and its influence on the flow field characteristics and aerodynamic loads around the train is lacking.In this paper,the construction of the inflow turbulence simulation method,the analysis of the interaction behavior of the inflow turbulence/flow structure,and the characteristics of the flow field and aerodynamic loads around the highspeed train are carried out.The main work is as follows:(1)A numerical simulation method for turbulent inflow and turbulence maintainance for high-speed trains is constructed.The IDDES turbulence model and synthetic eddy method are combined to construct the numerical simulation method for inflow turbulence.Based on the spatial decaying rate of the turbulent kinetic energy along the streamwise direction under different grid scales and spatial convection schemes,the matching relationship of simulation parameters to achieve optimal turbulent kinetic energy maintenance is clarified,and turbulent kinetic energy flow decay curve along the flow direction under different oncoming turbulence intensities and turbulence integral scales is obtained.Based on the wind tunnel test data of simple bluff bodies such as finite wall-mounted square cylinder and Ahmed model and high-speed trains,the applicability of this method to the action mechanism of surrounding flow under turbulent inflow conditions is further verified.(2)The mechanism and influence of the longitudinal oncoming turbulent flow on the drag,lift and wake flow dynamics of the high-speed train are proved.The research on the flow field characteristics and aerodynamic loads of high-speed trains with different longitudinal oncoming turbulence intensities and turbulence integral scales was systematically studied,and the differences between uniform inflow and turbulent inflow conditions on high-speed train resistance,lift and wake flow dynamics were clarified.Under the condition of longitudinal turbulent inflow,the relationship between train flow field characteristics and aerodynamic loads and turbulent inflow parameters is revealed.Increasing the turbulence intensity and turbulence integral scale of the oncoming turbulence flow will significantly increase the velocity gradient of the bottom layer of the train surface boundary layer and the total thickness of the boundary layer,reduce the negative pressure distribution of the train surface,and then affect the lift characteristics of the train;the oncoming turbulent flow can significantly improve the wake recovery of the train,to increase the flow velocity of the bottom of the train,thereby increasing the aerodynamic resistance of the train.At the same time,the oncoming turbulent flow will significantly increase the lateral force pulsation of the train and aggravate the lateral vibration of the train.(3)The mechanism and influence of the transverse oncoming turbulent flow on the lateral force,overturning moment and flow field structure on the leeward side of the high-speed train are revealed.Under crosswind conditions,the flow field characteristics around the train are mainly dominated by unsteady flow separation and reattachment.The position and strength of the shear layer separation will affect the flow field structure and aerodynamic load characteristics around the train.Combined with the γ-Reθ transition model,the prediction accuracy of the train’s aerodynamic load is improved,and the numerical simulation method of the flow field characteristics of the high-speed train under the crosswind condition is improved.Furthermore,the research on the flow field characteristics and aerodynamic loads of high-speed trains caused by different transverse turbulence intensities and turbulence integral scales is carried out.The evolution of the vortex structure on the leeward side of the train,the time-average aerodynamic and moment characteristics,the spectral characteristics of the aerodynamic load and the distribution of the aerodynamic admittance function are analyzed in detail.The mechanism of the interaction between the turbulent oncoming flow and the roof separation shear layer is clarified,that is,the entrainment and carrying capacity of the shear layer is enhanced,the curvature of the separation shear layer is increased,and the shear layer is closer to the body on the leeward side.This results in an increase in the lateral force and overturning moment of the train.The distribution of the aerodynamic admittance function is relatively uniform at low frequencies,and as the frequency increases,the aerodynamic admittance increases gradually.With the increase of turbulence intensity,the aerodynamic admittance function decreases;with the increase of turbulence integral scale,the aerodynamic admittance function increases gradually.The relevant research conclusions and achievements can deepen the understanding of the flow field characteristics and aerodynamic loads around the train under the condition of turbulent inflow,and provide data support and theoretical basis for the subsequent research on the comfort and safety of train operation.