Research On The Influencing Factors And Standard Model For Train Wind Tunnel Test In Crosswind

Wind tunnel test serves as one of the significant research methods of train aerodynamics and the verification basis of numerical algorithm.The reliability and accuracy of the acquired data are expected to be very high.However,the current train wind tunnel tests mostly focus on the discussion and analysis of the results,and pay little attention to the influencing factors of the model itself and supporting facilities.Moreover,the lack of accuracy verification of the data is not conducive to the calibration,and it is difficult to ensure the accuracy and effectiveness of the train aerodynamics under crosswinds.In this paper,wind tunnel test and numerical simulation are employed to study the aerodynamic impact of local geometric details of vehicle model,typical ground configuration layouts and similarity parameters in crosswinds.On the basis,the standard train model is proposed,and the correlation and correction of train model in multiple wind tunnels are carried out.Specific research work includes:(1)The aerodynamic mechanism of local geometric details of the train model in the wind tunnel test is revealed.Aiming at the balance between the modeling details and the simulation accuracy,the influence of the inter-carriage gap between adjacent vehicles,the length and end shape of the downstream half vehicle and the simplified threshold of the bogie on the overall and local train aerodynamics are systematically studied.The mapping relationships between gap spacings and the vehicle aerodynamic loads are established.A reasonable aerodynamic design of the plane form plus 0.5L_m of the downstream vehicle length is obtained.Moreover,the simplified threshold of the bogie is determined as D≤100 mm,which considers both the vehicle aerodynamic load and bottom flow field.(2)A comprehensive ground configuration layout based on finite static&infinite moving boundary is proposed.The validity that finite static ground configuration replaces realistic infinite boundary during train wind tunnel test still remains questionable.Therefore,the distortion mechanism of three-dimensional flow at the end of high embankment is thoroughly analyzed.The rationality of the speed-up effect on the embankment,namely,the so-called Baker hypothesis is verified.The mapping law of train aerodynamic load coefficient with dimensionless length E/H and slopeγat the front end of embankment is obtained.Based on the width limitation of the realistic wind tunnel and the moving boundary,the reasonable front length range confines within 10<E/H<20,and slopeγ≤33.7.The aerodynamic load error is less than 5%providing that the extension length of ballastless track is no less than 2H.The relationship between the development of the floor boundary layer and the train loads are explored,and the reasonable installation range of the model is finally determined.(3)The influence law of the similarity parameters on train wind tunnel test under full yaw angle is revealed.Full-yaw-angle tests are carried out on the Reynolds number,blockage ratio and scale effects.The Reynolds number effect on the pressure sensitivity of streamlined nose under various yaws is investigated.Theεcorrection method for train/embankment blockage is proposed,and the original vehicle lift and lateral force error within the full geometric similarity region is reduced from 13.7%to 0.3%at most.It is recommended that the model scale for train wind tunnel tests is within 1/20 based on the loads variation and flow field information atβ=90°.(4)On the basis of the above research,a train standard model is developed.The load and pressure correction system for the train standard model tested in multiple wind tunnels is established.In view of the lack of verification on the data accuracy of the train wind tunnel test,four correlation tests including two different floor configurations are carried out in three independent wind tunnels in China.The data accuracy under different yaws is evaluated.Based on the mean value,the one-to-one correction relationship of each wind tunnel data is established,and the sperman correlation coefficients are above 0.99.The standard train model is thus verified and confirmed.The research results of this paper have certain theoretical significance and application to ensure the accuracy of train wind tunnel test.