Analysis And Correction Of Automobile Wind Tunnel Test Data Under High Blocking Conditions

The fuel consumption of automobiles is closely related to the aerodynamic characteristics of automobiles when driving on open roads.With the increase of the total production of automobiles in China and the rapid development of expressways,human beings have to face a series of energy and environmental problems.It is the most direct and effective way to improve the fuel economy to reduce the driving resistance of the vehicle on the road.In the development process of new automobile products,automobile wind tunnel test is an indispensable part of the whole vehicle development process.Although the wind tunnel test can measure the component forces of the vehicle in six directions to a certain extent,there is still a large deviation between the measured results and the real road conditions due to the influence of the wind tunnel structure.If the measured model is a small-scale model,the deviation will be reduced to some extent.However,the small-scale model cannot completely restore the geometric shape of the real vehicle.Therefore,it is of great significance to study the calculation results under such high blocking conditions with full-size real vehicle as the model.In this paper,the 3/4 open vehicle wind tunnel and a 1:1 SUV model are taken as the research objects.The CFD numerical simulation method is mainly used to study four contents: the difference analysis of wind tunnel and open road surface,the quality analysis of air wind tunnel flow field,the interference study of wind tunnel structure,and the analysis and correction of aerodynamic resistance under different wind tunnel structures.For the difference analysis of wind tunnel and open road,the difference of aerodynamic characteristics of vehicles in virtual wind tunnel and open road is mainly studied.Firstly,according to the actual wind tunnel environment,the virtual wind tunnel model including the stable section,nozzle,collecting port and other structures was established,and the actual SUV model was simulated and compared with the experimental data to verify the correctness of the simulation strategy.In the aspect of difference analysis,because the measurement of the model’s aerodynamic force needs the parameter of the incoming flow velocity from the infinite distance,the relation formula between the measured static pressure difference and the wind speed is fitted by the stationary chamber method for the virtual wind tunnel,and the incoming flow velocity is further measured to be equivalent to the condition of the large computational domain.Secondly,the pressure distribution on the surface of the model and the aerodynamic resistance of the model in the virtual wind tunnel and the large computational domain are compared emphatically.In addition,the pressure distribution of the front and rear flow fields of the model is also studied.Finally,the quality of the flow field in the test section under the air wind tunnel condition is analyzed,including the distribution of static pressure gradient,velocity and airflow deflection Angle,and the reason for the difference of aerodynamic resistance of the model is analyzed from the perspective of flow field quality.As for the influence of wind tunnel structure,due to the limited test conditions,the simulation method is also used to provide engineering reference.The main structures that affect the measurement data of the model are the nozzle and the collection port.For the nozzle interference,the change of aerodynamic resistance of the vehicle was analyzed by scaling the vehicle overall and adjusting the distance between the vehicle and the nozzle.Meanwhile,the flow field near the nozzle was analyzed,including the change of wind speed at the nozzle section and the change of internal static pressure gradient.For the interference of the collecting port,the transient numerical simulation of the virtual wind tunnel under vehicle condition was carried out to clarify the fluid flow state in the shear layer and near the collecting port.Secondly,the opening Angle of the collecting port and the distance between the collecting port and the tail of the model were selected as the variables to analyze the causes of the pressure change at the tail of the model under different working conditions from the two aspects of the flow field change in the wake area of the model and the pressure gradient change in the test section.Finally,to take into consideration the disturbance of wind tunnel nozzle and collecting mouth,and the influence of model in different location of the test section,under different working conditions,to model the flow field and its near has carried on the simulation research on aerodynamic characteristics,analyzes the model of location to its aerodynamic resistance and observe the influence of the longitudinal section of test section flow field changes,and semi-empirical method is used to modify each influence factor of drag coefficient,The difference before and after the correction is analyzed.