| The aerodynamic drag of the car when driving on the road has a direct impact on the fuel consumption of the car.Nowadays,the number of car owner in China is constantly increasing,which makes the consumption of non-renewable resources such as petroleum increased.How to reduce the fuel consumption of the car has become a problem that automakers must face,and this also poses a great challenge to the improvement of the aerodynamic drag of the automobile.The development of vehicle aerodynamic characteristic is inseparable from the wind tunnel test.The automotive wind tunnel can largely simulate the driving conditions of the car on the road,which greatly facilitates the direct measurement of the aerodynamic force.However,there are many influence factors in the wind tunnel test,which will affect the measurement of the aerodynamic force.Therefore,it is necessary to study the wind tunnel test to improve the accuracy of the wind tunnel experiment.The main research objects of this paper are the Jilin University's wind tunnel and 1:2 MIRA scale model.The CFD software STAR-CCM + was used to study three aspects: the wind tunnel blockage,the ground effect simulation system and the impact of model support.For wind tunnel blockage,the influence of nozzle interference and axial static pressure gradient in the wind tunnel test section are studied.First,how to test the velocity in the wind tunnel test section by using the plenum method is studied.Because the determination of the test section velocity directly affects the measurement of the model's aerodynamic force,it is studied through the analysis of different velocity conditions,and the relationship between the static pressure difference and velocity was confirmed;Secondly,for the nozzle interference,some cases were set by changing the distance of the model from the nozzle,then the model aerodynamic drag changes,the distribution of velocity and pressure in front of the model,and the flow field in the nozzle were analyzed.Then,some corrections of the aerodynamic drag of the model were made to make the results more accurate.Last,for the axial static pressure gradient of the wind tunnel test section,the different axial static pressure gradient distribution in the wind tunnel was simulated by changing structure of the simulation domain.The changes of aerodynamic drag and lift,the rear flow field and the distribution of the model surface pressure were analyzed,and finally some corrections of the aerodynamic drag were made to correct the influence of axial static pressure.For the analysis of the ground effect simulation system,this paper further analyzed the Jilin University's wind tunnel suction system based on previous studies.Firstly,the best suction rate of suction system is confirmed by three aspects.The static pressure gradient,the flow angularity and the distribution of the boundary layer in the test section were analyzed respectively to confirm that at the best suction rate,the suction system can optimize the distribution of the boundary layer best and reduce its influence to the static pressure as well as the flow angularity.Secondly,the influence of the suction system on the aerodynamic force of the model is analyzed.For the changes of the aerodynamic drag of the model,the suction system can change the distribution of the boundary layer and the static pressure distribution in the test section,these two changes can both influence the drag of the mode,then the influence of the variation of the boundary layer thickness on the aerodynamic drag of the model and the influence of the variation of the static pressure distribution are analyzed by setting different cases.Finally,for the aspect of model support,a new type of support platform in the wind tunnel of Jilin University was simulated.The influences on the flow velocity,static pressure distribution in the wind tunnel test section and the boundary layer distribution on the platform for different structures in front of the support platform were analyzed to evaluate the effect of the support platform synthetically. |
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