Study On Aerodynamic Characteristics Of The Near Wake Structure Of Pick-up

The aerodynamics is one of the important characteristics ofautomobile, It directly affects the automobiles'dynamics,economics,stabilities, comfort and security .However, as the one of the morepopular vehicle style, The study on the pickup about aerodynamiccharacteristics is not enough.Now the lately study about pickup is the study of G.M. Corporationand University of Michigan, They finished the moderate Reynolds numberswind tunnel test on the generic pickup model, In this test, They getthe mean pressure on the symmetry plane, unsteady pressure in the bed,and Particle Image Velocimetry (PIV) measurements of the flow in thenear wake.And G.M. Corporation and fluent Corporation finished the CFDanalysis on the pickup generic models, and the Canada NRC researchcentre have finished some kinds of pickup wind tunnel tests, This paperbased on the study that related to the anterior study and use the genericpickup model. All the models used in this paper are completed by thesoftware CATIA. This paper uses the CFD methods to analyze the pickupmodels, and by the studying can get a better understanding to theaerodynamics of pickup and provide a base to the further study aboutthe pickup.Because of the specialties of structure to pickup and Consideringthe recirculating flow region in the bed, This paper do disposal tothe pickup models, for examples, semi-closing in the bed, full-closingin the bed and lengthen the bed. Through the contrast between the CFDresults, We can find the impact about shape changing on the models.To ensure the enough space to simulate the real aerodynamics ofthe pickup, This paper set the size of computational region reasonably,The size is 11*model length, 7*model width and 4*model high.The meshing ways all in the numerical simulation is hexahedralmeshing, and when finished the hexahedral meshing we should fullyconsidering the structure of pickup and make the block catch it so thatcan ensure the veracity of the results.This paper use the software Fluent to finish the numericalsimulation, and to find the difference between the different models,this paper use the same condition as the first numerical simulation,for example, turbulence models, boundary conditions, and solutionprocedure.Through the numerical simulation, We find that the press andvelocity distribution is the same as the common car, the mainlydifference is in the bed, there is a big recirculating flow region anda pair of eddy along the model X direction, and the two eddies issymmetrical about the portrait symmetry plane and end to the tailgate,and not far away the tailgate there is the two eddies reform again,with the distance to the tailgate the eddies become irregular fromregular and more and more weak, in the end It disappears. along thevertical direction of the model also have two eddies, and also symmetryabout the portrait symmetry plane, With the Z value becomes bigger,the eddies' condition become more complex, By analyzing the pressdistribution on the tailgate we can find that the press of the reartailgate is bigger than the press of the front tailgate, and the pressdifference bring a force along the pickup moving direction, It mayreduce the drag to some certain extent.Semi-closing the bed can make the goods in the bed suffer from thenatural effect, It can enlarge the function to pickup and retain theinhered characteristic structure, from the numerical simulationSemi-closing the bed We can see that the recirculating flow regionbecome smaller, and the eddies over the bed is become more and moresmaller because the air flow from both sides, and the eddies disappearnear the tailgate, because of without the tailgate ,the airflow fromthe front mix together fast and make the drag become bigger, and theeddies' condition is almost the same as the numerical simulation thathave stated, and just more complex.From the numerical simulation full-closing the bed, We can see thatthe aerodynamic characteristics change a lot, as other models, thepress and velocity distribution at the front of the model is not big,but at the rear model the eddies change a lot, and there is two eddieson the portrait symmetry plane of the rear model, and bring thedifferent eddies from other numerical simulation, but the conditionis almost the same, and at the vertical direction there also have apair of eddies on the portrait symmetry plane.By analyzing the numerical simulation lengthening the bed, We canfind how the length of the pickup impact on the aerodynamics performance.From the results we can see that the recirculating flow region becomebigger as the length of the bed becoming longer, this results in thelots of energy loss, and from the velocity we can see the same eddiesin the bed, and there is an approximative recirculating flow regionin the horizontal plane,all the change is the reason that drag is becomebigger.From the study on the outside flow field to the pickup models, Wesee clearly the outside flow field of the pickup, and get a goodfoundation to the further study about the pickup.