Numerical Simulation Research Of Influence Of TAXI's Top Lampshade On Car's Aerodynamic Characteristics

The aerodynamic characteristics parameter is one of the most important performance parameters for road vehicles , which has significant effects on the dynamic performance, fuel economy and maneuvering stability. Energy problem has become more and more outstanding in modern times and oil price has been surging, all of witch make it be of importance to reduce the fuel consumption through the reduction of air resistance for the vehicle at high speed.We usually focus on the box van as an advertice or noticing people. Even now we do not pay enough attention on the effect of aerodynamics of the lampshade upon the TAXIS.This dissertation focus on the aerodynamic accessories, taking a advertising box van of a China-made taxi as a example. Standard k-εmodel was adopted to carry out the CFD simulation of flow around the automobile for five kinds of models. Some optimizing work were made for the box van through analysis.First by reverse methods a model that bears resemblance to the external shape of the real vehicle was made in use of the CATIA software for the car, on the basis of witch four group of models were established. Then the models established were induced into ICEM software to carry out the grid division. And the overall scheme is tetrahedron plus hexahedron plus tri-prism and then the divided mesh was induced into the FLUENT software to get the speed distribution graph and the press distribution graph etc which are used to make the analysis to draw the conclusion.Respectively in this paper five models have been schemed to establish:Model 1——numeric stimulation was carried out for the whole vehicle solely without the installation of the box van.Model 2——install a box van that set crossly with common shape on the vehicle, implementing the whole numeric stimulation.Model 3——on the basis of the former scheme that was mentioned, the box van was reduced in proportion and there is a distance of 30mm between the box van of the top of the vehicle.Model 4——on the basis of the former scheme with the very size and distance, the shape of the box van was optimized and the streamline cross section was designed.Model 5——the last scheme was the condition that the lampshade were set longitudinally.The meshing project I adopted was the mesh of tetrahedron,hexahedron and three prisms. The hexahedron mesh was used to fitted the complexed figure of autobody. To saving time and EMS memory, the hexahedron mesh which was regular and converged rapidly was created from far beyond of the car area. The three prisms mesh could simulated the boundary effect better and the characteristic that airstream flowing around the car body. This time we needed to extend three layers mesh of this kind.In this paper, the main conclusions include:1.Because the external flow field of the car has typical features of large flow separation, strong eddy and the anisotropy of turbulent development, the standard k-εturbulent model is an appropriate model to be used in the CFD research of the car external flow field.2.The coefficient of aerodynamics drag of the car with crossing van is bigger than with the van which is setting longitudinally.3.For the typical box van, the carriage is higher than the cab, which makes air separated in this region. The research show that there is circumfluence in this region and a separation bubble is formed in the front of carriage roof, which lead to the increase of the aerodynamic drag coefficient of the box van. In order to prevent air separation in that region, we add a cab roof fairing to make air flow over this region smoothly, which make the aerodynamic drag coefficient drop by 10%.4.We also discover the clearance between cab and carriage will lead air flow through it, which increase the aerodynamic drag. it must be taken care when designing box van. In this paper, we research the external flow field of the lowduty box van, and discuss the feasibility of adding aerodynamic appendage. Especially the cab roof fairing decreases the aerodynamic drag. Our research will benefit the economy of energy.5.The car with longitudinally van is prefered in this article.6.The suggestion of the design of the crossing lampshade are, reducing the projected area ;setting some distance between the lampshade and the car roof; preferring to the figure which are fine aerodynamics characteristic.