Research On The Aerodynamic Drag Reduction Of The Passenger Car Based On Rear Accessories

Auto aerodynamic characteristics is one of the aspect that should be concernedconsiderably, this article takes a domestic produced fastback passenger car as theresearch model, aims at reducing the drag coefficient via install rear accessories. Themain method used in this article is CFD.The flow phenomenon of the fastback passenger car is described in this article,start with a simple model. With the help of the understand of the physical condition,proper simulation scheme is chosen. The simple cubic calculation area is implementhere which can ensure the high accuracy and short calculation time. As the flow onthe surface of the auto body should be focused, so the prism mesh has12layers andeach layer is very thin. besides, the rear flow structure is center point in this article, sothe size of the cell mesh at the rear of the auto is very small. As the smooth increase ofthe size of the cell from the body to the boundary of the calculation area can guaranteethe accuracy, so the way of generating the cell mesh is also explored which concludesthat for this research linear increase of the size is the best way cause it will have agood coordination of the number of the cells and the homogeneity. A lot ofexperiments on which turbulent model to choose have been done as well, k-omegaSST becomes the finally choice for its accuracy and less demand for computing cellsand devices. Comparison between wind tunnel experiment result, real modelsimulation result and simplified model simulation result makes the simulation resultmore reliable. Analysis of the simulation error has been made as well, the relationbetween the residuals and the predictable ability was established. According to thisrule,0.002Cd difference can be recognized, as the accessories may just have tinydifference, so this kind of accuracy is needed.Based on this simulation scheme, the basic delta-wing vortex generator is researched on the simplified passenger car, the position to install, size of the vortexgenerator and the number that will be installed are all taken into consideration, finally140mm distance from the rear of the vortex generator to the rear end of the roof of thepassenger car,0.5size of the original vortex generator and one vortex generator toinstall has the best drag coefficient reduction of0.004among all cases that have beentried. Different types of vortex generator was installed in this way and TYPE-Cbehaves the best, which has a reduction of0.005. The rear roof spoiler have also beeninvestigated, the attack angle and the chord length determine the CAD and the size ofthe rear roof spoiler, eight experiments have been done,23degrees attack angle and120mm chord length gets the best effect with a reduction of0.016. The side rearspoiler also take the attack angle and chord length as the main geometric limitation, inseven experiments, chord length of200mm and85degrees of attack angle is the bestcombination which reduce the Cd coefficient by0.004. eliminate the gap between therear window and the C-pillar and the rear roof end will also have the drag reductioneffect, the drag coefficient reduces by0.004. The install of rear wheel cover reducesthe drag as well, but as the way of how install haven’t been optimized, so the dragcoefficient only reduce0.003.The research of this article can provide the CFD simulation reference for thistype of auto. And with the help of lots of numerical simulation results the trend ofdrag coefficient change can be acknowledged with the installation of the vortexgenerator, rear roof spoiler, side rear spoiler and the rear wheel cover and so on, thiswill provide reference for future study on aerodynamic drag reduction effect of therear accessories.