Optimization Of Aerodynamic Performance And Research On Drag Reduction Of Non-smooth Surface For A Crossover

At of the end of 2019,the number of civilian vehicles in China has reached 261 million,and it is predicted that it will reach 500 million in the future.The huge number of vehicles is accompanied by huge fuel consumption.In 2018,oil consumption in China was 625 million tons,of which more than 40% was consumed by automobile.In the structure of refined oil consumption,the consumption of motor gasoline and diesel totals 232 million tons,accounting for 81.4% of the total social gasoline and diesel consumption.The massive consumption of fossil energy has brought severe energy security and environmental problems.In the energy consumption of automobiles,the energy used to overcome aerodynamic drag occupies a considerable proportion.Therefore,research on vehicle aerodynamic performance optimization and drag reduction is of great significance for improving vehicle performance,reducing energy consumption,and improving energy and environmental issues.Crossover vehicle is a kind of mixed vehicle that has emerged to meet consumers’ needs for multiple uses,and has quickly risen once it is on the market.As a combination of sedans,SUVs,roadsters and other kind of vehicles,the local aerodynamic characteristics of crossover will be quite different from these traditional vehicles.Therefore,research on aerodynamic performance optimization and drag reduction for crossover is of good commercial value.Based on this,CFD method is used in this essay to analyze the aerodynamic sensitive area of a new type of crossover,optimize its aerodynamic performance,and conduct research on drag reduction technology by non-smooth surface.The main research work is as follows:Based on a new crossover from a famous automobile company,the geometric model and calculation grid are established,and the influence of boundary condition settings,turbulence model and calculation domain size on the numerical calculation results of the aerodynamic resistance characteristics of the crossover is investigated.According to the force of each part of the crossover,the contribution of each part to the drag of the crossover is analyzed,the aerodynamic sensitive area of the crossover is determined,and the local flow characteristics and resistance causes of each aerodynamic sensitive area are analyzed in depth.Further,several aerodynamic performance optimization programs for the main aerodynamic sensitive area(engine compartment,front wheels,rear wheels,underbody,etc.)are designed,the flow characteristics and drag reduction effects of each optimization program and the united optimization program are analyzed,and their drag reduction mechanism is analyzed in-depth.In the underbody flow condition,the groove-type non-smooth surface drag reduction technology is proposed,the groove size is optimized,and the drag reduction mechanism of the groove non-smooth surface is revealed.The following conclusions can be drawn from the above research:1)The distribution of aerodynamic sensitive areas for crossovers and sedans is similar,but the degree of contribution of each aerodynamic sensitive area to the drag of the vehicle is quite different.Compared with sedans,the front face,rear,wheels and wheel compartments of crossovers generate greater resistance,and the drag of the underbody components contributes less,while the roof resistance of the two models has basically the same proportion.The underbody of the crossover has a greater impact on the drag,and is of a greater value for partial optimization of drag reduction.2)Via analyzing the flow characteristics of each aerodynamic sensitive area,six drag reduction programs are proposed.It is found that the air dam scheme is not suitable for the crossover,and other schemes have achieved certain drag reduction effects.The front wheel deflector effectively reduces the impact of airflow on the tire surface and the air flow into the wheel compartment,inhibits the flow separation of the wheel surface to a certain extent,and thus reduces the force on the wheel and the wheel compartment,optimizes the wake vortex,and improves the flow of the engine compartment,the rear wheels and the rear of the car,the maximum drag reduction rate of this scheme reaches to 6.48%.The drag reduction rates by sealing the engine compartment and rear compartment are 0.88% and 1.65% respectively,and have little effect on the flow in other aerodynamic sensitive areas.The drag reduction rate of the united optimization program is 13%.3)The drag reduction effect of the riblets is sensitive to the flow velocity and characteristic size.At a certain flow velocity,when the dimensionless depth is about 10,the riblets can hold up the streamwise vortex near the wall,suppress the growth of the streamwise vortex,and thus reduce the wall shear stress and achieve the goal of drag reduction,the best drag reduction rate is about 1.92%.The drag reduction effect of the transverse groove is closely related to the size and is not sensitive to speed.A continuous groove with a depth of 0.1 mm has the best drag reduction effect,with a maximum drag reduction rate of 9.32%.The drag reduction effect of the transverse groove is closely related to the stable downstream vortex column.