The Research On Non-smooth Surfaces For Control Of The Automobile Trailing Vortex Structure

With the rapid economic development, raise of the automotive industry and a wide range of highway construction, the actual speed of cars is faster and faster. The air resistance is secondary proportional to the traveling speed, increased air resistance is bound to improve vehicle fuel consumed. As the world's oil resources gradually reducing, seeking energy saving cars, reducing the running resistance of the car is important. The traditional method reducing the air resistance of the car has encountered a bottleneck, seek new ideas and methods aerodynamic drag reduction is imminent. The study found that bionic non-smooth surfaces are with good drag reduction. Intrduce drag reduction ideas under the non-smooth structure into an automobile body to study the effect of non-smooth flow field on the rear of the car, to achieve energy savings.The focus of this paper is for three kinds of models with different tail shape, respectively on the car top, luggage compartment cover and the tail part of layout concave non smooth structure. Analayse the vehicle speed change of surroundings, pressure, turbulence kinetic energy, turbulence dissipation rate variation parameter, research non smooth structure layout of automobile tail vortex formation control, fully aware of the non smooth surface on the tail vortex structure control behavior.Used the software UG to establish different tail shape of Mira model group and the dimple type structure, arranged on the car top and tail and step back car luggage compartment cover and through the wind tunnel experiment and CFD numerical simulation combining, comparative analysis under the same conditions set, car around the pressure field and the car by air drag coefficient of difference, to verify the reliability of the CFD numerical simulation technology. Through analysis of smooth type automobile and surface non smooth around the vehicle velocity, pressure, turbulence kinetic energy, turbulence dissipation rate changes and other parameters, and study the flow field around the formation and change. It is found that the non smooth structure can effectively improve the vehicle around the field. The layout of concave structure in the ladder back on top of the car and the baggage hatch, can delay the car at the top of the flow separation vortex of wind generated on the window's inhibition, the tail shear vortex is decreased and the vortex core moves forward, but also can make the tail of the main vortex core center after the shift, the tail of the main vortex vorticity decreases; in three different types of car tail back layout of concave structure, can make the air flow at the position of the tail shear vortex stagnation continued to downstream movement, reduce the friction loss of the tail wind, further reducing the size of vortex shear vortex, but also makes the flow more smoothly, from the top of the delay flow separation to the downstream development, suppression the tail of the main vortex injection volume, reduce the tail vortex.In this paper, studied and mastered non smooth structure's perturbation effect on generation and evolution mechanism. Analyzed the structure's control of perturbation effect and the formation of vortex, the result shows that the non smooth structure can delay the flow separation, control the wind window cat vortex and end shear vortex, also can inhibit the formation of the rear vortex. Provided important basis to effectively control the vehicle wake vortex structure, reduce the effect of vortex induced vibration and improve vehicle aerodynamic characteristics.