The Influence And Analysis Of Non-smooth Structure Effects On Aerodynamic Characteristic On Car Body Surface

With the rapid development of automotive industry and highways, the speed ofautomotive increased faster and faster. When the velocity of car exceed60km/h,30%-40%fuel consumption was used to overcome the air resistance. Because airresistance is proportional to the square of car’s speed and fuel power that air resistanceconsumed is proportional to the cube of car’s velocity, the automotive air resistance isdirectly affect the car’s fuel economy. The reduction of aerodynamic drag means thereduction of fuel consumption and achieve green environmental protection energyconservation and emissions reduction. With the continuous development of airdynamics research, reducing aerodynamic drag by automotive exterior streamlinedesign is more mature and a ofr the r drag reduction did a lot of space constraints.After a long period of evolution, organisms formed a kind of non-smooth skinsurface which can reduce drag and help them adapt to environment better. Accordingto the basic theory of bionics and non-smooth, a kind of non-smooth surfacestructure which has the effect of drag reduction can be designed. This is a kind ofgreen environmental protection method of drag reduction by putting a non-smoothstructure on the car surface to bring about drag reduction. The bionic non-smooth dragreduction needn’t add additional equipment, consume additional energy and space andpollute the air. A better drag reduction result can be obtained only by decorating somenon-smooth structure which has reasonable shapes size and arrangement on the bodysurface.This paper discuss the effect of non-smooth surface drag reduction via decoratingnon-smooth structure on SAE car model surface by means of computational lfuiddynamics numerical simulation method. Summarizing research situation of home andabroad, the problem and research emphasis which at present car body non-smooth dragreduction faced was pointed out. Selection principle, including bionic non-smoothsurface layout position, the bionic non-smooth geometry shape and the bionicnon-smooth surface size, was stated in detail. Regarding the lfow of CFD numericalsimulation as the main line，this paper expounds the building of SAE automotive model，discretization of the calculation area，the settings of boundary conditions and solver inturn. In order to ensure the reliability of numerical simulation, SAE car model windtunnel test data and numerical simulation results were compared. The effect of non-smooth surface decorating position, non-smooth surface geometry shape and thedepth of pit type non-smooth surface on the properties of SAE car model aerodynamicproperty are analyzed in detail. Finally, according to the results of numericalsimulation the non-smooth surface drag reduction mechanism was analyzed further anda new thought of non-smooth surface designing was put forward. The pit shape wasoptimized through the single variable and gradient method. Studies have shown thatdecorating non-smooth surface on the tail of can get better drag reduction effect.Non-smooth surface drag reduction is mainly by reducing the pressure drag betweenrfont and rear of vehicles, and the change of frictional resistance is not very obvious.The drag reduction effect of pit type non-smooth surface is very obvious, especiallywhen the depth of pit is8mm.No matter pits, grooves or ribbed non-smooth surface, itsinterior will produce reverse rotation of the eddy current. Because non-smooth surfacecontour curvature and size had a great influence on drag reduction effect, gradientmethod can obtain a better non-smooth surface contour curvature and size quickly andeiffciently.