Mechanism Research On Aerodynamic Drag Reduction Of Vehicle Body With Bionic Non-smooth Surfaces

Rapid growth of automobile consumption led to an accelerating increase in energy consumption, the energy problem has become more and more serious. In 2010 vehicle fuel consumption will account 43% of the country's total fuel consumption, which will be the major factor in the growth of oil consumption; when the vehicle speed exceeds 60km/h, air resistance will costs 30%-40% of the total fuel consumption. In other words, drag reduction would be significant to energy-saving.Based on latest researches on aerodynamic drag reduction, bionic non-smooth surface drag reduction and body CFD, this paper proposed a new method to reduce the air resistance by using the bionic non-smooth surface in the body design for the first time, which breaks through the bottleneck in drag reduction.In order to verify the mentioned idea, firstly, researches on biological surface such as dung beetle, tiger sharks, shells, feathers of pigeon, etc were carried out, to extract the convex hull, pits, grooves and other forms of non-smooth units. Secondly, a three-dimensional modeling method was introduced which is based on the trait gene of model and selected pits, grooves and other forms of non-smooth unit which cover on the body. Thirdly, problems about the data interfaces between Hypermesh and Fluent were resolved successfully. Hypermesh is a professional meshing software for improving the accuracy of the grid, while Fluent has powerful analysis funcations which help to improve the analysis efficiency, and the realizable turbulence model amended by the near-wall was chosed. Lastly, by comparing the calculated values of air drag coefficient with the real test ones, the result shows that the margin of error is about±4%, so this method is reliabily and can be refered in other related researches.In order to find non-smooth units which have the best drag-reducing effect, we selected the engine cover lid and body cap which are covered by different kinds non-smooth units, as the vehicle speed is 30m/s, we choosed the Pit-type? unsmooth unit on the engine cover lid, the result shows that the distance between the units S is 6.0mm,the width of the unit d is 2.0mm and the depth of the unit h is 1.50mm, the air drag coefficient Cd=0.29196 which is reduced by 8.68%; when we choosed the Pit-type unsmooth unit on the body cap, the result shows that the distance between the units S is 12.0mm,the width of the unit d is 3.0mm and the depth of the unit h is 1.5mm, the air drag coefficient Cd=0.28673 which is reduced by 10.31%; when we choosed the Ribs non-smooth unit, the result shows that the distance between the units S is 6.0mm, the width of the unit d is 1.0mm and the height of the unit h is 0.5mm, the air drag coefficient Cd=0.29032 which is reduced by 9.19%. In order to further determine the reliability of analytical models, researching on the pressure distribution of the body surface and symmetry with different grid numbers, from the result we could find these models has the same pressure distribution.In order to further analyse the drag laws of bionic unsmooth face on the body, the velocity vector and turbulent.kinetic energy distribution on different sections of the was studied. The result shows that, with the use of the non-smooth units, the shape and strength of trailing vortex were changed, and the change from conical vortex to cylindrical vortex reduced the Pressure drag, thereby the air drag coefficient was decreased.We use the non-smooth units to reduce the drag which extends the field and improves Fuel Economy and Dynamic.