The Analysis Of Non-smooth Unit Structure Effects On Vehicle Aerodynamic Characteristic

With the development of society and economy and the improvement of people’s living standard, automobiles have entered thousands of households and become the necessities of life. Rising number of automobile consumption lead to increasing energy consumption, people also more and more concerned about the price of oil. Today, with the continuous development of design technology, the cars is designed which must meet basic safety, comfort, and high speed, at the same time, decreasing resistance and improving the economic applicability of cars has also become an important research topic.This paper mainly studies the research development of bionic non-smooth surface, and based on the theory of non-smooth drag reduction, determines the selection principles of bionic non-smooth surface morphology by combining with the application of non-smooth surface drag reduction and selects three kinds of classic non-smooth unit cell. By the analysis of the flow field of MIRA steps back model, determines selection principles of the layout location of the non-smooth unit cell. Guided by the theory of boundary layer, determines the selection principles of unit cell size.Computational fluid dynamics numerical simulation method and the process of establishing MIRA step back model were introduced in detail. Proposed to obtain high quality grid, fixed boundary conditions setting in solving software, set the solution parameters. Through simulation experiment, proves the feasibility of numerical simulation scheme, ensures the uniformity and accuracy of the test.Through the research of pit type non-smooth unit cell separately, found that the reduction effect of non-smooth surface is affected by depth, spacing and arrangement location of pit type non-smooth unit cell. Drag reduction effect of pit type non-smooth unit cell’s combination arrangement is better than that of single layout.Drag reduction rate was regarded as test indexes, analyzed the test data by using the orthogonal experiment, primary and secondary relations of non-smooth unit cell structure factors’ drag reduction effect was obtained. On the basis of test data, the paper analyzed the impact of non-smooth surface on flow field, and the effect on pressure drag and friction resistance. Then studied the reduction mechanism of non-smooth unit cell for further, found the internal rotating vortex generated in the pit which can produce the effect of air bearing. Swirl flow is also generated inside the groove type non-smooth unit cell to make form low speed flow layer of steady velocity gradient inside the unit cell. Convex hull Non-smooth unit cell also can form a stable velocity gradient. Different forms of non-smooth unit cell decorated on the surface of the body can change the flow of the gas flowing through the non-smooth surface boundary layer, reduce the velocity gradient, increase the boundary layer thickness, reduce the energy loss caused by shear forces work, and reduce the pressure drag of the body.Through the analysis of impact of non-smooth unit structure on aerodynamic influence, the paper provides the conditions of the application of drag reduction aspect, and laid the foundation for the further study of non-smooth unit cell.