| In the 21 century, With the rapid growth of high-grade highway traffic mileage, the average speed of automotive is greatly improved. For high-speed automotive, aerodynamic characteristics has significant effect on its performance. So a good aerodynamic characteristics is indispensable. Automotive aerodynamic characteristics research has become an urgent issue. It is one of the most important characteristics. It has a direct impact on the power performance, fuel economy, steering stability, comfort and safety. As we all know, aerodynamic drag is directly proportional to the square of its speed. So the decrease of aerodynamic drag can not only improve the automotive dynamic performance, but also can improve its fuel economy. As the oil is nonrenewable resources and is exhausted. Reducing automotive aerodynamic drag is particularly important. But the traditional methods of drag reduction have apparently met bottleneck. To explore new method is becoming more and more urgent. It has been found many creatures in nature which with non-smooth surface has significant drag reduction effect. Inspired by this, the non-smooth surface was used in automotive aerodynamic drag reduction.This paper decorated pit, convex and groove non-smooth surface at MIRA stepped back model’s tail. CFD numerical simulation and wind tunnel test was adopted to analysis its aerodynamic drag reduction effect. Then, geometric feature parameters of non-smooth surface was optimized. The results showed the non-smooth surface after optimization has better aerodynamic reduction effect compared to the original one. To provide a method and reference for non-smooth surface design.First of all, CFD simulation was applied to compute the drag coefficient of non-smooth MIRA model. The results showed all of the non-smooth MIRA model have certain aerodynamic drag effect. On the other hand, the CFD CD of original MIRA model is compared to the wind tunnel CD to verify the accuracy of CFD simulation.Secondly, Three piece of transparent thin film made of PVC were processed to pit non-smooth surface and pasted at the top, bottom and tail of MIRA model respectively. After that, wind tunnel test had been carried out in HD-2 wind tunnel. The relative error between test CD and simulation CD are all below the allowable value. The wind tunnel test verified the reliability of the non-smooth surface’s drag reduction effect.Finally, aerodynamic drag coefficient was set as the optimization goal, depth, horizontal spacing and longitudinal spacing (or angle) of non-smooth unit were set as the design variables. Then Kriging approximate model was built for optimization. After computation, optimization geometric characteristic parameters and drag coefficients was obtained. It showed that the non-smooth models after optimization have better drag reduction effect. This provide a method for design of non-smooth surface’s geometric parameters.CFD simulation results showed pit, convex and groove non-smooth surface all had certain aerodynamic drag reduction effect when they decorated at the MIRA stepped back model’s tail. The aerodynamic drag reduction rates are 2.26%,1.69% and 1.23%. Then non-smooth surface MIRA model wind tunnel test was carried out in HD-2 wind tunnel. Verified the drag reduction effect of non-smooth surface. At last, research on the optimization of non-smooth surface’s geometric parameters. Aerodynamic drag reduction rates are 4.41%,3.97% and 4.11% compared to the mode before optimization. The optimization of non-smooth surface provide a method to design non-smooth surface. Any other similar design of non-smooth surface all can reference to this method which may save much time and energy. |
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