车身非光滑表面边界层流场特性及侧风减阻分析

发布时间：2018-06-13 08:53

本文选题：边界层 + 非光滑表面　；参考：《湖南大学》2016年硕士论文

【摘要】：随着汽车行业的不断发展以及高速路网的不断完善,汽车实际行驶速度得到很大提高,这将大大影响汽车的气动阻力。行驶速度越大,其气动阻力也越大,若能减小气动阻力,则意味着燃油消耗的降低。随着汽车空气动力学的发展,减小车身气动阻力的传统方法已经成熟并遇到技术瓶颈,需要寻求新型气动减阻方法和思路。国内外研究发现仿生非光滑表面具有较好的减阻效果,因此可以将非光滑结构引入汽车车身,实现汽车的节能减阻。本文基于标准MIRA阶梯背模型,将凹坑型非光滑结构引入汽车顶部表面,研究顶部近壁面边界层内关键流场参数的变化以及这些变化对尾流造成的影响,并分析其减阻机理。最后进一步考虑侧风状态下凹坑型非光滑结构的减阻效果以及对汽车行驶造成的影响。首先选择非光滑单元体形态、布置位置和尺寸建立非光滑车身模型,利用CFD数值模拟仿真方法对光滑、非光滑汽车模型进行仿真,并通过与MIRA模型风洞试验对比验证表明数值模拟方法的可靠性。其次从非光滑表面边界层内的流场特性出发,分析气流速度、边界层厚度、壁面剪切力、表面摩擦阻力等流场参数的变化及其对边界层分离后尾流状态、湍流强度、湍流耗散率等方面的影响来探究非光滑结构的减阻机理。最后通过采用稳态侧风数值模拟,对比分析了0~30°范围内(横摆角以3°递增)的光滑模型与非光滑模型的车身周围流场特性。对气动力系数和气动力进行了计算,并根据车身外流场的速度、压力、湍动能分布图,分析侧风状态下,非光滑结构的引入对于汽车气动特性特别是气动阻力的影响。
[Abstract]:With the continuous development of the automobile industry and the continuous improvement of highway network, the actual vehicle speed has been greatly improved, which will greatly affect the aerodynamic resistance of the vehicle. The greater the speed, the greater the aerodynamic resistance. If the aerodynamic resistance can be reduced, it will mean the reduction of fuel consumption. With the development of automobile aerodynamics, the traditional method of reducing aerodynamic resistance of automobile body has been mature and met with technical bottleneck, so it is necessary to seek new aerodynamic drag reduction method and train of thought. Domestic and foreign studies show that bionic non-smooth surface has better drag reduction effect, so non-smooth structure can be introduced into vehicle body to achieve energy saving and drag reduction. Based on the standard MIRA step back model, the crater type non-smooth structure is introduced into the top surface of the vehicle to study the change of the key flow field parameters in the boundary layer near the wall of the top and the influence of these changes on the wake, and the mechanism of drag reduction is analyzed. Finally, the drag reduction effect of non-smooth concave structure under crosswind and its influence on vehicle driving are further considered. Firstly, the non-smooth vehicle body model is established by selecting the non-smooth unit shape, arranging the position and size, and simulating the smooth and non-smooth vehicle model by CFD numerical simulation method. The reliability of the numerical simulation method is verified by comparing with the wind tunnel test of MIRA model. Secondly, based on the characteristics of the flow field in the non-smooth boundary layer, the variation of the flow field parameters, such as the flow velocity, the thickness of the boundary layer, the wall shear force, the friction resistance of the surface, the wake state and the turbulence intensity of the boundary layer after separation are analyzed. The drag reduction mechanism of non-smooth structures is studied by the influence of turbulent dissipation rate. Finally, by using steady state cross-wind numerical simulation, the characteristics of the flow field around the body of the smooth model and the non-smooth model in the range of 0 掳30 掳(3 掳increase in yaw angle) are compared and analyzed. The aerodynamic coefficient and aerodynamic force are calculated. According to the velocity, pressure and turbulent kinetic energy distribution of the body flow field, the influence of the introduction of non-smooth structure on the aerodynamic characteristics, especially the aerodynamic resistance, is analyzed under the crosswind condition.
【学位授予单位】：湖南大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：U461.1

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