【作者】 吴军；

【导师】 钟志华； 谷正气；

【作者基本信息】 湖南大学 ， 车辆工程， 2005， 博士

【摘要】 汽车的气动特性对汽车的动力性、经济性、舒适性和安全性等等有着极其重要的影响,例如:汽车在高速行驶时,整车气动阻力与速度的平方成正比,而风阻系数的减少则可大大降低汽车的油耗,提高汽车的经济性;另外,汽车在高速状态下的侧风稳定性则是对汽车安全性的重要指标之一。而汽车外流场的流动尤其是尾部大范围的分离和湍流流动对汽车气动性能至关重要,所以,如何应用准确的湍流运动物理数学模型,对汽车外流场的气动特性进行深入分析已成为当前汽车空气动力学数值仿真研究领域面临的重点和难点之一。传统的汽车外流场数值仿真所应用的湍流模型大都是基于“通常”条件推导而成,而汽车外流场有着其独特的流动特性,因此本文认为需要在对汽车外流场的近壁特性进行深入分析的基础上,建立更为适用汽车外流场的湍流模型。 从理论方面,本文运用张量表示理论、近壁特性分析和低雷诺数修正的方法,通过对机理完善的雷诺应力方程进行简化,建立了全应力湍流模型; 从计算方面,本文在理论模型的基础上对新概念车和典型汽车气动特性进行数值仿真,获得升阻力系数、压力系数以及外流场的各种仿真结果: 从试验方面,本文运用粒子图像速度场仪(PIV)、风洞试验的手段对新概念车的外流场特性进行了深入的研究,并验证了数值计算的结果。 本论文的主要创新点和研究工作包括: 1、综述国内外汽车外流场数值仿真的研究现状和发展动态。首次针对汽车车身外流场的特点提出建立低雷诺数非线性涡粘性湍流模型的思路。基于雷诺应力输运方程进行简化,推导出包含原始精确模型机理的显式代数应力模型(其实际体现为非线性涡粘性模型);然后应用近壁特性分析方法,对非线性涡粘性模型进行低雷诺数修正,保证雷诺正应力和剪切应力在近壁处都能够得到体现;最后综合k-ω方程和k-ε方程及低雷诺数非线性涡粘性模型形成完整的双方程框架下低雷诺数非线性湍流模型,简称全应力输运模型(Whole Stress Transport Model—WST)。 2、全应力湍流模型相对当今汽车工程界常用的k-ε等线性涡粘性湍流模型包含有更完整的低雷诺数雷诺应力模型的机理,其综合了k-ω模型和k-ε模型的优点,既克服了k-ε模型在附面层内由于涡粘性系数各项同性导致的分辨率低的缺点,可以反应近壁区雷诺应力的各向异性,从而具有附面层内的高分辨率;更多还原

【Abstract】 The aerodynamic characteristics are very important to the automobile dynamic performances, the fuel consumption, the comfort and the safety. For example, the decrease of the aerodynamic drag force coefficient which is proportional to the square of the velocity can greatly reduce the fuel consumption especially at the high speed. The vehicle stability in the lateral wind is also a crucial guideline for the vehicle safety performance especially at the high speed.Because the separated flow and turbulence behind the automobile have great effect on the automobile aerodynamics, the precise turbulence model for the accurate simulation of the automobile aerodynamic characteristics has become the most difficult problem and keystone in the simulation. The turbulence models applied in the traditional simulation of the automobile external flow field are commonly based on the "general" condition. In fact, the automobile external flow field has some different aspects from the "general" condition. So, a more suitable turbulence model should be developed based on the property of the automobile external flow field.From the theory aspect, a new turbulence model has been developed based on RSM equations combining the analysis of near-wall asymptotic behavior in the automobile external flow field with the tensor theory and low-Re modification.From the calculation, the aerodynamics simulations of the new concept vehicle and the traditional car get the drag and lift coefficients and other results based on the newly developed turbulence model.From the experiment, the aerodynamics of the new concept vehicle has been investigated by the PIV and the wind-tunnel experiment which verify the simulation results.In particular, the following work including the innovation has been completed:1. Summarize the domestic and international research and development status of the automobile external flow field numerical simulation. For the first time, a new LRNLEVM (low-Re Nonlinear Eddy Viscosity Model) is brought forward based on the property of the automobile external flow field. In the modeling process, the EASM (Explicit Algebraic Stress Model) including the detailed mechanism of the更多还原