1、汽车空气动力学仿真概要汽车空气动力学仿真 Vehicle Aerodynamics Simulation 张扬军 Zhang Yang-Jun 清华大学汽车工程系应用空气动力学组 汽车安全与节能国家重点实验室 Applied Aerodynamics Group, Dept of Auto Eng., Tsinghua Univ. State Key Lab of Automotive Safety and Energy Vehicle Aerodynamics Simulation 汽车空气动力学仿真 1 2 3 4 5 6 汽车空气动力学概述 汽车空气动力学仿真特点 汽车空气动力学仿真难点
2、 汽车空气动力学仿真平台 仿真平台(VASS应用 总结与展望 1 2 3 4 5 6 Introduction to Road Vehicle Aerodynamics Some Salient Features of Road Vehicle Flow Simulation Main Difficulties of Road Vehicle Flow Simulation Vehicle Aerodynamics Simulation System (VASS VASS Applications Conclusions and Open Features 1 汽车空气动力学概述 1.1 空气
3、动力学对汽车性能的影响 1.2 汽车空气动力学性能 1.3 汽车空气动力学特点 1.4 空气动力学研究方法 Introduction to Vehicle Aerodynamics 1.1 1.2 1.3 1.4 Vehicle Attributes Affected by Aerodynamics Vehicle Aerodynamics Characteristics Peculiarities of Road Vehicle Aerodynamics Methods for Vehicle Aerodynamic 1.1 空气动力学对汽车性能的影响 Vehicle Attributes
4、Affected by Aerodynamics 动力性 经济性 舒适性 安全性 美观性 Maximum speed & Acceleration Fuel Economy Comfort Safety Visibility 1.2 汽车空气动力学性能 Vehicle Aerodynamics Characteristics 气动力气动力矩 油耗、操纵稳定性 流场结构 流动机理、气动噪声、 雨水流动、尘土堆积 aerodynamic force and moment coefficients fuel economy, handling stability flow structure flo
5、w mechanism, aerodynamic noise, rain water, dust accumulating 1.2 汽车空气动力学性能 Vehicle Aerodynamics Characteristics 冷却 散热器、发动机、制动器 和差速器冷却 通风与换气 进出风口位置、风量、风 速及风路，除结雾性能 cooling radiator, engine, brake, and differential cooling ventilation & air-exchange properly locate openings for air inlets and outlets
6、, air flow rate, velocity, air flow path, defrosting, etc. 1.2 汽车空气动力学性能 Vehicle Aerodynamics Characteristics 空气动力分量 阻力 升力 侧向力 侧倾力矩 横摆力矩 纵倾力矩 相关的动力性能 油耗、最高车速、加速 行驶稳定性 抗侧风能力(侧移 抗侧风能力(侧移 抗侧风稳定性 行驶稳定性 力 力矩 air force components air drag air forces lift side force rolling moment yawing moment pitching mo
7、ment performance fuel economy, top speed, acceleration direction stability crosswind crosswind crosswind direction stability moment 1.3 汽车空气动力学特点 Vehicle Aerodynamics peculiarities 研究空间有限 目标多元化 无法量化比较 流动复杂 many details primarily determined by “other than aerodynamic” arguments the objectives of aero
8、dynamics differing widely difficult to be quantified for weighing the relative importance complex flow 1.3 汽车空气动力学特点 Vehicle Aerodynamics peculiarities 研究空间有限 车身设计主要由机械工程学、人体工程学和美学 等决定，外形和车内空气动力学设计优化的研究 与应用均仅能在有限的机动空间中进行 many details primarily determined by “other than aerodynamic” arguments With th
9、e race car being the only exception, the shape of a road vehicle is not primarily determined by the need to generate specific aerodynamic effects-as, for instance, an airplane is designed to produce lift 1.3 汽车空气动力学特点 Vehicle Aerodynamics peculiarities 无法量化比较 汽车空气动力学优化设计与控制研究需 考虑艺术、时尚和喜好。而艺术、时尚 和喜好与
10、气动性能的重要性是无法具体 量化比较的。 difficult to be quantified for weighing the relative importance While the process of weighing the relative importance of a set of needs from various disciplines is generally comparable to that in other branches of applied fluid mechanics, the situation in vehicle aerodynamics is
11、 unique in that an additional category of arguments has to be taken into account: art, fashion, and taste. In contrast to technical and economic factors, these additional arguments are subjective in nature and cannot be quantified. 1.3 汽车空气动力学特点 Vehicle Aerodynamics peculiarities 目标多元化 共同目标 不同目标 低阻力
12、 负升力 通风与空调 气动噪声 侧风敏感性 赛车、高速车 轿车、公共汽车 轿车、公共汽车 轿车、厢式车 the objectives of aerodynamics differing widely desirable for all road vehicle: low drag different requirements: negative lift race cars, high speed cars ventilation & air cond. cars, buses crosswind sensitivity cars, vans low wind noise cars, buse
13、s 1.3 汽车空气动力学特点 Vehicle Aerodynamics peculiarities 几何结构复杂 流动复杂 粘性 湍流 强三维性 非定常 旋涡分离 内外流相互作用 热交换 地面效应 complex geometry external flow and internal flow interaction heat exchange ground effect Viscosity turbulence strong 3D effects unsteady vortex & flow separation 1.4 空气动力学研究方法 Methods for Vehicle Aero
14、dynamics 风洞试验 堵塞效应 地面效应 投资大 周期长 内部流动困难 数值仿真 发展迅速 应用广泛 新途径 wind-tunnel testing: blockage ground proximity effect high cost cost time difficulties for internal flow CFD, numerical simulation developed quickly widely used new design tool Features of Vehicle Aerodynamics Simulation 2 汽车空气动力学仿真特点 可预先研究 不
15、受条件限制 信息丰富 成本低 周期短 used in early design stage nearly no limitations more information low cost saving time Features of Vehicle Aerodynamics Simulation 2 汽车空气动力学仿真特点 可预先研究 性能研究 设计优化 提供依据 used in early design stage performance research during the early design period, it can generate information before
16、a testable model even exists. design & optimize aerodynamic design and performance study may be studied iterativelly wide range of design options CFD simulation is well suited to the analysis of a wide range of shape options, etc. 设计初期：空气动力学性能预测、分析 与气动设计交叉进行，得最佳气动设计 为汽车造型、空调和通风系统的设计与 布置提供依据。 Feature
17、s of Vehicle Aerodynamics Simulation 2 汽车空气动力学仿真特点 不受条件限制 流动参数 范围广泛 无干扰效 应等影响 不受湍流、风速风向、气温气压以及Re数 等限制，能给出流场参数定量结果。 无洞壁干扰、风洞试验段堵塞效应，可避免风 洞试验的支架干扰、模型弹性变形等技术问题 以及道路试验条件和交通状况的影响 Without the limitations of turbulence,wind velocity, pressure, temperature and Reynolds numbers etc. numerical methods are not
18、 necessarily burdened with the limitations of the wind tunnel. For example, computational space can be made large enough to eliminate blockage effects. Features of Vehicle Aerodynamics Simulation 2 汽车空气动力学仿真特点 信息丰富 各种行驶状况 瞬态气动特性 各种行驶状况，获得比风洞试验更丰富的 信息，包括试验难以测量和解释的信息 侧风时瞬态气动特性影响操纵稳定性的研 究，数值仿真比风洞试验方法更具
19、优势 非定常气动干扰 同向及对开时非定常气动干扰等试验 难于研究，仿真更有其独特优点 much more information available than from a routine experiment sometimes a CFD simulation permits the investigation of situations that can note be realistically duplicated in a wind tunnel, such as transient crosswind sensitivity. the aerodynamics of two ve
20、hicles in the passing or overtaking mode, for example, poses a difficult problem for wind tunnel tests. Features of Vehicle Aerodynamics Simulation 2 汽车空气动力学仿真特点 70s 风洞试验 数值仿真 100h 成本低 周期短 90s 1800h 成本降低了近100倍 low cost saving time CFD is becoming markedly more economical as time goes due to the revo
21、lutionary advances in computer technology Difficulties of Vehicle Aerodynamics Simulation 3 汽车空气动力学仿真难点 1、几何结构复杂，网格建模困难 complex geometry, grid generation difficult Difficulties of Vehicle Aerodynamics Simulation 3 汽车空气动力学仿真难点 2、为充分发展湍流，不能按层流计算流动 full developed turbulent flow Difficulties of Vehicle
22、Aerodynamics Simulation 3 汽车空气动力学仿真难点 3、流动强三维性，难于简化分析 strong three-dimensional effects,2D solution is not suitable Difficulties of Vehicle Aerodynamics Simulation 3 汽车空气动力学仿真难点 4、各种尺度旋涡，闭式、开式分离流动；机 理还不很清除，物理数学模型问题 vortex flow, closed or open regions of separated flow Difficulties of Vehicle Aerodyna
23、mics Simulation 3 汽车空气动力学仿真难点 5、地面效应，航空成果难 于直接应用 ground proximity effect, aircraft industry methods are not always directly applicable or suitable to treat problems of vehicle aerodynamics. Difficulties of Vehicle Aerodynamics Simulation 3 汽车空气动力学仿真难点 6、流场与温度场耦合,热源难于确定 flow field coupling temperatur
24、e field, engine cooling, etc. Difficulties of Vehicle Aerodynamics Simulation 3 汽车空气动力学仿真难点 7、流场相互作用问题，存在内外流耦合问题 internal and external flow fields are closely related. Both flow fields must be considered together Difficulties of Vehicle Aerodynamics Simulation 3 汽车空气动力学仿真难点 8、流动非定常，定常体系 难于考虑 flow is
25、 unsteady, however, the aerodynamic design system is a steady one. 4 汽车空气动力学数值仿真平台 Vehicle Aerodynamics Simulation System (VASS 4.1 开发背景 4.2 技术方案 4.3 系统组成 4.4 仿真环境 4.5 技术水平 4.6 主要特色 background technical blue print system introduction simulation environment technical level main features 4.1 仿真平台开发背景
26、Background of VASS Development 国 外 国际上各有关厂、所和学校在80年代初 就开始了相关研究并建立了仿真系统 国 内 我国还处于起步阶段,还没有相应仿真 系统 background overseas: CFD is a development tool domestic: no CFD system for vehicle aerodynamics simulation 4.1 仿真平台开发背景 Background of VASS Development 清华大学 985项目 轿车车身车型总体设计关键技术和轿车数字 化工程均将汽车空气动力学仿真平台作为主要研究
27、内 容，希为汽车车型车身设计能力的提高提供技术支持 vehicle aerodynamics simulation system (VASS development is one of the main research subjects at Tsinghua University 4.2 仿真平台技术方案 Technical Blue Print for VASS 网格系统 流场控制方程 方程求解方法 湍流模型 分区生成结构/非结构杂交化网格 雷诺平均NS方程RANS 有限体积法FVM 二方程湍流模型/低Re数修正 The capability of an unstructured hyb
28、rid grid method to compute the Navier-Stokes equations is discussed for complex flows around automobile configurations. The unstructured hybrid grid, which is composed of a structured or a semistructured grid for the near-wall viscous region, a prismatic grid for the exterior regular computational d
29、omain, and an unstructured grid for the remainder of the computational domain, is used to treat such viscous flows. The Navier-Stokes equations are solved on the hybrid grid by a cell-vertex, upwind finite volume method. 4.3 仿真平台系统组成 VASS Introduction 主要模块 非结构网格生成模块 结构网格生成模块 数学物理模型选择模块 初始条件设定模块 边界条件
30、设定模块 计算控制条件设定模块 数值计算模块 气动力及气动力矩计算模块 main modules unstructured grid generation prismatic grid generation theoretical model selection initial condition determination boundary condition determination calculation control determination numerical computation aerodynamic force and moment cal. 4.3 仿真平台系统组成
31、VASS Introduction 系统窗口 system windows 4.3 仿真平台系统组成 VASS Introduction 系统窗口 system windows 4.3 仿真平台系统组成 VASS Introduction 系统窗口 system windows 几何数据引入、网格生成、网格检查、边界条件生成、边界条件检查、流体热物性质、工况条件、 计算控制参数、仿真计算、后处理、结果输出 Hardware, software & Operating System 4.4 仿真平台仿真环境 硬件环境： 操作系统： 软件环境: 内存256MB 硬盘空间3G Windows NT
32、或 UNIX ICEM-CFD 4.0 STAR-CD 3.1 simulation environment hardware operating system software memory 256MB hard disk 3G Windows NT or UNIX ICEM-CFD 4.0 STAR-CD 3.1 4.5 仿真平台技术水平 VASS Evaluation 专业性：能够有效模拟复杂的三维汽车 流场的粘性湍流流动。 通用性：能对于不同车型生成自适应网 格，并可模拟多种工况条件， 参数设置方便 平台具有良好的操作性和可扩容性 specialized in vehicle aero
33、dynamics simulation, automatic adaptive grid system generation, suitable to extensive situations,easy to operate 4.5 仿真平台技术水平 VASS Evaluation 核心软件可靠，仿真精度高 ICEMCFD，STARCD 国际汽车界广泛实用 系统验证考核 国际通用考核汽车流场计算准确性的 Ahmed 模型， 气动阻力试验值 0.184, 计算值 0.181, 误差 1.63% The numerical accuracy of VASS has been discussed by comparing with
