计及车身附件气动干涉影响的汽车流场数值仿真研究

以降低汽车气动阻力、获得最优气动造型为目的,应用计算流体动力学方法对某轿车内外流场进行了数值仿真,分析并总结了车身附件气动干涉和发动机舱内空气流动对整车气动性能的影响.计算结果表明:车身附件对整车气动特性有较大影响.其中,底部结构和轮胎的影响较大;余者(后视镜、雨刮器和门把手)的影响很小.考虑了车身附件的影响后,气动阻力约增加23%;加上发动机舱内空气流动的影响,整车气动阻力共增大约35%.分析还表明,车轮的转动有利于改善车底气流与尾流的相互作用,使气动阻力稍有降低.     

关于摩托车导流罩的造型（1）

摩托车导流罩起着提高整车美感和顺导气流，改善整车空气动力特性的作用。因此，导流罩的造型应满足空气动力学性能和美学要求。同时它对摩托车的气动阻力，气动升力，气动侧向力等摩托车的空气动力特性有着重要影响。     

轻卡外流场数值模拟及货箱优化设计

对某轻卡进行外流场的数值模拟,通过对模型的流场特性的分析,研究气动阻力产生的主要原因。将车厢高度和车厢与驾驶舱距离作为两个影响因子,采用拉丁超立方设计方法和最小二乘法创建二阶响应面模型,利用混合整型优化法进行参数优化,优化后与原型设计相比,整车气动阻力明显减小,表明该方法能有效地提高整车空气动力学性能和CFD优化效率。     

前阻流板对汽车气动性能的影响(续1)

文章针对某轿车模型,从整车减阻的目标出发,利用STAR-CCM+软件,采用空气动力学数值模拟的方法,研究了汽车前部阻流板对整车气动阻力和冷却模块通风量等影响。结果表明,通过在前车体下部添加阻流板,整车的气流状态得到改善,具有减小整车气动阻力和提高冷却模块的冷却性能等重要作用。阻流板的高度和位置是影响其减阻效果的关键因素。通过添加前阻流板和封闭前格栅等措施,达到了预期的整车减阻目标。     

集装箱半挂运输车气动特性的数值仿真及改进

为降低车身的气动阻力,文中应用CFD软件对某款集装箱半挂运输车简化模型进行数值仿真,以揭示车身周围空气流动的机理.首先分析了原车型的车身周围流场的流动特性,然后加装导流罩并研究改变其圆角半径和驾驶室与集装箱的间距对整车气动阻力系数的影响规律.     

某电动车底部后端的降阻研究

文章基于仿真分析的方法,针对某电动汽车的底部后端区域进行了降阻研究。研究发现,当电动汽车后端没有挡板覆盖时,后端零件的压力损失较大,使得整车气动阻力较高。通过增加后端挡板,可以有效改善底部后端的流场分布,改善整车的气动阻力。挡板的角度和高度对于挡板的气动阻力影响较大,在实际开发中需要进行优化。研究表明,当挡板角度为30°、高度为-5 mm时,对整车气动阻力的贡献量最大,整车Cd值降低了0. 005。     

摩托车底盘测功机阻力的设定

摩托车工况法排放污染物测试及整车底盘动力性能测试都需要进行摩托车道路行驶阻力的测定及底盘测功机上摩托车行驶阻力的设定，利用惯性滑行法测定和计算摩托车道路行驶阻力，并进行底盘测功机上带车滑行试验调整行驶阻力系数，可以保证底盘测功机能够较精确地模拟摩托车实际道路行驶阻力。     

微型客车气动阻力性能研究及优化设计

综合利用计算流体力学数值仿真分析与风洞试验验证相结合的方法对某量产微型客车进行整车全细节空气动力学仿真分析和研究。对比分析前保险杠、后视镜、车窗等零部件对气动阻力的影响。研究表明,采用优化前保险杠并增加导流板、修改后视镜造型、车窗一体化设计等方案,可使该车气动阻力系数减少约6%。     

商用车驾驶室导流罩气动造型设计

根据某商用车驾驶室的形状特征,设计了4款驾驶室导流罩方案,安装在商用车上进行整车空气动力特性的数值模拟,以得到减阻效果最好的导流罩方案,并总结其气动特性规律。在此基础上,重新设计了一款更加合理的导流罩,安装在整车上进行数值模拟,对其减阻性能进行分析。结果表明:初始设计的4款导流罩的减阻效果不一,有的反而增加了阻力,而根据导流罩流场特性重新设计的导流罩,引导车头气流平顺通过车身表面,减阻效果显著提高。     

某SUV气动减阻优化及其流场机制

为了提高整车燃油经济性,本文以某款SUV车型为研究对象,将仿真与试验相结合改善汽车行驶过程中的气动阻力系数。首先通过风洞试验确定对整车气动阻力有重要影响的区域或部件,其次对气动阻力系数贡献值较大的部件或区域进行减阻优化。结果表明,前轮阻风板、尾灯和尾翼对整车气动阻力系数贡献值较大。对前轮阻风板的改型,有效降低正压区面积以及减弱车轮干扰阻力;对尾灯和尾翼的优化设计,改善了尾部负压区,缩短了分离流在后窗上部的再附着的距离。基于本征正交分解方法进行局部流场信息的提取和分析可知,1阶与2阶模态主要构成了该SUV尾流场的关键流态。经试验与仿真验证,相比于初始方案,气动优化组合设计减阻率可达7.5%。本文为新一代SUV改型与升级换代提供了理论基础与技术支持。     

Optimal control to modelling motorcycle rider steering: local versus global coordinate systems in rider preview

The response of a motorcycle is heavily dependent on the rider’s control actions, and consequently a means of replicating the rider’s behaviour provides an important extension to motorcycle dynamics. The primary objective here is to develop effective path-following simulations and to understand how riders control motorcycles. Optimal control theory is applied to the tracking of roadway by a motorcycle, using a non-linear motorcycle model operating in free control by steering torque input. A path-following controller with road preview is designed by minimising tracking errors and control effort. Tight controls with high weightings on performance and loose controls with high weightings on control power are defined. Special attention is paid to the modelling of multipoint preview in local and global coordinate systems. The controller model is simulated over a standard single lane-change manoeuvre. It is argued that the local coordinates point of view is more representative of the way that a human rider operates and interprets information. The simulations suggest that for accurate path following, using optimal control, the problem must be solved by the local coordinates approach in order to achieve accurate results with short preview horizons. Furthermore, some weaknesses of the optimal control approach are highlighted here.     

侧风状态下轿车气动特性数值模拟方法的研究

采用3种不同方法,利用计算流体力学软件FLUENT对侧风状态下轿车的气动特性进行了数值模拟,得到了不同侧风状态下轿车气动阻力系数和侧力系数随横摆角而变化的曲线。讨论了不同方法的优缺点并将模拟结果与风洞实验进行对比,结果表明采用合适的数值模拟方法可省时省力地获得接近于实验的结果。     

The Effect of Topboxes on Motorcycle Stability

Hot wire anenometry measurements have been made in the wake of a model motorcycle and rider mounted in a windtunnel. Only in tests with a topbox present is there clear evidence of eddy shedding. Calculations have been performed on the corresponding full-scale motorcycle to determine the frequencies of the weave and wobble modes. Comparison with the wake frequencies extrapolated to full size show that at speeds of 31-34 m/s they coincide with those of the wobble mode which is found to be efficiently coupled to the aerodynamic excitation.     

A nonlinear virtual rider for motorcycles

This work presents a virtual rider for the guidance of a nonlinear motorcycle model. The target motion is defined in terms of roll angle and speed. The virtual rider inputs are the steering torque, the rear-wheel driving/braking torque and front-wheel braking torque. The virtual rider capability is assessed by guiding the nonlinear motorcycle model in demanding manoeuvres with roll angles of 50° and longitudinal accelerations up to 0.8 g. Considerations on the effective preview distance used by the virtual rider are included.     

On the wobble mode of a bicycle

Wheel shimmy and wobble are well-known dynamic phenomena at automobiles, aeroplanes and motorcycles. In particular, wobble at the motorcycle is an (unstable) eigenmode with oscillations of the wheel about the steering axis, and it is no surprise that unstable bicycle wobble is perceived unpleasant or may be dangerous, if not controlled by the rider in time. Basic research on wobble at motorcycles within the last decades has revealed a better understanding of the sudden onset of wobble, and the complex relations between parameters affecting wobble have been identified. These fundamental findings have been transferred to bicycles. As mass distribution and inertial properties, rider influence and lateral compliances of tyre and frame differ at bicycle and motorcycle, models to represent wobble at motorcycles have to prove themselves, when applied to bicycles. For that purpose numerical results are compared with measurements from test runs, and parametric influences on the stability of the wobble mode at bicycles have been evolved. All numerical analysis and measurements are based on a specific test bicycle equipped with steering angle sensor, wheel-speed sensor, global positioning system (GPS) 3-axis accelerometer, and 3-axis angular velocity gyroscopic sensor.     

基于骑乘安全性的摩托车色彩设计研究

色彩对摩托车安全性有着直接的影响。色彩设计不仅在视觉上美化了摩托车产品,影响人的心理和情感,还会影响骑乘者视觉的反应速度及准确性。与色彩相关联的摩托车安全性设计主要包括仪表设计、方向把操作按键面板设计、整车色彩设计及骑乘者的头盔及着装设计。     

Study on the effects of motorcycle anti-lock-braking-system for skilled and less-skilled riders: regarding braking in a turn

The effectiveness of ABS for the motorcycle has been evaluated by comparison with deal braking. However, it is almost impossible for the typical rider to perform ideal braking in an emergency. We conducted braking in a turn test by skilled and less-skilled riders, for the purpose of evaluating the effectiveness of ABS for the typical rider and obtaining data for a method of evaluating motorcycle ABS performance. It was shown that ABS for the motorcycle is effective for both skilled and less-skilled riders in terms of braking distance and vehicle stability.     

Comparative investigation on the aerodynamic effects of combined use of underbody drag reduction devices applied to real sedan

To reduce the aerodynamic drag, the performance of the underbody aerodynamic drag reduction devices was evaluated based on the actual shape of a sedan-type vehicle. An undercover, under-fin, and side air dam were used as the underbody aerodynamic drag reduction devices. In addition, the effects of the interactions based on the combination of the aerodynamic drag reduction devices were investigated. A commercial sedan-type vehicle was selected as a reference model and its shape was modeled in detail. Aerodynamic drag was analyzed by computational fluid dynamics at a general driving speed on highway of 120 km/h. The undercover reduced the slipstream area through the attenuation of the longitudinal vortex pair by enhancing the up-wash of underflow, thereby reducing the aerodynamic drag by 8.4 %. The under-fin and side air dam showed no reduction in aerodynamic drag when they were solely attached to the actual complex shape of the underbody. Simple aggregation of the effects of aerodynamic drag reduction by the individual device did not provide the accurate performance of the combined aerodynamic drag reduction devices. An additional aerodynamic drag reduction of 2.1 % on average was obtained compared to the expected drag reduction, which was due to the synergy effect of the combination.     

基于GA-BP神经网络的汽车空气阻力系数预测研究

针对整车空气动力性能开发中数值计算耗时长的问题，提出一种基于GA-BP神经网络的汽车空气阻力系数预测方法。将汽车部分特征参数作为输入变量，经外流场仿真得到的空气阻力系数作为输出变量，获取数据集。采用遗传算法对BP神经网络进行参数寻优，最终建立基于遗传算法的BP神经网络模型，验证不同训练集数量对模型预测精度的影响。结果表明，GA-BP神经网络在训练样本较少时也能维持较高的预测精度，可用于汽车空气阻力系数的快速测。     

圆顶车厢载货车外流场数值模拟及附加装置优化设计

对EQ1118GA圆顶车厢运输车进行外流场的数值模拟,通过对模型的表面压力和流场特性的分析,研究EQ1118GA运输车气动阻力产生的主要原因,以此为依据为优化其空气动力学性能设计了4种不同的导流罩,并分别对它们进行数值模拟计算,得到具有最佳减阻效果的导流罩。