Assessment of a Vehicle's Transient Aerodynamic Response
Assessment of a Vehicle's Transient Aerodynamic Response
复制标题
车辆瞬态空气动力响应的评估
DOI：
10.4271/2012-01-0449
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发表时间：
2012
期刊：
影响因子：
--
通讯作者：
A. Gaylard
中科院分区：
文献类型：
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作者：
N. Oettle;Oliver Mankowski;D. Sims;R. Dominy;Claire Freeman;A. Gaylard
由于自然风的湍流、其他车辆的不稳定尾流以及穿过路边障碍物的静止尾流，道路上的车辆会遇到不稳定流。人们越来越关注用于开发的稳定流动条件与道路上发生的瞬态流动条件之间的潜在差异。本文旨在确定稳态条件下进行的测量是否可用于预测阵风环境中道路上车辆的空气动力学行为。该项目包括在两个全尺寸风洞中进行测量，包括使用 Pininfarina TGS、Exa Powerflow 中的稳态和瞬态入口模拟，以及道路和赛道上的测试活动。本文特别关注稳定的风洞测量和道路测试，分别代表最成熟的开发环境和客户体验的环境。前侧玻璃上的表面压力测量用于比较，因为该区域表现出复杂的流动，对偏航角高度敏感，并且这也是一个重要区域，特别是考虑到风噪声。研究发现，如果已知瞬态道路环境，则只要方法足够严格，就可以使用稳态风洞测量来准确预测瞬态表面压力。导纳或传递函数技术通常用于比较瞬态和稳态结果，当自激和外部施加的不稳定谱重叠时，这些方法的局限性就显示在此处。引入了一种新方法来获得“真实”传递或导纳函数，不会因自激不稳定的存在而感到困惑。研究发现，空气动力导纳在 2-10 Hz 频率范围内接近一致，然后逐渐下降。
A vehicle on the road encounters an unsteady flow due to turbulence in the natural wind, due to the unsteady wakes of other vehicles and as a result of traversing through the stationary wakes of roadside obstacles. There is increasing concern about potential differences between the steady flow conditions used for development and the transient conditions that occur on the road. This paper seeks to determine if measurements made under steady state conditions can be used to predict the aerodynamic behaviour of a vehicle on road in a gusty environment. The project has included measurements in two full size wind tunnels, including using the Pininfarina TGS, steady-state and transient inlet simulations in Exa Powerflow, and a campaign of testing on-road and on-track. The particular focus of this paper is on steady wind tunnel measurements and on-road tests, representing the most established development environment and the environment experienced by the customer, respectively. Measurements of the surface pressure on the front sideglass were used for comparisons as this area exhibits a complex flow which is highly sensitive to yaw angle and which is also an important region, for wind noise considerations in particular. It was found that, if the transient on-road environment is known then steady-state wind tunnel measurements can be used to predict accurately the transient surface pressures, provided the methodology is sufficiently rigorous. Admittance or transfer function techniques are commonly used to compare transient and steady-state results and the limitations of these methods are shown here when the spectra of self-excited and externally imposed unsteadiness overlap. A new method is introduced to obtain a “true” transfer or admittance function, unconfused by the presence of self-excited unsteadiness. The aerodynamic admittance was found to be close to unity up to a frequency of 2-10 Hz and it then drops progressively.