Computational Method to Determine the Cooling Airflow Utilization Ratio of Passenger Cars Considering Component Deformation

Jan Marcel Hübner, Mathias Hähnel, Sven Lange, Matthias Lemke, Ivan Joksimovic
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Abstract

In order to improve the efficiency of passenger cars, developments focus on decreasing their aerodynamic drag, part of which is caused by cooling air. Thus, car manufacturers try to seal the cooling air path to prevent leakage flows. Nevertheless, gaps between the single components of the cooling air path widen due to the deformation of components under aerodynamic load. For simulating the cooling airflow utilization ratio (CAUR), computational fluid dynamics (CFD) simulations are used, which neglect component deformation. In this paper, a computational method aiming at sufficient gap resolution and determining the CAUR of passenger cars under the consideration of component deformation is developed. Therefore, a partitioned approach of fluid structure interaction (FSI) simulations is used. The fluid field is simulated in OpenFOAM, whereas the structural simulations are conducted using Pam-Crash. In order to validate the simulation results, the CAUR of a battery electric and an internal combustion engine powered vehicle is determined at a specifically developed cooling air test rig. Additionally, wind tunnel measurements determining wall pressures and component deformations are conducted. Furthermore, an experimental method was developed to measure three-dimensional deformations applying the “Structure from Motion” method to phosphorescent marker points. It could be shown, that areas of deformation can be detected by the developed simulation method and that the deformations negatively influence the CAUR. Comparing the results of the FSI simulations to single CFD simulations, this work was able to reduce the maximum estimation error of the CAUR from +12 %P to +3 %P. Finally, remaining error sources are outlined.
考虑部件变形的乘用车冷却气流利用率计算方法
为了提高乘用车的效率,研发工作的重点是减少空气阻力,其中一部分阻力是由冷却空气造成的。因此,汽车制造商试图密封冷却空气通道以防止泄漏。然而,由于部件在空气动力载荷作用下会发生变形,冷却气路各部件之间的间隙会扩大。在模拟冷却气流利用率(CAUR)时,使用的是计算流体动力学(CFD)模拟,这种方法忽略了部件的变形。本文开发了一种计算方法,旨在获得足够的间隙分辨率,并在考虑部件变形的情况下确定乘用车的 CAUR。因此,本文采用了流体结构相互作用(FSI)模拟的分区方法。流体场使用 OpenFOAM 进行模拟,而结构模拟则使用 Pam-Crash 进行。为了验证模拟结果,在专门开发的冷却空气试验台架上测定了电池电动汽车和内燃机驱动汽车的 CAUR。此外,还进行了风洞测量,以确定壁压和部件变形。此外,还开发了一种应用 "运动结构 "方法测量磷光标记点三维变形的实验方法。结果表明,所开发的模拟方法可以检测到变形区域,并且变形对 CAUR 有负面影响。将 FSI 模拟结果与单一的 CFD 模拟结果进行比较,这项工作能够将 CAUR 的最大估计误差从 +12 %P 降低到 +3%P。最后,概述了其余误差来源。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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