Aerodynamic Drag Reduction of a Platoon of Generic Tractor-Trailers equipped with Base Flaps under Realistic Boundary Conditions

欧盟内部道路交通排放的大部分二氧化碳是重型车辆排放的，它们产生了大约30%的温室气体，尽管它们只占所有道路车辆的4%。这种情况证明，提高这些车辆的燃油效率符合政治和经济的共同利益。在高速公路上，气动阻力约占标准40吨欧洲拖拉机-挂车组合总损失的40%。其中一个主要来源是车辆尾部下游的大片分离区。在过去的10年里，特别是在美国，已经做出了许多努力来开发商业解决方案，例如显著减少空气动力阻力的底部襟翼。在过去的几十年里，这些附加设备是几个基础研究的对象。因此，单辆卡车可以实现的好处是众所周知的。最近，欧盟修改了立法，允许在卡车尾部安装总长度为0.5米的附加装置。此外，自动驾驶的最新进展开辟了通过以非常小的车辆间距排成一排来减少阻力的新方法。然而，斜底襟翼的应用彻底改变了尾迹内部的流场及其基本动力学。因此，与孤立的车辆相比，后续车辆的入射流量条件将显著偏离。通过底部襟翼的流场修改可能会改变与排中相关的后续车辆的最佳距离以及最佳襟翼角度。因此，基础瓣的效果可能会抵消排成一排的好处。因此，需要详细考虑这两种方法的组合(基础瓣应用和排成排)。拟议项目的重点是根据对有和没有底板的通用拖拉机-挂车模型的流动动力学的基本理解来制定指导方针，以实现所涉及车辆以及整个排的最大减阻。因此，本研究将探讨襟翼倾斜角、车辆距离、车辆排数对流场及相关阻力的影响。尤其对于道路车辆来说，地面效应是一个重要的方面。在许多研究中，这种效应表现为静止的地面，在某些情况下表现为移动的带子。在这项研究中，将使用一种特殊的实验装置：柏林工业大学的250米水拖曳水箱设施，通过将淹没的模型移动到静止的地面上，实现真实的边界条件和高雷诺数。基于预期结果，工业界和学术界可以开发和实现包括自适应底襟翼和自动驾驶在内的创新技术，以显著减少未来重型汽车的空气动力阻力，从而减少二氧化碳排放。

The major part of CO2 emitted by road traffic within the European Union is ascribed to heavy-duty vehicles which generate about 30 % of the greenhouse gases although they represent only 4 % of all road vehicles. This situation justifies the common interest of politics and economy to increase the fuel efficiency of those vehicles. On highways the aerodynamic drag contributes to about 40 % of the overall losses of a standard 40 t European tractor-trailer combination. One major source represents the large separation area downstream of the vehicle rear end. Many efforts have been undertaken particularly in the USA during the last 10 years to develop commercial solutions such as base flaps which significantly reduce the aerodynamic drag. These add-on devices were object of several fundamental studies within the last decades. The achievable benefits are, therefore, well known for single trucks. Recently, the legislation of the EU has been modified allowing the application of add-on devices with a total length of 0.5 m to the rear end of trucks. Additionally, recent progress in automated driving opens new ways for drag reduction through platooning with very small inter-vehicle spacing. However, the application of inclined base flaps completely changes the flow field within the wake and its underlying dynamics. Consequently, the incident flow conditions of following vehicles will significantly deviate compared to vehicles in isolation. The flow field modifications through the base flaps may change the optimal distance to following vehicles associated in a platoon as well as the optimal flap angle. Therefore, the efficacy of base flaps may negate the benefits of platooning. As a result the combination of both approaches (base flap application and platooning) needs to be considered in detail. The proposed project focuses on the elaboration of guidelines based on the fundamental understanding of the flow dynamics of a platoon of generic tractor-trailer models with and without base flaps to achieve the maximum drag reduction for the involved vehicles as well as the complete platoon. Therefore, the influence of the flap inclination angle, the vehicle distance, and the number of vehicles comprising the platoon on the flow field and the related drag values will be investigated in this study. Especially for road vehicles an important aspect is the ground effect. In many studies this effect was represented by a stationary ground and in some cases as a moving belt. In this study a particular experimental setup will be used: A 250 m water towing tank facility of the TU Berlin enabling realistic boundary conditions and high Reynolds numbers by moving the submerged models over a stationary ground. Based on the anticipated results, industry and academia can develop and realize innovative technologies including adaptive base flaps and automated driving to significantly reduce the aerodynamic drag and thus the CO2 emissions of future heavy-duty vehicles.