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

欧盟道路交通排放的CO2的主要部分是重型车辆，它们产生约30%的温室气体，尽管它们仅占所有道路车辆的4%。这种情况证明提高这些车辆的燃料效率符合政治和经济的共同利益。在高速公路上，空气动力阻力约占标准40 t欧洲牵引车-拖车组合总损失的40%。一个主要来源是车辆后端下游的大分离区。在过去的10年里，特别是在美国，人们已经做出了许多努力，以开发诸如底部襟翼之类的商业解决方案，这些襟翼可以显著地减小气动阻力。这些附加设备是过去几十年中几项基础研究的对象。因此，单辆卡车的可实现效益是众所周知的。最近，欧盟的立法已经修改，允许在卡车后端应用总长度为0.5米的附加装置。此外，自动驾驶的最新进展为通过具有非常小的车辆间间距的队列减少阻力开辟了新的途径。然而，倾斜底部襟翼的应用完全改变了尾流内的流场及其基本动力学。因此，后续车辆的事故流条件与孤立车辆相比将显著偏离。通过底部襟翼的流场修改可以改变到队列中相关联的跟随车辆的最佳距离以及最佳襟翼角度。因此，底部襟翼的功效可能会抵消编队的好处。因此，需要详细考虑这两种方法（底部襟翼应用和队列）的组合。拟议项目的重点是根据对一排有和没有底部襟翼的通用牵引车-拖车模型的流动动力学的基本理解制定准则，以实现所涉车辆以及整个排的最大减阻。因此，在这项研究中，襟翼倾角的影响，车辆的距离，和车辆组成的队列上的流场和相关的阻力值的数量将进行调查。特别是对于公路车辆，一个重要方面是地面效应。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。在这项研究中，一个特殊的实验装置将被使用：一个250米的水拖曳水池设施的TU柏林，使现实的边界条件和高雷诺数的水下模型在静止的地面上移动。基于预期的结果，工业界和学术界可以开发和实现创新技术，包括自适应底部襟翼和自动驾驶，以显着降低空气动力学阻力，从而减少未来重型车辆的二氧化碳排放。

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.