Investigation of the Unsteady Wake behind a Generic Tractor-Trailer with Different Boundary Conditions

由于迫切的立法和客户对低排放和低油耗的要求，现代汽车工业面临着严峻的挑战。排放量的很大一部分是由长途运输的重型卡车造成的。在巡航高速公路上，大部分卡车的燃料消耗在克服其气动阻力上，这主要来自拖车后面的尾流区域。因此，当有效控制时，该区域提供了最大的潜力来减少其整体阻力。最近，拖拉机几何形状的改变和附加装置的应用提供了一些阻力改善。然而，目前大多数关于被动和主动流量控制方法的研究都是考虑这些方法的综合效果，而没有详细研究其潜在机制。此外，还很少强调对牵引车-拖车尾流的详细调查。该区域流体力学非常复杂，并且由高度湍流，非静止结构主导，这仍然是钝体空气动力学领域的一个挑战。迄今为止，对这些结构的三维、随时间变化的相互作用所知的细节还不够。特别是对于道路车辆来说，地面效应是一个重要的方面。许多研究考虑一个静止的地面或在某些情况下一个移动的带。然而，这些实验边界条件只模拟了车辆在道路上行驶的情况。这些不同边界条件的影响还没有得到适当的解决。此外，实验研究的雷诺数差异很大，但对其影响的重视不够。考虑到这一主题对科学界和工业界的重要性，拟议的研究旨在解决这些未解决的问题和不一致之处。一个通用的1/10比例牵引车-拖车模型的尾迹将在三种不同的测试设备中进行测试，这些设备具有不同的实验边界条件和广泛的雷诺数范围。柏林工业大学的一个闭环风洞将在静止的地面上模拟地面效应，而瑞典查尔默斯理工学院的一个类似大小的风洞提供了一个移动的地面。第三个测试设施是柏林工业大学的一个水拖箱，用于研究移动模型在静止地面上的影响。对不同边界条件下模型尾流结构的时间分辨流场测量结果进行了分析和比较。对尾迹流场与机体基压之间相互作用的进一步了解，将成为减小尾迹尺寸的被动（如整形）和主动控制的基础。在拟议的研究中，广泛的基线调查将有助于在通过流体振荡器进行主动分离控制的模型的后表面上应用适当的基础襟翼几何形状。

Due to pressing legislation and customer requirements on low emissions and fuel consumption, the modern vehicle industry is faced by demanding challenges. A significant portion of emissions is contributed by long hauling heavy trucks. At cruising highway velocities most of the trucks fuel is consumed by overcoming its aerodynamic drag which largely originates from the wake region behind the trailer. Therefore, this region provides the most potential for reducing its overall drag when effectively controlled. Recently, alterations in the tractors geometry and the application of add-on devices have provided some drag improvements. However, most of the current research on passive and active flow control methods is considering an integral effect of these methods without detailed investigation of the underlying mechanisms. Also, little emphasis has yet been placed on the detailed investigation of the tractor-trailers wake without alterations. This region is fluid mechanically very complex and dominated by highly turbulent, non-stationary structures which remain a challenge in the field of bluff body aerodynamics. Only insufficient detail on the three-dimensional, time-dependent interaction of these structures is known to date. Especially for road vehicles an important aspect is the ground effect. Many studies consider a stationary ground or in some cases a moving belt. However, these experimental boundary conditions only simulate the conditions of a vehicle moving on a road. The impact of these differing boundary conditions has not been properly addressed yet. Also, experimental studies vary significantly in Reynolds number without sufficient emphasis on its effect. Considering the significance of this topic for the scientific community and industry, the proposed study is aimed at addressing some of these unanswered questions and inconsistencies. The wake of a generic 1/10th-scale tractor-trailer model will be examined in three different test facilities with different experimental boundary conditions and over a wide range of Reynolds numbers. A closed-loop wind tunnel at the TU Berlin will simulate the ground effect with a stationary ground, whereas a similarly sized wind tunnel at Chalmers Institute of Technology (Sweden) provides a moving ground. The third test facility is a water towing tank at the TU Berlin to study the effects of a moving model over a stationary ground. Time-resolved flow field measurements of the models wake structures will be analysed and compared for different boundary conditions. The increased knowledge of the interaction between the flow field in the wake and the bodys base pressure will form a cornerstone in passive (e.g., shaping) and active control for minimizing the wake size. In the proposed study, the extensive baseline investigation will aid the application of appropriate base flap geometries to the rear face of the model supported by active separation control through fluidic oscillators.