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。排放的很大一部分是由长途运输的重型卡车造成的。在高速公路巡航速度下，大部分卡车燃料通过克服其气动阻力而消耗，该气动阻力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小其总体阻力。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，目前对被动和主动流量控制方法的研究大多是考虑这些方法的整体效果，而没有详细研究其内在机制。此外，很少有人把重点放在详细调查的拖拉机拖车尾流没有改变。该区域是流体机械非常复杂的，并且由高度湍流的非静止结构主导，这在海崖体空气动力学领域中仍然是一个挑战。只有不足的细节，这些结构的三维，随时间变化的相互作用是已知的日期。特别是对于公路车辆，一个重要方面是地面效应。许多研究考虑静止的地面，或者在某些情况下考虑移动的带。然而，这些实验边界条件仅模拟车辆在道路上移动的条件。这些不同边界条件的影响尚未得到适当解决。此外，实验研究在雷诺数上变化很大，但没有充分强调其影响。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其中一些悬而未决的问题和不一致之处。将在三个不同的测试设施中使用不同的实验边界条件和较宽的雷诺数范围来检查通用1/10比例拖拉机拖车模型的尾流。柏林工业大学的一个闭环风洞将模拟静止地面的地面效应，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。第三个试验设施是柏林工业大学的一个水拖曳水池，用于研究静止地面上移动模型的影响。将对不同边界条件下的模型尾流结构的时间分辨流场测量结果进行分析和比较。对尾流中的流场和机体的基础压力之间的相互作用的了解的增加将形成被动（例如，成形）和用于最小化尾流尺寸的主动控制。在所建议的研究中，广泛的基线调查将有助于在通过射流振荡器的主动分离控制支持的模型后表面上应用适当的底部襟翼几何形状。

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.