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，现代汽车行业面临着严峻的挑战。很大一部分排放是由长途运输的重型卡车贡献的。在公路巡航速度下，大多数卡车的燃料是通过克服其空气动力阻力来消耗的，而空气动力阻力主要来自拖车后面的尾流区。因此，当有效控制时，该区域提供了最大的潜力来减少其总体阻力。最近，拖拉机几何结构的改变和附加装置的应用提供了一些阻力改进。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，而没有对其内在机理进行详细的研究。此外，对没有改动的拖拉机拖车尾迹的详细调查也很少受到重视。这一区域的流体力学非常复杂，并且以高度湍流的非定常结构为主，这在钝体空气动力学领域仍然是一个挑战。到目前为止，关于这些结构的三维、依赖于时间的相互作用的细节还不够详细。尤其对于道路车辆来说，地面效应是一个重要的方面。许多研究认为地面是静止的，或者在某些情况下是移动的地带。然而，这些实验边界条件只模拟了车辆在道路上行驶的条件。这些不同边界条件的影响尚未得到适当处理。此外，实验研究在雷诺数方面差异很大，对其影响没有足够的重视。考虑到这一专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矛盾之处。一个普通的1/10比例的拖拉机-挂车模型的尾迹将在三个不同的实验设备中进行测试，这些设备具有不同的实验边界条件和较大的雷诺数范围。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将提供一个移动的地面。第三个测试设施是柏林工业大学的一个水拖曳水箱，用于研究静止地面上移动模型的影响。对不同边界条件下模型尾迹结构的时间分辨流场测量结果进行了分析和比较。对尾迹内流场和机身基本压力之间相互作用的更多了解将形成被动(例如，整形)和主动控制的基石，以最小化尾迹尺寸。在拟议的研究中，广泛的基线调查将有助于将适当的底部襟翼几何形状应用于通过流体振荡器进行主动分离控制的模型的背面。

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.