Experimental and numerical investigations of vortex decay in a rotating system.

直升机周围的复杂流场是由涡及其相互作用所支配的。这里特别重要的是在叶片处发展并与气流对流的叶尖涡流。一方面，这些涡流在某些飞行情况下会通过与后续叶片的相互作用产生噪音（BVI）;另一方面，靠近地面的旋翼尾流也会激起松散的颗粒，如沙子或雪。由此导致的视力丧失会带来重大的安全风险。在这方面，涡流的形成、守恒和衰减以及它们的运动是飞行物理学的一个重要课题。此外，多年来，由于数值耗散过大，对这些涡流的模拟研究受到很大的影响，因此无法保证涡流的物理正确性。然而，最近，可以取得相当大的进展，通过改进的方法，更高阶以及精细的空间分辨率，使涡流被保存足够长的时间。然而，与此同时，可以观察到新的衰变过程和二级结构，其物理机制目前尚不清楚，因为迄今为止还没有足够高质量的实验结果来可靠地排除数值误差。这就是拟议项目的用武之地。在实验方面，将利用目前的高精度测量技术对实际相关的衰减过程，特别是悬停飞行中的翼尖涡流进行详细的研究。重点是在涡年龄的物理机制，如不稳定性或涡配对，有助于衰减的主要结构，以及哪些扰动参数发挥作用的问题。同时，这将为数值模拟中应在何处以及如何发生可比较的衰减设定标准。要探讨的是，程序和模型的数值变化影响这些衰减过程，并从中得出适当的指导方针，使模拟的涡流衰减类似于实际的位置和机制尽可能接近。在这种情况下，实验确定的依赖于操作参数也要考虑在内，以便正确的过程是represented.Various机制的短波和长波的不稳定性和涡配对是已知的基本调查对个别涡。总的来说，目前的项目旨在澄清这些可以转移到直升机旋翼上的旋转系统的程度，以及如何在数值模拟中最好地再现它们。在这些发现的基础上，进一步的发展可以有助于更有效和更安全的直升机旋翼。

The complex flow field around helicopters is dominated by vortices and their interaction. Of particular importance here are the tip vortices that develop at the blades and are convected with the flow. On the one hand, these vortices generate noise (BVI) in certain flight situations through interaction with following blades; on the other hand, this rotor wake near the ground can also stir up loose particles such as sand or snow. The resulting loss of vision poses a significant safety risk. In this respect, the formation, conservation and decay of vortices as well as their motion define an important topic of flight physics.In addition, for many years the investigation of these vortices with the help of simulations was considerably impaired by too large numerical dissipation, so that the physically correct preservation of the vortices was not guaranteed. Recently, however, considerable progress could be achieved by improved methods of higher order as well as refined spatial resolution, enabling the vortices to be preserved sufficiently long. At the same time, however, new decay processes and secondary structures could be observed, whose physical mechanisms are currently unclear, since so far no sufficiently high-quality experimental results are available to rule out numerical errors reliably. This is where the proposed project comes in. On the experimental side, detailed investigations of the actually relevant decay processes, in particular of the tip vortices in hovering flight, are to be carried out using current high-precision measurement technology. The focus is on the question at which vortex age which physical mechanisms, such as instabilities or vortex pairing, contribute to the decay of the primary structures, and which disturbance parameters play a role. At the same time, this will set the standard for where and how a comparable decay should occur in the numerical simulation. It is to be explored which numerical variations of procedures and models influence these decay processes and to derive appropriate guidelines from this, so that the simulated vortex decay resembles the actual one in location and mechanism as close as possible. In this context, the experimentally identified dependence on operating parameters is also to be taken into account, so that the correct process is represented.Various mechanisms of short- and long-wave instabilities and vortex pairing are known from fundamental investigations on individual vortices. Overall, the current project is intended to clarify the extent to which these can be transferred to the rotating system on the helicopter rotor, and how they can best be reproduced in numerical simulations. Building on these findings, further developments could then contribute to more efficient and safer helicopter rotors.