Identification and modelling of coherent structures in trailing vortex break-up

尾涡是飞机飞行的固有特征，是飞机尾迹中观察到的漩涡空气运动的主要原因。它们对飞机构成飞行中的危险，因此对飞行路线和机场起飞和降落的时间构成限制。在航空喷雾应用中，尾涡对喷气发动机尾气污染物和农药的扩散也有很大影响。目前正在进行大量的研究工作来预测并在可能的情况下控制尾涡的发展。一般来说，目标是通过激发存在于其中的固有不稳定模式来限制涡旋的寿命。对这些不稳定性进行了广泛的理论研究，但在实验室中直接测试它们的存在的尝试相对较少。尽管如此，已经提出了许多限制涡流寿命的装置，其中一些已经取得了一定的成功。安装在翼尖上的展向定向喷嘴是一种已经证明有能力降低旋流速度和增加旋涡扩散速度的装置。目前的研究方案是对由叶尖喷流形成的尾涡进行实验室测试，并确定激发的涡不稳定性模式和随后产生的涡破碎的相干结构。然后将这项研究的结果与现有的涡旋不稳定性理论进行比较，以期更好地理解这一现象。特别是，如果扰动设计得更精确，就有可能减少实现涡旋破碎所需的能量。实验方法将包括流动成像和先进的模式识别技术。一旦确定，还将尝试对这些“相干结构”对涡旋发展的影响进行建模。最终，对旋涡动力学的更好理解将导致更有效的旋涡控制。

Trailing vortices are an inherent feature of aircraft flight and are primarily responsible for the swirling air motions observed in an aircraft wake. They present an in-flight hazard to aircraft and therefore place constraints on flight paths and the timing of take-off and landings at airports. Trailing vortices also have a strong influence on the dispersion of jet engine exhaust pollutants and pesticides in aerial spray applications. There is a substantial ongoing research effort to predict and, if possible, control the development of trailing vortices. Generally the objective is to limit vortex longevity by exciting the inherent modes of instability that exist within them. There has been extensive theoretical study of these instabilities but relatively few attempts to directly test for their presence in the laboratory. In spite of this fact many devices have been proposed to limit vortex longevity and some have been moderately successful. One device that has demonstrated the ability to reduce the rate of swirl velocity and increase the rate of vortex diffusion is spanwise directed air jets mounted on the wing tips. The present research proposal is to conduct laboratory testing on a trailing vortex formed with tip jets and identify the modes of vortex instability excited and the subsequent coherent structures of vortex break-up that they produce. A comparison will then be made between the findings of this study and the existing theories of vortex instability with the expectation that the phenomenon can be better understood. In particular it may be possible to reduce the energy required to achieve vortex break-up if the disturbance is more precisely designed. The experimental methods used will include flow imaging and advanced pattern recognition techniques. Once identified attempts will also be made to model the effect of these "coherent structures" on vortex development. Ultimately an improved understanding of vortex dynamics will lead to more effective vortex control.