Experimental investigation of the effect of coherent secondary structures upon a tip vortex

相干二级结构对尖端涡流影响的实验研究

• 批准号: EP/H030360/1
• 负责人: David Birch
• 金额: $ 12.62万
• 依托单位: University of Surrey
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2010
• 资助国家: 英国
• 起止时间: 2010 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FH030360%2F1
• 关键词: Experimental; investigation; effect; coherent; secondary

A vortex occurs when some of the fluid within a larger volume is caused to rotate, and is one of the most important phenomena in fluid mechanics. Vortices may range in size from microns (such as those formed around the beating wings of a mosquito) to hundreds of kilometers (such as hurricanes), and are of great importance in a large number of engineering applications. Vortex flows are of particular interest in the aircraft industry, since part of an aircraft's drag is the result of the formation of large vortices by the wing tips. As the engines propel the aircraft forward, part of the engine power is used to no other benefit than stirring the air behind the aircraft. If the wing tip vortex could be reduced in strength, the aircraft drag would decrease, reducing the amount of fuel burned. This would lead to both decreased carbon emissions and operating costs. The large vortices in the aircraft wake also pose a danger to other aircraft, so a minimum distance must be kept between them. Since the vortices are strongest at low speed such as during takeoff and landing, this wake hazard is what limits runway capacity. If the vortex could be destabilized and forced to break up and dissipate more quickly, airports would be able to accommodate a larger number of flights without needing additional runways. The strength and stability of a wing-tip vortex can be greatly reduced by introducing turbulence (or random disturbances) into the flow ahead of the wing. These disturbances interact with the vortex, transport energy away from it and reduce its strength. However, in wind tunnel tests, the disturbances are usually introduced by placing a series of heavy bars ahead of the wing; on a real aircraft, this would not be possible. Instead, in this study, small and carefully designed 'bumps' will be strategically placed on the surface of the wing in order to generate similar disturbances.Since there are infinitely many possible combinations of bump geometries and locations, it is first necessary to study the vortex and how it is affected by smaller disturbances. To begin with, despite the engineering importance of these flows, it still isn't clear whether or not there are naturally-occurring disturbances inside a vortex. Also, vortices are in many ways analogous to the flow over flat walls. Though similar disturbances occur naturally in wall flows and play a vital role in their development, very little attention has been given to the role played by the disturbances in vortex flows. If it can be shown that very small disturbances can have an effect on large vortices, this in itself would be an extremely important result: many flow simulation computer codes assume that the direct interaction between very small disturbances and very large vortices is impossible. Finally, all vortices- regardless of how they were generated, how strong they are or how 'disturbed' they may be- appear to evolve in exactly the same way. While this similarity has already been noticed, it is still not clear why it happens. Once the vortex and the way it responds to disturbances is better understood, this understanding will be used to intelligently develop a wing surface which can reduce aircraft drag (cutting down both cost and carbon emissions) and increase airport capacity.

当较大体积内的一些流体发生旋转时，就会产生涡流，这是流体力学中最重要的现象之一。漩涡的大小可以从微米（比如蚊子拍打翅膀周围形成的漩涡）到数百公里（比如飓风）不等，在大量的工程应用中非常重要。飞机工业对涡旋流特别感兴趣，因为飞机阻力的一部分是由机翼尖端形成的大涡流的结果。当发动机推动飞机前进时，发动机的部分动力除了搅动飞机后面的空气外没有其他好处。如果能降低翼尖涡的强度，飞机阻力就会减小，燃油消耗也会减少。这将减少碳排放和运营成本。飞机尾流中的大涡流也对其他飞机构成危险，因此它们之间必须保持最小距离。由于涡旋在起飞和降落等低速时最强，这种尾流危害限制了跑道容量。如果能破坏涡流的稳定，迫使它更快地破裂和消散，机场就能容纳更多的航班，而不需要额外的跑道。通过在机翼前方的气流中引入湍流（或随机扰动），可以大大降低翼尖涡的强度和稳定性。这些干扰与涡旋相互作用，将能量从涡旋中转移出去，并降低涡旋的强度。然而，在风洞试验中，干扰通常是通过在机翼前方放置一系列重杆来引入的；在真正的飞机上，这是不可能的。相反，在这项研究中，小而精心设计的“凸起”将被战略性地放置在机翼表面，以产生类似的干扰。由于有无限多种可能的碰撞几何形状和位置组合，首先有必要研究涡旋及其如何受到较小的干扰。首先，尽管这些气流在工程上具有重要意义，但我们仍然不清楚涡旋内部是否存在自然发生的扰动。此外，涡旋在许多方面类似于平壁上的流动。虽然类似的扰动在壁面流动中自然存在，并对壁面流动的发展起着至关重要的作用，但对涡旋流动中扰动所起的作用却很少关注。如果能够证明非常小的扰动可以对大的涡产生影响，这本身就是一个极其重要的结果：许多流动模拟计算机代码假设非常小的扰动和非常大的涡之间的直接相互作用是不可能的。最后，所有的漩涡——不管它们是如何产生的，它们有多强，或者它们可能有多“受干扰”——似乎都以完全相同的方式进化。虽然这种相似性已经被注意到，但尚不清楚为什么会发生这种情况。一旦对涡旋及其对扰动的反应方式有了更好的了解，这种理解将被用于智能地开发一种机翼表面，这种机翼表面可以减少飞机阻力（降低成本和碳排放），并增加机场容量。

项目成果

Calibration and Use of n-Hole Velocity Probes

• DOI: 10.2514/1.j053130
• 发表时间: 2015-02-01
• 期刊: AIAA JOURNAL
• 影响因子: 2.5
• 作者: Shaw-Ward, Samantha;Titchmarsh, Alex;Birch, David M.
• 通讯作者: Birch, David M.

Optimal Calibration of Directional Velocity Probes

• DOI: 10.2514/1.j056762
• 发表时间: 2018-07-01
• 期刊: AIAA JOURNAL
• 影响因子: 2.5
• 作者: Shaw-Ward, Samantha;McParlin, Stephen C.;Birch, David M.
• 通讯作者: Birch, David M.

Boundary conditions and vortex wandering

边界条件和涡流

• DOI: 10.1017/jfm.2014.169
• 发表时间: 2014
• 期刊: Journal of Fluid Mechanics
• 影响因子: 3.7
• 作者: Jammy S