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Experimental investigation of turbulent structures and non-equilibrium effects in axial wake vortices via particle image velocimetry.

机译：通过粒子图像测速技术对轴向尾流涡流中湍流结构和非平衡效应的实验研究。

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摘要

Vortices are a common phenomenon in fluid flows that arise as kinetic energy dissipates into heat via viscous interaction. They arise naturally at large scales in the form of dust devils, tornadoes, and as a counter-rotating vortex pair in the wake of aircraft. It is important to understand the conditions leading to their formation, their duration, and their dissipation in order to forecast or prevent undesirable effects. Among these deleterious effects is a decrease in safety of aircraft operations in the wake of other aircraft, an extremely common situation at airports around the world. A large number of mathematical models and experimental data sets exists to help explain various aspects of axial wake vortex behavior, but current models fail to explain why many vortices remain tightly wound with slowly decaying azimuthal velocities about their cores the length of time for which they have been observed. The current study builds upon the theoretical work of Ash, Zardadkhan and Zuckerwar [Ash et al., 2011], and tests specific attributes of a turbulent axial vortex for agreement with non-equilibrium pressure relaxation theory. This theory provides an exact solution to a modified version of the Navier-Stokes equations for an axial vortex, with a resulting velocity model that agrees with leading empirical models. In the present investigation, axial wake vortices were created with a bi-wing vortex generator in a low speed wind tunnel, at free stream velocities between 15 and 33 m/s. Stereo particle image velocimetry was employed to map three dimensional velocity vectors at positions between 5.4 and 10 chord lengths downstream of the vortex generator, and at a sampling rate of 1Hz for 200 seconds. A Reynolds time averaging approach was employed to express instantaneous velocity measurements as localized mean and fluctuating components and to study turbulent structures within the vortices. Periodicity in turbulent energy and Reynolds stress structures was observed by comparing vortex velocity fields normalized by age, based on free stream velocity and downstream distance. The cores of these vortices appeared to periodically ingest turbulent energy and compress it into approximately one half of local core radii. The cyclical ingestion of turbulence was shown to have the effect of tightening the core radius in the wake of the vortex generator center body. If this phenomenon persists for the life of the vortex, it could provide an explanation for the longevity of the azimuthal velocity component, as observed in natural wake vortices.
机译：涡旋是流体流动中的一种普遍现象，当动能通过粘性相互作用耗散到热中时会产生涡流。它们自然而然地以尘土飞龙，龙卷风的形式自然地出现，并且在飞机尾随时作为反向旋转的涡流对出现。重要的是要了解导致其形成的条件，持续时间和耗散条件，以便预测或防止不良影响。在这些有害影响中，有在其他飞机之后导致飞机运行安全性下降的现象，这是世界各地机场极为普遍的情况。存在大量的数学模型和实验数据集来帮助解释轴向尾流涡流行为的各个方面，但是当前模型无法解释为什么许多涡流仍然围绕其核心缓慢衰减的方位角速度保持紧密缠绕的时间长度被观察到。当前的研究基于Ash，Zardadkhan和Zuckerwar的理论工作[Ash et al。，2011]，并测试了湍流轴向涡流的特定属性，以与非平衡压力松弛理论相吻合。该理论为轴向涡旋的Navier-Stokes方程的修改版提供了精确的解决方案，其最终速度模型与领先的经验模型相符。在本研究中，在低速风洞中使用双翼涡流发生器以15至33 m / s的自由流速度创建轴向尾流涡流。使用立体粒子图像测速仪将三维速度矢量映射到涡流发生器下游的5.4和10弦长之间的位置，并以1Hz的采样率进行200秒。使用雷诺时间平均方法将瞬时速度测量值表示为局部平均值和波动分量，并研究涡旋内的湍流结构。通过根据自由流速度和下游距离比较按年龄归一化的涡旋速度场，观察到湍流能量和雷诺应力结构的周期性。这些漩涡的核心似乎会周期性地吸收湍流能量，并将其压缩到局部核心半径的一半左右。结果表明，在涡流发生器中心体中，周期性摄入湍流具有收紧核半径的作用。如果这种现象在涡流的寿命中持续存在，则可以解释在自然尾涡中观察到的方位角速度分量的寿命。

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  • 作者

    Ely, Jeffry William.;

  • 作者单位

    Old Dominion University.;

  • 授予单位 Old Dominion University.;
  • 学科 Aerospace engineering.;Mechanical engineering.
  • 学位 M.S.
  • 年度 2016
  • 页码 161 p.
  • 总页数 161
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 古生物学;
  • 关键词

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