Modeling clear-air turbulence with vortices using parameter-identification techniques
Modeling clear-air turbulence with vortices using parameter-identification techniques
复制标题
使用参数识别技术对带有涡流的晴空湍流进行建模
DOI：
10.2514/3.20176
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发表时间：
1984
期刊：
影响因子：
--
通讯作者：
R. S. Mehta
中科院分区：
文献类型：
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作者：
R. S. Mehta
与晴空湍流相关的风的涡旋模型被证明对描述实际的航空公司遇到严重湍流是有用的。该模型由嵌入在势场中的固体芯的旋涡阵列组成。使用改进的牛顿-拉夫森算法识别涡旋的大小和强度及其位置等参数。使用手动辨识启动方案来最小化初始参数估计中的误差，并且发现辨识算法对于剩余的误差是稳健的。通过对一架商用客机的湍流过程的分析，证明了该模型和估算方法的成功。分析发现，在这次相遇中，中心直径为1000英尺的涡旋，切向速度为87英尺/S。李尔-空气湍流(CAT)是一种鲜为人知的现象，发生在对流层中上层和平流层下部，对飞机构成安全威胁。最严重的情况是具有一定周期性的突然、猛烈的骚乱。美国国家航空航天局艾姆斯研究中心和美国国家运输安全委员会正在调查这一问题。由于CAT的持续时间和发生距离都很小，一直是一个很难研究的现象。然而，在最近的过去，配备了数字飞行数据记录器的宽体商用飞机与CAT相遇过几次，来自这些记录器的数据，以及来自空中交通管制(ATC)雷达记录的额外数据，使得有可能获得与CAT相遇相关的风的详细描述。利用这些风数据和前人对CAT的理论研究，建立了CAT过程中的风环境模型。这些研究1‘6预测CAT是大气中稳定分层的切变层破裂的结果，这种情况被称为开尔文-亥姆霍兹不稳定性。剪切层卷曲成一个旋涡阵列，形成开尔文“猫眼”图案(图1)。涡旋的旋转方向取决于剪切层分解的方式，如参考文献中所讨论的。7.为了与实际遭遇的数据进行比较/理论，使用了参数识别技术来将涡旋阵列模型产生的风与数据进行匹配。这已经在两次实际相遇中成功完成，并在之前的一篇论文中得到了报道。7类似的技术早先曾被用于研究飞机的操纵涡流。8本文的目的是描述涡流模型以及用于将该模型与猫相遇中发现的风进行匹配的参数识别技术。首先，描述了涡流模型及其与飞行器飞行轨迹的关系。然后，简要讨论了确定模型参数的算法，并对模型参数的确定进行了说明。
A vortex model of winds associated with clear-air turbulence is shown to be useful for characterizing actual airline encounters with severe turbulence. The model consists of an array of vortices with solid-body cores embedded in a potential flowfield. Parameters such as the size and strength of the vortices and their locations are identified using a modified Newton-Raphson algorithm. A manual identification startup scheme is used to minimize errors in the initial parameter estimates, and the identification algorithm is found to be robust in regard to the remaining errors. The analysis of a turbulence experience involving a commercial airliner demonstrates the success of the model and estimation procedure. The analysis finds vortices with core diameters of 1000 ft and tangential velocities of 87 ft/s in this encounter. LEAR-air turbulence (CAT) is a little-understood phenomenon that occurs in the mid to upper troposphere and the lower stratosphere and that poses a safety hazard to aircraft. The most severe cases are characterized by sudden, violent disturbances with definite periodicity. This problem is being investigated by the NASA Ames Research Center in con- junction with the National Transportation Safety Board. Because of the small scale in both duration and distance over which CAT occurs, it has been a difficult phenomenon to study. However, in the recent past, wide-bodied commercial aircraft equipped with digital flight-data recorders have had a few encounters with CAT, and the data from these recorders, along with additional data from air-traffic control (ATC) radar records, have made it possible to obtain a detailed description of the winds associated with CAT encounters. A model of the wind environment during CAT has been developed using these wind data and previous theoretical studies of CAT. These studies1'6 predict that CAT is a result of the breakdown of stably stratified shear layers in the at- mosphere, a condition known as Kelvin-Helmholtz instability. The shear layers roll up into a vortex array which forms in a Kelvin "cat's eyes" pattern (Fig. 1). The direction of rotation of the vortices depends on the way the shear layer breaks down, as discussed in Ref. 7. To compare /theory with data from actual encounters, parameter-identification techniques have been used to match the winds produced by a vortex-array model to the data. This has been done successfully with two actual encounters and is reported in a previous paper.7 A similar technique had been used earlier to study an airplane's traling vortices.8 The pur- pose of this paper is to describe the vortex model and the parameter-identification techniques used to match the model to the winds found in a CAT encounter. First, a vortex model and its relation to an aircraft flight path is described. Next, the algorithm used to determine the model parameters is discussed briefly, followed by an explana-