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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >Lidar and numerical studies on the different evolution of vortex pair and secondary wake in young contrails
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Lidar and numerical studies on the different evolution of vortex pair and secondary wake in young contrails

机译：激光雷达和年轻轨迹转换过程中涡对和次级尾流不同演变的数值研究

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Vortex-regime evolution of contrails is investigated by focusing on the role of ambient humidity. Lidar cross-section measurements and observational analysis are combined with numerical simulations of fluid dynamics and microphysics. Contrail evolution behind four-turbofan aircraft is classified into three different scenarios. In the case of ice-subsaturated air, a visible pair of wingtip vortices is formed that disappears at the end of the vortex regime. In case of ice supersaturation, a diffuse secondary wake evolves above the wingtip vortices. It is due to detrainment of ice particles growing by sublimation of ambient humidity. A vertical wake-gap opens between the wingtip vortices and the secondary wake. It is due to subsaturated air moving upward along the outer edges of the sinking vortex tubes accumulating around the upper stagnation point of the vortex system. The vertical wake-gap preferably occurs in the wake of heavy (four turbofans) aircraft, since the vortices behind light aircraft migrate down too slowly. The secondary wake is composed of nonspherical particles larger than the ones in the wingtip vortices which are spherical particles and/or particles smaller than approx 0.5 #mu#m. In most cases the secondary wake is the only part of a contrail that persists after vortex breakdown. This is because the ice in the vortex tubes evaporates due to adiabatic heating as the vortices travel downward. Only in the rare case of higher ambient ice supersaturation (>2%) do both parts of a contrail contribute to the persistent ice cloud. The number of ice crystals initially formed is typically reduced by a factor of 200 by evaporation (60% ambient humidity). This leads to a high population of interstitial particles. The results imply that formation of persistent contrails can be minimized by technical means.
机译：通过关注环境湿度的作用来研究凝结尾迹的涡流区演变。激光雷达的横截面测量和观测分析与流体动力学和微观物理学的数值模拟相结合。四涡轮风扇飞机背后的轨迹演变可分为三种不同的情况。在冰不饱和的空气中，形成了一对可见的翼尖涡流，这些涡流在涡流结束时消失了。在冰过饱和的情况下，在翼尖涡流上方会形成弥散的次级尾流。这是由于环境湿度升华导致冰粒生长受阻。在翼尖涡流和次要尾流之间打开垂直尾流间隙。这是由于过饱和空气沿着沉降的涡流管的外边缘向上移动，并在涡流系统的上止点附近积聚。垂直尾流间隙最好发生在重型飞机（四架涡轮风扇飞机）的尾流中，因为轻型飞机后面的涡流向下移动的速度太慢。次级尾流由非球形颗粒组成，该非球形颗粒大于翼尖涡旋中的球形颗粒和/或小于约0.5＃μm的颗粒。在大多数情况下，次要尾流是凝结尾迹中涡流破裂后唯一持续存在的部分。这是因为随着涡流向下传播，由于绝热加热，涡流管中的冰蒸发。仅在极少数情况下，较高的环境冰过饱和度（> 2％）时，凝结尾迹的两个部分才有助于持久的冰云。最初形成的冰晶数量通常会因蒸发（环境湿度为60％）而减少200倍。这导致大量的间隙颗粒。结果表明，可以通过技术手段将持久性凝结尾迹的形成降至最低。

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