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Experimental investigation of the near-surface flow dynamics in downburst-like impinging jets
Environmental Fluid Mechanics ( IF 2.2 ) Pub Date : 2022-05-30 , DOI: 10.1007/s10652-022-09870-5
Federico Canepa, Massimiliano Burlando, Djordje Romanic, Giovanni Solari, Horia Hangan

Abstract

Downbursts are strong downdrafts that originate from thunderstorm clouds and create vigorous radial outflows upon hitting the ground. This study is part of the comprehensive experimental research on downburst outflows produced as large-scale impinging jets in the WindEEE Dome simulator at Western University, Canada. The 2800 tests carried out form the largest database of experimental measurements on downburst winds developed thus far, which is made available to the public in its whole and described in detail in a complementary study. Therefore, the current manuscript merely focuses on the data post-processing outcomes and interpretation of results from a selected subset of measurements. Impinging jets are here simulated as transient phenomena in which velocity time series are characterized by a sudden ramp-up of velocity, followed by the velocity peak, a short statistically stationary region, and the final velocity slowdown, as it is expected to occur in the actual downbursts. A dominant velocity peak that was systematically observed in all velocity records is associated with the radial advection of the primary vortex in the outflow. Depending on the radial distance from the downdraft, the primary vortex was sometimes preceded by a secondary, much smaller, vortex close to the surface. Vertical profiles of mean velocity and turbulence intensity are for the first time characterized through the extent of a downburst-like event in the spatiotemporal domain. Particularly, these profiles rapidly change in relation to the passage of the primary vortex and consequent variation of the surface layer thickness. This study lays out a foundation for an experimental model of non-stationary downburst outflows to come.



中文翻译:

下暴式冲击射流中近地表流动动力学的实验研究

摘要

下暴流是来自雷暴云的强烈下沉气流,在撞击地面时会产生强烈的径向外流。本研究是加拿大西部大学 WindEEE Dome 模拟器中大规模撞击射流产生的下暴流综合实验研究的一部分。进行的 2800 次测试形成了迄今为止开发的最大的下暴风实验测量数据库,该数据库全部向公众提供,并在补充研究中详细描述。因此,目前的手稿仅关注数据后处理结果和对选定测量子集结果的解释。撞击射流在这里被模拟为瞬态现象,其中速度时间序列的特征是速度突然上升,紧随其后的是速度峰值、一个短暂的统计静止区域和最终的速度减慢,因为它预计会在实际的下暴中发生。在所有速度记录中系统地观察到的主要速度峰值与流出物中主涡旋的径向平流有关。根据与下降气流的径向距离,主涡旋之前有时会出现一个靠近地表的、小得多的次生涡旋。平均速度和湍流强度的垂直剖面首次通过时空域中类似下暴事件的程度来表征。特别地,这些轮廓相对于主涡流的通过和随之而来的表面层厚度的变化而迅速变化。

更新日期:2022-05-31
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