Abstract This paper presents the numerical study on the flight behaviour of spherical compact debris in a tornado-like wind field. The tornado-like vortex corresponding to a swirl ratio of 0.7 was generated using Large-eddy Simulation and the trajectories of 2250 individual debris particles placed in the flow were computed using Lagrangian-particle tracking. The debris corresponded to five groups (A, B1, B2, B3 and C) based on the value of the Tachikawa number (K) which ranged between 0.6 and 2.5. An analysis of the simulated flow field revealed that the tornado-like vortex consisted of two main features - a core at the centre with low velocity ( ∼ 0.25 m/s) which was surrounded by thick vortex wall composed of high velocity magnitudes ( ∼ 9.4 m/s). Updraft flows were observed around the core of the vortex and as a result, debris positioned around the core radius region were found to be 24% more likely to become wind-borne than debris positioned at the vortex wall region. Three groups of debris (B1, B2 and B3) with varying mass and density were studied for the aerodynamic similarity by retaining the fixed value of K = 1.2; all three debris groups exhibited the propensity to travel with similar flight characteristics. An analysis of the data pertaining to the fight behaviour of the three debris group (A, B1 and C) with varying K revealed that the low mass debris group A (K = 2.5) had the highest propensity to become wind-borne and was more likely to travel for the longest time with considerable variability observed in individual debris trajectories. However, somewhat counterintuitively, the high mass debris group C (K = 0.6) were found to have the furthest impact range despite their short flight duration; this was due the high mass debris being ejected out of the vortex with greater inertia, while debris with a lower mass had a tendency to be trapped in the flow that circulates around the vortex core.

中文翻译：

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类龙卷风涡旋中碎片飞行的数值研究

摘要 本文介绍了类似龙卷风风场中球形致密碎片飞行行为的数值研究。使用大涡模拟生成对应于 0.7 漩涡比的龙卷风状涡流，并使用拉格朗日粒子跟踪计算放置在流中的 2250 个单独碎片粒子的轨迹。根据立川数 (K) 介于 0.6 和 2.5 之间的值，碎片对应于五组（A、B1、B2、B3 和 C）。对模拟流场的分析表明，类似龙卷风的涡旋由两个主要特征组成 - 一个位于中心的低速 (~ 0.25 m/s) 核心，周围环绕着由高速度级 (~ 9.4小姐）。在涡旋核心周围观察到上升气流，因此，发现位于核心半径区域周围的碎片比位于涡旋壁区域的碎片更容易被风传播。通过保持K=1.2的固定值，研究了质量和密度不同的三组碎片（B1、B2和B3）的气动相似性；所有三个碎片组都表现出具有相似飞行特性的旅行倾向。对有关具有不同 K 的三个碎片组（A、B1 和 C）的战斗行为的数据进行的分析表明，低质量碎片组 A（K = 2.5）具有最高的风载倾向，并且更多在单个碎片轨迹中观察到相当大的可变性的情况下，可能会传播最长的时间。然而，有点违反直觉的是，大质量碎片群 C (K = 0. 6) 尽管飞行持续时间很短，但被发现具有最远的影响范围；这是因为质量大的碎片以更大的惯性从涡旋中喷出，而质量较小的碎片倾向于被困在围绕涡旋核心循环的流动中。