This experimental study investigates the falling characteristics of spheroidal particles with varying geometrical anisotropy, characterized by the aspect ratio (). The aspect ratio is systematically varied from prolate () to oblate (), while the Archimedes number (), representing the ratio of gravitational force to viscous force, spans from 491 to 1389. The density ratio between the particle material and the fluid is maintained at , providing controlled experimental conditions with two parameters, and , influencing the spheroid’s fall. High-speed cameras capture the falling patterns and positions, leading to a phase diagram categorizing the trajectories into quasi-vertical, rectilinear, zigzagging oblique for prolate, and zigzagging rotation and spiral for oblate spheroids. The characteristics of the paths, velocities, and inclinations are analyzed, drawing comparisons with prior studies and examining similarities and differences. Subsequent analysis focuses on the kinematic characteristics, particularly drag coefficients and oscillatory properties. The drag coefficients of falling spheroids are found to be generally larger than those reported for fixed spheroids, with the discrepancy more pronounced for oblates. The dimensionless oscillatory frequency, represented by the Strouhal number variant , is discovered to be geometry-independent when an appropriate characteristic length is adopted, converging to a value of approximately 0.124. Other oscillatory variables also normalize to a consistent curve. Finally, the fluorescent visualization technique reveals distinct wake structures behind spheroids in different falling modes. The vortex shedding influences spheroids differently in the fluid mode versus the fluid–solid mode, showcasing a strong coupling between wake structures and falling trajectories. This comprehensive study provides the first experimental map of dynamically varying falling characteristics across a broad parameter range of for spheroids, enhancing our understanding of the impact of geometrical anisotropy on their falling behavior.

中文翻译：

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球体落入水中的实验研究：从长椭圆形到扁圆形

本实验研究研究具有不同几何各向异性的球状颗粒的下落特性，以长宽比 () 为特征。长径比从扁长 () 到扁圆 () 系统变化，而表示重力与粘性力之比的阿基米德数 () 范围从 491 到 1389。颗粒材料与流体之间的密度比保持不变at ，提供具有两个参数的受控实验条件， 和 ，影响球体的下落。高速摄像机捕捉下落模式和位置​​，生成相图，将轨迹分类为准垂直、直线、长球体的之字形倾斜、扁球体的之字形旋转和螺旋。分析了路径、速度和倾斜度的特征，与先前的研究进行比较并检查异同。随后的分析重点是运动学特性，特别是阻力系数和振荡特性。研究发现，下落球体的阻力系数通常大于固定球体的阻力系数，其中扁球体的差异更为明显。当采用适当的特征长度时，由斯特劳哈尔数变体 表示的无量纲振荡频率被发现与几何无关，收敛到大约 0.124 的值。其他振荡变量也归一化为一致的曲线。最后，荧光可视化技术揭示了不同下落模式下球体背后的独特尾流结构。在流体模式和流固模式下，涡旋脱落对球体的影响不同，显示出尾流结构和下落轨迹之间的强耦合。这项综合研究提供了第一个在球体的广泛参数范围内动态变化跌落特性的实验图，增强了我们对几何各向异性对其跌落行为影响的理解。