Experiments are conducted in a Ø600 mm tank to analyse the 3D motion of buoyant particles in the free-surface vortex flow. The experiments revealed two stages in the particle motion: stage 1 is the helical motion along the vortex air core and stage 2 is the axial motion inside the vortex core. The stage 1 motion is sensitive to the particle’s initial conditions by showing a chaotic behaviour and quantified by determining the largest Lyapunov exponent. Consequently, the predictability (forecast horizon) of the particle’s motion is limited. A motion parameter is proposed that indicates if a continuous downward motion along the air core occurs. The dynamics in the stage 2 motion is determined by the imbalance between the particle’s buoyancy force and fluid drag force. The drag appears to be determined by the Taylor column drag force as present in rotating fluids. Based on this force, a motion condition is proposed that indicates if axial motion inside the vortex core occurs.

实验在 Ø600 毫米的水箱中进行，以分析自由表面涡流中浮力粒子的 3D 运动。实验揭示了粒子运动的两个阶段：第 1 阶段是沿着涡流空气核的螺旋运动，第 2 阶段是涡核内部的轴向运动。阶段 1 运动对粒子的初始条件敏感，表现为混沌行为，并通过确定最大的李雅普诺夫指数进行量化。因此，粒子运动的可预测性（预测范围）是有限的。提出了一个运动参数，该参数指示是否发生沿空心的连续向下运动。第 2 阶段运动的动力学由粒子的浮力和流体阻力之间的不平衡决定。阻力似乎由旋转流体中存在的泰勒柱阻力决定。基于该力，提出了一种运动条件，该运动条件指示涡核内部是否发生轴向运动。