A series of 8 laboratory experiments was used to investigate the dynamics of a few almost neutrally-buoyant finite-size particles in the entire volume of a rectangular tank open to air and filled with water. Stirring was achieved by a cylinder executing a two-dimensional periodic Lissajoux figure. The rate and direction of stirring by the cylinder was varied. The particle motions were analysed using a tracking method developed for the experimental design. The Reynolds number associated with the large-scale stirring motion was in a turbulent range of [5,693–11,649] across all experiments. The absence of stirring in the direction of the cylinder axis, the constant interference of the cylinder with the eddies and the presence of walls and the free-surface resulted in a flow that was both inhomogeneous and anisotropic as recorded by the particle motion. Despite these unusual conditions, the single-particle dispersion across all experiments could be seen to follow a ballistic regime until about two-fifths of the particle Lagrangian velocity auto-correlation time $T_L$. It was followed by a brief diffusive regime between $T_L$ and 2.5T${}_L$, after which the presence of the boundaries prevented further dispersion. Such evolution is consistent with classic predictions for fluid tracer dispersion in homogeneous and isotropic turbulence. Particle-pair dispersion was more complex. Both the fixed time-averaged and length-scale-dependent particle-pair dispersion rates averaged across pairs showed the ballistic dispersion regime, whereas the subsequent diffusive regime was better borne out by the length-scale-dependent particle-pair dispersion. A super-diffusive Richardson regime was not unmistakably detected. Substantial variability was however found across the different pairs of particles, which was linked to differences in the decorrelation time of the velocity difference as a result of the inhomogeneity of the turbulence. For short initial separations, some particle pairs had a better separation of the time scales delimiting the ballistic and diffusive regimes and showed hints of a brief Richardson regime.

进行了一系列的8个实验室实验，以研究在敞开并充满水的矩形水箱的整个容积中，一些几乎中性浮力的有限尺寸颗粒的动力学。通过执行二维周期性Lissajoux图形的圆柱体来实现搅拌。圆筒的搅拌速度和方向是变化的。使用为实验设计开发的跟踪方法分析了粒子运动。在所有实验中，与大规模搅拌运动有关的雷诺数在[5,693-11,649]的湍流范围内。在气缸轴线方向上没有搅拌，圆柱对涡流的不断干扰，以及壁和自由表面的存在导致了流动，该流动既不均匀又各向异性，这由粒子运动记录。尽管存在这些异常条件，但可以看出，所有实验中的单粒子分散都遵循弹道状态，直到粒子拉格朗日速度自相关时间的五分之二为止${Ť}_{\mathrm{大号}}$。随后是短暂的扩散制度${Ť}_{\mathrm{大号}}$ 和2.5T${}_{\mathrm{大号}}$，之后边界的存在阻止了进一步的分散。这样的演变与流体示踪剂在均匀和各向同性湍流中扩散的经典预测是一致的。颗粒对分散更复杂。固定时间平均和成对的与长度比例有关的颗粒对分散速率均显示出弹道分散状态，而随后的扩散方式则由与长度成比例的颗粒对分散更好地证实。并没有明确地发现超级扩散的理查森政权。但是，在不同的粒子对之间发现了很大的变异性，这与湍流不均匀性导致的速度差异的去相关时间差异有关。对于短暂的初始分离，