In this study, the spreading velocities within the droplet impact on a sapphire glass surface is investigated with the aid of particle image velocimetry (PIV) method. Experiments are performed for unheated and heated surfaces and droplets with impact velocities ranging from 1.12 to 2.40 m/s which correspond to Weber numbers in the range 40–190. It was observed that the radial velocity is linear throughout a relatively large range of spreading radius. However, the velocity profiles show a non-linear shape outside radial positions owing to the capillary and viscous forces over time. For high-Weber numbers, the linearity of radial velocity profile is more evident due to the viscosity effects in the lamella which are insignificantly relative to the inertia forces. Also, the spreading velocities within the droplet pair are investigated at room temperature using the same methods. Another stagnation point formation was observed in the interaction area. In the last part, radial velocity measurements within the liquid lamellas were compared with analytical and computational models for the temperature of unheated surface. For high-Weber case, the analytical model quite agrees with the linear parts of the radial velocity profiles in the interior radial positions. For moderate Weber case, the predicted radial velocity profile only agrees well with the linear parts of experimental data during early spreading process, but the inconsistency between the analytical model and PIV results rises in the later spreading and receding phases. Comparing the results with the computational simulation show that there is a good agreement for both linear and non-linear parts in radial velocity profiles.

中文翻译：

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固体表面上单液滴和双液滴相互作用内的 PIV 测量

在这项研究中，借助粒子图像测速 (PIV) 方法研究了液滴撞击蓝宝石玻璃表面的扩散速度。对未加热和加热的表面和液滴进行了实验，其冲击速度范围为 1.12 至 2.40 m/s，对应于 40-190 范围内的韦伯数。据观察，径向速度在相对较大的扩散半径范围内是线性的。然而，由于毛细管力和粘性力随着时间的推移，速度分布在径向位置外呈现非线性形状。对于高韦伯数，由于薄片中的粘度效应与惯性力无关，径向速度分布的线性更加明显。还，使用相同的方法在室温下研究液滴对内的扩散速度。在相互作用区域观察到另一个停滞点形成。在最后一部分，液体薄片内的径向速度测量值与未加热表面温度的分析和计算模型进行了比较。对于高韦伯情况，分析模型与内部径向位置的径向速度分布的线性部分非常一致。对于中等韦伯情况，预测的径向速度剖面仅在早期扩展过程中与实验数据的线性部分吻合良好，但在后期扩展和后退阶段，分析模型与 PIV 结果之间的不一致增加。