Abstract:

The influence of continuous-phase velocity pulsation on the generation and morphology of polymer droplets in microchannels is studied using three-dimensional direct numerical simulation. Based on the elastoviscoplastic Saramito model and the fluid volume method, combined with the local adaptive mesh refinement technology, the droplet generation process and morphological characteristics were analyzed. The results show that elastoviscoplastic velocity pulsation promotes droplet generation, and the maximum stretching length of the dispersed phase first decreases and then increases as the pulsation frequency rises. The pulsation amplitude shortens the stretching length of the dispersed phase. Under the influence of pulsation, the droplet morphology undergoes significant changes. When droplet velocity dominates, significant axial tensile stresses appear at the head and sides of the droplet. When the continuous-phase velocity dominates, the tensile stress on the sides of the droplet decreases significantly, and the droplet length is compressed. Furthermore, under velocity pulsations of the continuous phase, the average droplet length is adjustable between 102 μm and 193 μm. The average length and width of the droplets are controlled by pulsation frequency, with little influence from the pulsation amplitude.

Key words: pulsatile flow, polymer droplet, microchannel, non-Newtonian fluid, elastoviscoplasticity, numerical simulation

摘要：

采用三维直接数值模拟方法，研究了连续相速度脉动对微通道内聚合物液滴生成与形貌的影响规律。基于黏弹塑性Saramito模型和流体体积法，结合局部自适应网格细化技术，分析了液滴的生成过程与形态特征。结果表明，适当的速度脉动可以促进液滴生成，分散相的最大拉伸长度随脉动频率的增加呈现先减小后增大的趋势，脉动振幅的增加会缩短分散相的拉伸长度。脉动作用下，液滴形貌发生显著变化。当液滴速度占主导地位时，液滴头部和侧面会出现明显的轴向拉伸应力。而当连续相速度占主导地位时，液滴侧面拉伸应力显著减小，液滴长度被压缩。此外，连续相速度脉动下，液滴平均长度可以调控在102~193 μm。液滴平均长度和宽度由脉动频率主导，振幅的影响较小。

关键词: 脉动流, 聚合物液滴, 微通道, 非牛顿流体, 黏弹塑性, 数值模拟