Abstract A parametric study on the stability and morphology of the liquid cone in a flow focusing process is carried out through experimental and numerical methods. For the numerical simulations, we solve the Navier-Stokes equations coupled with a diffuse interface method. A scaling analysis which considers the competition between the viscous shear stress and the interfacial tension force is proposed, showing the effect of flow rates, geometrical parameters and liquid physical properties on the cone instability. The experimental and numerical results validate the scaling law and further show the effects of parameters on the cone morphology. We study the flow fields inside the liquid cone, with emphatic focus on the recirculation flow pattern which occurs at relatively high viscosity ratio between the focusing and the focused liquids. The occurrence of recirculation flow is close related to the tangential velocity distribution at both sides of the cone interface, and the change of flow rates and geometrical parameters is found to significantly affect the size of the recirculation flow. This study is expected to give a guidance to the optimization of process parameters in flow focusing system, which would contribute to the formation of a stable cone-jet structure and the production of microdroplets with high throughput.

中文翻译：

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流动聚焦中液锥稳定性和形貌的参数研究

摘要 通过实验和数值方法对流动聚焦过程中液锥的稳定性和形貌进行了参数研究。对于数值模拟，我们求解 Navier-Stokes 方程和漫反射界面方法。提出了考虑粘性剪切应力和界面张力之间竞争的比例分析，显示了流速、几何参数和液体物理性质对锥体不稳定性的影响。实验和数值结果验证了标度律，并进一步显示了参数对锥体形态的影响。我们研究了液锥内部的流场，重点关注在聚焦和聚焦液体之间相对较高的粘度比下发生的再循环流型。再循环流的发生与锥体界面两侧的切向速度分布密切相关，发现流速和几何参数的变化对再循环流的大小有显着影响。该研究有望为流动聚焦系统工艺参数的优化提供指导，这将有助于形成稳定的锥形射流结构和高通量微滴的产生。