Jaensson Nick O, Mitrias Christos, Hulsen Martien A, Anderson Patrick D
Department of Mechanical Engineering, Eindhoven University of Technology , P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
Dutch Polymer Institute (DPI) , P.O. Box 902, 5600 AX Eindhoven, The Netherlands.
Langmuir. 2018 Jan 30;34(4):1795-1806. doi: 10.1021/acs.langmuir.7b03482. Epub 2018 Jan 17.
Simulations of rigid particles suspended in two-phase shear flow are presented, where one of the suspending fluids is viscoelastic, whereas the other is Newtonian. The Cahn-Hilliard diffuse-interface model is employed for the fluid-fluid interface, which can naturally describe the interactions between the particle and the interface (e.g., particle adsorption). It is shown that particles can migrate across streamlines of the base flow, which is due to the surface tension of the fluid-fluid interface and a difference in normal stresses between the two fluids. The particle is initially located in the viscoelastic fluid, and its migration is investigated in terms of the Weissenberg number Wi (shear rate times relaxation time) and capillary number Ca (viscous stress over capillary stress). Four regimes of particle migration are observed, which can roughly be described by migration away from the interface for Wi = 0, halted migration toward the interface for low Wi and low Ca, particle adsorption at the interface for high Wi and low Ca, and penetration into the Newtonian fluid for high Wi and high Ca. It is found that the angular velocity of the particle plays a large role in determining the final location of the particle, especially for high Wi. From morphology plots, it is deduced that the different dynamics can be described well by considering a balance in the first-normal stress difference and Laplace pressure. However, it is shown that other parameters, such as the equilibrium contact angle and diffusion of the fluid, are also important in determining the final location of the particle.
本文给出了刚性颗粒悬浮于两相剪切流中的模拟结果，其中一种悬浮流体是粘弹性的，另一种是牛顿流体。采用Cahn-Hilliard扩散界面模型来描述流体-流体界面，该模型能够自然地描述颗粒与界面之间的相互作用（例如颗粒吸附）。结果表明，颗粒能够跨越主流的流线迁移，这是由于流体-流体界面的表面张力以及两种流体之间法向应力的差异所致。颗粒最初位于粘弹性流体中，并根据魏森贝格数Wi（剪切速率乘以松弛时间）和毛细管数Ca（粘性应力与毛细管应力之比）对其迁移进行了研究。观察到颗粒迁移的四种状态，大致可描述为：对于Wi = 0，颗粒远离界面迁移；对于低Wi和低Ca，颗粒向界面的迁移停止；对于高Wi和低Ca，颗粒吸附在界面上；对于高Wi和高Ca，颗粒渗透到牛顿流体中。研究发现，颗粒的角速度在确定颗粒的最终位置方面起着很大作用，尤其是对于高Wi的情况。从形态图可以推断，通过考虑第一法向应力差和拉普拉斯压力的平衡，可以很好地描述不同的动力学过程。然而，结果表明，其他参数，如平衡接触角和流体扩散，在确定颗粒的最终位置方面也很重要。
