Department of Microsystems Engineering, University of Freiburg, Freiburg, Germany.
Philos Trans A Math Phys Eng Sci. 2011 Jun 28;369(1945):2565-73. doi: 10.1098/rsta.2011.0077.
Forced oscillations in sessile droplets can be exploited in electrowetting mixing of fluid fractions. The necessary complex flows and large shape deformations require a numerical investigation of fluid dynamics in the transient regime. We provide a means to characterize oscillations qualitatively and quantitatively with the goal to examine and to classify flow patterns occurring inside. A superposition of different harmonic excitation patterns gives the possibility to control the convective flow. In this investigation, we apply a generic and accurate multi-phase smoothed particle hydrodynamics model to a two-dimensional three-phase flow and consider an oscillating droplet sitting on a substrate and immersed in a fluidic phase. These vibrations are investigated in two ways: the analysis of a step response due to an abrupt change of the contact angle is applied to identify the resonance frequencies. Secondly, the time evolution of the shape of the droplet in terms of harmonic functions is determined. Their amplitudes are examined in the time and frequency domain. This gives the possibility to relate resonance frequencies to mode shapes and to detect a coupling between them. Our approach is successfully applied to different numerical case studies.
在不移动液滴的情况下，强迫振荡可用于电润湿混合分数的混合。必要的复杂流动和大的形状变形需要对瞬态流场进行数值研究。我们提供了一种定性和定量描述振荡的方法，目的是检查和分类内部发生的流动模式。不同谐波激励模式的叠加使得控制对流流动成为可能。在这项研究中，我们将一种通用且精确的多相光滑粒子流体动力学模型应用于二维三相流，并考虑了一个在基底上振动的液滴，其沉浸在流体相中。这两种振动分别通过两种方式进行研究：分析由于接触角突然变化而产生的阶跃响应，以确定共振频率。其次，根据谐波函数确定液滴形状的时间演化。它们的幅度在时间和频域中进行检查。这使得将共振频率与模态形状相关联并检测它们之间的耦合成为可能。我们的方法成功应用于不同的数值案例研究。
