短暂的反气泡：直接数值模拟的时空演化
Ephemeral Antibubbles: Spatiotemporal Evolution from Direct Numerical Simulations
摘要：
反气泡是由高密度流体中的低密度流体壳层组成的，它有着广泛的应用前景。我们表明，通过广泛的直接数值模拟（DNSs），在两个和三个维度（2D和3D），时空演化的反气泡可以自然地描述耦合Cahn-Hilliard-Navier-Stokes（CHNS）方程的二元流体。我们的DNSs捕捉优雅的重力引起的变薄和破碎的反泡通过时间演化的Cahn-Hilliard标量序参量场$ϕ$，它不断变化的接口，所以我们不需要强制执行复杂的边界条件在移动的反泡接口。为了确保我们的结果是强大的，我们补充我们的CHNS模拟与尖锐的接口体积的流体（VoF）DNS。我们跟踪的反泡的厚度和计算的反泡的寿命对几个参数的依赖性，我们表明，我们的DNS结果与各种实验结果一致，特别是，与反泡的手臂收缩后，破碎的尺度为$σ^{1/2}$，其中$σ$是表面张力的速度。
英文摘要：
Antibubbles, which consist of a shell of a low-density fluid inside a high-density fluid, have several promising applications. We show, via extensive direct numerical simulations (DNSs), in both two and three dimensions (2D and 3D), that the spatiotemporal evolution of antibubbles can be described naturally by the coupled Cahn-Hilliard-Navier-Stokes (CHNS) equations for a binary fluid. Our DNSs capture elegantly the gravity-induced thinning and breakup of an antibubble via the time evolution of the Cahn-Hilliard scalar order parameter field $ϕ$, which varies continuously across interfaces, so we do not have to enforce complicated boundary conditions at the moving antibubble interfaces. To ensure that our results are robust, we supplement our CHNS simulations with sharp-interface Volume-of-Fluid (VoF) DNSs. We track the thickness of the antibubble and calculate the dependence of the lifetime of an antibubble on several parameters; we show that our DNS results agree with various experimental results; in particular, the velocity with which the arms of the antibubble retract after breakup scales as $σ^{1/2}$, where $σ$ is the surface tension.
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