Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session F38: Focus Session: Modeling, Computations and Applications of Wetting/Dewetting Problems IIFSI
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Chair: Shahriar Afkhami, New Jersey Institute of Technology Room: 304 |
Monday, November 20, 2017 8:00AM - 8:13AM |
F38.00001: Contact Line Dynamics Gunilla Kreiss, Hanna Holmgren, Martin Kronbichler, Anthony Ge, Luca Brant The conventional no-slip boundary condition leads to a non-integrable stress singularity at a moving contact line. This makes numerical simulations of two-phase flow challenging, especially when capillarity of the contact point is essential for the dynamics of the flow. We will describe a modeling methodology, which is suitable for numerical simulations, and present results from numerical computations. The methodology is based on combining a relation between the apparent contact angle and the contact line velocity, with the similarity solution for Stokes flow at a planar interface. The relation between angle and velocity can be determined by theoretical arguments, or from simulations using a more detailed model. In our approach we have used results from phase field simulations in a small domain, but using a molecular dynamics model should also be possible. In both cases more physics is included and the stress singularity is removed. [Preview Abstract] |
Monday, November 20, 2017 8:13AM - 8:26AM |
F38.00002: Incorporating contact angles in the surface tension force with the ACES interface curvature scheme Mark Owkes In simulations of gas-liquid flows interacting with solid boundaries, the contact line dynamics effect the interface motion and flow field through the surface tension force. The surface tension force is directly proportional to the interface curvature and the problem of accurately imposing a contact angle must be incorporated into the interface curvature calculation. Many commonly used algorithms to compute interface curvatures (e.g., height function method) require extrapolating the interface, with defined contact angle, into the solid to allow for the calculation of a curvature near a wall. Extrapolating can be an ill-posed problem, especially in three-dimensions or when multiple contact lines are near each other. We have developed an accurate methodology to compute interface curvatures that allows for contact angles to be easily incorporated while avoiding extrapolation and the associated challenges. The method, known as Adjustable Curvature Evaluation Scale (ACES), leverages a least squares fit of a polynomial to points computed on the volume-of-fluid (VOF) representation of the gas-liquid interface. The method is tested by simulating canonical test cases and then applied to simulate the injection and motion of water droplets in a channel (relevant to PEM fuel cells). [Preview Abstract] |
Monday, November 20, 2017 8:26AM - 8:39AM |
F38.00003: An energy-stable phase-field method for moving contact line problems Pengtao Yue The phase-field method has become a popular numerical tool for moving contact-line problems because it can easily regularize the contact-line singularity by diffusion. Another advantage of the phase-field method is its energy law, which guarantees that the whole system is dissipative. This energy law, however, may not be satisfied if the equations are not discretized appropriately. In this talk, we will present an energy-stable scheme for the fully coupled phase-field and Navier-Stokes equations. A finite-element method and a modified Crank-Nicolson method are used for spatial and temporal discretizations, respectively. For two fluids with matched densities, the fully discretized system satisfies the exact physical energy law and is unconditionally stable. As a result, the numerical solution is dissipative and free of parasitic currents. For non-matched densities, the scheme only satisfies the energy law approximately; but it is sufficient to keep the parasitic currents well under control. A C++ code is developed based on the open source finite element library deal.ii and is made parallel by multi-threading. To demonstrate the efficiency and accuracy of the proposed method, we will present some 2D and 3D simulations including capillary rise and sliding drop. [Preview Abstract] |
Monday, November 20, 2017 8:39AM - 8:52AM |
F38.00004: Energetic Variational Approach to Multi-Component Fluid Flows Arkadz Kirshtein, Chun Liu, James Brannick In this talk I will introduce the systematic energetic variational approach for dissipative systems applied to multi-component fluid flows. These variational approaches are motivated by the seminal works of Rayleigh and Onsager. The advantage of this approach is that we have to postulate only energy law and some kinematic relations based on fundamental physical principles. The method gives a clear, quick and consistent way to derive the PDE system. I will compare different approaches to three-component flows using diffusive interface method and discuss their advantages and disadvantages. The diffusive interface method is an approach for modeling interactions among complex substances. The main idea behind this method is to introduce phase field labeling functions in order to model the contact line by smooth change from one type of material to another. [Preview Abstract] |
Monday, November 20, 2017 8:52AM - 9:05AM |
F38.00005: A finite-element model for moving contact line problems in immiscible two-phase flow Alec Kucala Accurate modeling of moving contact line (MCL) problems is imperative in predicting capillary pressure vs. saturation curves, permeability, and preferential flow paths for a variety of applications, including geological carbon storage (GCS) and enhanced oil recovery (EOR). The macroscale movement of the contact line is dependent on the molecular interactions occurring at the three-phase interface, however most MCL problems require resolution at the meso- and macro-scale. A phenomenological model must be developed to account for the microscale interactions, as resolving both the macro- and micro-scale would render most problems computationally intractable. Here, a model for the moving contact line is presented as a weak forcing term in the Navier-Stokes equation and applied directly at the location of the three-phase interface point. The moving interface is tracked with the level set method and discretized using the conformal decomposition finite element method (CDFEM), allowing for the surface tension and the wetting model to be computed at the exact interface location. A variety of verification test cases for simple two- and three-dimensional geometries are presented to validate the current MCL model, which can exhibit grid independence when a proper scaling for the slip length is chosen. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA-0003525. [Preview Abstract] |
Monday, November 20, 2017 9:05AM - 9:18AM |
F38.00006: Simulating condensation on microstructured surfaces using Lattice Boltzmann Method Alexander Alexeev, Yaroslav Vasyliv We simulate a single component fluid condensing on 2D structured surfaces with different wettability. To simulate the two phase fluid, we use the athermal Lattice Boltzmann Method (LBM) driven by a pseudopotential force. The pseudopotential force results in a non-ideal equation of state (EOS) which permits liquid-vapor phase change. To account for thermal effects, the athermal LBM is coupled to a finite volume discretization of the temperature evolution equation obtained using a thermal energy rate balance for the specific internal energy. We use the developed model to probe the effect of surface structure and surface wettability on the condensation rate in order to identify microstructure topographies promoting condensation. [Preview Abstract] |
Monday, November 20, 2017 9:18AM - 9:31AM |
F38.00007: Numerical investigation of sliding drops on an inclined surface Dominique Legendre, Annaig Pedrono Despite it apparent simplicity, the behavior of a drop on an inclined solid surface is far to be properly reproduced by numerical simulation. It involves static, hysteresis and dynamic contact line behaviors. Depending on the fluid properties, the hysteresis and the wall inclination, different drop shapes (rounded, corner or pearling drop) can be observed. The 3D numerical simulations of sliding droplets presented in this work are based on a Volume of Fluid (VoF) solver without any interface reconstruction developed in the JADIM code (Dupont {\&} Legendre J. Comp. Phys. 2010). The surface tension is solved using the classical CSF (Continuum Surface Force) model and a sub grid model is used to describe under hysteresis conditions both the shape, the dissipation of the non resolved scales of a moving contact line. Numerical simulations are compared with the experiments of LeGrand et al. J. Fluid Mech. 2005. The agreement with experiments is found to be very good for both he critical angle of inclination for siding as well as for the specific shapes: rounded, corner and pearling drops. The simulations have been used to extend the range of hysteresis covered by the experiments. [Preview Abstract] |
Monday, November 20, 2017 9:31AM - 9:44AM |
F38.00008: Numerical study of drop spreading on a flat surface Sheng Wang, Olivier Desjardins In this talk, we perform a numerical study of a droplet on a flat surface with special emphasis on capturing the spreading dynamics. The computational methodology employed is tailored for simulating large-scale two-phase flows within complex geometries. It combines a conservative level-set method to capture the liquid-gas interface, a conservative immersed boundary method to represent the solid-fluid interface, and a sub-grid curvature model at the triple-point to implicitly impose the contact angle of the liquid-gas interface. The performance of the approach is assessed in the inertial droplet spreading regime, the viscous spreading regime of high viscosity drops, and with the capillary oscillation of low viscosity droplets. [Preview Abstract] |
Monday, November 20, 2017 9:44AM - 9:57AM |
F38.00009: Electrostatic cloaking of surface structure for dynamic wetting Junichiro Shiomi, Satoshi Nita, Minh Do-Quang, Jiayu Wang, Yu-Chung Chen, Yuji Suzuki, Gustav Amberg Dynamic wetting problems are fundamental to the understanding of the interaction between liquids and solids. Even in a superficially simple experimental situation, such as a droplet spreading over a dry surface, the result may depend not only on the liquid properties but also strongly on the substrate-surface properties; even for macroscopically smooth surfaces, the microscopic geometrical roughness can be important. In addition, as surfaces may often be naturally charged, or electric fields are used to manipulate fluids, electric effects are crucial components that influence wetting phenomena. Here we investigate the interplay between electric forces and surface structures in dynamic wetting. While surface microstructures can significantly hinder the spreading, we find that the electrostatics can “cloak” the microstructures, i.e. deactivate the hindering. We identify the physics in terms of reduction in contact-line friction, which makes the dynamic wetting inertial force dominant and insensitive to the substrate properties. Reference: S. Nita, M. Do-Quang, J. Wang, Y. Chen, Y. Suzuki, G. Amberg, J. Shiomi, “Electrostatic cloaking of surface structure for dynamic wetting”, Science Advances, e1602202 (2017). [Preview Abstract] |
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