Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session G12: Multiphase Flows: Diffused Interface, Finite Volume Methods and Applications |
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Chair: Pedro Milani, Stanford University Room: C123 |
Monday, November 21, 2016 8:00AM - 8:13AM |
G12.00001: Parasitic Currents in Diffuse-Interface Two-Phase Flow Simulations Pedro Milani, Seyedshahabaddin Mirjalili, Ali Mani Two phase flow phenomena are important in a wide range of applications, such as bubble generation in ocean waves and droplet dynamics in fuel injectors. Several methods can be used to simulate such phenomena. The focus of this study is the diffuse-interface method, in which the interface is described via a mixing energy and spans a few computational cells, while surface tension is modeled as a force density term on the right-hand side of the momentum equation. The advantages of this method include the ability to easily simulate complex geometries since it does not require special treatment around the interface, and to conserve mass exactly. However, this method suffers from parasitic currents, an unphysical velocity field generated close to the interface due to numerical imprecisions in the surface tension term. This can be a serious problem in low speed flows, where the parasitic currents are significant compared to the velocity scale of the problem. In this study, we consider a wide range of diffuse-interface schemes for two-phase flows, including different options for discrete representation of the surface tension force. By presenting an assessment of each method's performance in scenarios involving parasitic currents, we develop accuracy estimates and guidelines for selection among these models. [Preview Abstract] |
Monday, November 21, 2016 8:13AM - 8:26AM |
G12.00002: A compressible multiphase framework for simulating supersonic atomization Jonathan D. Regele, Daniel P. Garrick, Zahra Hosseinzadeh-Nik, Mohamad Aslani, Mark Owkes The study of atomization in supersonic combustors is critical in designing efficient and high performance scramjets. Numerical methods incorporating surface tension effects have largely focused on the incompressible regime as most atomization applications occur at low Mach numbers. Simulating surface tension effects in high speed compressible flow requires robust numerical methods that can handle discontinuities caused by both material interfaces and shocks. A shock capturing/diffused interface method is developed to simulate high-speed compressible gas-liquid flows with surface tension effects using the five-equation model. This includes developments that account for the interfacial pressure jump that occurs in the presence of surface tension. A simple and efficient method for computing local interface curvature is developed and an acoustic non-dimensional scaling for the surface tension force is proposed. The method successfully captures a variety of droplet breakup modes over a range of Weber numbers and demonstrates the impact of surface tension in countering droplet deformation in both subsonic and supersonic cross flows. [Preview Abstract] |
Monday, November 21, 2016 8:26AM - 8:39AM |
G12.00003: Multiphase flows in confinement with complex geometries Benjamin Aymard, Marc Pradas, Urbain Vaes, Serafim Kalliadasis Understanding the dynamics of immiscible fluids in confinement is crucial in numerous applications such as oil recovery, fuel cells and the rapidly growing field of microfluidics. Complexities such as microstructures, chemical-topographical heterogeneities or porous membranes, can often induce non-trivial effects such as critical phenomena and phase transitions . The dynamics of confined multiphase flows may be efficiently described using diffuse-interface theory, leading to the Cahn-Hilliard-Navier-Stokes(CHNS) equations with Cahn wetting boundary conditions. Here we outline an efficient numerical method to solve the CHNS equations using advanced geometry-capturing mesh techniques both in two and three dimensional scenarios. The methodology is applied to two different systems: a droplet on a spatially chemical-topographical heterogeneous substrateand a microfluidic separator. [Preview Abstract] |
Monday, November 21, 2016 8:39AM - 8:52AM |
G12.00004: Evaluating curvature for the volume of fluid method via interface reconstruction Fabien Evrard, Fabian Denner, Berend van Wachem The volume of fluid method (VOF) is widely adopted for the simulation of interfacial flows. A critical step in VOF modelling is to evaluate the local mean curvature of the fluid interface for the computation of surface tension. Most existing curvature evaluation techniques exhibit errors due to the discrete nature of the field they are dealing with, and potentially to the smoothing of this field that the method might require. This leads to the production of inaccurate or unphysical results. We present a curvature evaluation method which aims at greatly reducing these errors. The interface is reconstructed from the volume fraction field and the curvature is evaluated by fitting local quadric patches onto the resulting triangulation. The patch that best fits the triangulated interface can be found by solving a local minimisation problem. Combined with a partition of unity strategy with compactly supported radial basis functions, the method provides a semi-global implicit expression for the interface from which curvature can be exactly derived. The local mean curvature is then integrated back on the Eulerian mesh. We show a detailed analysis of the associated errors and comparisons with existing methods. The method can be extended to unstructured meshes. [Preview Abstract] |
Monday, November 21, 2016 8:52AM - 9:05AM |
G12.00005: Computation of Two-Phase Flows with an Interface-Capturing Method on Arbitrarily-Shaped Polygonal Meshes Hiroshi Otake, Takeshi Omori, Takeo Kajishima Arbitrarily-shaped polyhedral meshes are convenient for the computation of industrial flow systems which often have complex geometries. In two-phase flow problems, however, the employment of such meshes is rather challenging due to a poor accuracy of the existing methods based on the VOF (Volume of Fluid) method. In the previous work, we proposed an advection scheme for the interface indicator function on three-dimensional polyhedral meshes using the THINC (Tangent of Hyperbola Interface Capturing) method and a procedure to estimate interface curvatures on these meshes with the accuracy comparable to the conventional methods which employ structured meshes. To incorporate these schemes into the calculation of the Navier-Stokes equation, it is further required to eliminate the local numerical oscillation of the indicator function. In the present study, we discuss our recent improvement in the way to integrate the flux of the indicator function on cell faces and demonstrate its effectiveness in the calculation of two-phase flows performed on two-dimensional polygonal meshes. [Preview Abstract] |
Monday, November 21, 2016 9:05AM - 9:18AM |
G12.00006: Numerical Investigation on Sensitivity of Liquid Jet Breakup to Physical Fuel Properties with Experimental Comparison Dokyun Kim, Luis Bravo, Katarzyna Matusik, Daniel Duke, Alan Kastengren, Andy Swantek, Christopher Powell, Frank Ham One of the major concerns in modern direct injection engines is the sensitivity of engine performance to fuel characteristics. Recent works have shown that even slight differences in fuel properties can cause significant changes in efficiency and emission of an engine. Since the combustion process is very sensitive to the fuel/air mixture formation resulting from disintegration of liquid jet, the precise assessment of fuel sensitivity on liquid jet atomization process is required first to study the impact of different fuels on the combustion. In the present study, the breaking process of a liquid jet from a diesel injector injecting into a quiescent gas chamber is investigated numerically and experimentally for different liquid fuels (n-dodecane, iso-octane, CAT A2 and C3). The unsplit geometric Volume-of-Fluid method is employed to capture the phase interface in Large-eddy simulations and results are compared against the radiography measurement from Argonne National Lab including jet penetration, liquid mass distribution and volume fraction. The breakup characteristics will be shown for different fuels as well as droplet PDF statistics to demonstrate the influences of the physical properties on the primary atomization of liquid jet. [Preview Abstract] |
Monday, November 21, 2016 9:18AM - 9:31AM |
G12.00007: A sharp interface in-cell-reconstruction method for volume tracking phase interfaces in compressible flows Dominic Kedelty, Carlos Ballesteros, Ronald Chan, Marcus Herrmann To accurately predict the interaction of the interface with shocks and rarefaction waves, sharp interface methods maintaining the interface as a discontinuity are preferable to capturing methods that tend to smear the interface. We present a hybrid capturing/tracking method (Smiljanovski et al., 1997) that couples an unsplit geometric volume tracking method (Owkes \& Desjardins, 2014) to a finite volume wave propagation scheme (LeVeque, 2010). In cells containing the phase interface, states on either side are reconstructed using the jump conditions across the interface, the geometric information of the volume tracking method, and the cell averages of the finite volume method. Cell face Riemann problems are then solved within each phase separately, resulting in area fraction weighted fluxes that update the cell averages directly. This, together with a linearization of the wave interaction across cell faces avoids the small cut-cell time step limitation of typical tracking methods. However, the interaction of waves with the phase interface cannot be linearized and is solved using either exact or approximate two-phase Riemann solvers with arbitrary jumps in the equation of state. Several test cases highlight the capabilities of the new method. [Preview Abstract] |
Monday, November 21, 2016 9:31AM - 9:44AM |
G12.00008: Effect of Eccentricity in Compound Droplets Subject to a Simple Shear Flow. Sangkyu Kim, Sadegh Dabiri A double emulsion, or a compound droplet, is a system where two liquids are separated by an immiscible third liquid, thereby forming an emulsion inside an emulsion. Compound drops benefit from this separation in applications such food sciences, microfluidics, pharmaceutical engineering, and polymer sciences. While the subjects of double emulsion preparations, deformations, and breakup mechanisms are well-explored, the time-evolution of non-concentric compound drops has received far less analytical or computational scrutiny. In this work, we present computational results using finite volume method with front-tracking approach for initially spherical and non-concentric compound drops in a shear flow. Our findings for low Reynolds number flows show that: 1. The surrounding shear flow to the outer drop induces a rotational velocity field inside it, causing the inner drop to tumble with the flow, 2. the tumbling motion persists in time, and acts to increase the eccentricity of the compound drop, and 3. the hemisection-plane to the outer drop that is aligned with the plane of the simple shear defines an unstable equilibrium for inner drop's center, and the inner drop continuously drifts away from that plane. This work suggests a means of favorably configuring compound drops suitable for breakups, and helps to understand their migration in channel flows. [Preview Abstract] |
Monday, November 21, 2016 9:44AM - 9:57AM |
G12.00009: High-order positivity-satisfying scheme for multi-component flows Khosro Shahbazi A high-order maximum-principle-satisfying scheme for the multi-component flow computations featuring jumps and discontinuities due to shock waves and phase interfaces is presented. The scheme is based on high-order weighted-essentially non-oscillatory (WENO) finite volume schemes and high-order limiters to ensure the maximum principle or positivity of the various field variables including the density, pressure, and order parameters identifying each phase. The two-component flow model considered besides the Euler equation of gas dynamics consists of advection of two parameters of the stiffened gas equation, characterizing each phase. The design of the high-order limiter is based on limiting the quadrature values of the density, pressure and order parameters reconstructed using a high-order WENO scheme. The convergence and the order of accuracy of the scheme is illustrated using the smooth isentropic vortex problem with very small density and pressure. The effectiveness and robustness of the scheme in computing the challenging problem of shock wave interaction with a cloud of bubbles tightly clustered and placed in a body of liquid is also demonstrated. [Preview Abstract] |
Monday, November 21, 2016 9:57AM - 10:10AM |
G12.00010: Simulating shock-bubble interactions at water-gelatin interfaces Stefan Adami, Jakob Kaiser, Ivan Bermejo-Moreno, Nikolaus Adams Biomedical problems are often driven by fluid dynamics, as in vivo organisms are usually composed of or filled with fluids that (strongly) affected their physics. Additionally, fluid dynamical effects can be used to enhance certain phenomena or destroy organisms. As examples, we highlight the benign potential of shockwave-driven kidney-stone lithotripsy or sonoporation (acoustic cavitation of microbubbles) to improve drug delivery into cells. During the CTR SummerProgram 2016 we have performed axisymmetric three-phase simulations of a shock hitting a gas bubble in water near a gelatin interface mimicking the fundamental process during sonoporation. We used our multi-resolution finite volume method with sharp interface representation (level-set), WENO-5 shock capturing and interface scale-separation and compared the results with a diffuse-interface method (Kobayashi et al., Phys. Med. Biol. 56(19), 2011). Qualitatively our simulation results agree well with the reference. Due to the interface treatment the pressure profiles are sharper in our simulations and bubble collapse dynamics are predicted at shorter time-scales. Validation with free-field collapse (Rayleigh collapse) shows very good agreement. [Preview Abstract] |
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