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 R12: Multiphase Flows: Level Set Method and Applications |
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Chair: Mario Trujillo, University of Wisconsin-Madison Room: C123 |
Tuesday, November 22, 2016 1:30PM - 1:43PM |
R12.00001: A Performance Comparison Between a Level Set Method and an Unsplit Volume of Fluid Method Olivier Desjardins, Robert Chiodi, Mark Owkes The simulation of high density ratio liquid-gas flows presents many numerical difficulties due to the necessity to track the interface and the discontinuities in physical properties associated with the interface. Two main categories of methods used to track the interface are level set methods and volume of fluid (VOF) methods. In particular, conservative level set methods track and transport the interface using a scalar field, with the interface profile represented by a hyperbolic tangent function of a finite thickness. Volume of fluid methods, on the other hand, store the percentage of each fluid in the computational cells. Both methods offer distinct advantages, however, the strengths and weaknesses of each method relative to each other have yet to be thoroughly investigated. This work compares the accuracy and computational efficiency for an accurate conservative level set method and an unsplit VOF method using canonical test cases, such as Zalesak's disk, the deformation of a circle, and the deformation of a sphere. The mass conservation and ability to correctly predict instability for a more complex case of an air-blast atomization of a planar liquid layer will also be presented. [Preview Abstract] |
Tuesday, November 22, 2016 1:43PM - 1:56PM |
R12.00002: Comparing volume of fluid and level set methods for evaporating liquid-gas flows John Palmore, Olivier Desjardins This presentation demonstrates three numerical strategies for simulating liquid-gas flows undergoing evaporation. The practical aim of this work is to choose a framework capable of simulating the combustion of liquid fuels in an internal combustion engine. Each framework is analyzed with respect to its accuracy and computational cost. All simulations are performed using a conservative, finite volume code for simulating reacting, multiphase flows under the low-Mach assumption. The strategies used in this study correspond to different methods for tracking the liquid-gas interface and handling the transport of the discontinuous momentum and vapor mass fractions fields. The first two strategies are based on conservative, geometric volume of fluid schemes using directionally split and un-split advection, respectively. The third strategy is the accurate conservative level set method. For all strategies, special attention is given to ensuring the consistency between the fluxes of mass, momentum, and vapor fractions. The study performs three-dimensional simulations of an isolated droplet of a single component fuel evaporating into air. Evaporation rates and vapor mass fractions are compared to analytical results. [Preview Abstract] |
(Author Not Attending)
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R12.00003: Numerical Simulation of Two-phase flow with Phase Change Using the Level-set Method Hongying Li, Jing Lou, Lunsheng Pan, Yitfatt Yap Multiphase flow with phase change is widely encountered in many engineering applications. A distinct feature involves in these applications is the phase transition from one phase to another due to the non-uniform temperature distribution. Such kind of process generally releases or absorbs large amount of energy with mass transfer happened simultaneously. It demands great cautions occasionally such as the high pressure due to evaporation. This article presents a numerical model for simulation of two-fluid flow with phase change problem. In these two fluids, one of them changes its state due to phase change. Such a problem then involves two substances with three phases as well as two different interfaces, i.e. the interface between two substances and the interface of one substance between its~two phases. Two level-set functions are used to capture the two interfaces in the current problem. The current model is validated against one-dimensional and two-dimensional liquid evaporation. With the code validated, it is applied to different phase change problems including (1) a falling evaporating droplet and the rising of one bubble and (2) two-fluid stratified flow with solidification of one fluid. Comparisons on the bubble and droplet topologies, flow and temperature fields are made for the first case between the falling evaporating droplet and the falling droplet without evaporation. For the second demonstration case, the effect of the superheated temperature on the solidification process is investigated. [Preview Abstract] |
Tuesday, November 22, 2016 2:09PM - 2:22PM |
R12.00004: Stabilized Conservative Level Set Method with Adaptive Wavelet-based Mesh Refinement Navid Shervani-Tabar, Oleg V. Vasilyev This paper addresses one of the main challenges of the conservative level set method, namely the ill-conditioned behavior of the normal vector away from the interface. An alternative formulation for reconstruction of the interface is proposed. Unlike the commonly used methods which rely on the unit normal vector, Stabilized Conservative Level Set (SCLS) uses a modified renormalization vector with diminishing magnitude away from the interface. With the new formulation, in the vicinity of the interface the reinitialization procedure utilizes compressive flux and diffusive terms only in the normal direction to the interface, thus, preserving the conservative level set properties, while away from the interfaces the directional diffusion mechanism automatically switches to homogeneous diffusion. The proposed formulation is robust and general. It is especially well suited for use with adaptive mesh refinement (AMR) approaches due to need for a finer resolution in the vicinity of the interface in comparison with the rest of the domain. All of the results were obtained using the Adaptive Wavelet Collocation Method, a general AMR-type method, which utilizes wavelet decomposition to adapt on steep gradients in the solution while retaining a predetermined order of accuracy. [Preview Abstract] |
Tuesday, November 22, 2016 2:22PM - 2:35PM |
R12.00005: Gradient Augmented Level Set Method for Two Phase Flow Simulations with Phase Change C.R. Lakshman Anumolu, Mario F. Trujillo A sharp interface capturing approach is presented for two-phase flow simulations with phase change. The Gradient Augmented Levelset method is coupled with the two-phase momentum and energy equations to advect the liquid-gas interface and predict heat transfer with phase change. The Ghost Fluid Method (GFM) is adopted for velocity to discretize the advection and diffusion terms in the interfacial region. Furthermore, the GFM is employed to treat the discontinuity in the stress tensor, velocity, and temperature gradient yielding an accurate treatment in handling jump conditions. Thermal convection and diffusion terms are approximated by explicitly identifying the interface location, resulting in a sharp treatment for the energy solution. This sharp treatment is extended to estimate the interfacial mass transfer rate. At the computational cell, a d-cubic Hermite interpolating polynomial is employed to describe the interface location, which is locally fourth-order accurate. This extent of subgrid level description provides an accurate methodology for treating various interfacial processes with a high degree of sharpness. The ability to predict the interface and temperature evolutions accurately is illustrated by comparing numerical results with existing 1D to 3D analytical solutions. [Preview Abstract] |
Tuesday, November 22, 2016 2:35PM - 2:48PM |
R12.00006: Multiscale level-set method for accurate modeling of two-phase immiscible flow with deposited thin-films on solid surfaces Motaz Abu Alsaud, Amir Riaz, Hamdi Tchelepi We developed a multiscale sharp interface method based on the level-set for two-phase immiscible flow with pre-existing thin-films on solid surfaces. The lubrication approximation theory is used to model the thin- film equation efficiently. The incompressible Navier-Stokes, level-set, and thin-film evolution equation are coupled sequentially to capture the physics occurring at multiple length scales. The proposed multiscale method is validated through comparison with the augmented Young-Laplace equation that includes the Van der Waals intermolecular force for a static meniscus in a capillary tube. The viscous bending in the advancing interface over precursor film problem is captured by the numerical method and agrees with the Cox-Voinov theory. The problem of a moving-bubble inside a capillary tube is modeled, and the results compare well with both theory and experiments. In addition, the performance of the new approach is assessed by studying the spurious currents for capillary-dominated flows at low capillary numbers. The method is applicable for flows with a capillary number as low as ${Ca = 10^{−6}}$. [Preview Abstract] |
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