Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 55, Number 16
Sunday–Tuesday, November 21–23, 2010; Long Beach, California
Session CU: Multiphase Flows II |
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Chair: Marios Soteriou, United Technologies Room: Hyatt Regency Long Beach Regency A |
Sunday, November 21, 2010 1:00PM - 1:13PM |
CU.00001: Phase field method for interfacial fluid flow with soluble surfactant Minh Do-Quang, Stefan Engblom, Anna-Karin Tornberg, Gustav Amberg In this study, a simulation of flow of two immiscible fluids with a soluble surfactant is studied using a diffuse interface formulation. The finite element method with adaptive mesh refinement is used to solve the Navier-Stokes equations together with the phase field equation. This system allows us to simulate the motion of a free surface in the presence of surface tension and the effect of surfactant. The method is validated for simple test cases and the computational results are found to be in a good agreement with the analytical solutions. The method is then being applied to study the effect of surfactant on motion and deformation of buoyancy-driven bubbles, and drop breakup and coalescence in a circular tube. We also discuss the free energy used in this approach and some ways to improve it. [Preview Abstract] |
Sunday, November 21, 2010 1:13PM - 1:26PM |
CU.00002: Strategies for Multiphase Flows with High Density Ratios Olivier Desjardins, Vincent Moureau While numerical methods for multiphase flows have progressed significantly in the past few years, simulating realistic flows with high density ratios remains a major hurdle, especially when combined with high shear, as encountered in air-blast atomization devices. In order to alleviate this issue in the context of level set methods, two strategies are investigated that aim at improving the consistency between level set and momentum transport. The first strategy relies on transporting an auxiliary density field created from the level set function and using it for creating consistent momentum fluxes. The second strategy relies on a two-velocity ghost fluid approach where both gas and liquid velocities are considered, allowing to decouple velocity gradients on each side of the phase-interface. Both approaches are shown to provide improved robustness and accuracy even in the presence of high density ratio and high shear. Advantages and limitations of these techniques are discussed for canonical two-phase flow configurations and for realistic fuel injection applications. [Preview Abstract] |
Sunday, November 21, 2010 1:26PM - 1:39PM |
CU.00003: A Sub-Grid Model for Surface Tension Induced Phase Interface Dynamics Marcus Herrmann In many flows involving liquid/gas phase interfaces, small scale interface dynamics play an important role. In atomization of liquids, for example, surface tension forces can dominate the final stages of topology change events. Resolving such surface tension dominated small scale interface dynamics in a flow solver quickly becomes prohibitively expensive, especially for turbulent flows of engineering relevance. However, filtering the governing equations introduces unclosed terms that require modeling, among them the filtered surface tension force. In single phase flows, models, like the Large Eddy Simulations approach, rely on the existence of a cascade process, which is not necessarily present in two phase flows with surface tension forces. We thus propose a novel sub-grid model for the surface tension force based on the Refined Level Set Grid method that does not imply the existence of a cascade process. It is based on a local Taylor analogy, with surface tension acting as a local spring and viscosity as a local damper. We present results for the sub-grid motion of oscillating drops and sub-grid Rayleigh-Plateau instabilities commonly encountered in turbulent atomization. [Preview Abstract] |
Sunday, November 21, 2010 1:39PM - 1:52PM |
CU.00004: Contact-line motion past sharp corners: from spreading to jetting Peter Spelt, Yi Sui A level-set method for the simulation of two-phase flows with moving contact lines has been adapted to simulate contact-line motion past sharp corners numerically. The method is not restricted to creeping-flow regimes, and alleviates the stress singularity at a moving contact line by the use of a slip condition. First, the detailed flow behaviour is studied at the instance when the contact line moves past a corner, as well as that at later times, to see to what extent this deviates from conventional spreading behaviour. The method is then used to investigate the motion of a liquid out of an injection channel. Several flow regimes are observed, including a transition from spreading to jetting. [Preview Abstract] |
Sunday, November 21, 2010 1:52PM - 2:05PM |
CU.00005: A Numerical Approach for Simulating Incompressible Two-Phase Flows Considering Surface Tension Effect Sang Hun Choi, Myung Hwan Cho, Hyoung Gwon Choi, Jung Yul Yoo A novel level set method is proposed to simulate the incompressible two-phase flow considering the effect of surface tension. A mixed element is adopted, so that the continuity and Navier-Stokes equations are solved by using the Q2Q1 integrated finite element method, and the level set function is solved by using the Q1Q1 finite element method. For reinitialization of level set function, a direct approach method is employed, instead of solving hyperbolic type equation. In order to verify the accuracy and robustness of the code, the present method is applied to a few benchmark problems including the Rayleigh instability, bubble rising, and bubble breaking problems. It is confirmed that the present results are in good qualitative and quantitative agreements with the existing studies. [Preview Abstract] |
Sunday, November 21, 2010 2:05PM - 2:18PM |
CU.00006: A mass-conserving volume of fluid method for two-phase incompressible isotropic turbulence Alberto Baraldi, Antonino Ferrante We implemented and investigated a volume of fluid (VoF) method for capturing the motion of an initially spherical interface in incompressible velocity fields. First, we tested the interface reconstruction and advection algorithms in analytical velocity fields: linear translation, solid body rotation, and Taylor-Green vortex. These tests showed that the implemented VoF method conserves mass with machine accuracy. Then, we tested the VoF in incompressible isotropic turbulence. In order to compute the geometrical error, the instantaneous velocity field extracted from DNS was artificially reversed in time by means of a cosine time-function. During this test, the spherical interface, with a diameter of Taylor-length-scale size, deforms, breaks, reconnects and returns to its initial position. Also in this test, our results show that the VoF method conserves mass with machine accuracy. Furthermore, the topology changes are captured without any ad hoc treatment. Thus, we conclude that the implemented VoF is suitable for DNS of two-phase (e.g.~gas-liquid or liquid-liquid) incompressible isotropic turbulence. [Preview Abstract] |
Sunday, November 21, 2010 2:18PM - 2:31PM |
CU.00007: A volume-of-fluid interfacial flow solver with advected normals Mehdi Raessi, Javad Mostaghimi, Markus Bussmann We introduce an implementation of the advecting normals method in a volume-of-fluid interfacial flow solver. The advected normals are used to compute the interface curvature for calculating the surface tension force, and for reconstructing the interface in a volume-conserving volume-of-fluid method. To improve the performance of the method in under-resolved regions of the flow, where normals vary sharply, a curvature-based criterion is used to detect and correct poorly defined normals. We present results of advection as well as actual flow problems and demonstrate that the new method is well suited for problems that involve large interface deformation and breakup. [Preview Abstract] |
Sunday, November 21, 2010 2:31PM - 2:44PM |
CU.00008: Numerical simulation of two-phase flows in complex geometries by combining two different immersed-boundary methods Bo Yin, Haoxiang Luo Two-phase flows in various industrial applications often occur in complex geometries. To simulate this type of flows, we have combined two different immersed-boundary methods to handle the fluid-fluid and the fluid-solid interfaces separately. For the fluid-fluid interface, a diffuse-interface method is employed where the discontinuities of the material properties and the traction jump are all regularized using an approximate Dirac's Delta function. For the fluid-solid interface, ghost nodes and a local flow reconstruction are employed to complement the finite-difference discretization and to incorporate the boundary conditions. A single-block Cartesian mesh is used to discretize the entire domain. Both 2D and 3D codes have been implemented. Validation and code applications will be demonstrated at the conference. *Supported by the ACS Petroleum Research Fund. [Preview Abstract] |
Sunday, November 21, 2010 2:44PM - 2:57PM |
CU.00009: Multi-scale modeling of compressible multi-fluid flow with sharp-interface method Xiangyu Hu, Nikolaus Adams One important issue associated with the complexity of the dynamically evolving material interface is the scale- or mixing-dependent dynamics, which suggests very different physical phenomena depending on resolution and mixing of the material interface. We would like to present an idea of multi-scale modeling, in which the interface interaction is modeled as mechanical non-equilibrium or equilibrium depending on the scale measurement or resolvability of the interface. The work based on my previously developed conservative sharp-interface method for compressible multi-phase flows. In this finite-volume method, the interface is presented by a level-set function and the interface interaction is modeled by solving two-material Riemann problem. To extend this method for multi-scale modeling, two important issues have been addressed: one is to a scale-separation algorithm for identifying the resolved and unresolved interface; the other is to a mechanical equilibrium model and its coupling to the sharp-interface model with simple and efficient approaches. [Preview Abstract] |
Sunday, November 21, 2010 2:57PM - 3:10PM |
CU.00010: Multiscale Issues in DNS of Multiphase Flows Gretar Tryggvason, Siju Thomas, Jiacai Lu, Bahman Aboulhasanzadeh In direct numerical simulations (DNS) of multiphase flows it is frequently found that features much smaller than the ``dominant'' flow scales emerge. Those features consist of thin films, filaments, drops, and boundary layers, and usually surface tension is strong so the geometry is simple. Inertia effects are also small so the flow is simple and often there is a clear separation of scales between those features and the rest of the flow. Thus it is often possible to describe the evolution of this flow by analytical models. Here we discuss two examples of the use of analytical models to account for small-scale features in DNS of multiphase flows. For the flow in the film beneath a drop sliding down a sloping wall, we capture the evolution of films that are too thin to be accurately resolved using a grid that is sufficient for the rest of the flow by a thin film model. The other example is the mass transfer from a gas bubbly rising in a liquid. Since diffusion of mass is much slower than the diffusion of momentum, the mass transfer boundary layer is very thin and can be captured by a simple boundary layer model. The coupling of the model for the unresolved features to the rest of the flow is discussed for both examples. [Preview Abstract] |
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