Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session C24: Multiphase Flows: Computational Methods I |
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Chair: Gretar Tryggvason, Johns Hopkins University Room: 606 |
Sunday, November 24, 2019 8:00AM - 8:13AM |
C24.00001: Effect of topology changes on the breakup of a periodic liquid jet Alberto Roman-Afanador, Stephane Zaleski, Gretar Tryggvason, Jiacai Lu The breakup of a periodic jet is examined computationally, using a front-tracking/finite-volume method, where the interface is represented by connected marker points moving with the fluid, while the governing equations are solved on a fixed grid. Tracking the interface allows control of whether topology changes take place or not. The Reynolds and Capillary numbers are kept relatively low so most of the flow is well resolved. The effect of topology changes is examined by following the jet until it has mostly disintegrated, for different ''coalescence'' criteria, based on the thickness of thin films and threads. It is found that while the overall breakup is relatively insensitive to the exact conditions for topology changes, various quantitative measures of the evolution are not. The evolution of both two-dimensional and fully three-dimensional flows is examined. It is found that although there is a significant difference between the evolution when no breakup takes place and when it does, once breakup takes place the evolution is relatively insensitive to exactly how it is triggered for a range of coalescence criteria. However, excessively aggressive coalescence leads to different outcomes [Preview Abstract] |
Sunday, November 24, 2019 8:13AM - 8:26AM |
C24.00002: A robust multiphase flow solver for high density ratio wave structure interaction problems Amneet Pal S. Bhalla In this talk, we present a robust, adaptive numerical scheme for simulating high-density ratio and high shear multiphase flows on locally refined staggered Cartesian grids that adapt to the evolving interfaces and track regions of high vorticity. The algorithm combines the interface capturing level set method with a variable-coefficient incompressible Navier-Stokes solver that is demonstrated to stably resolve material contrast ratios of up to six orders of magnitude. The discretization approach ensures second-order pointwise accuracy for both velocity and pressure with several physical boundary treatments, including velocity and traction boundary conditions. To ensure the stability of the numerical scheme in the presence of high density and viscosity ratios, we employ a consistent treatment of mass and momentum transport in the conservative form of discrete equations. We demonstrate through several test cases that the lack of consistent mass and momentum transport in non-conservative formulations, which are commonly used in practice can yield very large numerical error and very poor accuracy for convection-dominant high-density ratio flows. Finally, we combine our robust multiphase fluid solver with an efficient implementation of immersed boundary method to simulate wave-structure interaction problems. Several cases from practical ocean and marine engineering applications, including simulations of wave energy converter devices are presented. [Preview Abstract] |
Sunday, November 24, 2019 8:26AM - 8:39AM |
C24.00003: Efficient, Discretely Conservative Multi-Material Phase Transport on Unstructured Meshes Using the Interface Reconstruction Library Robert Chiodi, Peter Brady, Neil Carlson The Truchas Multiphysics solver was developed at Los Alamos National Laboratory in order to simulate advanced metal casting processes of exotic materials. These processes involve complicated mold geometries that require the use of unstructured meshes in order to adequately resolve the shape of the mold. To enable the accurate simulation of the filling of these molds with liquid metal, we have implemented an unsplit geometric multi-material volume of fluid method capable of individually tracking the many constituent ingredients involved in metal casting. This was done using a newly developed, open-source library, the Interface Reconstruction Library, which handles the difficult computational geometry and interface reconstruction methods needed in geometric volume of fluid methods. In this talk, we will detail how to implement an efficient algorithm for discretely conservative multi-material phase advection on unstructured meshes. Its computational performance and solution accuracy on both hexahedron and tetrahedron meshes will be compared to the current state-of-the-art for a suite of canonical test cases. This abstract is approved for release under LA-UR-19-27091. [Preview Abstract] |
Sunday, November 24, 2019 8:39AM - 8:52AM |
C24.00004: Two-way coupled Euler-Lagrange simulations with particles and mesh spacing of arbitrary sizes Berend van Wachem, Fabian Denner, Fabien Evrard The Euler-Lagrange (EL) approach is widely used to simulate particulate flows, because of the relatively low computational cost and the straightforward modelling of particle-particle interactions. Since relying on an assumption of separation of scales between the general features of the flow (resolved on the underlying fluid mesh) and those at the scale of the particles (not resolved on the mesh), the EL method typically requires tracked particles to be much smaller than the grid cells in which the flow equations are solved, commonly referred to as the "particle-in-cell" approach. For the cases that require high fluid mesh refinement, this can strongly limit the size of the particles that can be accurately tracked. In this work, we propose an EL approach that alleviates the particle size restrictions. It relies upon the filtering of the flow equations with a particle marker function; a process in which a length-scale is chosen. We also present a model for the reconstruction of the undisturbed flow velocity and volume fraction at the particle locations, based on the study of the flow through a regularised momentum source and/or a volume fraction dimple. The ability of the proposed framework to accurately track particles of arbitrary sizes is shown with an array of test-cases. [Preview Abstract] |
Sunday, November 24, 2019 8:52AM - 9:05AM |
C24.00005: A hybrid PIC-DEM approach for multi-phase computational fluid dynamics Roberto Porcu, Ann Almgren, Michele Rosso, Jordan Musser, William Fullmer, Andrew Myers, Oscar Antepara MFiX-Exa is a new code being developed by the National Energy Technology Laboratory and Lawrence Berkeley National Laboratory as part of the U.S. Department of Energy's Exascale Computing Project. MFiX-Exa originated by combining the discrete element method (DEM) modules of the classic MFiX code (\url{mfix.netl.doe.gov}) with a modern low Mach number projection method for the continuous fluid phase. The new algorithm is implemented using the AMReX software framework for massively parallel block-structured applications (\url{amrex-codes.github.io}). Despite the ever-increasing computational power offered by world-leading supercomputers, DEM is still prohibitively expensive for the modeling of large industrial-scale problems. Other methods, as particle-in-cell (PIC), are less computationally intensive, but they tend to be less accurate than DEM. In this work, we exploit the efficiency of PIC and accuracy of DEM to introduce a hybrid multi-phase PIC-DEM approach. Overall, the strategy relies on applying the PIC model to particle-dense regions while keeping the DEM model for the dilute parts of the domain. Within this setup, the modeling of the PIC/DEM transitions is proposed. The method and results are to be presented in the context of chemical loop reactors simulations. [Preview Abstract] |
Sunday, November 24, 2019 9:05AM - 9:18AM |
C24.00006: Practical results from a stochastic 3-dimensional multiphase flow solver Brian Turnquist, Mark Owkes Uncertainty quantification (UQ) of multiphase flow systems is a developing field. While some work has been done to generate useful data regarding these flows, finding the best methodologies to efficiently do so is required. Due to the complicated nature of multiphase systems it can be difficult to collect experimental results and expensive to run simulations. To more fully understand the impact of input uncertainty on the outputs and physics in general, it is helpful to build up useful statistical data. The multiUQ project is a novel, intrusive stochastic multiphase flow program utilizing Navier-Stokes and a conservative level set approach with polynomial chaos for random variables. This code is now being developed in 3-D, providing stochastic results of real-world situations. Implementing a density-decoupled pressure solution method, the solver can now utilize more advanced approaches to solving the pressure Poisson equation, such as the multigrid method found in the HYPRE package. We present results of a stochastic falling droplet and atomizing jet, utilizing Sobol indices to determine the interactions which most impact system variability. [Preview Abstract] |
Sunday, November 24, 2019 9:18AM - 9:31AM |
C24.00007: Applying the Height Function Method to Conservative Dual Grids Kristopher Olshefski, Mark Owkes The atomization process is significantly affected by the surface tension force, which controls the size and distribution of droplets. The surface tension force is directly proportional to the interface curvature and an accurate calculation of curvature is essential for predictive simulations of atomization.The height function method is a common technique to compute an accurate curvature as it is straightforward to implement and provides a second-order calculation. Additionally, using a Rudman dual mesh (Int. J. Numer. Meth. Fluids, 1998), which discretizes density on a twice as fine mesh, provides consistent and conservative discretizations of mass and momentum. This work extends the standard height function method to include information from the Rudman dual mesh. When a dual grid is used, the standard height function method fails to capture fine grid interface perturbations and these perturbations can grow. The proposed method leverages a fine-grid height function method to compute the fine-gird interface perturbations and uses a fine-grid velocity field to oppose the fine-grid perturbations. This approach maintains consistent mass and momentum transport while also providing accurate interface transport that avoids non-physical dynamics. [Preview Abstract] |
Sunday, November 24, 2019 9:31AM - 9:44AM |
C24.00008: A Scalable Immersed Boundary Method for Multiphase Flow Simulation Yunchao Yang, S. Balachandar We developed a highly scalable immersed boundary method (IBM) algorithm for multiphase flow simulation. In particular, a Double Bin Ghost Particle (DBGP) algorithm is designed to obtain the distributed data storage and scalable data transferring features for the particle phase. The proposed algorithm uses a new Queen/Worker data structure to indicate the particle-level and marker-level quantities and communications. In the DBGP algorithm, each particle is represented by a queen marker and surface worker markers. The queen marker determines the motion and total force of a particle. The worker marker performs the fluid-particle interaction, including velocity interpolation and force projection. A double binning system is determined through the Cartesian binning of the physical domain to relate each MPI rank with its overlapping bins. By searching the bin-to-rank map, all remote MPI ranks influenced by the local particle can be readily identified. The ghost queen marker is generated in the remote MPI rank based on the local queen marker and the queen binning structure, and same for the ghost worker maker. Experimental results show that the algorithm is efficient and scalable on large-scale computations. [Preview Abstract] |
Sunday, November 24, 2019 9:44AM - 9:57AM |
C24.00009: Techniques for sharp numerical simulations of incompressible multiphase flows Raphael Egan, Frederic Gibou We present recent progress and developments to enable numerical simulations of incompressible two-phase flows in a fully sharp fashion, avoiding smearing of any fluid properties across interfaces. We use distributed adaptive cartesian Quadtree/Octree grids with a levelset method to represent the interface(s). The ability to solve elliptic interface problems with sharp jump conditions and discontinuous coefficients is essential to such applications. We discuss the corresponding numerical challenges and illustrate them with respect to the governing jump conditions and the balance of viscous stress across the interface. We present numerical methods to address these challenges and to ensure accurate solutions in infinity norm (i.e., even for points close to the interface) for accurate interface dynamics. [Preview Abstract] |
Sunday, November 24, 2019 9:57AM - 10:10AM |
C24.00010: Numerical simulations of the full ink-jet printing processes: From jetting to evaporation Christian Diddens, Yaxing Li, Tim Segers, Hans Reinten, Youri De Loore, Herman Wijshoff, Detlef Lohse Ink-jet printing requires to perfectly control both the jetting of droplets and the subsequent droplet evaporation and absorption dynamics. Considerable complexity arises due to the fact that ink is constituted of a mixture of different liquids, surfactants and pigments. Using a sharp-interface ALE finite element method, we numerically investigate the main aspects of ink-jet printing, both on the jetting side and on the drying side. We show how a short pause in jetting can result in clogged nozzles due to solvent evaporation and discuss approaches how to prevent this undesired phenomenon. Once the droplets have been jetted on paper and is evaporating, the print quality can be deteriorated by the well-known coffee-stain effect, i.e. the preferential deposition of particles near the rim of the droplet. This can be prevented in several ways, e.g. employing controlled Marangoni flow via surfactants or co-solvents or printing on a primer layer jetted in beforehand, thus creating a homogeneous deposition pattern for a perfect final printout. [Preview Abstract] |
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