Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session H7: CFD: Computational Methods and Modeling of Multiphase Flows IV |
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Chair: Dimitrios Pavlidis, Imperial College London Room: 107 |
Monday, November 23, 2015 10:35AM - 10:48AM |
H7.00001: Three-dimensional numerical simulations of three-phase flows Dimitrios Pavlidis, Zhizhua Xie, Pablo Salinas, Chris Pain, Omar Matar The objective of this study is to investigate the fluid dynamics of three-dimensional three-phase flow problems, such as droplet impact on a gas-liquid interface and bubble rising through a liquid-liquid interface. An adaptive unstructured mesh modelling framework is employed here to study three-phase flow problems, which can modify and adapt unstructured meshes to better represent the underlying physics of multiphase problems and reduce computational effort without sacrificing accuracy. The numerical framework consists of a mixed control volume and finite element formulation, a ‘volume of fluid’ type method for the interface capturing based on a compressive control volume advection method and second-order finite element methods, and a force-balanced algorithm for the surface tension implementation, minimising the spurious velocities often found in such flow simulations. The surface tension coefficient decomposition method has been employed to deal with surface tension pairing between different phases via a compositional approach. Numerical examples of some benchmark tests and the dynamics of three-phase flows are presented to demonstrate the ability of this method. [Preview Abstract] |
Monday, November 23, 2015 10:48AM - 11:01AM |
H7.00002: A Scalable Parallel Fast Marching Method Yajing Gale, Marcus Herrmann The fast marching method is an efficient strategy to solve the Eikonal equation with broad applications in computational fluid dynamics. However, the traditional fast marching method is a purely sequential algorithm and thus not straightforward to parallelize. In this presentation, four parallel fast marching methods are discussed: the non-blocking parallel fast marching method (NB-PFMM), the blocking parallel fast marching method (B-PFMM), the extended domain-blocking parallel fast marching method (DB-PFMM), and the layered-blocking parallel fast marching method (LB-PFMM). When combined with proper domain decomposition approaches, these methods are not only efficient but can scale over a wide range of processor counts. The applicability and performance of the different parallel fast marching methods are presented and compared as applied to a variety of test cases. [Preview Abstract] |
Monday, November 23, 2015 11:01AM - 11:14AM |
H7.00003: A framework for embedding molecular-level information in continuum-scale simulations of interfacial flows Edward Smith, Panagiotis Theodorakis, Erich Muller, Richard Craster, Omar Matar Molecular dynamics provides a means of resolving the contact-line paradox. The price to pay for this insight is computational, with droplet simulations limited to the nanoscale. In order to model problems of engineering interest, the molecular contact line must be abstracted and included as part of a continuum scale simulation. Coupling, using dynamic molecular simulation in place of empirical or approximate closure relations, provides a means of doing just this. Molecular simulation of two phase Couette flow can reproduce the key features of the moving contact line. This sheared liquid bridge has the advantage that a steady state can be obtained, providing an unlimited source of data for statistical analysis. In this talk, we will present highlights from molecular dynamics simulation of the moving contact line. Using interface tracking, the dynamics of the contact line are examined, with results compared to published experimental studies. Good agreement is observed despite the difference in scale between the molecular model and experiments. Potential applications of this method are discussed, including coupled simulation which incorporates the molecular detail for surfactant-driven spreading. [Preview Abstract] |
Monday, November 23, 2015 11:14AM - 11:27AM |
H7.00004: Attenuation of numerical artefacts in the modelling of fluid interfaces Fabien Evrard, Berend G.M. van Wachem, Fabian Denner Numerical artefacts in the modelling of fluid interfaces, such as parasitic currents or spurious capillary waves, present a considerable problem in two-phase flow modelling. Parasitic currents result from an imperfect evaluation of the interface curvature and can severely affect the flow[Denner and van Wachem, Numer. Heat Trans. B-Fund. 65, 218 (2014)], whereas spatially underresolved (spurious) capillary waves impose strict limits on the time-step and, hence, dictate the required computational resources for surface-tension-dominated flows [Denner and van Wachem, J. Comp. Phys. 285, 24 (2015)]. By applying an additional shear stress term at the fluid interface, thereby dissipating the surface energy associated with small wavelengths, we have been able to considerably reduce the adverse impact of parasitic currents and mitigate the time-step limit imposed by capillary waves. However, a careful choice of the applied interface viscosity is crucial, since an excess of additional dissipation compromises the accuracy of the solution. We present the derivation of the additional interfacial shear stress term, explain the underlying physical mechanism and discuss the impact on parasitic currents and interface instabilities based on a variety of numerical experiments. [Preview Abstract] |
(Author Not Attending)
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H7.00005: A Multiphase Open Boundary Treatment for Interface Capturing Methods Manuel Gale, Marcus Herrmann Open or outflow boundaries are present in a number of fluid dynamics problems, both internal and external. The main characteristic of this type of boundary is that flow variables are not known and must be computed such that the resulting flow field yields are both stable and accurate. With a focus on incompressible flow, there have been numerous boundary treatments with relevance to finite-element and finite-volume methods. However, while single phase outflow conditions have been widely studied, the work in multiphase outflow boundaries is limited. In this work, the single phase boundary treatment approach of Dong et al. (2014) is extended to multiphase flows using a fractional-step method in combination with either a level-set or volume-of-fluid interface capturing method. The kinetic energy influx through the outflow boundary is locally balanced to improve stability under heavy reverse flow conditions that can arise from having two fluids with high density ratio. Presented is a detailed mathematical description of the outflow boundary condition and representative numerical tests for both single and multiphase flows. [Preview Abstract] |
Monday, November 23, 2015 11:40AM - 11:53AM |
H7.00006: Interface Surface Area Tracking for the Conservative Level Set Method Stephanie Firehammer, Olivier Desjardins One key question in liquid-gas flows is how to model the interface between phases in a way that is mass, momentum, and energy conserving. The accurate conservative level set (ACLS) method of Desjardins et al. [O. Desjardins, V. Moureau, H. Pitsch, An accurate conservative level set/ghost fluid method for simulating turbulent atomization, J. Comput. Phys. 227 (18) (2008) 8395-8416] provides a tool for tracking a liquid-gas interface with minimal mass conservation issues; however, it does not explicitly compute the interface surface area and thus nothing can be said a priori about the balance between kinetic energy and surface energy. This work examines an equation for the transport of interface surface area density, which can be written in terms of the gradient of the volume fraction. Furthermore this presentation will outline a numerical method for jointly transporting a conservative level set and surface area density. Finally, we will explore oppportunities for energy conservation via the accurate exchange of energy between the flow field and the interface through surface tension, with test cases to show the results of our extended ACLS method. [Preview Abstract] |
Monday, November 23, 2015 11:53AM - 12:06PM |
H7.00007: Consistent and conservative framework for incompressible multiphase flow simulations Mark Owkes, Olivier Desjardins We present a computational methodology for convection that handles discontinuities with second order accuracy and maintains conservation to machine precision. We use this method in the context of an incompressible gas-liquid flow to transport the phase interface, momentum, and scalars. Using the same methodology for all the variables ensures discretely consistent transport, which is necessary for robust and accurate simulations of turbulent atomizing flows with high-density ratios. The method achieves conservative transport by computing consistent fluxes on a refined mesh, which ensures all conserved quantities are fluxed with the same discretization. Additionally, the method seamlessly couples semi-Lagrangian fluxes used near the interface with finite difference fluxes used away from the interface. The semi-Lagrangian fluxes are three-dimensional, un-split, and conservatively handle discontinuities. Careful construction of the fluxes ensures they are divergence-free and no gaps or overlaps form between neighbors. We have tested and used the scheme for many cases and demonstrate a simulation of an atomizing liquid jet. [Preview Abstract] |
Monday, November 23, 2015 12:06PM - 12:19PM |
H7.00008: Thermodynamically Consistent Physical Formulation and an Efficient Numerical Algorithm for Incompressible N-Phase Flows Suchuan Dong This talk focuses on simulating the motion of a mixture of N (N>=2) immiscible incompressible fluids with given densities, dynamic viscosities and pairwise surface tensions. We present an N-phase formulation within the phase field framework that is thermodynamically consistent, in the sense that the formulation satisfies the conservations of mass/momentum, the second law of thermodynamics and Galilean invariance. We also present an efficient algorithm for numerically simulating the N-phase system. The algorithm has overcome the issues caused by the variable coefficient matrices associated with the variable mixture density/viscosity and the couplings among the (N-1) phase field variables and the flow variables. We compare simulation results with the Langmuir-de Gennes theory to demonstrate that the presented method produces physically accurate results for multiple fluid phases. Numerical experiments will be presented for several problems involving multiple fluid phases, large density contrasts and large viscosity contrasts to demonstrate the capabilities of the method for studying the interactions among multiple types of fluid interfaces. [Preview Abstract] |
Monday, November 23, 2015 12:19PM - 12:32PM |
H7.00009: A minimally diffusive interface function steepening approach for compressible multiphase flows Jonathan Regele Interface capturing methods for contacts and shocks are commonly used in compressible multiphase flows. Artificial diffusion is inherently necessary to stabilize jump discontinuities across shocks and contacts. Contacts suffer from diffusion more severely than shock waves because their characteristics are not convergent like shocks. Interface steepening procedures are commonly used to counteract numerical diffusion necessary to maintain a sharp interface function. In this work, a modification to the sharpening approach used in Shukla, Pantano, and Freund [J. Comp. Phys, 229, 2010] is developed that minimizes the artificial diffusion across the interface while maintaining a monotonic interface function. The method requires fewer iterations for convergence and provides a steeper interface function. Examples in one and two dimensions demonstrate the method's performance. [Preview Abstract] |
Monday, November 23, 2015 12:32PM - 12:45PM |
H7.00010: Numerical simulation of compressible multiphase flows using the Parallel Adaptive Wavelet-Collocation Method Mohamad Aslani, Jonathan Regele Numerical simulation of incompressible multiphase flows to describe fluid atomization is becoming more common. However, compressible multiphase flow simulations are mostly limited to shock-bubble interactions with only a few studies involving shock waves impacting liquid droplets. A methodology for simulating compressible multiphase flow is developed from existing approaches for the Parallel Adaptive Wavelet-Collocation Method. The method uses an interface capturing function with a steepening procedure for the fluid interface. Simulations of shock waves impacting liquid droplets illustrate the numerical capabilities. [Preview Abstract] |
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