Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session M3: Multiphase Flows VII |
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Chair: Chris Blake Ivey, Stanford University Room: 325 |
Tuesday, November 26, 2013 8:00AM - 8:13AM |
M3.00001: Improved volume of fluid method based on polyhedral streamtubes and embedded height functions Christopher Ivey, Parviz Moin A conservative advection scheme based on the use of edge-matched flux polyhedra to integrate the volume fraction evolution equation on general grids is presented. The algorithm prevents the formation of over/undershoots of the volume fraction by enforcing that the flux polyhedra do not over/underlap, removing the need for unphysical and inaccurate redistribution algorithms. Accuracy of the method derives from the edge-matched flux polyhedra's approximation of the local stream tube. Integrity of the interface representation is maintained by the use of height functions over a local cartesian stencil embedded in the mesh. Three-dimensional tests demonstrate the conservation and accuracy of the new volume of fluid method for interface tracking in general topologies. [Preview Abstract] |
Tuesday, November 26, 2013 8:13AM - 8:26AM |
M3.00002: Generalization of the Volume-of-Fluid method with realizable and planarity preserving transport of geometric moments Vincent Le Chenadec In two-phase flow applications, Volume-of-Fluid methods rely on a local reconstruction of the interface, performed either by approximating the interface normal based on the neighboring volume fraction values, or by designing error estimates quantifying the deviation between the exact and the reconstructed interfaces. Such estimates may be either non-local, in which case they involve neighboring volume fraction values, or local, in which case additional geometric information is required (centers of mass of each fluid, matrices of inertia,...). The latter approach presents obvious advantages in terms of computational overhead and accuracy. Transport equations for these high-order geometric moments exist, but their discretization represents a challenge, in particular when it comes to planarity preservation and realizability. In this work, we propose a geometric discretization which guarantees these properties for arbitrary moments, and its application to the first-order generalization of the Volume-of-Fluid method (Moment-of-Fluid). Within this framework, the emphasis is then set on the reconstruction, and particularly on the solution of the underlying non-linear constrained minimization. Finally, transport and reconstruction algorithms are tested in standard 2D and 3D cases. [Preview Abstract] |
Tuesday, November 26, 2013 8:26AM - 8:39AM |
M3.00003: A Conservative Level Set Method on an Overset High-Resolution Cartesian Grid Manuel Gale, Marcus Herrmann Distance function level set approaches for capturing moving interfaces in multi-phase flows generally possess a major drawback: the enclosed mass is poorly conserved. Alternative methods such as the volume-of-fluid (VOF) and coupled level-set VOF provide better mass conservation, yet they face some unique challenges. Olsson and Kreiss (2005, 07) proposed a conservative level set (CLS) method that defines the level set scalar as a hyperbolic tangent away from the phase interface iso-surface. While drastically improving mass conservation, the necessary introduction of an interfacial thickness length scale, coupled to the local flow solver resolution, may adversely impact interface dynamics in complex scenarios. We propose to decouple the interface thickness scale from the local flow solver resolution scale, by solving the conservative level set scalar on an overset, high resolution Cartesian mesh, using the Refined Level Set Grid (RLSG) method. The resulting CLS-RLSG solver is coupled to a fully unstructured flow solver to solve the Navier-Stokes equations in the incompressible limit. Several test cases will be presented demonstrating the performance of the resulting code infrastructure, focusing on the interplay of local flow solver-RLSG resolution and CLS interfacial thickness. [Preview Abstract] |
Tuesday, November 26, 2013 8:39AM - 8:52AM |
M3.00004: Entrainment Characteristics for variable-angle plunging liquid jets Suraj Deshpande, Mario Trujillo Simulations based on an algebraic VoF method are used to study the entrainment characteristics of a water jet plunging into a quiescent pool at angles ranging from 10 to 90 deg. with pool. Our previous study of shallow plunging jets (Deshpande et al. 2012) revealed a discernible frequency in the formation of large air cavities. This contrasts the well-documented chaotic entrainment at steeper inclinations, suggesting a different entrainment mechanism exists for shallow angles. Quantitatively, it is found that larger cavities and greater volume of entrained air occur at shallower angles (10, 12 deg.). A precursor to the formation of these large cavities is the presence of a stagnation region in the zone of impingement. Using a local mass and momentum balance, we show that this stagnation region deflects the incoming jet at wide angles producing large air cavities. Entrainment in shallow jets is similar to the initial impact of the jet with a pool, but it occurs periodically. The recurrence is a consequence of jet disruption by traveling waves on the pool. Qualitative analysis, supported with simulations, demonstrates linear scaling of entrainment period with Froude number. [Preview Abstract] |
Tuesday, November 26, 2013 8:52AM - 9:05AM |
M3.00005: The effect of residence time on the dynamics of a condensating aerosol in a Hiemenz-type stagnation flow Amjad Alshaarawi, Kun Zhou, Gianfranco Scribano, Antonio Attili, Fabrizio Bisetti The effect of residence time on the formation and growth of a condensating aerosol is simulated in a Hiemenz-type stagnation flow setup, for which a unique and well-defined time scale characterizes the velocity field. In this configuration, a hot stream saturated with dibutyle phthalate (DBP) vapor mixes with a cold dry stream. A mixing layer forms at the stagnation plane triggering supersaturation and droplets are generated by homogeneous nucleation. Aerosol dynamics are simulated using the Quadrature Method of Moments (QMOM). Two regimes related to the flow residence time are observed, i.e., a nucleation regime and a condensation regime. The nucleation regime, at short residence times, is characterized by the consumption of DBP vapor into droplets having a negligible effect on the vapor phase. In this regime, both the number density and volume fraction of droplets increase with residence time. In the condensation regime, at long residence times, vapor condensation consumes the vapor phase considerably. For longer residence times, more vapor is consumed, resulting in lower number densities due to the lower nucleation rates, whereas the volume fraction saturates. [Preview Abstract] |
Tuesday, November 26, 2013 9:05AM - 9:18AM |
M3.00006: Three-dimensional advected normals method for calculating interfacial normals and curvatures in two-phase flows Ashish Pathak, Mehdi Raessi We present an extension of the advected normals method to three-dimensional two-phase flows, including contact line problems. In this method, a mass-conserving volume-of-fluid method is used to track fluid volumes, while the unit vectors normal to the fluid interfaces are advected by solving an additional transport equation. Interface curvature is computed directly from the advected normals. RK3 scheme is used for discretizing the temporal gradient of the normals transport PDE, and spatial gradients are calculated using Lax-Friedrichs flux splitting scheme with WENO-5, which provides a more robust solution, especially in cases where the velocity field may contain spurious currents. Efficacy of the method in accurate evolution of normals is demonstrated in 3D test cases with prescribed velocity, where the normals and curvatures are shown to converge with second and first order accuracy, respectively. Furthermore, the method was extended to handle contact line problems in 3D. Normal vectors around the contact line and along the contact surface are used as boundary conditions to impose the contact angle. Additionally, to solve the normals evolution PDE, an extension of the normals field below the contact surface is required, which is obtained using natural neighbor interpolation. [Preview Abstract] |
Tuesday, November 26, 2013 9:18AM - 9:31AM |
M3.00007: Unifying binary fluid diffuse-interface models in the sharp-interface limit David Sibley, Andreas Nold, Serafim Kalliadasis Flows involving free boundaries occur widely in both nature and technological applications, existing at liquid-gas interfaces (e.g. between liquid water and water vapour) or between different immiscible fluids (e.g. oil and water, and termed a binary fluid). To understand the asymptotic behaviour near a contact line, a liquid-gas diffuse-interface model has been investigated recently [1]. In contrast, here we investigate the behaviour between two ostensibly immiscible fluids, a binary fluid, using related models where the interface has a thin but finite thickness. Quantities such as the mass fraction of the two fluid components are modelled as varying smoothly but rapidly in the interfacial region. There has been a wide variety of models used for this situation, based on Cahn--Hilliard or Allen--Cahn theories coupled to hydrodynamic equations, and we consider the effect of these differences using matched asymptotic methods in the important sharp-interface limit, where the interface thickness goes to zero. Our aim is to understand which models represent better the classical hydrodynamic model and associated free-surface boundary conditions. \\[4pt] [1] Sibley, Nold, Savva, Kalliadasis. Eur. Phys. J. E 36, 26 (2013) [Preview Abstract] |
Tuesday, November 26, 2013 9:31AM - 9:44AM |
M3.00008: Linear stability analysis of miscible two-fluid flow in a channel with velocity slip at the walls Sukhendu Ghosh, R. Usha, Kirti Chandra Sahu The linear stability characteristics of pressure-driven three-layer flow of two miscible liquids with same density and varying viscosity in a channel with velocity slip at the wall are examined.The flow system is destabilizing when a more viscous fluid occupies the region closer to the wall with slip. For this configuration, a new mode of instability,namely,the overlap mode, similar to the one which appears in the corresponding flow in a rigid channel, occurs for high mass diffusivity of the two fluids,when the critical layer of the disturbance overlaps the viscosity stratified layer.The co-existence of several overlap modes, TS mode are also observed under certain circumstances.The flow is unstable at low Reynolds numbers for a wide range of wave numbers for low mass diffusivity.A configuration with less viscous fluid adjacent to the wall is stabilizing at moderate miscibility. It is possible to achieve stabilization or destabilization of miscible two-fluid flow in a channel with wall slip by appropriately choosing the viscosity of the fluid layer adjacent to the wall. In addition, the velocity slip at the wall has a dual role in stabilizing the flow system.The flow system can be either stabilized or destabilized by designing the walls of the channel as hydrophobic surfaces. [Preview Abstract] |
Tuesday, November 26, 2013 9:44AM - 9:57AM |
M3.00009: Three-dimensional simulations of pressure-driven displacement flow of two immiscible liquids using a multiphase Lattice Boltzmann approach Prasanna R. Redapangu, Kirti Chandra Sahu, S.P. Vanka A three-dimensional multiphase lattice Boltzmann approach is used to study the pressure-driven displacement flow of two immiscible liquids of different densities and viscosities in an inclined square duct. A three-dimensional-fifteen-velocity (D3Q15) lattice model is used. The simulations are performed on a graphics processing unit (GPU) based machine. The effects of channel inclination, viscosity and density contrasts are investigated. The contours of the density and the average viscosity profiles in different planes are plotted and compared with two dimensional simulations. We demonstrate that the flow dynamics in three-dimensional channel is quite different as compared to that of two-dimensional channel. In particular, we found that the flow is relatively more coherent in three-dimensional channel than that in two-dimensional channel. A new screw-type instability is seen in the three-dimensional channel which cannot be observed in two-dimensional simulations. [Preview Abstract] |
Tuesday, November 26, 2013 9:57AM - 10:10AM |
M3.00010: Analysis of the two-phase flow in the wake of a transom stern Kelli Hendrickson, Gabriel Weymouth, Dick Yue The objective of this effort is to understand the physical and air entrainment characteristics of the two-phase flow in the wake of a transom stern. High-resolution numerical simulations are performed on the wake of a canonical transom stern at large scales using conservative Volume-of-Fluid (cVOF) and implicit Large Eddy Simulation (iLES). Boundary Data Immersion Method (BDIM) is used to simulate the dry transom stern wake region at three different Froude numbers and two different effective viscosities. A novel Lagrangian cavity identification algorithm based on computer graphics techniques enables the analysis of the temporal evolution of the entrained air cavities. Analysis of the simulation results for the flow structure and air entrainment of the large air cavities will be presented, including the scaling with ship parameters. [Preview Abstract] |
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