Bulletin of the American Physical Society
76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023; Washington, DC
Session J36: Multiphase Flows: Computational Methods III |
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Chair: Zhen Li, Clemson University Room: 202B |
Sunday, November 19, 2023 4:35PM - 4:48PM |
J36.00001: Assessment of Numerical Methods for Two Phase Shear Layers zoe barbeau, Sanjiva K Lele Atomization occurs when a liquid jet from a nozzle is discharged into a stagnant or moving gas causing the gas-liquid interface to become unstable and break up into a collection of droplets. The objective is to simulate a simplified problem of a 3D, planar two-phase mixing layer between a co-flowing liquid and high-speed gas stream in a compressible regime, relevant to rocket propulsion. The performance of 6th order staggered, compact finite difference method with the 5-equation model, 2nd interface sharpening, and localized continuum surface force method for surface tension modeling is evaluated for basic flows related to the two-phase mixing layer. 8th-order filtering is currently used for robustness with the longer-term objective of minimizing numerical dissipation. Surface tension test cases of a high-density stationary droplet and Laplace number = 24,000 droplet show low spurious current levels and 2nd order convergence of spurious currents with refinement. This combination of methods is robust for high density ratios, showing promise to simulate shear-induced breakdown of a temporal two-phase shear layer.
Funded by the US Department of Energy PSAAP-III Program at Stanford University (Award DE-NA0003968) and by U.S. Department of Energy, Office of Science, Office of Advanced Scientific Computing Research, Department of Energy Computational Science Graduate Fellowship (Award Number DE-SC0022158).
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Sunday, November 19, 2023 4:48PM - 5:01PM |
J36.00002: Analysis of interfacial sharpening techniques for upwind-biased shock- and interface-capturing methods in diffuse interface simulations of shock-dominated compressible two-phase flows Deniz Bezgin, Henry Collis, Shahab Mirjalili, Ali Mani, Nikolaus Adams In compressible two-phase flows, WENO-type upwind-biased spatial discretization schemes are a popular choice to provide sufficient numerical dissipation for stabilizing material interfaces and shock discontinuities. In contrast to shocks, material interfaces are not inherently self-sharpening. Thus, in the presence of numerical dissipation, material interfaces will continuously diffuse unless interfacial sharpening is applied. In this work, we investigate the interplay of WENO-type spatial discretization schemes and interfacial sharpening techniques in the five-equation diffuse interface model. We consider multiple variants of the conservative diffuse-interface method and compare them against the well-established THINC scheme and the baseline WENO scheme without interfacial sharpening. We consider 2D and 3D canonical test cases of shock-dominated compressible flows with large density ratios. We analyze the interaction between aforementioned interface regularization techniques and the underlying WENO-type discretization and evaluate how the interface regularization affects the temporal interface evolution. |
Sunday, November 19, 2023 5:01PM - 5:14PM |
J36.00003: Robust implementation of the four equation model for compressible two-phase flows using ENO-type schemes and application to simulation of "cold" combustors Henry Collis, Deniz Bezgin, Shahab Mirjalili, Ali Mani ENO-type schemes provide a general approach to capturing flow discontinuities without adding substantial numerical dissipation. While these schemes have "essentially" non-oscillatory solutions, for high-Mach flows even small oscillations in flow variables can lead to simulation failure. In particular, the high-density ratios common in two-phase flows demand stricter robustness criteria than single-phase compressible flow. Obtaining robust solutions for high-Mach two-phase flow requires enforcing positivity of pressure, mass, the squared speed-of-sound, and boundedness of phase volume fraction. In this work, a positivity-preserving framework was constructed for the four-equation two-phase model and implemented into the highly-parallel Hypersonic Task based Research (HTR) Solver. The positivity-preserving scheme is conservative and applied locally for minimum degradation of the base-line ENO-type scheme. The positivity-preserving framework was applied to multiple high-Mach two-phase flows including the simulation of a multiphase "cold" combustor on curvilinear grids. |
Sunday, November 19, 2023 5:14PM - 5:27PM |
J36.00004: Semi-Lagrangian Pressure Solver for Accurate, Consistent, and Conservative Volume-of-Fluid Simulations Julian L Fox, Mark F Owkes In this work, a novel discretization of the incompressible Navier-Stokes equations for a gas-liquid flow is developed. Simulations of gas-liquid flows are often performed discretizing time with a predictor -> pressure -> corrector approach and the phase interface is represented by a volume of fluid (VOF) method. Recently, unsplit, geometric VOF methods have been developed that use a semi-Lagrangian discretization of the advection term within the predictor step. A disadvantage of the current methods is that an alternative discretization (e.g.~finite volume or finite difference) is used for the divergence operator in the pressure equation. Due to the inconsistency in discretizations, a correction to the semi-Lagrangian advection term is required to achieve mass conservation, which increases the computational cost and reduces the accuracy. In this work, we explore the idea of using a semi-Lagrangian discretization for the divergence operators in both the advection term and the pressure equation. The proposed discretization avoids the correction to semi-Lagrangian fluxes improving the accuracy. Additionally, this method has the potential to reduce the computational cost of VOF simulations for gas-liquid flows. |
Sunday, November 19, 2023 5:27PM - 5:40PM |
J36.00005: Numerical modeling of an encapsulated microbubble using an immersed boundary-lattice Boltzmann method Morteza Garousi, Michael L Calvisi Encapsulated microbubbles (EMBs) are 1-10 microns in diameter and are used for various biomedical applications, such as ultrasound imaging and intravenous drug delivery. EMBs have a thin encapsulating layer of lipid, protein or polymer to stabilize them against dissolution in the bloodstream. When an EMB is subjected to ultrasound, the high compressibility of its gas core leads to both spherical and nonspherical oscillations. Numerical modeling of an EMB is a challenging problem that requires accounting for fluid-structure interaction (FSI) between a thin viscoelastic solid layer, a viscous incompressible exterior liquid, and a compressible interior gas. In this work, a numerical method is presented for modeling nonspherical, axisymmetric EMBs that uses the lattice Boltzmann method (LBM) to solve the fluid dynamics of the liquid and gas phases and the immersed boundary (IB) method to account for the FSI between the encapsulation and surrounding fluids. The primary advantage of this hybrid IB-LBM is its front tracking feature, i.e., the shape of the bubble surface is directly determined without need for its reconstruction. Simulations of the IB-LBM of a spherical bubble subjected to acoustic forcing are validated against the Rayleigh-Plesset equation. In addition, the accuracy of the IB-LBM model is investigated with respect to the stencil choice for the kernel function used for velocity interpolation and force spreading and the choice of time integration scheme for advecting the bubble surface. |
Sunday, November 19, 2023 5:40PM - 5:53PM |
J36.00006: High-fidelity simulations of fluid-solid interactions during liquid metal casting processes Jiazhen Qiao, Amir Riaz, Elias Balaras The preset work focuses on modeling of the initial stages of dross formation resulting from the interaction of the laminar/turbulent jet impinging on a free-surface. In the presence of air, a thin metal oxide layer forms on the surface of the liquid changing the dynamics of the jet as well as the resulting air-entrainement. The basis for the proposed formulation is our in-house, two-phase flow solver for incompressible flows, where we included the thin, highly deformable film that is formed on the liquid-gas interface. The frequent breakups of this oxidized layer render classical fluid-structure interaction methods where the solid is considered in a Lagrangian reference frame impractical. To address this issue we developed a fully Eulerian approach to model the liquid-gas-solid interactions. In particular, we use level set formulations to track both fluid-solid interfaces and the strain history of the deformable solid. The latter is accomplished by constructing a dynamic grid using three reference level set functions (one for each dimension) advected by the local velocity field. A unified framework is used to solve the equations governing the fluid and solid dynamics on the same fixed grid. Across the interface the shear modulus transitions smoothly from the bulk shear modulus to zero in a few computational cells. |
Sunday, November 19, 2023 5:53PM - 6:06PM Author not Attending |
J36.00007: Abstract Withdrawn
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Sunday, November 19, 2023 6:06PM - 6:19PM |
J36.00008: A three-dimensional adaptive mesh refinement multiphase flow solver for simulating non-isothermal gas-liquid-solid flows with phase change Ramakrishnan Thirumalaisamy, Amneet Pal S Bhalla We present a numerical framework for simulating non-isothermal gas-liquid-solid flows with phase change. Such flows are commonly found in engineering processes like welding, casting, and metal additive manufacturing. These processes involve fluid flow, heat transfer, solidification/melting, and fluid-structure interaction. Material properties vary vastly in these processes due to the presence of distinct phases in the domain. Moreover, the phases can evolve over time into other phases. As a result, numerical simulations of these engineering processes are quite challenging. We present a robust, scalable, and efficient three-dimensional computational framework with adaptive mesh refinement (AMR) for modeling non-isothermal and high-density contrasting gas-liquid-solid flows. The framework combines the level set method with the enthalpy method to track the three phases in the domain. A new low Mach equation is derived to capture volume changes due to phase change. The proposed method discretely conserves momentum, momentum, and energy. We demonstrate the practical utility of the framework by simulating engineering problems like modeling pipe defects during metal casting or porosity defects during metal solidification. |
Sunday, November 19, 2023 6:19PM - 6:32PM |
J36.00009: A coupled two-level set and volume-of-fluid method to simulate fluid-structure interaction of an elastic membrane in a viscous fluid Bashir Alnajar, Michael L Calvisi This work presents a fully Eulerian approach to simulate a cylindrical fluid-membrane interaction. The approach is named the coupled two-level set and volume-of-fluid (C2LSVOF) method owing to its use of the volume-of-fluid (VOF) method to enforce mass conservation, and two-level set (LS) functions to determine the interface shape and the elastic membrane forces. The spatio-temporal flow field is discretized by a single-field, finite difference formulation of incompressible, immiscible Navier-Stokes equations on a stationary grid. The second-order operator split method is used to advect the volume fraction and level set functions by alternating the starting sweep direction at each time step. One level set is advected without implementing the reinitialization algorithm so that its gradient, which can be directly related to the membrane stretching, can be preserved. We apply this approach to benchmark problems involving modeling the large deformation of a flexible elastic membrane in viscous incompressible fluids on each side of the membrane with different density and viscosity ratios. The findings are validated using a stretched and pressurized membrane immersed in a test fluid. |
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