Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session J13: CFD: LBM, SPH, Mesh Free |
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Chair: Alessandro Gabbana, Los Alamos National Laboratory (LANL) Room: 155 C |
Sunday, November 24, 2024 5:50PM - 6:03PM |
J13.00001: Numerical Investigation of Combined Effects of Thermocapillary Flows and Buoyant Convection in Self-Rewetting Fluids using Lattice Boltzmann method Bashir Mohamed Elbousefi, William Taylor Schupbach, Kannan Premnath Self-rewetting fluids (SRFs), such as aqueous solutions of high carbon content alcohols (e.g., n-butanol), show anomalous nonlinear (quadratic) variations of surface tension with temperature involving a positive gradient in certain ranges, leading to different thermocapillary convection compared to normal fluids (NFs). They have recently been used for enhancing thermal transport in a variety of applications. We use a robust lattice Boltzmann (LB) method based on central moments and multiple relaxation times to simulate the fluid motions and the transport of energy, and systematically study the combined effects of thermocapillary convection and buoyant convection in SRFs enclosed within a cavity. The attendant Marangoni stress condition as well as the imposed nonuniform heat fluxes on the free surface are both implemented using a novel moment-based boundary condition approach in the LB method. We investigate the effect of the dimensionless quadratic sensitivity coefficient of surface tension on temperature and other characteristic parameters at different Rayleigh numbers on the flow patterns and rates of heat transfer in SRFs and compare them with those arising in NFs. |
Sunday, November 24, 2024 6:03PM - 6:16PM |
J13.00002: Implicit Central Moment Lattice Boltzmann Method for Viscoelastic Flows for a Wide Range of Weissenberg Numbers Hassan Hwisa, William Taylor Schupbach, Kannan Premnath Viscoelastic flows are characterized by nonlinear interactions between polymeric viscoelastic stress and the fluid motions. The solution of the viscoelastic stress (VES) tensor, whose behavior is prototypically modeled using the Oldroyd-B model, can encounter numerical stability issues under large disparities in the relaxation time scale of VES and the flow time scales, or the Weissenberg numbers (Wi). We present lattice Boltzmann (LB) schemes that use central moments and multiple relaxation times in their collision steps for the solution of both the VES and the fluid motions. We propose a novel approach to address the stability issue in the computation of VES by introducing a locally implicit formulation to account for the associated stiff source terms based on the velocity gradient tensor in the model using a L-stable and second order method based on the trapezoidal rule in conjunction with the backward difference formula (TR-BDF2) via a Strang splitting around the collision step. Furthermore, we propose time-dependent conditions on the VES at the boundaries that are fully consistent with the underlying model. We demonstrate the validity and robustness of our new formulation for different benchmarks including shear-driven viscoelastic flows for a wide range of Wi. |
Sunday, November 24, 2024 6:16PM - 6:29PM |
J13.00003: Efficient Simulation of Axisymmetric Swirling Flows via a Lattice Boltzmann Method using Transformations Based on Orthogonal Coordinates Abuajaila B Kowas, William Taylor Schupbach, Kannan Premnath Axisymmetric flow equations represent a dimensional reduction of three-dimensional flows where axial symmetry can be exploited. If such flows involve boundary layers or shear layers, they can be more efficiently resolved by the clustering of grids that follow the flow features. However, the standard lattice Boltzmann (LB) methods are generally restricted to uniform Cartesian grids. To overcome this limitation, we develop a new LB method that solves the axisymmetric Navier-Stokes equations based on general orthogonal coordinates in a computational domain. We construct a collision model whose equilibria as well as the geometric body forces depend on the metric coefficients and their spatial derivatives arising from the variable grids used in the physical domain. The swirl effects in such flows are accounted for by computing the azimuthal momentum that satisfies a convection-diffusion type equation with a source term in general orthogonal coordinates using another LB scheme. Both these LB methods are designed to accommodate the usual collide-and-stream steps while still effectively allowing the use of variable grids, and their collision operators are based on central moments. We show the efficacy of our approach for various canonical axisymmetric flows including swirl effects. |
Sunday, November 24, 2024 6:29PM - 6:42PM |
J13.00004: Lattice Boltzmann Method for Computing 3D Navier-Stokes Equations in Orthogonal Curvilinear Coordinates: Flow Simulations using Clustered and Body-Conforming Grids William Taylor Schupbach, Eman O Yahia, Kannan Premnath The use of clustered grids that adapt with the nature of multiscale flows and the body-fitted grids for flow over curved geometries greatly facilitate efficient flow simulations. The standard lattice Boltzmann (LB) methods, however, use uniform Cartesian grids and implement conditions on the boundaries via cut-cell approaches. We develop improved LB methods that accommodate both these aspects naturally by constructing equilibria and body forces via using a Chapman-Enskog analysis that recover the 3D Navier-Stokes equations in orthogonal curvilinear coordinates (OCC) in a computational space using the D3Q27 lattice. The presence of variable grids or curved boundaries in the physical space are represented via the OCC related metric factors and a tensor associated with their spatial derivatives in the LB collision operator. This significantly extends our recent work on the 2D OCC-LBM (Yahia & Premnath, 2024) and uses our Fokker-Planck central moment-based collision model (Schupbach & Premnath, 2024) for further improvements in stability for flow simulations using OCC. The method is modular in nature and maintains the simplicity of the collide-and-stream steps. Simulations of various 3D benchmark flow cases demonstrate the capabilities of our 3D OCC-LBM. |
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