566 research outputs found
Unstructured un-split geometrical Volume-of-Fluid methods -- A review
Geometrical Volume-of-Fluid (VoF) methods mainly support structured meshes,
and only a small number of contributions in the scientific literature report
results with unstructured meshes and three spatial dimensions. Unstructured
meshes are traditionally used for handling geometrically complex solution
domains that are prevalent when simulating problems of industrial relevance.
However, three-dimensional geometrical operations are significantly more
complex than their two-dimensional counterparts, which is confirmed by the
ratio of publications with three-dimensional results on unstructured meshes to
publications with two-dimensional results or support for structured meshes.
Additionally, unstructured meshes present challenges in serial and parallel
computational efficiency, accuracy, implementation complexity, and robustness.
Ongoing research is still very active, focusing on different issues: interface
positioning in general polyhedra, estimation of interface normal vectors,
advection accuracy, and parallel and serial computational efficiency.
This survey tries to give a complete and critical overview of classical, as
well as contemporary geometrical VOF methods with concise explanations of the
underlying ideas and sub-algorithms, focusing primarily on unstructured meshes
and three dimensional calculations. Reviewed methods are listed in historical
order and compared in terms of accuracy and computational efficiency
A fully Eulerian solver for the simulation of multiphase flows with solid bodies: application to surface gravity waves
In this paper a fully Eulerian solver for the study of multiphase flows for
simulating the propagation of surface gravity waves over submerged bodies is
presented. We solve the incompressible Navier-Stokes equations coupled with the
volume of fluid technique for the modeling of the liquid phases with the
interface, an immersed body method for the solid bodies and an iterative
strong-coupling procedure for the fluid-structure interaction. The flow
incompressibility is enforced via the solution of a Poisson equation which,
owing to the density jump across the interfaces of the liquid phases, has to
resort to the splitting procedure of Dodd & Ferrante [12]. The solver is
validated through comparisons against classical test cases for fluid-structure
interaction like migration of particles in pressure-driven channel, multiphase
flows, water exit of a cylinder and a good agreement is found for all tests.
Furthermore, we show the application of the solver to the case of a surface
gravity wave propagating over a submerged reversed pendulum and verify that the
solver can reproduce the energy exchange between the wave and the pendulum.
Finally the three-dimensional spilling breaking of a wave induced by a
submerged sphere is considered
A Level Set Approach to Eulerian-Lagrangian Coupling
We present a numerical method for coupling an Eulerian compressible flow solver with a Lagrangian solver for fast transient problems involving fluid-solid interactions. Such coupling needs arise when either specific solution methods or accuracy considerations necessitate that different
and disjoint subdomains be treated with different (Eulerian or Lagrangian)schemes.
The algorithm we propose employs standard integration of the Eulerian
solution over a Cartesian mesh. To treat the irregular boundary cells that
are generated by an arbitrary boundary on a structured grid, the Eulerian
computational domain is augmented by a thin layer of Cartesian ghost cells.
Boundary conditions at these cells are established by enforcing conservation
of mass and continuity of the stress tensor in the direction normal to the
boundary. The description and the kinematic constraints of the Eulerian
boundary rely on the unstructured Lagrangian mesh. The Lagrangian mesh
evolves concurrently, driven by the traction boundary conditions imposed
by the Eulerian counterpart.
Several numerical tests designed to measure the rate of convergence and
accuracy of the coupling algorithm are presented as well. General problems
in one and two dimensions are considered, including a test consisting of an
isotropic elastic solid and a compressible fluid in a fully coupled setting
where the exact solution is available
Numerical Study of Interfacial Flow using Algebraic Coupled Level Set-Volume of Fluid (A-CLSVOF) Method
Solving interfacial flows numerically has been a challenge due to the lack of sharpness and the presence of spurious currents at the interface. Two methods, Algebraic Coupled Level Set-Volume of Fluid (A-CLSVOF) method and Ghost Fluid Method (GFM) have been developed in the finite volume framework and employed in several interfacial flows such as Rayleigh-Taylor instability, rising bubble, impinging droplet and cross-flow oil plume. In the static droplet simulation, A-CLSVOF substantially reduces the spurious currents. The capillary wave relaxation shows that this method delivers results comparable to those of more rigorous methods such as Front Tracking methods for fine grids. The results for the other interfacial flows also compared well with the experimental results. Next, interfacial forces are implemented by enlisting the finite volume discretization of Ghost Fluid Method. To assess the A-CLSVOF/GFM performance, four cases are studied. In the case of the static droplet in suspension, the combined A-CLSVOF/GFM produces a sharp and accurate pressure jump compared to the traditional CSF (continuum surface force) implementation. For the linear two-layer shear flow, GFM sharp treatment of the viscosity captured the velocity gradient across the interface. For a gaseous bubble rising in a viscous fluid, GFM outperforms CSF by almost 10%. Also, a Decoupled Pressure A-CLSVOF/GFM method (DPM) has been developed which separates pressure into two pressure components, one accounting for interfacial forces such as surface tension and another representing the rest of flow pressure. It is proven that the DPM implementation results in more efficiency in PISO (Pressure Implicit with Splitting of Operators) loop. A two-phase solver is used to study buoyant oil discharge in quiescent and cross-flow ambient. Different modes of breakup including dripping, jetting (axisymmetric and asymmetric) and atomization for cross-flow oil jet are captured
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