1,974 research outputs found
MFC: An open-source high-order multi-component, multi-phase, and multi-scale compressible flow solver
MFC is an open-source tool for solving multi-component, multi-phase, and bubbly compressible flows. It is capable of efficiently solving a wide range of flows, including droplet atomization, shock–bubble interaction, and bubble dynamics. We present the 5- and 6-equation thermodynamically-consistent diffuse-interface models we use to handle such flows, which are coupled to high-order interface-capturing methods, HLL-type Riemann solvers, and TVD time-integration schemes that are capable of simulating unsteady flows with strong shocks. The numerical methods are implemented in a flexible, modular framework that is amenable to future development. The methods we employ are validated via comparisons to experimental results for shock–bubble, shock–droplet, and shock–water-cylinder interaction problems and verified to be free of spurious oscillations for material-interface advection and gas–liquid Riemann problems. For smooth solutions, such as the advection of an isentropic vortex, the methods are verified to be high-order accurate. Illustrative examples involving shock–bubble-vessel-wall and acoustic–bubble-net interactions are used to demonstrate the full capabilities of MFC
Double-distribution-function discrete Boltzmann model for combustion
A 2-dimensional discrete Boltzmann model for combustion is presented.
Mathematically, the model is composed of two coupled discrete Boltzmann
equations for two species and a phenomenological equation for chemical reaction
process. Physically, the model is equivalent to a reactive Navier-Stokes model
supplemented by a coarse-grained model for the thermodynamic nonequilibrium
behaviours. This model adopts 16 discrete velocities. It works for both
subsonic and supersonic combustion phenomena with flexible specific heat ratio.
To discuss the physical accuracy of the coarse-grained model for nonequilibrium
behaviours, three other discrete velocity models are used for comparisons.
Numerical results are compared with analytical solutions based on both the
first-order and second-order truncations of the distribution function. It is
confirmed that the physical accuracy increases with the increasing moment
relations needed by nonequlibrium manifestations. Furthermore, compared with
the single distribution function model, this model can simulate more details of
combustion.Comment: Accepted for publication in Combustion and Flam
Recent advances in the simulation of particle-laden flows
A substantial number of algorithms exists for the simulation of moving
particles suspended in fluids. However, finding the best method to address a
particular physical problem is often highly non-trivial and depends on the
properties of the particles and the involved fluid(s) together. In this report
we provide a short overview on a number of existing simulation methods and
provide two state of the art examples in more detail. In both cases, the
particles are described using a Discrete Element Method (DEM). The DEM solver
is usually coupled to a fluid-solver, which can be classified as grid-based or
mesh-free (one example for each is given). Fluid solvers feature different
resolutions relative to the particle size and separation. First, a
multicomponent lattice Boltzmann algorithm (mesh-based and with rather fine
resolution) is presented to study the behavior of particle stabilized fluid
interfaces and second, a Smoothed Particle Hydrodynamics implementation
(mesh-free, meso-scale resolution, similar to the particle size) is introduced
to highlight a new player in the field, which is expected to be particularly
suited for flows including free surfaces.Comment: 16 pages, 4 figure
Numerical Simulation of Compressible Flows with Interfaces
Compressible interfacial flows exist in a variety of applications: reacting fronts, droplet break up, jets and sprays in high speed, shock passage in foams, etc. These flows behave in a complex multi-scale way including interface deformation, wave interface interaction and complex transport phenomena.
In the first section, the interaction of a laminar flame with a compression wave is investigated. More precisely, the evolution of the burning interface is investigated and discussion over different compression waves and their effects on the flame geometry and burning rate are made.
In the second part, a numeral framework for simulation of compressible multiphase flows using adaptive wavelet collocation method is developed. This study was originally motivated by the desire for a numerical tool capable of simulating the atomization process during start-up conditions in a supersonic combustor. To model such physics, the solver needs to handle high density ratios, transport terms and capillary effects.
The multi-scale behaviour of these flows requires a multi-scale approach. Parallel Adaptive
Wavelet Collocation Method (PAWCM) makes use of second generation wavelets to dynamically adapt the grid to localized structures in the flow in time and space. This approach allows the solution to be approximated using a subset of the points that would normally be used with a uniform grid scheme. Thus, computation on this subset is efficient and high levels of data compression is achieved
Smoothed Dissipative Particle Dynamics model for mesoscopic multiphase flows in the presence of thermal fluctuations
Thermal fluctuations cause perturbations of fluid-fluid interfaces and highly
nonlinear hydrodynamics in multiphase flows. In this work, we develop a novel
multiphase smoothed dissipative particle dynamics model. This model accounts
for both bulk hydrodynamics and interfacial fluctuations. Interfacial surface
tension is modeled by imposing a pairwise force between SDPD particles. We show
that the relationship between the model parameters and surface tension,
previously derived under the assumption of zero thermal fluctuation, is
accurate for fluid systems at low temperature but overestimates the surface
tension for intermediate and large thermal fluctuations. To analyze the effect
of thermal fluctuations on surface tension, we construct a coarse-grained Euler
lattice model based on the mean field theory and derive a semi-analytical
formula to directly relate the surface tension to model parameters for a wide
range of temperatures and model resolutions. We demonstrate that the present
method correctly models the dynamic processes, such as bubble coalescence and
capillary spectra across the interface
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