24,976 research outputs found
The XDEM Multi-physics and Multi-scale Simulation Technology: Review on DEM-CFD Coupling, Methodology and Engineering Applications
The XDEM multi-physics and multi-scale simulation platform roots in the Ex-
tended Discrete Element Method (XDEM) and is being developed at the In- stitute
of Computational Engineering at the University of Luxembourg. The platform is
an advanced multi- physics simulation technology that combines flexibility and
versatility to establish the next generation of multi-physics and multi-scale
simulation tools. For this purpose the simulation framework relies on coupling
various predictive tools based on both an Eulerian and Lagrangian approach.
Eulerian approaches represent the wide field of continuum models while the
Lagrange approach is perfectly suited to characterise discrete phases. Thus,
continuum models include classical simulation tools such as Computa- tional
Fluid Dynamics (CFD) or Finite Element Analysis (FEA) while an ex- tended
configuration of the classical Discrete Element Method (DEM) addresses the
discrete e.g. particulate phase. Apart from predicting the trajectories of
individual particles, XDEM extends the application to estimating the thermo-
dynamic state of each particle by advanced and optimised algorithms. The
thermodynamic state may include temperature and species distributions due to
chemical reaction and external heat sources. Hence, coupling these extended
features with either CFD or FEA opens up a wide range of applications as
diverse as pharmaceutical industry e.g. drug production, agriculture food and
processing industry, mining, construction and agricultural machinery, metals
manufacturing, energy production and systems biology
Numerical study of acoustic oscillations and combustion instabilities in solid propellant rocket
A numerical analysis of unsteady motions in solid rocket motors has been conducted. A fully coupled
implicit scheme based on a dual time-stepping integration algorithm has been adopted to solve the governing
equations and associated boundary conditions. A narrow pressure pulse is imposed at the head end to
simulate unsteady acoustic oscillations in the combustion chamber. Pressure increases when the front of the
pulse reaches near the nozzle area. Self-generated oscillations with frequency of standing wave propagates
upstream in the combustion chamber. Investigation of transient response of gas-phase dynamics to traveling
pressure wave and its effects on propellant combustion reveals several aspects: Combustion responses have
a strong relationship with vorticity fluctuations in case of high turbulent intensity on the propellant surface.
Temperature fluctuations of the propellant surface in the head end region seem to be very unstable and
independent of the pressure wave. Surface temperature without turbulence effect looks more sensitive to
temperature fluctuations in the primary flame zone. Stability of surface temperature is strongly related to
turbulent intensity on the propellant surface
A review of wildland fire spread modelling, 1990-present, 1: Physical and quasi-physical models
In recent years, advances in computational power and spatial data analysis
(GIS, remote sensing, etc) have led to an increase in attempts to model the
spread and behaviour of wildland fires across the landscape. This series of
review papers endeavours to critically and comprehensively review all types of
surface fire spread models developed since 1990. This paper reviews models of a
physical or quasi-physical nature. These models are based on the fundamental
chemistry and/or physics of combustion and fire spread. Other papers in the
series review models of an empirical or quasi-empirical nature, and
mathematical analogues and simulation models. Many models are extensions or
refinements of models developed before 1990. Where this is the case, these
models are also discussed but much less comprehensively.Comment: 31 pages + 8 pages references + 2 figures + 5 tables. Submitted to
International Journal of Wildland Fir
Investigation of the transient fuel preburner manifold and combustor
A computational fluid dynamics (CFD) model with finite rate reactions, FDNS, was developed to study the start transient of the Space Shuttle Main Engine (SSME) fuel preburner (FPB). FDNS is a time accurate, pressure based CFD code. An upwind scheme was employed for spatial discretization. The upwind scheme was based on second and fourth order central differencing with adaptive artificial dissipation. A state of the art two-equation k-epsilon (T) turbulence model was employed for the turbulence calculation. A Pade' Rational Solution (PARASOL) chemistry algorithm was coupled with the point implicit procedure. FDNS was benchmarked with three well documented experiments: a confined swirling coaxial jet, a non-reactive ramjet dump combustor, and a reactive ramjet dump combustor. Excellent comparisons were obtained for the benchmark cases. The code was then used to study the start transient of an axisymmetric SSME fuel preburner. Predicted transient operation of the preburner agrees well with experiment. Furthermore, it was also found that an appreciable amount of unburned oxygen entered the turbine stages
Spray combustion experiments and numerical predictions
The next generation of commercial aircraft will include turbofan engines with performance significantly better than those in the current fleet. Control of particulate and gaseous emissions will also be an integral part of the engine design criteria. These performance and emission requirements present a technical challenge for the combustor: control of the fuel and air mixing and control of the local stoichiometry will have to be maintained much more rigorously than with combustors in current production. A better understanding of the flow physics of liquid fuel spray combustion is necessary. This paper describes recent experiments on spray combustion where detailed measurements of the spray characteristics were made, including local drop-size distributions and velocities. Also, an advanced combustor CFD code has been under development and predictions from this code are compared with experimental results. Studies such as these will provide information to the advanced combustor designer on fuel spray quality and mixing effectiveness. Validation of new fast, robust, and efficient CFD codes will also enable the combustor designer to use them as additional design tools for optimization of combustor concepts for the next generation of aircraft engines
Center for low-gravity fluid mechanics and transport phenomena
Research projects in several areas are discussed. Mass transport in vapor phase systems, droplet collisions and coalescence in microgravity, and rapid solidification of undercooled melts are discussed
A new lattice Boltzmann model for interface reactions between immiscible fluids
In this paper, we describe a lattice Boltzmann model to simulate chemical reactions taking place at the interface between two immiscible fluids. The phase-field approach is used to identify the interface and its orientation, the concentration of reactant at the interface is then calculated iteratively to impose the correct reactive flux condition. The main advantages of the model is that interfaces are considered part of the bulk dynamics with the corrective reactive flux introduced as a source/sink term in the collision step, and, as a consequence, the model’s implementation and performance is independent of the interface geometry and orientation. Results obtained with the proposed model are compared to analytical solution for three different benchmark tests (stationary flat boundary, moving flat boundary and dissolving droplet). We find an excellent agreement between analytical and numerical solutions in all cases. Finally, we present a simulation coupling the Shan Chen multiphase model and the interface reactive model to simulate the dissolution of a collection of immiscible droplets with different sizes rising by buoyancy in a stagnant fluid
The Astrochemical Evolution of Turbulent Giant Molecular Clouds : I - Physical Processes and Method of Solution for Hydrodynamic, Embedded Starless Clouds
Contemporary galactic star formation occurs predominantly within
gravitationally unstable, cold, dense molecular gas within supersonic,
turbulent, magnetized giant molecular clouds (GMCs). Significantly, because the
chemical evolution timescale and the turbulent eddy-turnover timescale are
comparable at typical GMC conditions, molecules evolve via inherently
non-equilibrium chemistry which is strongly coupled to the dynamical evolution
of the cloud.
Current numerical simulation techniques, which include at most three decades
in length scale, can just begin to bridge the divide between the global
dynamical time of supersonic turbulent GMCs, and the thermal and chemical
evolution within the thin post-shock cooling layers of their background
turbulence. We address this GMC astrochemical scales problem using a solution
methodology, which permits both complex three-dimensional turbulent dynamics as
well as accurate treatment of non-equilibrium post-shock thermodynamics and
chemistry.
We present the current methodology in the context of the larger scope of
physical processes important in understanding the chemical evolution of GMCs,
including gas-phase chemistry, dust grains and surface chemistry, and turbulent
heating. We present results of a new Lagrangian verification test for
supersonic turbulence. We characterize the evolution of these species according
to the dimensionless local post-shock Damk\"{o}hler number, which quantifies
the ratio of the dynamical time in the post-shock cooling flow to the chemical
reaction time of a given species.
Lastly, we discuss implications of this work to the selection of GMC
molecular tracers, and the zeroing of chemical clocks of GMC cores.Comment: 35 pages, 7 figures, 16 tables. Accepted to MNRAS. Revised to correct
some typographic error
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