21 research outputs found
Efficient Algorithm on a Non-staggered Mesh for Simulating Rayleigh-Benard Convection in a Box
An efficient semi-implicit second-order-accurate finite-difference method is
described for studying incompressible Rayleigh-Benard convection in a box, with
sidewalls that are periodic, thermally insulated, or thermally conducting.
Operator-splitting and a projection method reduce the algorithm at each time
step to the solution of four Helmholtz equations and one Poisson equation, and
these are are solved by fast direct methods. The method is numerically stable
even though all field values are placed on a single non-staggered mesh
commensurate with the boundaries. The efficiency and accuracy of the method are
characterized for several representative convection problems.Comment: REVTeX, 30 pages, 5 figure
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Quasi-steady droplet phase change in the presence of convection
Simple expressions for the rate of change of droplet mass and droplet temperature are derived for an arbitrary convective environment, under the assumptions: (1) unity Lewis number, or constant Lewis number and equal gas-phase species C/sub p/, and (2) uniform conditions on the droplet surface. Supplemented by a suitable droplet heat-flux correlation, these equations form a simple, but quite general, droplet phase change model
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Improved accuracy general remapping algorithm
Most numerical methods in fluid dynamics can be classified as being either Lagrangian or Eulerian. An important group of methods, however, is a combination of both. These methods generally derive from the ALE (Arbitrary-Lagrangian-Eulerian) method of Hirt et al. A computational cycle in these methods is divided into two main phases: a lagrangian phase and a rezone or remap phase (these two terms are used interchangeably). The remapping phase conservtively transfers quantities, calculated in the Lagrangian phase, from the Lagrangian mesh to some other specified mesh. For example, in a given time step the remap phase may be omitted, in which case the computation is purely Lagrangian, or the remapping may be back to the original mesh, in which case the computation is Eulerian. The remapping step, therefore, corresponds to the effect of the advection terms in Eulerian equations. It may also be viewed as a conservative interpolation procedure from one mesh to another, and so it is also useful in other more general applications, such as in adaptive mesh computations. In this paper a new method is extended to the case of a more accurate density distribution: the density distribution within a cell is allowed to be linear, while preserving the average value of density over the cell. The orientation of this planar surface is given by the average local density gradient. Such a linear distribution, while more accurate in general, can cause undershoots or overshoots in regions of rapidly changing densities. This is avoided by placing monotonicity limits on the allowable gradients, similar to those used by Van Leer in one-dimension
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Numerical simulation of reactive flow in internal combustion engines. [CONCHAS-SPRAY code]
Multidimensional numerical simulations of the reactive fluid flow in an internal combustion engine cylinder are useful in helping engine designers obtain insight into the physical mechanisms governing efficiency and pollutant formation. A comprehensive numerical model for internal combustion engine cylinder simulations that has been developed at Los Alamos is described. The model is currently embodied in a two-dimensional (axisymmetric) computer code called CONCHAS-SPRAY. Work is in progress on a three-dimensional code with the same features
Sur le calcul des vitesses des noeuds dans les codes multidimensionnels Lagrangiens
SIGLECNRS RP 148 (811) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc