ParaView (under Data→Save Data). In this case it may be necessary to apply an image resampling filter first (with the x, y and z cell count) to generate data on a structured grid.
Note
Other filters hat may prove helpful:
transform
for symmetry operations,append datasets
to combine mirrored datasets with the original,calculator
to generate the grain number (e.g. from phase fractions) andpass arrays
to select only the desired output array.
Since MICRESS® expects cell centred coordinates it may be necessary to edit the header as shown in Figure 2. After the grains are read in as grain structure the profile is adjusted to generate a smooth profile from the sharp interface (but blocky) grain structure. The solid fraction achieved in this way should be checked in the MICRESS® generated output to check if it matches the input structure with sufficient accuracy and possibly adjust the input structure (e.g. by using another threshold when marking cells as solid).
Note
Profile adjustment can take some time for large structures, so you might want to generate a restart file with adjusted profile and start from there (with
steady_restart
or frozen phase field) when adjusting convergence parameters.
The steady start option is employed to establish the flow pattern at time step 0. With this option MICRESS® tries to determine a large value for the time steps used to establish a steady pattern (for these steps the time limits do not apply). The number of preliminary time steps is chosen with the pre_iter
option, it should be large enough to establish a steady fluid flow pattern. When this is the case the final time steps converge very fast, so verbosity
should be kept at 2
for verification.
In some cases the automatic time steps may become too large to achieve convergence, especially when eddies are forming. If this is the case freeze the phase field as in the cylinder examples, start with small time steps and converge the flow pattern in successive runs using restarts while adjusting time steps and convergence parameters.
Figure 2 Changes to present
POINT
data asCELL
data.
# vtk DataFile Version 3.0
vtk output
ASCII
DATASET STRUCTURED_POINTS
DIMENSIONS 199 100 100
SPACING 1 1 1
ORIGIN 0 0 0
POINT_DATA 1990000
SCALARS solid double
LOOKUP_TABLE default
0 0 0 0 0 0 0 0 0
...
# vtk DataFile Version 3.0
vtk output
ASCII
DATASET STRUCTURED_POINTS
DIMENSIONS 200 101 101
SPACING 1 1 1
ORIGIN 0 0 0
CELL_DATA 1990000
SCALARS korn float
LOOKUP_TABLE default
0 0 0 0 0 0 0 0 0
...
Example | A009_Flow _Permeability | B017_Flow _Cylinder_Karman | T030_Flow _Cylinder_Laminar |
---|---|---|---|
Dimension | 3-D | 2-D | |
Grid size | 199x100x100 cells | 200x75 cells | 200x100 cells |
Grid spacing | 1 microns | 0.5 microns | |
Interface thickness | 2.5 cells | 5 cells | |
Boundary conditions |
|
|
|
In Figure 3 the flow patterns caused by a cylindrical object are compared for two different Reynolds numbers. For low Reynolds numbers a very simple stationary pattern occurs, at higher Reynolds numbers eddies will form behind the obstacle, and at even higher Reynolds numbers periodically changing patterns like a Karman vortex street may evolve after some simulation time.
Figure 3 Flow around a cylinder
Re = 1.6 \cdot 10^{-2}
Re = 100
The white circle indicates the grain geometry from the driving file. In the Karman example the grid distance is quite large, so the interaction of melt flow with the phase field interface can be seen: The solid fraction has a braking effect on the fluid flow, so melt flow can pass (tangentially) through the phase field interface but is slowed down.
For the dendritic structure the simulation yields a steady velocity field with an average velocity v_x = 2.8 \cdot 10^{-5} m/s. The average pressure gradient g given in the input equals the pressure difference over the length in x direction.
The dynamic viscosity from the material data section for fluid flow is given by the kinematic viscosity at the density \mu = ν \cdot \rho = 7 \cdot 10^{-3} kg/ms.
From these values the permeability results as k = \frac{\mu \cdot v_x}{g} = 3.9 \cdot 10 ^{-11} m^2.
The value for the liquid fraction of the simulation domain is provided in the tabulated fractions as 84%.