Hello and welcome!
In this video,
we will learn what the volume mesh quality is
and how to improve it in the
Ansys Fluent Meshing Watertight Geometry Workflow.
The volume mesh has a significant influence
on the accuracy and stability of a simulation.
To ensure an accurate modeling of the fluid flow physics
and all the necessary flow features,
it is not only critical to ensure appropriate mesh resolution
but also the creation of high-quality mesh.
Mesh quality refers to the quality of the cells
that make up the volume mesh.
The evaluation of quality can be done using various measures
such as skewness, aspect ratio, warp etc.,
which are defined primarily based on the cell shape.
The default measure reported in
Watertight Geometry Workflow
is the Orthogonal Quality or Orthogonality.
Once the volume mesh is created,
the minimum mesh quality measure
over the entire volume mesh
is printed to the console window.
Depending on the reported value,
the volume mesh can either be finalized
and transferred to Fluent for performing the simulation
or an improve the mesh quality
can be performed to improve the quality of the volume
mesh before switching to the solution mode.
Let us now look at how the Orthogonal quality measure is defined.
It is the measure of alignment
between the vectors normal to the cell faces
and the vectors connecting cell centroid
with face centroids,
which is determined with the help of this equation,
and also between vectors
normal to the cell faces
and the vectors connecting cell centroids,
which is determined with the help of this equation.
The minimum value that results from these 2 equations
for all faces
is the orthogonal quality for the cell.
It ranges from 0, which is poor, to 1,
which is perfect.
A mesh should have minimum orthogonal quality
always greater than 0.01,
but it is highly recommended to maintain it above 0.1,
whenever possible.
Let us now understand how to check
and improve the mesh quality in
the Ansys Fluent Meshing Watertight Workflow
with the help of a demo problem.
Launch Ansys Fluent in meshing mode.
Go to File, Read, and select Mesh,
and then pick the provided mesh file.
Once Fluent finishes reading the file,
you will notice that the watertight geometry workflow
has been automatically setup
and all the tasks till the Add Boundary Layers task
have already been successfully completed.
The model we have here is that of a
generic two-element rear wing
found on a formula series type race car,
enclosed within a virtual wind tunnel.
Except for the inlet and the outlet,
all the other sides of the wind tunnel
and the wing geometry are considered as walls.
The model consists of only the fluid domain
with the wing considered as a void.
Now, let’s generate the volume mesh with the default settings for this demo.
Once the mesh is generated,
Fluent displays the mesh quality value in the Console window,
as shown here.
Alternatively, mesh quality can also be checked by clicking on Mesh tab at the top,
and then on 'Check Quality'.
This will display the 'Minimum Orthogonal Quality' value,
along with the Maximum Aspect Ratio in the Console window,
as shown here.
If the user is interested in computing and displaying
other mesh quality measures,
navigate to ‘Cell Limits’ under the Report tab
and select ‘Quality Measure’
from the pop-up box.
In the ‘Quality Measure’ pop-up window,
select the appropriate quality measure
and hit apply,
and after selecting the required cell zone in which the
quality measure needs to be computed,
hit ‘compute’.
This calculates and displays the minimum, maximum and the average values of the
selected mesh quality measure in the selected region.
It may be necessary to check other mesh quality metrics
such as skewness,
and specifically for polyhedra or poly-hexcore meshes
the warp factor on the faces,
to ensure that the generated mesh is of good quality.
In our demo, the orthogonal mesh quality is '0.05'.
Note that we are using 4 processors for creating the mesh.
There may be differences in the mesh quality and overall cell count
if a different number of processors is used.
As it is recommended to maintain the quality above 0.1,
we need to improve the mesh quality,
which can be done with the help of an additional task in the workflow.
Right-Click on 'Generate the Volume Mesh' task,
select 'Insert new task' and
click on 'Improve Volume Mesh'.
In the Improve Volume Mesh task,
the basic user input required is the 'Cell Quality Limit'.
Here the user can specify the minimum acceptable orthogonal quality
for the mesh.
The default value is 0.15
and the range is between 0.01 to 0.5.
Let's keep the default value for this demo.
The settings under the Advanced Options can be left at their default values
for most of the cases.
For more information on each of these settings,
please refer to the User Guide.
Click on the 'Improve Volume Mesh' button.
Fluent will now re-generate the volume mesh
with the objective of improving the quality.
Fluent will aggressively change the volume mesh in an effort
to satisfy the user entered value.
It is recommended for the user to check the new volume mesh
to ensure it is appropriate for their need.
After the improve operation,
the minimum orthogonal quality is '0.151',
which is substantially higher than the original quality
and is also above the user specified value.
Alternatively, the user can set the mesh quality threshold criterion
within the generate the volume mesh task.
In the advanced options,
irrespective of the Volume Fill With method,
the user can specify the 'Quality Improve Limit' value,
which specifies the threshold below which the
quality improvements are automatically invoked
while generating the volume mesh.
By default, the value is set to 0.05.
However, the user can change this value as required.
Once the user is satisfied with the mesh quality,
the mesh can now be considered simulation-ready
and can be transferred to the
Ansys Fluent fluid flow solver
to perform simulations.
The single-window user interface of
Ansys Fluent was created
keeping user’s experience
while navigating the end-to-end simulation workflow in mind.
The user can simply click on ‘Switch to Solution’ button,
located on top left corner of the ribbon
to transfer the mesh to Ansys Fluent solver.
Alternatively, the user can also invoke the
‘switch-to-solution-mode' text command
in the console window.
Let's summarize what we learnt.
We understood what the volume mesh quality is
and how to check it in
Ansys Fluent Meshing Watertight Geometry Workflow.
We also discussed how to improve the volume mesh
using an additional task in the workflow.
Finally, we touched upon the different ways
to switch to the solution mode.
With that, let's end the lesson.