Hello and welcome. In this Ansys How to Video, we will discuss the details of
the proximity size control in the Local Sizing task of the Ansys Fluent Meshing
Watertight Workflow. So, let's get started!
The local sizing task allows us to gain better control over the sizing of the mesh elements by
letting us define mesh size controls that operate on specific localized portions of the domain.
Proximity size control type is used for refining the mesh
by specifying the number of cells to be used to resolve gaps either between edges or faces.
Let's learn about this size control in detail by getting our hands dirty with Watertight workflow
in Ansys Fluent Meshing. Let's start fluent in meshing mode. Set the number of processes
and the working directory accordingly. Once Fluent launches, select ‘Watertight workflow’
from the dropdown menu and import the provided geometry as shown here.
This geometry consists of an enclosure
around a PCB containing geometrically identical pairs of heat sinks and capacitors as shown here.
Keep in mind that this is a representative geometry intended for instructional use only.
Select Yes for this question under Add Local Sizing task. Now under Size Control Type
select – Proximity. You will notice that additional settings are added to the task.
The proximity sizing requires 4 main parameters to be defined:
Min & Max Sizes, Growth rate and the cells per gap. The Local Min and Max Sizes allows
us to specify the minimum and maximum sizes of the elements for the surface mesh, respectively. Keep
in mind that these sizes are measured between the proximity boundaries. The Growth Rate specifies
the increase in element edge length with each succeeding layer. These settings prevent the mesh
from becoming too fine or too coarse on the scoped surfaces. Let's select ‘walls_heatsink-1
and set the local min and max sizes to 0.3 and 1, respectively
and keep the default value for Growth Rate.
The main parameter for this control type is the ‘Cells Per Gap’ setting.
This setting allows us to set a minimum number of layers of elements to be generated in the gaps.
These gaps are defined in either of two ways – the area between two opposing boundary edges of a face
or the internal volumetric region between two faces. Set the cells per gap to 4.
Lastly, we need to define the scope of this localized size control in the ‘scope to’ field.
We can localize the size control to faces, edges, or ‘faces and edges’. The last option,
I.e. ‘Faces and Edges’ on proximity can be used when the prescribed number of cells across the gap
need to be respected on all transverse sections of proximity walls. Let's set the scope to ‘Faces’
and click on ‘Add local sizing’. You can see that the proximity local sizing task is added to the
workflow. Now create a similar local sizing for ‘walls_heatsink-2’ but set the cells per gap to 2,
to see the impact of this parameter.
We will keep the defaults for the ‘Generate the Surface mesh task’
as we want to focus on local sizing in this video. Click on ‘Generate the Surface Mesh’
and Fluent meshing will create the surface mesh based on these settings.
Let's look at the generated surface mesh to see the effect of the proximity local sizing.
First let's hide the enclosure, the inlet and the outlet surface
and zoom into the heat sinks. The impact of the proximity size control, specifically
the cell per gap parameter is clear when looking at the mesh for the two heat sinks.
The surface mesh for the heatsink on the left has been generated with Cell per gap
of 2 whereas the one on the right is generated using a cell per gap of 4,
which is evident from the number of cells that are present in the gaps.
Before we wrap up, lets quickly see the effect of different scoping options.
Let's go back the proximity size control for heatsink-1,
change the ‘cells per gap’ to 2 and select ‘Edges’ under ‘Scope To’.
Now let's generate the surface mesh again.
Here is the generated surface mesh.
You can clearly see the effect of scoping the local sizing to edges
compared to faces by comparing the surface meshes on the two heat sinks.
The local sizing is applied only at the edge of the face and the size of
the elements increases while moving away from the edge where the sizing is being applied.
To summarize, in this video we looked at the proximity Size control
for the Local Sizing task. This size control
allows us to control the local sizing based on the number of cells per gap setting,
which we understood using a hands-on example. With that we have come to the end of this video!