Hello and welcome! In this video, we will focus on some tasks which may be useful after the volume mesh has been generated. These tasks
can be used to extend the volume mesh beyond the original domain and translate or rotate the mesh.
Eager to explore them, let’s go!
The Watertight Geometry Workflow provides some useful tasks, which are ‘Extrude Volume Mesh’ and ‘Transform Volume Mesh’, that can
be added to the workflow after the volume mesh has been generated. The Extrude Volume Mesh task can be used to extend the
boundary surfaces of the initial mesh beyond the boundaries of the original computational domain. This can be useful in cases like fluid
flow through a pipe, where extending the fluid region on the inlet side may be required to allow the flow to develop. Transform Volume
Mesh task provides the ability to rotate or translate the volume mesh, with the option to create copies while applying these
transformations. Let us see these tasks in action beginning with the Extrude Volume Mesh task.
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
Generate the Volume Mesh task have already been successfully completed. This is because the mesh that we just read into Fluent has
originally been created using the watertight workflow and saved after completing Generate the Volume Mesh task. Such files when read
back into Fluent retain the information regarding their workflow. The model we have here is that of a generic ball or check valve,
which consists of only the fluid domain and the void region of the valve. To add ‘Extrude Volume Mesh’ task to the
workflow, right-Click on 'Generate the Volume Mesh' task, select 'Insert new task' and click on ‘Extrude Volume Mesh'. Select the boundary
surface which needs to be extruded. In this demo, we will select the inlet surface. The extruded region is created by extending each
surface mesh element of the boundary surface, layer by layer, and the layer heights are calculated in a geometric fashion depending on
the user inputs. There are two extrusion methods available to choose from – ‘Total Height’ and ‘First Height’. First, let us go with
the default option ‘Total Height’. In this method the total height of the extrusion needs to be specified along with Number of Layers and
Growth Rate. In this demo, we will change the total height to 30 mm and the number of layers to 15 while keeping the growth rate at default
value. In the console, the first height and last height of the layers are reported which are calculated using the inputs provided. A preview
box is displayed to visualize the extents of the extrusion prior to executing the task. Click on Extrude Mesh to execute the task. An extruded
region with the specified total height and the number of layers is created from the inlet surface, with the height of each layer
progressively increasing depending on the specified growth rate. The inlet surface has automatically moved from its original position to
a new position, which is at the top surface of the extruded region. To create the extrusion by specifying the height of the first layer, select
‘First Height’ for the extrusion method. Let us change the first height to 1mm and keep all other inputs same as before. The console
reports the calculated last layer height and the total height of the extrusion. On updating the volume mesh an extruded region is created
from the inlet surface according to the inputs provided in the task. Observe that, when the extruded mesh is clicked on, the adjacent
region also gets selected. This is because, the ‘Merge with Adjacent Region’ option in the advanced options, was selected by default.
When the option is deselected, the extruded and the adjacent regions are not merged and can be selected separately.
The ‘Growth Pattern’ option is used to select the pattern in which the extrusion layers must grow. The Extrude Volume Mesh task allows
extrusion by selecting multiple boundary surfaces at the same time. Moreover, extrusion is not limited to only planar surfaces and can
be applied to curved surfaces as well. In all the cases, whether it is planar or curved surface, the extrusion process is performed normal to
the selected surfaces. However, there are some limitations to the tasks, such as, not being applicable to zones that are already
connected to cells. For more details on these limitations, please refer to the user guide. Let’s now discuss the workings of the
‘Transform Volume Mesh’ task. Using this task, translational or rotational transformations can be applied to the volumetric mesh. First is the
Translational type of transformation, which is the default option. The model used here is a small section of a cross flow heat exchanger
which when repeated along y and z axes gives the complete heat exchanger. After selecting the mesh object from the list for translational
shifting, enter the values by which the selected volume mesh must be shifted in the X, Y and Z directions. When the ‘Create Copy and
Translate’ option is set to ‘yes’, which is the default, copies of the original mesh are created and shifted, and not the original mesh itself.
You can create more than one copies for the transformation by specifying the number here. To apply the translation directly to the original
mesh, just set the option to ‘no, only translate’. Use the ‘Preview Transformation’ button to see the preview of what the volume mesh
transformation will look like in the graphics window. In our demo, let’s create two copies of the volume mesh and shift them by 40 mm in
the y-direction. The two copies of the original volume mesh are named by adding an underscore and its copy number to the original
cell zone name. This is because the default setting of ‘Rename cell and face zones’ was retained as ‘yes’. If the option is set to ‘no’ then
the copied cell zones will be created with names that use colons and the copy’s ID. The same naming methodology applies to copied
face zones as well. Next, let’s explore the second type of transformation which is the ‘Rotational’ type.
Most of the inputs for rotational transformation are similar to the translational type except for few differences. For rotational transformations,
the Rotation Axis Origin, the coordinates of the rotational vector, and the angle by which the mesh has to rotate need to be specified. In the
demo, five copies of the original mesh are created which are rotated about the X -direction.
When the model has no periodicity, then the manual method for transformation is utilized by default as already seen. However, when
translational or rotational periodicity is detected in the model, the method of transformation is set to ‘Automatic – use existing periodics’ by
default. The manual option is also available along with the default option. For rotational periodicity, the values for the angle, the origin
and rotation axis direction are automatically extracted from the periodic settings. The number of copies is automatically set to
produce a full 360-degree model, however, this can be changed as required. On the other hand, in case of translational periodicity, the
shift direction and distance are automatically assigned as per the periodic settings. When using the automatic method, the
‘Merge the cell and face zones?’ input appears, which is set to ‘yes’ by default. This will merge the all the cell and face zones to create one
entity and avoid any zone duplication. The cell and face zone names of the original mesh are applied to the corresponding merged zones. If
only cell zones need to be merged and face zones are to be kept as separate entities, then set ‘Merge the cell and face zones?’ option to
‘only cell zones’ and set this option to ‘no’ if you do not want any merging to happen. Note that, when the transformation is performed using the
automatic method, the periodic boundaries on the original mesh, will be replaced with interfaces between the mesh copies which will
be changed to the type ‘internal’ after transformation. To summarize, in this lesson, we explored two
tasks that can be useful after the volume mesh has been generated. The first is the ‘Extrude Volume Mesh’ task, which can extend planar or
curved boundary surfaces of the volume mesh, based on the user inputs. The second is the ‘Transform Volume Mesh’ task which allows for
translational and rotational types of transformation to be performed on the volume mesh. The transformations may be applied to
the original mesh or to its copies. With this, we come to the end of the lesson!