hello
and welcome
the mesh generation process in modern
day cfd starts with either a cad
geometry where a user is attempting to
create a new mesh
or
an existing mesh file where the goal is
to modify the mesh
because of this
there are two import options available
in ansys fluid meshing watertight
geometry workflow
the cad import which starts from a cad
geometry
and the mesh import which starts either
from an existing mesh file or a fluent
case file
in this video
we will focus only on the cad import
geometry part specifically on how to
prepare your cad geometry so that it can
be successfully imported into the
watertight workflow
[Music]
let's focus on the cad geometry first
an important requirement for using the
watertight workflow is that the cad
geometry must be relatively clean with
watertight regions
the keywords here are clean and
watertight
cleancat refers to error-free geometries
the check geometry operation ansys
spaceclaim is recommended method to
inspect the cad file for errors such as
bad or non-manifold faces
to perform this operation
right click on the part and select check
geometry
if the cad is clean you will get the
message
no geometry problems were found
if error messages are displayed it is
advisable to fix them in space claim
before importing the geometry into the
watertight workflow
sometimes these fixes might involve
deleting the bad faces
and recreating them
watertight cads refer to geometries with
no gaps holes or leaks
if the geometry has holes or leaks
spaceclaim displace them as a surface
object in the structure tree
in such scenarios we must simply
identify and plug these holes by
creating the missing faces
tools such as stitch
gaps and missing faces in the repair tab
of ansys spaceclaim are quite useful
once the geometry becomes watertight
this surface object is automatically
converted into a 3d volume or body
users interested in meshing geometries
with imperfections which cannot be
easily fixed should instead use the
fault tolerant meshing workflow in
fluent machine
to get more information about this
workflow please refer to the fluent
user's guide
the cad geometries used in the
watertight workflow can be a single body
part like this exhaust manifold
or a combination of multiple bodies like
the printed circuit board enclosure
the cad import type supports any
combination of fluids and or
solid bodies to perform for example a
conjugate heat transfer analysis
in fact the imported geometries may only
be either solids or fluids
in this example we observe that there
are several components of pcb and each
component contains multiple solid bodies
while the fluid volume can be extracted
in ansys space claim
which can be done using the volume
extract tool in the prepare tab
it is not necessary to do this while
creating the cad geometry
this fluid volume can also be extracted
automatically using the surface mesh
created on the solid geometry directly
in the meshing workflow
it is important to highlight that the
surface mesh is created on all the
surfaces of the solid geometry
including the non-wetted surfaces
and this operation may consume
additional time and memory especially
for complex geometries
it is therefore
best to prepare the geometry by removing
unnecessary assemblies from the cad file
before importing it into the watertight
workflow
in addition to the solid and fluid
volumes
the watertight workflow also supports
importing of geometries with voids
when dealing with multi-body parts
like this electronics enclosure
care should be taken to ensure that each
of these bodies fluid or solid
should be individually watertight
as a rule of thumb
the share topology operation in space
claim between these multiple bodies
should be performed before importing the
cad into the fluent machine
this option can be found in the
workbench tab of ansys spaceclaim
and it allows us to generate a conformal
mesh
if successful
the shared faces and edges are
highlighted in purple color
and it is recommended to perform the
check geometry operation before and
after the share topology operation
care should be taken to ensure that the
geometry is clean and well connected
before importing it to fluent machine in
most cases
the regular share option
should be sufficient to connect all the
entities on the clean cad
the force share is not mandatory but can
be used after the regular share to force
the sharing automatically or manually on
individual entities according to the set
tolerances
the cad import also supports the import
of fully enclosed bodies such as an
aircraft or a racing car placed inside
an enclosure for external aerodynamic
simulations
in such cases it is not required to
subtract the solid body from the
enclosure at the cad geometry stage
moreover
sharing the topology between the solid
body and the enclosure is not
recommended for such
problems baffle type geometrical
features
often seen in mixing tanks or heat
exchangers are also supported cad
entities in the watertight workflow
it is important however to share the
topology
especially on the edges
finally
it is recommended to group surfaces and
create labels in space claim
before importing the geometry into
fluent machine
these labels are useful in adding local
sizes and are subsequently identified by
fluent when assigning boundary
conditions during the modeling stage of
the simulation
these groups of surfaces or boundaries
are also referred to as named selections
and to create them in space claim you
can use the groups panel
select all surfaces you would like to
group and click on create ns button as
shown
you can use the control and left mouse
click to make multiple selections
for example we will select the following
four faces and label them as outlet
ansys fluent will automatically read
this label and assign the pressure
outlet boundary condition based on the
naming convention
the details about typical naming
conventions on boundaries such as inlets
outlet far field symmetry wall and
internal or interior
can be found in the fluent user's guide
in summary
the cad geometries imported into the
watertight workflow must be clean and
watertight
the share topology operation must be
performed on all the geometries
involving multiple bodies
that can include both fluids and or
solids and or voids
it is extremely useful and convenient to
spend a few minutes on creating groups
in ansys space claim before importing
the cad geometry into fluent meshing
this brings us to the end of our video
you