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BatCar Tutorial

 
Bat Car Tutorial                                                  
 
Open file in Ennova
Make a new directory BATCAR on your host/server computer in your account. From the Ennova Website download the file BATCAR.igs to this directory.
 
If Client/Server is on the same computer, navigate to the directory and open BATCAR.igs.  If the Server is remote, choose the IP of that computer from the list and navigate as usual.  There is no difference when running Ennova at a user level if the Server is local or remote, except for this step.
 
 
 
BATCAR on loading is all RED edges
Surfaces are not connected.  They do not form any closed volume or surface quilt / shell.
 
Car repair
In fact, in addition to the surfaces not being connected, there are not enough surfaces to form a volume.  Nor are there any enclosed outer CFD volumes.
To fix this geometry:
 
      Create an outer CFD Box
      Stitch and Repair the car surfaces
      Add any remaining surfaces that form holes
      Obtain a closed CFD volume
 
We will start by repairing the geometry and building half the car.  Use the Repair icon (Band aid) menu and click on Set Geometry and Repair Tolerances.
 
Set the Tolerances as follows:
 
      Merge Tolerance 0.11
      Defeature Tolerance 0.00 (here we are effectively turning off defeature)
      Angle Tolerance 0.784
 
 
 
Automatic Repair – Initial Results
After Automatic Repair we find 8 areas where Ennova has not 100% repaired.  The goal was to make the entire model BLACK (except a RED single edge around where the symmetry plane will be).
 
You may have noticed that we set the defeature tolerance to zero. Typically there will be features in the CAD that are not important to CFD.  These features can be removed later, but once removed may be difficult to bring back if neededOur suggested approach is to defeature as a last step. Please note that if applying a very fine boundary layer mesh, there are some small fillets that may be important to the boundary layer flow.
 
8 different initial results are left to resolve.
 
 
 
Resolving Initial Results – Remedy 1
Result:  Extra Surfaces Require Removal
 
Select the top RED edge with RMB, and Select Attached Faces.
 
 
 
Then Remove the selected face again with RMB and the initial result is resolved.
Extra RED edges disappear and the model is watertight and BLACK.
 
 
If we had selected a BLACK edge, then two of the faces would have been selected/highlighted.  These selected faces are not displaced. 
Use RMB -> Show Items to display them.
 
 
Resolving Initial Results – Remedy 2
Result:  Tail Surfaces - Extra and Missing
 
There is an extra volume in the tail fin area of the car marked by the YELLOW edges.  Ennova can pick this entire volume minus the shared faces automatically.  Use RMB -> Select Attached Manifold.  Select one of the BLACK interior edges.
 
 
Once the region is selected, use RMB -> Remove to remove the extra geometry.
 
 
The tail surface is missing, so there are some surfaces in the bottom that should trim to each other but do not. 
 
 
 
 
 
Next we will look in detail and learn some more Ennova commands.
 
 
 
 
First we will fix the tail surface and then split and connect the floor.
 
 
Note:  We could have increased the internal tolerances to allow Ennova to do some of this work automatically, but here we want to demonstrate various repair methods.
 
Concentrating on the area in the circle, we see a surface is missing.  First use RMB -> Project Vertex on the edge to create a new vertex.
 
Next, click-select the first vertex, select the second vertex using CTRL and then use RMB -> Create Edge between Nodes.  Notice that the RMB is context sensitive, so with different items selected there will be different commands available.  Do the same for the other nodes of the rectangle.
 
Now there will be 2 RED edges and 2 BLUE edges.  The RED are connected to one surface and the BLUE are free.  Experiment with RMB -> Select Attached to verify.
 
 
Next, pick the 4 edges and RMB -> Create Face from Edges to make a new face.  Notice the edges change color to match the new status.
 
 
 
 
 
 
On the fin, select one RED (single) edge and use RMB -> Create face from single edges
 
 
A new face is created to fill the loop and all edges are BLACK.
 
 
 
 
 
There is one more missing Face.  Select the edges as shown and use RMB -> Create Face from Edges again,
 
 
 
and the Remedy 2 is complete.
 
 
 
 
 
Resolving Initial Results – Remedy 3
Result:  Missing Edge and Face
 
Here we use the exact same methodology as in Remedy 2.  We first create an edge between the two nodes,
 
 
 
and then select the 4 edges to create a new face.
 
 
 
Resolving Initial Results – Remedy 4
Result:  Surface Gaps at Edges
 
Here the CAD model cockpit does not intersect well with the car body.  The surfaces don’t quite line up and there are gaps.
 
 
First use your previous skills to build the missing face in the green circle.
Hint:  Use RMB -> Create edges(s) and RMB -> Create Face from Edges.
 
 
 
 
 
The new face is highlighted.
 
 
Next, select the face and the new bottom edge of the new face.  Use this edge to RMB -> Split Face at Edge.
 
 
 
 
 
Now Project Vertex to the top edge and create and edge followed by a split using the same sequence as we learned previously. 
 
 
Then we have the following topology.
 
 
 
 
 
Finally, split the back surface.
 
 
Now the topology is correct at the gutter of the rear of the cockpit.  It is not correct at the front, but we will address that in Remedy 6.
 
 
Resolving Initial Results – Remedy 5
Result:  Surface Gaps on Faces
 
Here the wheels are open and need the backs filled.  Use RMB -> Create Face from Single Edges.  Note:  For simple loops, do not click and choose every edge.  Just pick one and Ennova will fill find the loop.
 
 
 
Do the same for the front wheels.  Some surfaces are missing as we saw before and some surfaces are too far apart to connect.
 
 
Resolving Initial Results – Remedy 6
Result:  Disconnected Car Hood and Windshield
 
First locate tiny weird geometry at the hood and windshield inside the green circle. 
 
 
 
Select nodes and merge them with RMB -> Merge Nodes.
 
 
Then use RMB -> Create an Edge through nodes that are missing and use RMB -> Split Face at Edges to cut the windshield.
 
 
 
 
 
 
Select the resulting triangle surface and Remove
 
 
Then select long face edge (RED) and RMB -> Create Face from Single Edges.
 
 
 
 
 
 
 
 
Now the area should be locally watertight (BLACK).
 
 
Merge the two nodes at the end of the RED edges as these surfaces need to be forced to connect.  Remember as we are working on the topology, even if the CAD surfaces do not connect in real life, in our mesh space we simply declare them to be connected.  This is one of the principle advantages of performing CAD repair in Ennova versus a traditional CAD engine.
 
 
 
Once the nodes are connected, use RMB -> Merge with Adjacent Edges to connect the surfaces.
 
 
Next we will finalize the front end of the work we did in Remedy 4 and remove any excess trimmed surfaces.  Looking at the geometry (still in the region of the last green circle), we see the highlighted surface is not long enough to reach the front of the trench between the cockpit and the body.  So we will project nodes, create edges and finally create a face and then perform splits exactly the same as in the rear.
 
 
Start by splitting out the corner surface.  Remove the two surface “ears”.
 
 
Finally, following the green arrows, project the node to the two edges.
 
 
 
 
Create edges through the new and old nodes and then create the missing face. 
 
 
Split the end face corner.
 
 
 
 
Remove the outside of the unwanted face.
 
 
Then split the remaining face along the shelf.
 
 
 
 
 
 
Find a BLACK edge connected to a RED edge on the bottom of the shelf that we split off.  Collect all the surfaces that are extra and connect back to the main body via a YELLOW edge by using RMB -> Select Attached Manifold
 
 
Make sure you have what is highlighted and then remove this manifold.
 
 
 
 
 
The area should now be BLACK indicating that all is locally watertight.
 
 
 
Resolving Initial Results – Remedy 7
Result:  Unfilled Loops in the Wheels
 
Use RMB -> Create Face Single Edge to fill all the loops in both wheels.  There are 10 loops that need to be filled.
 
 
Hint:  On the group list pane, try turning off nodes, double and multiple edges.  That way, only RED lines are visible.
 
 
 
Resolving Initial Results – Remedy 8
Result:  Gaps Between Floor and Car on Symmetry Plane
 
Zoom in on the rear of the car and use RMB -> Create Vertex on Edge at the corner of the edge that does not have a vertex.
 
 
 
Next, use RMB -> Project Vertex to Edge by selecting the Green arrow vertex and RED arrow edge to make the new vertex.  Then create the missing edges and faces to fill the gaps.
 
 
Fill in the three faces including the triangle step face.
 
 
 
 
 
 
 
 
Now the region should be locally waterproof.
 
 
On the front end of the car the floor/body intersection is not valid as indicated by an extra RED edge.  Start by merging the end nodes.
 
 
 
 
 
Then, one of the edges will share both end nodes. Now use RMB -> Merge Adjacent Edges.
 
 
 
BATCAR CAD Repair Complete
That concludes the repair of the car.  This stage of the tutorial model is saved as caronlyrepair.ecf.  Notice that the car is all BLACK except the single edges that will connect to the CFD domain.
 
 
 
CFD Domain Set Up
Use the Box icon to add a box.  Set box to:
 
      Start Point (5350, 0., -84.5)
      End Point (6815, 285, 270)
 
 
Don’t forget to press “add” to finalize the box geometry in the model.
 
 
 
 
Geometry Repair
Select the edges of the model that are RED and lie on the symmetry plane and also select the symmetry plane itself.  Use RMB -> Split Face at Edges to connect the model to the symmetry plane. The edges will turn YELLOW at the connection.
 
 
Then select the new middle face.  Remove it with RMB -> Remove.
 
 
 
 
Finally, the wheels need to be trimmed to the floor.
 
 
After running the Stitch Surfaces command, the intersection of the wheels and floor will be trimmed.
 
 
Now the geometry repair is finished.
 
 
 
CFD Volumes
You will now see mainly BLACK edges and three YELLOW loops, one YELLOW loop for each wheel and one for the symmetry plane intersection with the car.
 
 
The next step is to extract the CFD volume.  Use the Volume command to compute the volumes.
 
 
RMB on the volume domains is not necessary.
Choose RMB -> Delete group and contents for volume 1, 3, 4, 5 and 6.
 
 
 
Ennova finds 6 volumes:
 
      Two wheel parts inside the box
      Two wheel parts outside the box
      The interior of the car
      The exterior of all the geometry (car + wheels) which is interior to the box
 
Volume 2 is the CFD domain we want.  We will remove the other domains for this analysis.
 
 
Boundary Conditions
It is convenient to setup the boundary conditions next.
 
      Inlet
      Outlet
      Tunnel Walls
      Floor
 
Select each surface in turn and use RMB -> Move to Group to rename each boundary.
 
 
 
Mesh Control
Ennova uses a parent child hierarchy as the control for the mesh.  If nothing is set for the child, then the child’s parent is used for control.  If the parent is not set, then the parent’s parent is used, etc.  The top default levels are the global parameters.
 
We will start by setting the global maximum mesh to size 35.  Ennova uses many clever algorithms to set mesh sizing and usually choosing a reasonable maximum size is sufficient to get a good starting mesh.
 
 
 
Surface Mesh
First we can test a mesh to have a look at our mesh sizing and to test its quality.  Obtaining a smooth error free surface mesh is key to obtaining a good CFD volume mesh.
 
Set the Surface Mesh Only radio button.
 
 
 
 
Generate the surface mesh by clicking the Topology Mesh icon.
 
 
Use the stethoscope to check the surface mesh.
 
 
 
It will report that the mesh passes all tests.
 
 
Set Up Boundary Layer Prisms
In Ennova there are several ways to input and control the prism layers.  Today we will use the dropdown box to control from which surfaces we will extrude prism layers.  We will then check the input using the spreadsheet.
 
 
Use the View Meshing Parameter icon to get to the prism control.
 
 
 
Prism Control
In the Control, highlight the volume and the groups that need prisms.
 
      Floor
      BATCAR
      BATCAR 2
      BATCAR 3
 
Next:
      Set prism control to volume
      Set height to 0.004
      Set growth ratio to 1.3
      Set number of layers to 35
 
Press Accept.  Open the mesh parameter settings spreadsheet and obtain a different representation of the model.
 
 
 
 
 
Volume Mesh with Prisms
Go back to the Setup Meshing icon and change the What to Mesh rule to Surface + Volume Mesh with Prisms.  When asked, select Yes to clear the existing mesh.
 
The complete mesh will be generated.
 
 
 
Mesh Diagnostics and View Slice
Check the mesh once it is complete.  You can run the same mesh diagnostics as we used for the surface mesh earlier.
 
Use the Slice Tool to view the interior mesh.
 
Export to Fluent Format
Use the Ennova Icon to find the Export command.  Choose Fluent Export.
 
The mesh is now complete.
 
 
 
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