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Author: Rajesh Bhaskaran & Yong Sheng Khoo, Cornell University Problem Specification |
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If you are having trouble following written tutorial, detailed video tutorials are available here |
Step 1: Create Geometry in GAMBIT
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If you would prefer to skip the mesh generation steps, you can download the mesh from here and go straight to step 4. |
In an external flow such as the flow past a cylinder, we have to define farfield boundaries and mesh the region between the cylinder geometry and the boundaries. Farfield boundaries should be placed well away from the cylinder such that the boundary conditions will not affect the flow near cylinder.
Figure above shows the geometry of such a case.
Strategy for Creating Geometry
To model this flow, we need a cylinder and farfield boundaries. We need finer meshes around the cylinder to capture the active region (call this radius of influence). Downstream of the flow, there will be wake generated by the cylinder, which requires finer mesh to better capture this phenomena. To be able to specify such regions, we split the model domain into different faces as shown below.
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Create a new directory called cylinder and start GAMBIT from that directory by typing gambit -id cylinder at the command prompt.
Under Main Menu, select Solver > FLUENT 5/6 since the mesh to be created is to be used in FLUENT 6.0.
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Create the cylinder using two arcs. The cylinder is created with two arc because they are going to be meshed differently. First Back arc span spans from -90 to 90 deg. Second Front arc span spans from 90 to -90 deg. Both arc with radius 1.
Operation Toolpad > Geometry Command Button 
> Edge Command Button 
> Create Edge 
> Arc 
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Next to Radius, enter 1. Next to Start Angle, enter -90. Next to End Angle, enter 90. Click Apply. Do the same for front arc but enter different value for angles.
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Operation Toolpad > Geometry Command Button > Edge Command Button > Move/Copy Edges 
Select the front cylinder edge. Make sure that the Copy is checked. Under Operation, select Scale. Next to Factor, enter a value of 10. This means that the radius of influence we create will be 10 times the size of the cylinder. Click Apply.
(Click here for animated steps)
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Create the vertices by entering the coordinates under Global.
Click the FIT TO WINDOW button to scale the display so that you can see all the vertices.
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Remember to change the coordinate Type to Cylindrical.
Split Edge at Outer Boundary
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Select the vertex and associated edge. Make sure to select Split edge. At the end of this, you should have 4 new vertices.
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Finally, connect all the remaining vertices KL, LM, NO, OP, FI and GJ.
The newly created vertices to form two new edges. The current geometry in Gambit should look like this:
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Operation Toolpad > Geometry Command Button > Face Command Button 
> Form Face 
This brings up the Create Face From Wireframe menu. Recall that we had selected vertices in order to create edges. Similarly, we will select edges in order to form a face.
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Create all the six faces by connecting appropriate edges.
Animated steps
We are now ready to mesh the geometry.
Go to Step 2: Mesh Geometry in GAMBIT
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