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  • FLUENT - Steady Flow Past a Cylinder - Step 1

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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 so that they are not under the influence of the flow around such that the boundary conditions will not affect the flow near cylinder.


Figure above shows the geometry of such case.

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Create the cylinder using two arc. First arc span from -90 to 90 deg. Second arc span from 90 to -90 deg. Both arc with radius 1.

Operation Toolpad > Geometry Command Button > Edge Command Button > Create Edge > Arc >

Input the following data and click Apply.

Radius

1

Start Angle

90

End Angle

450

After that, create a vertex at the bottom part of the cylinder by using split function.

Operation Toolpad > Geometry Command Button Image Removed > Edge Command Button Image Removed > Split Edge Image Removed

Select the cylinder edges. Then change the coordinate Type to Cylindrical and create a vertex by entering the angle, t as -90. Image Added

Info
titleRight mouse click on Cartesian next to Type to see more options.

Create Radius of Influence

Now we can proceed to create the geometry for radius of influence. Since both the cylinder and radius of influence is of same shape. We can create the radius of influence by copying and scaling up the cylinder.

Operation Toolpad > Geometry Command Button Image Modified > Edge Command Button Image Modified > Move/Copy Edges Image Modified
Select the cylinder edges. Make sure that the Copy is checked. Under Operation, select Scale. Next to Factor, enter a value of 4. This means that the radius of influence we create will be 4 times the size of the cylinder.

The current geometry should look like this:

Image Modified
 

editor NOTE (duplicate vertices created...)



Create Farfield Boundaries

Create Upstream Boundary

We will first create the semi-circle upstream boundary. 

Operation Toolpad > Geometry Command Button Image Modified > Edge Command Button Image Modified > Create Edge Image Modified > Arc Image Modified > Image Modified

Input the following data and click Apply.

Radius

10

Start Angle

90

End Angle

-90

Create Downstream Boundaries

In creating downstream boundaries, we will use bottom up approach where we first create vertices and join the vertices to form edges.

Create vertices with following coordinates:

Label

x

y

z

1

40

10

0

2

40

-10

0

Operation Toolpad > Geometry Command Button Image Modified > Vertex Command Button Image Modified > Create Vertex Image Modified

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.

Connect AB, BC and CD to form three edges.

Operation Toolpad > Geometry Command Button Image Modified > Edge Command Button Image Modified > Create Edge Image Modified 

Info
title"shift" + left click and drag to select

You should see have this geometry up till this step.

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