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Step 4: Set Up Problem in FLUENT

Launch Fluent

Lab Apps > FLUENT 6.3.26

Select 2ddp from the list of options and click Run.

The "2ddp" option is used to select the 2-dimensional, double-precision solver. In the double-precision solver, each floating point number is represented using 64 bits in contrast to the single-precision solver which uses 32 bits. The extra bits increase not only the precision but also the range of magnitudes that can be represented. The downside of using double precision is that it requires more memory.

Import Grid

Main Menu > File > Read > Case...

Navigate to the working directory and select the cylinder.msh file. This is the mesh file that was created using the preprocessor GAMBIT in the previous step. FLUENT reports the mesh statistics as it reads in the mesh:

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Also, take a look under zones. We can see the five zones farfield1, farfield2, farfield3,farfield4, and cylinder that we defined in GAMBIT.

Check and Display Grid

First, we check the grid to make sure that there are no errors.

Main Menu > Grid > Check

Any errors in the grid would be reported at this time. Check the output and make sure that there are no errors reported. Check the grid size:

Main Menu > Grid > Info > Size

The following info should appear:

Display the grid:

Main Menu > Display > Grid...

Make sure all 6 items under Surfaces is selected. Then click Display. The graphics window opens and the grid is displayed in it. You can now click Close in the Grid Display menu to get back some desktop space. The graphics window will remain.

Graphics Window Operation

Translation: The grid can be translated in any direction by holding down the Left Mouse Button and then moving the mouse in the desired direction.
Zoom In: Hold down the Middle Mouse Button and drag a box from the Upper Left Hand Corner to the Lower Right Hand Corner over the area you want to zoom in on.
Zoom Out: Hold down the Middle Mouse Button and drag a box anywhere from the Lower Right Hand Corner to the Upper Left Hand Corner.

Use these operations to zoom into the grid to obtain the view shown below.

The zooming operations can only be performed with a middle mouse button.

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White Background on Graphics Window

To get white background go to:
Main Menu > File > Hardcopy
Make sure that Reverse Foreground/Background is checked and select Color in Coloring section. Click Preview. Click No when prompted "Reset graphics window?"

You can also look at specific parts of the grid by choosing the boundaries you wish to view under Surfaces (click to select and click again to deselect a specific boundary). Click Display again when you have selected your boundaries.

Define Solver Properties

Main Menu > Define > Models > Solver

Under Time, select Unsteady. We will use the default 1st-Order ImplicitUnsteady Formulation for for now. Click OK.

Main Menu > Define > Models > Viscous
Laminar flow is the default. So we don't need to change anything in this menu. Click Cancel.

Main Menu > Define > Models > Energy

For incompressible flow, the energy equation is decoupled from the continuity and momentum equations. We need to solve the energy equation only if we are interested in determining the temperature distribution. We will not deal with temperature in this example. So leave the Energy Equation unselected and click Cancel to exit the menu.

Define Material Properties

Main Menu > Define > Materials...

Change Density to 75 and Viscosity to 1. These are the values that we specified under Problem Specification.

Click Change/Create. Close the window.

Define Operating Conditions

Main Menu > Define > Operating Conditions...

For all flows, FLUENT uses gauge pressure internally. Any time an absolute pressure is needed, it is generated by adding the operating pressure to the gauge pressure. We'll use the default value of 1 atm (101,325 Pa) as the Operating Pressure.

Click Cancel to leave the default in place.

Define Boundary Conditions

We'll now set the value of the velocity at the inlet and pressure at the outlet.

Use the following table to set boundary type of each zone.




velocity-inlet, V x = 1 m/s


velocity-inlet, V x = 1 m/s


velocity-inlet, V x = 1 m/s





Main Menu > Define > Boundary Conditions...

Select farfield1 under Zone. Change the Type of boundary as velocity-inlet. A new window will pop up. Change Magnitude, Normal to Boundary to Components  under Velocity Specification Method. Input value 1 next to X-Velocity. Click OK. Do the same for farfield2 and farfield3.

The (absolute) pressure at the farfield downstream is 1 atm. Since the operating pressure is set to 1 atm, the outlet gauge pressure = outlet absolute pressure - operating pressure = 0. Choose farfield4 under Zone. The Type of this boundary is pressure-outlet. Click on Set.... The default value of the Gauge Pressure is 0. Click Cancel to leave the default in place.

Lastly, click on cylinder under Zones and make sure Type is set as wall.

Click Close to close the Boundary Conditions menu.

Go to Step 5: Solve!

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