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Physics Setup

In the Workbench window, this is what you should see currently in the Project Schematic space.

Double click on Setup and which will bring up the FLUENT Launcher. When the FLUENT Launcher appears change the options to "Double Precision", and then click OK as shown below.The Double Precision option is used to select the 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. 

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Twiddle your thumbs a bit while the FLUENT interface comes up. This is where we'll specify the governing equations and boundary conditions for our boundary-value problem. On the left-hand side of the FLUENT interface, we see various items listed under Setup will launch. Click OK to select the default option. In left hand side of the new FLUENT window, we see Problem Setup and Solution tab. We will work from top to down to setup the physics. In bottom of the Setup items to set up our boundary-value problem. On the right hand side, we have the Graphics pane and, below that, the Command windows pane.

Display Mesh

 LetLet's first check whether we have the appropriate surfaces that we display the mesh that was created in the previous step. 

Setup > General > Mesh > Display... Image Removed
 

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The long, skinny rectangle displayed in the graphics window corresponds to our solution domain. Some of the operations available in the graphics window to interrogate the geometry and mesh are:

Translation: The model 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 in and interrogate our mesh.

You should have all the surfaces shown here.  You should check whether each surfaces correspond to the right geometry by unchecking unrelated surfaces and click Display to view the surface of interest in the Graphics window.
Next, we in the above snapshot.  Clicking on a surface name in the Mesh Display menu will toggle between select and unselect. Clicking Display will show all the currently selected surface entities in the graphics pane. Unselect all surfaces and then select each one in turn to see which part of the domain or boundary the particular surface entity corresponds to (you will need to zoom in/out and translate the model as you do this). For instance, the surface labeled heated_section should correspond to the part of the wall where heating occurs.

Specify Governing Equations

We ask FLUENT to solve the axisymmetric form of the governing equations. When you do this, the solver switches to cylindrical polar coordinates. So from here on, you should interpret the horizontal coordinate as axial and the vertical coordinate as radial will specify that the problem we are solving is axisymmetric.
General > Solver > 2D Space > Axisymmetric
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Now let's move on to setting up our model. We will first turn The energy equation is turned off by default. Turn on the energy equation. Note that in most cases, you'll have to double-click on an item to select it. 
Models > Energy - Off > Edit...
Turn on the Energy Equation and click OK.
 
Next, we will setup the Viscous model By default, FLUENT will assume the flow is laminar. Let's tell it that our flow is turbulent rather than laminar and that we want to use the k-epsilon turbulence model to simulate our turbulent flow. This means FLUENT will solve for mean (i.e. Reynolds-averaged) values of velocity, pressure and temperature. It will add the k and epsilon equations to the set of governing equations to calculate the effect of the turbulent fluctuations on the mean, as discussed in the Pre-Analysis step.

Models > Viscous - Laminar > Edit...

Under Model, select k-epsilon (2 eqn) and . Since we'll use the default settings for the k-epsilon turbulence model, click OK. 

This is what you should currently see under Models.
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Now let's move on to setting up the materials propertiesset the "material properties" i.e. properties of air that appear in our boundary value problem.

Materials > Fluid air >  Create/Edit... We will use the properties of heated air.

Since variations in absolute pressure are small in our pipe, we'll use a constant absolute pressure in the ideal gas law as discussed in the Pre-Analysis step. This is called the "Incompressible ideal gas" model in FLUENT (it's non-standard nomenclature).  Change the Density (kg/m3) from constant to incompressible-ideal-gas. The constant absolute pressure to be used in the ideal gas equation is specified later as Operating Pressure. Enter for following properties for air.

The other properties are also functions of temperature. However, we'll use constant values equal to the average values over the temperature range obtained in the experiment. Enter the following constant values:

Cp (Specific Heat) (j/kg-k): 1005
Thermal Conductivity (w/m-k): 0.0266
Viscosity (kg/m-s): 1.787e-5
Molecular Weight (kg/kgmol): 28.9797 
 
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https://confluence.cornell.edu/download/attachments/111221574/material%20properties.png

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Click Change/Create and Close the Create/Edit Materials window.

Let's set up the boundary conditions now. We will first specify our operating conditions.

Specify Boundary Conditions

FLUENT uses gauge pressure internally in order to minimize round-off errors stemming from small differences of big numbers. Anytime an absolute pressure is needed, it is generated by adding the so-called "operating pressure" to the gauge pressure:
  absolute pressure = gauge pressure + "operating pressure"

This "operating pressure" is also used in the "incompressible ideal gas" model as mentioned above. We will specify the "operating pressure" as equal to the measured ambient pressure since the absolute pressure in the pipe varies only slightly from this (you do get significant variations in gauge pressures though).

(double-click) Boundary Conditions > Operating Conditions...

Enter 98338.2 under Operating Pressure and click OK.

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Next we will specify the boundary condition for the centerline.

Boundary Conditions > centerlineaxis

Change the Type to  to axis and click OK. FLUENT will set all radial derivatives at this boundary to zero in accordance with the axisymmetric assumption.

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Now let's set up specify the boundary condition at the walls. By default, FLUENT correctly picks the Wall boundary type for these boundaries. It will impose the no-slip condition for velocity at these boundaries. Additionally, for the heated wall section, we need to specify the heat flux into the flow.

Boundary Conditions > heated_section > Edit...

A new Wall window will open. Click on Thermal tab and enter 34735210.9 85 next to Heat Flux (w/m2) and click OK. Image Removed

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https://confluence.cornell.edu/download/attachments/111221574/heated%20wall.png

 
As discussed in the Pre-Analysis step, we need to set:

• velocity and temperature (plus k and epsilon for the turbulence model equations) at the inlet
• pressure at the outlet

For subsonic flow, the flow adjusts to the pressure at the outlet (consider this as a signal you are sending the flow about what it needs to do inside the pipe).

Select: 
Now let's set the inlet boundary condition.
Boundary Conditions > inlet
Note that the boundary Type is automatically set to velocity-inlet. FLUENT has an automatic mechanism to set the pick a boundary condition type according to the name you give . So let's click and settings that you have selected previously (this can be dangerous if FLUENT selects the wrong boundary type and a lackadaisical user doesn't change it). In this case, it gets it right.

Click Edit... to set up the correct inlet parameters. A The Velocity Inlet window pop outpops up. Enter 2530.05 06 next to Velocity Magnitude (m/s). For Turbulent Kinetic Energy (m2/s2), enter value 0.09. For Turbulent Dissipation Rate (m2/s3), enter value 16. Note that k and epsilon are not measured and are rough guess values. Click OK to close the window.

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https://confluence.cornell.edu/download/attachments/111221574/velocity%20inlet_sm.png

. Under Turbulence, select the specification method to be Intensity and Viscosity Ratio.

 Use the default values for Turbulent Intensity (5%) and Turbulent Viscosity Ratio (10). These are plausible guess values for the turbulence level at the inlet. FLUENT will calculate k and epsilon at the inlet from these values and use them as boundary conditions for the k and epsilon equations.  The results should not be sensitive to these inputs since most of the turbulence is generated in the boundary layers (ideally, you should check the sensitivity of your calculation to this setting). 

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 Now  
Now click on Thermal tab and enter 298.15K for Temperature. Click OK to close the window.

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Finally, set up the outlet boundary condition.:

Boundary Conditions > Outlet
Again, proper FLUENT selects the pressure-outlet boundary Type is settype and its guess turns out to be right. 

Click Edit... to specify the gauge pressure at the outlet.

set up appropriate pressure outlet condition. Enter -1112.3 for Gauge Pressure and click OK. (From experiment, measured outlet pressure is 97225.9 Pa. Corresponding gauge pressure = 97225.9 Pa - reference operating pressure = -1112.3 Pa)
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https://confluence.cornell.edu/download/attachments/111221574/outlet%20pressure.png

.) The negative sign indicates that the pressure at the outlet is lower than the ambient value.  

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Now FLUENT knows all necessary elements of our beloved BVP (domain, governing equations and boundary conditions). In the Solution step, we'll prod the beast to obtain an approximate numerical solution to our BVP. 
We are done setting up the boundary conditions.

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