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Step 5: Solution

We'll use second-order discretization for the momentum equation, as in the laminar pipe flow tutorial, and also for the turbulence kinetic energy equation which is part of the k-epsilon turbulence model.

Main Menu > Solve > Controls > Solution...

Change Discretization for Momentum, Turbulence Kinetic Energy and Turbulence Dissipation Rate equations to Second Order Upwind (if you do not see all of the equations scroll down to see them)

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Main Menu > Solve > Monitors > Residual...

Notice that Convergence Criterion has to be set for the k and epsilon equations in addition to the three equations in the last tutorial. Set the Convergence Criterion to be 1e-06 for all five equations being solved.

Select Print and Plot under Options. This will print as well plot the residuals as they are calculated which you will use to monitor convergence.

Click OK.

Set Initial Guess

We'll use an initial guess that is constant over the entire flow domain and equal to the values at the inlet:

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In the Solution Initialization menu that comes up, choose inlet under Compute From. The Axial Velocity for all cells will be set to 1 m/s, the Radial Velocity to 0 m/s and the Gauge Pressure to 0 Pa. The Turbulence Kinetic Energy and Dissipation Rate (scroll down to see it) values are set from the prescribed values for the Turbulence Intensity and Hydraulic Diameter at the inlet.

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https://confluence.cornell.edu/download/attachments/90737468/03solution_init.jpg?version=1

Click Init. Close the Solution Initialization window.

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Type in pipe100x30.cas for Case File. Click OK. Check that the file has been created in your working directory.

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In the Iterate menu that comes up, change the Number of Iterations to 100. Click Iterate.

You'll find that not all residuals have fallen below 1e-6 in 100 iterations. Solve for 200 more iterations. The solution converges in a total of 229 iterations.

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Main Menu > File > Write > Data...

Enter pipe100x30.dat for Data File and click OK. Check that the file has been created in your working directory.

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