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The first thing we check for verification are the mass conservation. We check the inlet boundary conditions to ensure that the conditions are as we expectis the comparison with the analytical solution since we have one. Then, we do a mesh refinement and use a smaller time-step to check whether the results are consistent with the original calculation. By using a finer mesh and a smaller time-step, we investigate the effects of truncation error caused by spatial discretization and temporal discretization. Then we will do a case comparison for the results obtained after spatial and temporal refinement.

Mass conservation

Analytical Solution

Import this csv file and compare it to the Fluent solution at t* = 0.010. You can see how to import a csv file into CFD-Post at 2:46 in the Numerical Results video from the 3D Steady Diffusion tutorial. To check whether mass is conserved in this calculation, go back into Fluent and go to Reports → Fluxes and then under options, check "Mass flow rate". Then select the one inlet and two outlets. We would expect the mass flux to sum up to zero (or extremely small).
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As we can see from the window above, the mass fluxes add up to -2.125e-10, which is very close to zero. Thus, we can conclude that mass is conserved in the simulation. 

Mesh Refinement & Smaller Time-step

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It is also always a good habit to check that the mesh is refined enough. For example, you could use an element size that is half of what was used in the videos and compare the results.

For transient problems, often the time-step size is crucially important in obtaining an accurate solution. For example, in the image below, three different time-step sizes were used and three different results were obtained:

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However, you will notice if you run the simulation with a time-step size of 1e-6, you will obtain the same results as with a time-step size of 1e-5.

To recreate this graph, you can use the same Fluent cell as before, just make sure to re-initialize and to change the file name of the data export before re-running the simulation with a new time-step size. Then in CFD-Post you can simply load the new results in with the previous results. Remember that you can toggle which lines are visible under the "Line Display" tab of the chart you created.

Note
The time-step size is highly dependent on the physics of the problem, so don't expect to be able to use the same time-step size for different physical problems.

Validation

We do not currently have any experimental data for this problem. obtained from simulations with experimental results. In this case however, we do not have experimental data but we do have description of flow in the carotid artery, courtesy of your textbook. We find that the flow in the internal and external carotid arteries should be approximately 70% and 30% of the total flow in the common carotid artery. We can check this in Fluent by using the mass flow rate values we found earlier. 

References:

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