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Verification & Validation

Verification and validation is a formal process for checking results. Each of these terms has a specific meaning which we won't get into here. We'll act like consultants and do the bare minimum: we'll refine the mesh and make sure that the results are nearly independent of the mesh. We will also repeat the comparison with experiment which is a very important way to check simulation results.

Refine Mesh

Let's repeat the solution on a finer mesh with smaller cells. In workbench, under Forced Convection project, right click on Fluid Flow (FLUENT) and click duplicate. Rename the duplicate project to Force Convection Refined Mesh. You should have two project cells in workbench.
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Double click on Mesh for Forced Convection Refined Mesh. A new ANSYS Mesher window will open. Under Outline, expand mesh tree and click on Edge Sizing. Repeat the mesh steps, but this time use edge sizing of 50 and 0.02.
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Under Details of "Edge Sizing", enter 60 for Number of Divisions. Under Bias select:

"--- --- - -" and when asked for the bias factor please enter 20.

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Similarly, specify element size of 0.015m for Edge Sizing 2. 
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A bias was used for the vertical edges but not the horizontal edges to keep an optimum y+ value at the wall. This tutorial will not cover y+ values and their meanings, but it may be useful to know for future reference.

Click Update Image Removed to generate the new mesh. If you refer back to the mesh details and expand statistics, you will notice that the number of elements has increased to 19536, compared to 5508 of the original mesh.
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Close the ANSYS Mesher and go back to Workbench windows. Under Forced Convection Refined Mesh, right click on Fluid Flow (FLUENT) and click Update. Wait for a few minutes for FLUENT to obtain a solution.

We would want to compare the solution between the two meshes. To do that, drag the Solution cell of Forced Convection Refined Mesh to Results cell of Forced Convection.
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Finally, double click on Results cell of Forced Convection to compare. Under Outline tab, click on the results of interest to analyze.

How do the results below compare to the experimental results. Keep in mind the assumptions and plotting points for the simulation compared to the experimental results. Just because some of the results seem further away does not necessarily mean the simulation is wrong.

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Centerline Pressure

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 enlarged view

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Checklist

<iframe width="640" height="360" src="https://www.youtube.com/embed/odNQ8hHG7MA" frameborder="0" allowfullscreen></iframe>

Check Boundary Conditions

 <iframe width="640" height="360" src="https://www.youtube.com/embed/Fzrmdp_cS38" frameborder="0" allowfullscreen></iframe>

Check Mass and Energy Conservation

 <iframe width="640" height="360" src="https://www.youtube.com/embed/0ThDb-tVBQA" frameborder="0" allowfullscreen></iframe>

Check Energy Conservation via Mixed Mean Temperature Variation (Optional)

<iframe width="640" height="360" src="//www.youtube.com/embed/YXkGqLC64-Q" frameborder="0" allowfullscreen></iframe>

Check Numerical Error

 <iframe width="640" height="360" src="https://www.youtube.com/embed/Xmc8fLUX3hc" frameborder="0" allowfullscreen></iframe>

Validation Results

 <iframe width="640" height="360" src="https://www.youtube.com/embed/fkZnLfcbLlc" frameborder="0" allowfullscreen></iframe>

Go to Exercises

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Centerline Temperature

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enlarged view 

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Wall Temperature

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enlarged view 

 
What can you say about mesh refinement after comparing the results? 

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