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Step 7:

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Verification & Validation

In order to assess the numerical accuracy of the results obtained, it is necessary to compare results on different meshes. We'll re-do the calculation on a 100x60 mesh which has twice the number of nodes in the radial direction as the 100x30 mesh. You can download the 100x60 mesh here.

File > Read > Case...

Navigate to your working directory elect the pipe100x60.msh file you have created. Click OK. Display the grid. Check its size.

Finer Mesh Analysis

Repeat steps 4, 5, and 6 of this tutorial with the finer mesh.

When you get to step 6 of the tutorial, plot each of the graphs as described. However, for each of the plots, overlay the corresponding result for the coarser mesh so that we may compare them. To do this, after the plotting the finer mesh result, in the Solution XY Plot Window, click on Load File.... Navigate to your working folder, click on the appropriate filename for the previous result, eg. vel.xy for centerline velocity, and click OK. Click Plot. You'll see both results plotted in the same the graphics window.

(Click picture for larger image)

http://courses.cit.cornell.edu/fluent/pipe2/05centerline_velocity.htm

In the centerline velocity plot above, the white line represents the centerline velocity of the finer mesh, while the red line represents the velocity of the coarser mesh from before. As we can see, there isn't too much of a difference between the two plots. Save this plot as vel2.xy.

Now, let's take a look at the coefficient of skin friction. This time, load the cf.xy file to compare against the plot. This is the coefficient of skin friction plot:

 (Click picture for larger image)

http://courses.cit.cornell.edu/fluent/pipe2/05skin_friction.htm

Once again, we can see that due to the fine degree of each mesh, there isn't much difference between the two plots. Save this plot as cf2.xy. Now, study the velocity of the outlet by plotting and comparing to the graph in profile.xy.

(Click picture for larger image)

http://courses.cit.cornell.edu/fluent/pipe2/05outlet_velocity.htm

Once again, the finer mesh in this case doesn't offer much more precision than the coarser mesh. Save this plot as profile2.xy. Now let's take a look at the YPlus plot.

(Click picture for larger image)

http://courses.cit.cornell.edu/fluent/pipe2/05yplusplot.htm

As we can see, there is a significant increase in the accuracy of the plot from the finer mesh. Save this plot as yplus2.xy.

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In Problem 1, we will be looking at the effect of coarse meshes with uniform granularity.

Go to Problem 1

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