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Wall Shear

We plot the wall shear using the procedure shown in the video below.  

<iframe width="640" height="360" src="//www.youtube.com/embed/WiK1uBTdK-M?rel=0" frameborder="0" allowfullscreen></iframe>

Summary of the above video:

1. Click on the Chart Viewer tab
2. Click chart in the top toolbar
   1. Name it Wall Shear
3. Click on Data Series Tab
   1. In Location dropdown menu, choose Wall
4. Click o nX Axis tab
   1. under Variable, choose X
5. Click on Y Axis tab
   1. under Variable, choose Wall Shear X or Wall Shear
6. Click Apply
7. Go to Location in the tree
   1. Double click on Wall
   2. Increase Sampling from 50 to 200

We then consider the trends in the wall shear in the heated, mixing and flow development sections and try to justify them through physical reasoning.

<iframe width="640" height="360" src="//www.youtube.com/embed/NbdGrJTesZg?rel=0" frameborder="0" allowfullscreen></iframe>

Summary of the above video:

1. As you heat flow, velocity increases
   1. Momentum at any any average is going to increase when heat is added
2. The gradient of the velocity normal to the wall is higher, the wall shear is higher
   1. Wall shear increases in the heated region, as shown in the wall shear plot

You can spiff up your plot using the tips discussed below. This video also shows you how you could read in experimental results for comparing the wall shear between simulation and experiment.

<iframe width="640" height="360" src="//www.youtube.com/embed/6RNykoM86xA?rel=0" frameborder="0" allowfullscreen></iframe>

Summary of the above video:

1. To edit how the Wall shear graph is displayed
   1. Select Wall shear in tree
   2. Click on General, check Title and enter title in Title blank
   3. in Data Series, enter series name in Name blank
   4. in X Axis, enter x axis label in Custom Label blank
   5. same for Y Axis
   6. in Line Display, uncheck "Use series..." and type within Legend Name blank
   7. in Chart Display, under Sizes, toggle with the line sizes and fonts
   8. Apply
2. To add another data series
   1. go to Data series tab of Wall Shear
   2. click on New button
   3. Scroll down, click File as  Data Source
   4. Browse for csv file 
   5. Apply
3. To export the chart
   1. Click the button next to undo
   2. Select location to save
   3. Rename

When the simulation was repeated for conditions for which experimental data are available, we got the comparison shown below. The difference in the average wall shear in the heated section between the simulation and experiment is a respectable 4%. Note that the wall shear in turbulent flows is difficult to predict accurately due to the steep velocity gradients at the wall. 

Fanning Friction Factor

The Fanning friction factor, also called the skin friction coefficient, can be plotted using the procedure outlined below. 

<iframe width="640" height="360" src="//www.youtube.com/embed/Jcht7CAPzAc?rel=0" frameborder="0" allowfullscreen></iframe>

Summary of the above video:

1. Create Location > Point 
   1. (2.67, .0294, 0)
2. Probe wall shear at point: 
   1. Create Expression > Right Click > New Expression
   2. probe(Wall Shear)@w267 / 1.483 (Pa/K) /Tm267
3. Can duplicate for different locations for a plot

Final Plots

<iframe width="560" height="315" src="https://www.youtube.com/embed/x-flaXXU7xg?rel=0" frameborder="0" allowfullscreen></iframe>

Summary of the above video:

1. Display Wall Temperature vs. Position in pipe and compare with experimental data
2. Display Pressure Variation vs. Position in pipe and compare with experimental data
3. Display Temperature at Centerline vs. Position in pipe and compare with experimental data