To Cornell MAE 4272 Students: You need to repeat the FLUENT simulation with inputs from YOUR MEASUREMENTS in the lab and compare the FLUENT results for the wall temperature with experiment. |
Some of the results shown below were obtained with a pipe length of 6.096 which is slightly different from the current length of 6.045. So your results might be slightly different from those shown below.
Please make sure your project is saved in Workbench. Double click on Results in the Project Schematic window. This will open CFD-Post (the program used to analyze results from FLUENT computation.) Click on z axis in the triad (at the bottom right of the graphics window) to get the view along the z-axis.
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Summary of the Above Video:
You can save the image to a file using the camera icon highlighted below or using the Snipping Tool in Windows 7 (you can search for it under Start > Programs).
In developing the experiment, it was assumed that by the end of the adiabatic mixing stage, the flow will be well mixed. Do the results from the numerical solution simulation support this assumption?
Our next challenge is to produce velocity vectors. This is a very similar process to creating the temperature contours above.
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Summary of the Above Video:
We see that the flow speeds up as the density decreases in order to keep the same mass flow rate.
Does the flow become fully developed at the end of the first section?
Now let's look at the temperature variation along the center-line of the pipe. To do this we need to first create a line corresponding to the center-line:
Insert > Location > Line
Name it "Centerline" and click OK. On the lower left panel, you will see Details of Centerline. Enter the start and end locations of the line and the sampling frequency. Click Apply.
You will see centerline created under User Locations and Plots.
Insert > Chart
Please name this chart "Centerline Temperature". You will see Details of Centerline Temperature appear on the lower left.
We'll go through the tabs in the menu to specify the plot that we want. Select the General tab and name the chart "Temperature Variation along Pipe Axis".
Select the Data Series tab. Change Name and Location.
We want to see the variation of temperature with the length of the pipe. Therefore, temperature will be on the "y-axis" of the chart and axial position on the "x-axis" of the chart.
Click on X Axis tab. Next to Variable, choose X.
Click on Y Axis tab. Next to Variable, choose Temperature.
Click Apply. You will see Centerline Temperature created under Report in the Outline tab.
You need to repeat the FLUENT simulation with inputs from YOUR MEASUREMENTS in the lab. To compare the FLUENT results with experiment, you can export the FLUENT result into Excel. A sample comparison is shown below. You can export the FLUENT data in Excel format by clicking on the Export button in "Details of centerline temperature" |
<iframe width="560" height="315" src="https://www.youtube.com/embed/-Cvn7HPp9eY?rel=0" frameborder="0" allowfullscreen></iframe> |
Summary of the Above Video:
You need to repeat the FLUENT simulation with inputs from YOUR MEASUREMENTS in the lab and compare the FLUENT results for the wall temperature with experiment. A sample comparison is shown below. You can export the data by clicking on the Export button, as shown in the previous step. |
<iframe width="560" height="315" src="https://www.youtube.com/embed/oy3xJrmWNLo?rel=0" frameborder="0" allowfullscreen></iframe> |
Summary of the Above Video:
Create a plot of the pressure variation along the centerline of the pipe. Steps for this are similar to the plot of the centerline temperature that we did earlier.
There is no need to create a new line. We can use the "centerline" created earlier.
Insert > Chart
Follow steps from the Centerline Temperature plot above, making appropriate modifications. You should see the following plot.
You need to repeat the FLUENT simulation with inputs from YOUR MEASUREMENTS in the lab and compare the FLUENT results for the pressure with experiment. A sample comparison is shown below. |
Let's look at the velocity profiles before and after the heated section. To do this, we need to first create lines at x=1.83 m ((start of heated section), x=4.27 m (end of heated section) and x=6.045 m (end of mixing section).
First, create the line at x=1.83 m.
Insert > Location > Line
Name it "x183" and click OK. Enter the following coordinates (0.0294 m is the pipe radius).
Point 1 (1.83, 0, 0)
Point 2 (1.83, 0.0294, 0)
Enter 100 for Samples. Click Apply.
Similarly create lines at x=4.27 m and x=6.045 m.
Insert > Chart
Name this chart "Axial Velocity Profiles".
Select the General tab and name the chart "Axial Velocity Profiles".
Select Data Series tab. Change the name of the first data series to x=1.83 m. Under Data Source, specify x183 as Location.
Add a new data series by clicking on the "New" icon as shown below and repeat the above steps but for x=4.27 m.
Add a third data series by clicking on the "New" icon and repeating the steps for x=6.045 m. You should then have three items in the Data Series tab.
Specify x-axis variable: Velocity u
Specify y-axis variable: Y
Complete the plot. Here's what we get.
We notice that the flow accelerates due to the heating. As air is heated, its density decreases. So the velocity has to increase to maintain the same mass flow rate.
From energy conservation, we can show that the mixed mean temperature is constant in the flow development and mixing sections and varies linearly in the heated section. This is shown schematically in the following figure from the MAE 4272 lab manual.
The slope of Tm in the heated section can be obtained from the following equation which is derived from energy balance in the heated section:
Using the above equation, calculate the mixed mean temperature Tm at x=2.67 m. In the Verification & Validation section, you'll check that this value matches the Tm value calculated by integrating the temperature profile. This should be the case if energy is conserved in the simulation.
The following video show you the procedure for extracting the wall temperature at x=2.67 m. To repeat the calculation at a different axial location, you can right-click on appropriate items in the tree, duplicate and modify as necessary. You need to double-click on an item in the tree to modify it; this is easy to overlook.
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Summary of the above video:
To calculate the Nusselt no.:
This yields a nice curve of Nu vs x.
We plot the wall shear using the procedure shown in the video below.
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Summary of the above video:
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.
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Summary of the above video:
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:
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.
The Fanning friction factor, also called the skin friction coefficient, can be plotted using the procedure outlined below.
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Summary of the above video:
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Summary of the above video:
You can view the input summary (model, material properties, boundary conditions, etc) by clicking on Report in the menu bar of FLUENT. A small window will pop up and you can print the selected input summary directly in FLUENT.
Go to Step 7: Verification & Validation
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