Sign-up for free online course on ANSYS simulations!Step 6: Analyze Results
Velocity Vector
Let's first look at the velocity vector in the nozzle.
Display > Vectors...
Select Velocity under Vectors of and Velocity... under Color by. Set Scale to 0.4
Click Display.
We see that the flow is smoothly accelerating from subsonic to supersonic.
To include the lower half of nozzle, do the following:
Display > Views...
Select centerline and click Apply
White Background on Graphics Window
To get white background go to:
Main Menu > File > Hardcopy
Make sure that Reverse Foreground/Background is checked and select Color in Coloring section. Click Preview. Click No when prompted "Reset graphics window?"
Mach Number Contour
Let's now look at the mach number
Display > Contours
Select Velocity... under Contours of and select Mach Number. Set Levels to 30.
Click Display.
For 1D case, mach number is a function of x position. For 1D case, we are supposed to see vertical contour of mach numbers that are parallel to each other.
For 2D case, we are seeing curving contour of mach number. The deviation from vertical indicate the 2D effect.
Do note that 1D approximation is fairly accurate around the centerline of nozzle.
Pressure Contour Plot
Let's look at how pressure changes in the nozzle.
Display > Contours...
Select Pressure... and Static Pressure under Contours of. Use Levels of 30
Click Display.
Notice that the pressure decreases as it flows to the right.
Total Pressure Contour Plot
Let's look at the total pressure in the nozzle
Display > Contours...
Select Pressure... and Total Pressure under Contours of. Select Filled. Use Levels of 100.
Click Display.
Around the nozzle outlet, we see that there is a pressure loss because of the numerical dissipation.
Mach Number Plot
As in the previous tutorials, we are going to plot the velocity along the centerline. However, this time, we are going to use the dimensionless Mach quantity.
Plot > XY Plot
We are going plot the variation of the Mach number in the axial direction at the axis and wall. In addition, we will plot the corresponding variation from 1D theory. You can download the file here: mach_1D.xy.
Do everything as we would do for plotting the centerline velocity. However, instead of selecting Axial Velocity as the Y Axis Function, select Mach Number.
Also, since we are going to plot this number at both the wall and axis, select centerline and wall under Surfaces.
Then, load the mach_1D.xy by clicking on Load File....
(Click picture for large image)
Click Plot.
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How does the FLUENT solution compare with the 1D solution?
Is the comparison better at the wall or at the axis? Can you explain this?
Save this plot as machplot.xy by checking Write to File and clicking Write....
Pressure Plot
Let's look at the pressure along the centerline and the wall.
Plot > XY Plot
Make sure that under Y-Axis Function, you see Pressure... and Static Pressure. Under Surfaces, select centerline and wall. Click Plot.
It is good to write the data into a file to have greater flexibility on how to present the result in the report. At the same XY Plot windows, select Write to File. Then click Write... Name the file "p.xy" in the directory that you prefer.
Open "p.xy" file with notepad or other word processing software. At the top, we see:
(title "Static Pressure") (labels "Position" "Static Pressure")
First line tells us the properties we are comparing. For our case, we are looking at Static Pressure.
Second line tells us about the x and y label.
There is a header at the beginning of each the data sets so that we can differentiate which data sets we are looking at. For our case, we have "centerline" and "wall" data sets.
Following is an example of two data sets (centerline and wall).
((xy/key/label "centerline") -0.5 97015.3 -0.48 96949.9 . . . 0.5 6012.92 ) ((xy/key/label "wall") -0.5 100853 -0.480911 100496 . . . 0.5 2874.7 )
Try copy the appropriate data sets to excel and plot the results.
Temperature Contour Plot
Now we will plot the temperature contours and see how the temperature varies throughout the nozzle.
Back in the Contours window, under Contours Of, select Temperature... and Static Temperature.
Click Display.
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As we can see, the temperature decreases towards the right side of the nozzle, indicating a change of internal energy to kinetic energy as the fluid speeds up.
Go to Step 7: Refine Mesh