Compressible Flow in a Nozzle- Step 6

Problem Specification
1. Create Geometry in GAMBIT
2. Mesh Geometry in GAMBIT
3. Specify Boundary Types in GAMBIT
4. Set Up Problem in FLUENT
5. Solve!
6. Analyze Results
7. Refine Mesh
Problem 1
Problem 2

Step 6: Analyze Results

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 Plot.

(Click picture for large image)

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 Contour Plot

Sometimes, it is very useful to see how the pressure and temperature changes throughout the object. This can be done via contour plots.

Display > Contours...

First, we are going to plot the pressure contours of the nozzle. Therefore, make sure that under Contours Of, Pressure... and Static Pressure is selected.

We want this at a fine enough granularity so that we can see the pressure changes clearly. Under Levels, change the default 20 to 40. This increases the number of lines in the contour plot so that we can get a more accurate result.

Click Display.

(Click picture for large image)

Notice that the pressure on the fluid gets smaller as it flows to the right, as is consistent with fluid going through a nozzle.

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.

(Click picture for large image)

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