Page History

Step 6: Analyze Results

Plot Velocity Vectors

Let's plot the velocity vectors obtained from the FLUENT solution.

Display > Vectors

Set the Scale to 14 and Skip to 4. Click Display.

https://confluence.cornell.edu/download/attachments/104400192/step6_velocity_vector.jpg?version=1

From this figure, we see that there is a region of low velocity and recirculation at the back of cylinder.

Pressure Coefficient

 
Pressure coefficient is a dimensionless parameter defined by the equation Image Added where p is the static pressure, p _ref is the reference pressure, and q _ref is the reference dynamic pressure defined by

\large $$ q_{ref} = {1 \over 2}{\rho_{ref}v_{ref}^2}$$

The reference pressure, density, and velocity are defined in the Reference Values panel in Step 5.

Let's plot pressure coefficient vs x-direction along the cylinder.

Plot > XY Plot...

Change the Y Axis Function to Pressure

...

..., followed by Pressure Coefficient. Then, select cylinder under Surfaces.

Image Added

Click Plot.

Image Added

https://confluence.cornell.edu/download/attachments/104400192/step6_Cpplot.jpg?version=1

As can be seen, the pressure coefficient at the back is lower than the pressure coefficient at the front of the cylinder. The irrecoverable pressure is due to the separation at the back of cylinder and the frictional loss.

Now, letLet's take a look at the Contour of Pressure Coefficient variation around the cylinder.

Display > Contours

Under Contours of, choose Pressure.. and Pressure Coefficient. Select the Filled option. Increase the number of contour levels plotted: set Levels to 100.

Click Display.

https://confluence.cornell.edu/download/attachments/104400192/step6_Cp_contour.jpg?version=1

Because the cylinder is cylindricalsymmetry in shape, we see that the pressure coefficient profile is symmetry between the top and bottom of cylinder.

Plot Stream Function

LetNow, let's take a look at the Pressure Coefficient variation around the cylinderStream Function.

Display > Contours

Under Contours of, choose Pressure Velocity.. and Pressure Coefficient Stream Function. Select Deselect the Filled option. Increase the number of contour levels plotted: set Levels to 100.Click Display.
Because the cylinder is cylindrical, we see that the pressure coefficient profile is symmetry between the top and bottom of cylinder

Let's set the reference values necessary to calculate the pressure coefficient.

Report > Reference Values

Select farfield under Compute From.

Image Removed

The above reference values of density, velocity and pressure will be used to calculate the pressure coefficient from the pressure. Click OK.

Display > Contours...

Select Pressure... and Static Pressure from under Contours Of. Then select Pressure Coeffient.

Image Removed
(Click picture for larger image)

The pressure coefficient after the shockwave is 0.293, very close to the theoretical value of 0.289. The pressure increases after the shockwave as we would expect.

Click Display.

Image Added

https://confluence.cornell.edu/download/attachments/104400192/step6_streamline.jpg?version=1

Enclosed streamlines at the back of cylinder clearly shows the recirculation region.

Plot Vorticity Magnitude

Let's take a look at the Pressure Coefficient variation around the cylinder. Vorticity is a measure of the rate of rotation in a fluid.

Display > Contours

Under Contours of, choose Velocity.. and Vorticity Magnitude. Deselect the Filled option. Click Display.

Image Added

https://confluence.cornell.edu/download/attachments/104400192/step6_vorticity.jpg?version=1

Go to Step 7: Refine MeshGo to Step 7: Verify Results

See and rate the complete Learning Module

Go to all FLUENT Learning Modules