FLUENT - Turbulent Pipe Flow - Step 6

Step 6: Results

y+

Turbulent flows are significantly affected by the presence of walls. The k-epsilon turbulence model is primarily valid away from walls and special treatment is required to make it valid near walls. The near-wall model is sensitive to the grid resolution which is assessed in the wall unit y+(defined in section 10.9.1 of the FLUENT user manual). We'll gloss over the details for now and use the following rule of thumb: select the near-wall resolution such that y+ > 30or < 5 for the wall-adjacent cell. Look at section 10.9, Grid Considerations for Turbulent Flow Simulations, for details.

...

Click Plot.


Click here to see a higher resolution image. 
 
As we can see, the wall _y+_value is between 1.6 and 1.9 (ignoring the anomalous at the inlet). Since this is less than 5, the near-wall grid resolution is acceptable.

Save Plot

In the Solution XY Plot Window, check the Write to File box under Options. The Plot button should have changed to the Write... button. Click on Write.... Enter yplus.xy as the file name and click OK. Check that this file has been created in your FLUENT working directory.

Centerline Velocity

Under Y Axis Function, pick Velocity... and then in the box under that, pick Axial Velocity. Finally, select centerline under Surfaces since we are plotting the axial velocity along the centerline. De-select wall under Surfaces.

...

Save the data for this plot as vel.xy.

Coefficient of Skin Friction

The definition of the skin friction coefficient was discussed in the laminar pipe flow tutorial. The required reference values of density and velocity have already been set when plotting y+.

...

Save the data for this plot as cf.xy.

Velocity Profile

We'll plot the axial velocity at the outlet as a function of the distance from the center of the pipe.

...