FLUENT - Turbulent Pipe Flow - Step 6

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Problem Setup > Reference Values

Select inlet under Compute From to tell FLUENT to use values at the pipe inlet for the reference values. Check that the reference value for density is 1 kg/m³, velocity is 1 m/s, and coefficient of viscosity is 2e-5 kg/m-s as given in the Problem Specification.These reference values will be used to non-dimensionalize the distance of the cell center from the wall to obtain the corresponding y+ values.
 
Let's plot y+ values for wall-adjacent cells to check how it compares with the recommendation mentioned above.

Results > Plots > XY Plot > Set Up...

Make sure that Position on X Axis is set under Options. Also, make sure that 1 is the value next to X, and 0 is the value next to Y and Z under Plot Direction. Recall that this tells FLUENT to plot the x-coordinate value on the abscissa of the graph. Pick Turbulence...under Y Axis Function and select Wall Yplus from the drop down list under that. Since we want the y+ value for cells adjacent to the wall of the pipe, choose wall under Surfaces.

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.

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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.

Click on Curves... in the Solution XY Plot window. Select the solid line option under Pattern as shown below. Change Weight to 2. Select the blank option under Symbol. Click Apply and Close.

 
Turn on grid lines: In the Solution XY Plot window, click on Axes.... Turn on the grid by checking the boxes Major Rules and Minor Rules under Options. Leave Auto Range checked. Click Apply. Select Y under Axis and repeat. Click Apply and Close.

Uncheck Write to File. Click Plot.

Click here to see a higher resolution image.

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Go back to the Solution XY Plot Window. Under the Y Axis Function, pick Wall Fluxes..., and then Skin Friction Coefficient in the box under that. Under Surfaces, we are plotting the friction coefficient along the wall. Uncheck centerline surface.

Uncheck Write to File. Click Plot.

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Change the plot settings so that the radial distance from the axis is plotted as the ordinate: In the Solution XY Plot window, uncheck Position on X Axis under Options and choose Position on Y Axis instead. Under Plot Direction, change X to 0and Y to1. For the X Axis Function i.e. the abscissa, pick Velocity... and Axial Velocity under that.

Since we want to plot this at the outlet boundary, pick only outlet under Surfaces.

Uncheck Write to File. Click Plot.

Click here to see a higher resolution image. 

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