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Make sure that Position on X Axis is set under Options, 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.
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https://confluence.cornell.edu/download/attachments/90737470/04wallyplusfull.JPG?version=1 |
As we can see, the wall y+ value is between 1.6 and 1.9 (ignoring the anamolous at the inlet). Since this is less than 5, the near-wall grid resolution is acceptable.
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Uncheck Write to File. Click Plot.
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https://confluence.cornell.edu/download/attachments/90737470/04centerline_velocityfull.jpg?version=1 |
We can see that the fully developed region starts around x=5m with the centerline velocity becoming constant at a value of 1.195 m/s. This is quite a bit lower than the value of 2 m/s for the laminar case. Can you explain the difference based on the physical characteristics of laminar and turbulent flows?
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Uncheck Write to File. Click Plot.
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https://confluence.cornell.edu/download/attachments/90737470/04skin_frictionfull.jpg?version=1 |
We can see that the fully-developed value is 0.0085. Compare this with what you'd expect from the Moody chart.
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Uncheck Write to File. Click Plot.
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https://confluence.cornell.edu/download/attachments/90737470/04velocity_profilefull.jpg?version=1 |
The axial velocity is maximum at the centerline and zero at the wall to satisfy the no-slip boundary condition for viscous flow. Compare qualitatively the near-wall velocity gradient normal to the wall with the laminar case. Which is larger? From this, what can you say about the relative strengths of near-wall mixing in the laminar and turbulent cases?
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