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Exercises
Problem
Use FLUENT to resolve the developing flow in a pipe (same configuration as was done in the tutorial) for a pipe Reynolds number of 10,000 on the following meshes: 100x5, 100x20 with uniform spacing in the radial direction. Plot the skin friction cf as a function of axial location for each grid. Compare the exit value with the expected value for fully developed flow
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(e.g.,
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see
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White
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pgs.
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345-346).
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Recall
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that
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a
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key
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question
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for
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the
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integrity
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of
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the
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mesh
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is
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the
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non-dimensional
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value
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of
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the
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first
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nodal
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point:
| Latex |
|---|
} \large $$ {y_1}^+ = {u_*y \over v} = \sqrt{\tau_w \over \rho} {y_1 \over v} $$ {latex} |
This
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should
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be
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either
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less
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than
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4
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(so
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that
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you
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resolve
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down
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into
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the
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viscous
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sublayer)
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or
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greater
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than
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30
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(where
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wall
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functions
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can
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accurately
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compensate
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for
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the
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poorly
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resolved
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viscous
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sublayer).
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Intermediate
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values
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can
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lead
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to
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greater
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errors.
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Calculate
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the
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value
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of
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y
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1
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+
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for
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each
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mesh;
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use
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that
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to
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help
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explain
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(briefly)
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the
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trends
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in
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the
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agreement
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that
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you
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observe.
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Hints
If you no longer have the 100x5 or 100x20 mesh, you can download them here: pipe100x5.msh, pipe100x20.msh
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