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Transport in Thermofluids
ME220B
Homework #3
Problem 1:
Consider Poiseuille flow between parallel plates separated by a distance
W
.
Try to evaluate the appropriateness of critical Reynolds number Re
2300
D
≈
(rule of
thumb) based on our understanding of the transition between the laminar viscous sublayer
and turbulent inner region described by the law of the wall.
To this end, find an
expression for the wall coordinate at middistance between the plates
(
/ 2)
yW
+
in terms
of the coefficient of friction
f
c
and the Reynolds number Re
D
(based on hydraulic
diameter).
Assume that the flow between the plates is mostly enveloped by the viscous
sublayer and determine
f
c
as a function of Re
D
for a laminar
flow.
Combine this result
with the critical Reynolds to evaluate
(
/ 2)
+
. Does
(
/ 2)
+
fall within the
transition region between the viscous sublayer and the inner region of the wall
turbulence?
Comment on the significance of this result.
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 Winter '09
 Bennett

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