FLOWLAB SOLUTION
8.138
Use the
pipe_el
FlowLab template to investigate how the Reynolds number
affects the entrance region of a pipe flow.
Alter the Reynolds number of the problem by
varying the fluid properties and the inlet velocity,
U
.
Obtain data for Re = 100, 500, and
1000.
Demonstrate that the selected pipe diameter,
D
, and pipe length,
l
, are adequate for
studying entrance region flows (
hint: the pipe exit should be a sufficient distance
downstream of the anticipated end of the entrance region
).
Plot the static pressure along
the pipe for each of the Reynolds number cases and calculate the increased pressure drop
in the entrance region of the pipe.
Determine the entrance length,
l
e
, from your
calculations and compare them with those given in Equation 8.1 by plotting
l
e
/
D
as a
function of Re.
Provide several conclusion statements from this investigation.
Problem Setup
If the pipe diameter is held constant, the case with the highest Re value will produce the
largest entrance length. Therefore, for Re = 1000 and D = 0.2 m, the predicted entrance
length is 12 m. For this problem, the resulting pipe geometry to be used is D = 0.2 m and
L = 30 m.
The Reynolds number was varied by changing the inlet velocity of the Boundary
Conditions in the Physics section of the problem setup. The student could also change
fluid properties (density and viscosity) under the Materials section. The flow was set to
Laminar with no Heat Transfer.
A medium grid density was used for the three Reynolds number simulations for this
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 Spring '08
 all
 Fluid Dynamics, entrance length

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