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Old   March 23, 2013, 11:50
Default entrance length
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Dear friends

in a pipe flow,

How to find the entrance length for fully developed ideal flow?
I have defined the inlet velocity as function of time, in such case how do I find the entrace length?

Thank you
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Old   March 25, 2013, 09:34
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In your CFD model?

Measure it?

Use textbook calc?

What do you mean?
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Old   March 25, 2013, 11:56
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Laminar: L/D=0.06 Re
Turbulent: L/D=4.4 Re^(1/6)

L is entrance length, D diameter. Any textbook should cover this.

The fully developed flow is defined as the flow with no velocity gradients in flow directions. This should automatically imply steady state, since for transient case, the velocity profiles may change. Ultimately, even if you start as transient simulation, it will converge to a fully developed steady state solution.

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