entrance length

kmgraju · March 23, 2013, 10:50

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

singer1812 · March 25, 2013, 08:34

In your CFD model?

Measure it?

Use textbook calc?

What do you mean?

oj.bulmer · March 25, 2013, 10:56

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.

OJ

March 23, 2013, 10:50	entrance length	#1
kmgraju Senior Member Govindaraju Join Date: Apr 2010 Posts: 209 Rep Power: 17	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

March 25, 2013, 08:34		#2
singer1812 Senior Member Edmund Singer P.E. Join Date: Aug 2010 Location: Minneapolis, MN Posts: 511 Rep Power: 20	In your CFD model? Measure it? Use textbook calc? What do you mean? jthiakz likes this.

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March 25, 2013, 10:56		#3
oj.bulmer Senior Member OJ Join Date: Apr 2012 Location: United Kindom Posts: 473 Rep Power: 20	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. OJ