Field function to determine entrance length

Newgirl · October 9, 2017, 14:38

Hi all,

I'm new to the world of CFD and STAR CMM+.

I have a hollow pipe with steady flow,defined inlet velocity of 0.1 m/s and pressure outlet, segregated flow.

This is my parameters:
d =6mm
l =300mm
density= 1050 kg/m^3
viscosity= 3.5 mPas

I would like to determine the entrance length for this pipe. I have already determine it theoretically as 64.8 mm.

How can I determine this using a field function? Can I show the exact point where the flow becomes fully developed graphically?

Any advice and/or suggestions are welcome.

fluid23 · October 11, 2017, 14:29

You could create a field function to return du/dx at constant radius (assuming u is velocity and x is aligned with the pipe axis). Then you would want to look for a location where that gradient is zero (or reasonably close). You could maybe setup an XY plot and show x vs du/dx for a handful of radial locations and show where they all reach zero.

October 9, 2017, 14:38	Field function to determine entrance length	#1
Newgirl New Member Join Date: Oct 2017 Posts: 1 Rep Power: 0	Hi all, I'm new to the world of CFD and STAR CMM+. I have a hollow pipe with steady flow,defined inlet velocity of 0.1 m/s and pressure outlet, segregated flow. This is my parameters: d =6mm l =300mm density= 1050 kg/m^3 viscosity= 3.5 mPas I would like to determine the entrance length for this pipe. I have already determine it theoretically as 64.8 mm. How can I determine this using a field function? Can I show the exact point where the flow becomes fully developed graphically? Any advice and/or suggestions are welcome.

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October 11, 2017, 14:29		#2
fluid23 Senior Member Matt Join Date: Aug 2014 Posts: 947 Rep Power: 17	You could create a field function to return du/dx at constant radius (assuming u is velocity and x is aligned with the pipe axis). Then you would want to look for a location where that gradient is zero (or reasonably close). You could maybe setup an XY plot and show x vs du/dx for a handful of radial locations and show where they all reach zero.