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3.5 km long pipe

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Old   May 7, 2009, 05:12
Default 3.5 km long pipe
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idris shukri
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Does anyone know how to simulate a long 3.5 km pipe using fluent?? want to check visual pressure and temperature drop along the pipe?? do i have to draw a really 3.5 km long pipe?? or maybe can scale up?

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Old   May 7, 2009, 05:26
Ralf Schmidt
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yes... you have to draw it... if you want to model the whole pipe in one...

Use the gambit units as meters... So... draw the pipe 3500 units long... and in fluent define the units as meters.
BUT... to calculate the pressure drop and heat transfer correctly, you have to resolve the boundary layer... and that might take a really large number of cells perpendicular to the pipe axis.

To reduce the number of cells, you might take very long cells parallel to the axis (something like 0,5 meters) outside the areas, where you have flow disturbances (like bows or valves). Also, you might use symmetry effects...

If you have areas, you want to calculate in detail (like complicated obstacles) - you might model them separately. You can model the flow there in detail and transfer your results to a coarser mesh of the pipe outside that area... (its a multi level model)

One other thing: why you want to model that long pipe?? You might estimate / calculate pressure drop and heat transfer via a standard textbook. There are simple equations for pressure drop...

Best wishes
CFD - nothing but Colourful Fluid Dynamics

Last edited by Ralf Schmidt; May 7, 2009 at 06:43.
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Old   May 7, 2009, 07:05
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idris shukri
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Oh ok...maybe i can just use the simpler way ...anyway just want to check if Fluent capable of simulate the long pipe..thanks anyway.
one more thing, do you know how to simulate a 36 inch straight pipe with a 16 inch lateral T branch for the compressible flow. i just want to see the profiles at the the lateral branch. i have tried with the following boundary condition
Pin = inlet boundary
Pout = lateral outlet1 boundary
Pout2 = outlet2 boundary

i have assume a bigger pressure drop at the lateral than the outlet2,
At lateral the result show the pressure is dropping as expected because of the smaller pipe size but the result show an increase of pressure slightly after the branch at the 36 inch main line. is it supposed to drop??.
Why we cannot define the velocity condition for the compressible problem..seem the calculate velocity based on input pressure is too high compared to the actual i miss something to define?. pls advice
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