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ravi1650 June 2, 2009 09:23

3D flow in a pipe

I want to analyse velocity profile of fully developed(laminar) single phase flow in a pipe. For that I have created a pipe in GAMBIT and exported in Fluent with the inlet and outlet conditions as pressure conditions. We know the analytical solution in a pipe and it shud be parabolic at the outlet(when flow is fully developed)
When I am working with low reynold's number, the results are pretty much accurate(RMS error=1.5%) but when I work with high Re # like 1000, I get an error of around 20%. For example, for Re=500, the entrance length required is 3m (D=0.1), so I am woking on L=8m so that fluid is fully developed at the outlet and I have accurate results bt still I am getting error for high Re#. The error increasses as Re# increases.
Moreover, Can I create different interval spacing in axial direction and on the surface nodes in GAMBIT. Like, I have dia=0.1 and L=8m, so if I use Interval count of 60, then it will be fine for the face while coarser for the axial direction whreas if I use interval size of 0.001, it will be okay for the face but too much fine for the axial direction. So, Please help.


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