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#1 |
New Member
Micki Joe
Join Date: Apr 2014
Posts: 2
Rep Power: 0 ![]() |
Hi,
I have just started my journey with Fluent ![]() My settings are: material : water pipe : 2d rectangle 2000mm length, 100mm height model : laminar bc : velocity - inlet, outflow, wall inlet velocity: 0.005 m/s mesh: unstructured triangles What I'm expecting is parabolic velocity profile at exit. With my settings I found that the flow should fully develop at around 3m pipe length. ( ![]() So i made a set of meshes with increasing density. But during calculation of more finer meshes I noticed that my profiles change from "cute" parabolas to more of a turbulent flow profiles. I think pictures will show what I mean. And my question: Why it is so that with the same settings but different mesh densities I get different profiles for laminar flow ? Much thanks in advance for Your replays ![]() |
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#2 |
Member
Timm Severin
Join Date: Mar 2014
Location: Munich
Posts: 63
Rep Power: 12 ![]() |
I have basically the same question, and can add that the same problem occurs for OpenFOAM, thus assuming it's a numerical problem rather than the software (which I had guessed anyway).
I'm still in the process of running simulations and generating profiles, and can attach them soon. Rergarding your attached files: What is the difference between both pictures? Only the resolution of the profile?
__________________
PhD Student at the Institute of Biochemical Engineering at TU München Modelling of fluid dynamics in open photobioreactors. System: OpenFOAM 2.3.x, 64bit, 8 Core Xeon Workstation |
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#3 |
Senior Member
François Grégoire
Join Date: Jan 2010
Location: Canada
Posts: 392
Rep Power: 18 ![]() |
Hi,
I don't have the answer but I think the modeling is not right: - Modeling a 2D rectangle is like modeling a rectangular duct with infinite width. For a 2D circular pipe, you should model half of the pipe diameter, axisymmetric around pipe centerline. Bottom BC set to axis and top BC set to wall. - you could try to impose fully developed profile at velocity-inlet (via a simple udf...) - typical outlet BC is pressure-outlet, not outflow |
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