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simpleFoam: Non-uniform mesh near inlet & outlet causes incorrect velocity profile? |
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January 28, 2015, 06:17 |
simpleFoam: Non-uniform mesh near inlet & outlet causes incorrect velocity profile?
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New Member
Saumitra Joshi
Join Date: Dec 2012
Posts: 14
Rep Power: 13 |
Hi all!
I'm running a very simple case of steady state, incompressible, laminar pipe flow using simpleFoam. I created the mesh using snappyHexMesh. The following three types of meshes were generated: 1) Fully uniform hex-mesh (uniform spacing between cells in flow direction) 2) Non-uniform hex mesh without layers (finer cells near inlet and outlet, no layers) 3) Non-uniform hex mesh with layers (finer cells near inlet and outlet, layers present) - image below. Geometry: Straight cylindrical pipe Diameter: 1 cm, Length: 1 m Kinematic viscosity: 1e-6 m2/s Boundary Conditions: Velocity: -> Inlet: Uniform Fixed Value ux = 0, uy = 0.1 m/s, uz = 0 -> Outlet: Zero Gradient -> Wall: Uniform fixed value Pressure: -> Inlet, Wall: Zero Gradient -> Outlet: Fixed Value = 0 I'm using the GAMG solver for pressure (Abs tolerance: 1e-8, Rel tolerance: 1e-3, other settings default), PBiCG solver for velocity (Abs tolerance: 1e-8, Rel tolerance: 1e-3, other settings default). Residual for pressure and velocity is 1e-6. The Issue For case 1, I get very nice results. (Parabolic profile, Ucent = 2*Uavg, correct pressure drop). However for case 2 and 3, although the pressure drop is fine, the velocity profile along the center-line looks something like this: Firstly, the velocity reaches only about 0.19 m/s instead of 0.2. Also, there is a weird kink towards the end. I checked if this is because of interpolation issues, but that is not the case. I'm baffled. Is this because of the non-uniform mesh near inlet and outlet? If yes, why does it occur? |
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non uniform mesh problem, simplefoam, velocity field |
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