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April 30, 2012, 04:11 |
Layers and turbolence in Interfoam
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Senior Member
Daniele Vicario
Join Date: Mar 2009
Location: Novara, Italy
Posts: 142
Rep Power: 17 |
Hi,
I'm investigating on the importance of wall layers into turbolent flow using interfoam solver. I compared the same case using laminar/turbolent SST k-omega models and regular/wall-layered mesh. The test case is a simple 8mm diameter, 100mm long pipe. The inlet flow (water) speed is 3m/s. The rest is air. The above conditions give Re=24000. The meshes have been obtained by SHM (130KCells for no layers and 188KCells for 3-layers refinement). First big question: what should one check to validate the results ? I tried with pressure drop, comparing it with the moody chart obtained value, in this case Dp=1575Pa. 1. No-wall layers and laminar model (pictures lam-a30 and lam-p50) Dp @50ms=1191Pa 2. No wall layers and SST k-omega model (turb-a30 , turb-p50 , turb-y+30) y+ @30ms max is 49 at the water surface Dp @50ms=1975Pa 3. Wall layers (3) and laminar model (lamwall-a30 , lamwall-p50 , lamwall-y+30) Dp @50ms=1724Pa 4. Wall layers (3) and SST k-omega model (turbwall-a30 , turbwall-p50 , turbwall-y+30) y+ @30ms max is 13 at the water surface Dp @50ms=2373Pa For all the k-omega models I used the same 0-condition: Code:
k: internalField uniform 0.03375; boundaryField { inlet { type fixedValue; value $internalField; } outlet { type inletOutlet; inletValue $internalField; value $internalField; } walls { type kqRWallFunction; value $internalField; } } nut: internalField uniform 0; boundaryField { inlet { type calculated; value uniform 0; } walls { type nutkRoughWallFunction; Ks uniform 0.0000025; Cs uniform 0.5; value uniform 0.0; } outlet { type calculated; value uniform 0; } } omega: internalField uniform 600; boundaryField { inlet { type fixedValue; value $internalField; } outlet { type inletOutlet; inletValue $internalField; value $internalField; } walls { type omegaWallFunction; value $internalField; } } Questions: 1. All the Dp seem too far from the analitical value, maybe because in the simulation the flow is entering already turbolent ? 2. Do I have to keep y+ value as low as possible, even using wall function ? 3. About all this test cases: has any sense comparing a layered wall refined laminar case with a k-omega one (layered or not) ? Basically what I'd like to know is whether, working with Re within 20000-50000, one could save computation time layering the mesh but using a laminar model. Or one has always to add layers to the walls and use k-omega model ? Sorry for the long thread, thanks for any help.
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Daniele Vicario blueCFD2.1 - Windows 7 |
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