[danvica]

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:

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;
    }
 
 }

Note: On both the layered meshes some air seems trapped for a while onto the walls boundary, more in the k-omega model (lamwall-altr , turbwall-altr).

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.