CFD Online Discussion Forums - pressureGradientExplicitSource fvOptions

Hi all,
I am simulating a 2D-rib with periodic boundary conditions where OUTLET data is mirrored to INLET.
To keep the mass flow constant I am using pressureGradientExplicitSource in the fvOptions dictionary.

Quote:

momentumSource
{
type pressureGradientExplicitSource;
active on; //on/off switch
selectionMode all; //cellSet // points //cellZone

pressureGradientExplicitSourceCoeffs
{
fieldNames (U);
Ubar ( 1 0 0 );
gradPini gradPini [0 2 -2 0 0] 0; // initial pressure gradient
flowDir (1 0 0); // flow direction
}
}

So obviously I want to keep speed constant at 1m/s.
To look at avg(U) I select all cells of my geometry and use plotSelectionOverTime with only statistics chosen,
It works fine on a coarse mesh, consisting only of quadratic blocks (AR=1).
http://s2.postimg.org/ck61y5e21/Scre...3_15_46_03.png
http://s15.postimg.org/5brnorwkb/Scr...3_15_45_14.png

The velocity oscillates a little but becomes constant quickly at the desired value of 1.

But when I try to use a wall refined mesh

http://s29.postimg.org/ivs46wluf/Scr...3_15_49_23.png

http://s12.postimg.org/rimnybw0d/Scr...3_15_39_00.png

Velocity drops to 0.8 and remains there giving bad results for my simulation since I have to adjust a sink term for temperature according to mass flow (~velocity).

Does anybody has an idea what could cause this strange behaviour?

You can download my example calculation here:

https://owncloud.tu-berlin.de/public...f8946fcc142237

Every help is appreciated!
:)