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strange pressure behavior using interFoam for 3D micro-channel

Dear all:

Now I have a problem using interFoam, the case is quite easy, a square channel of 600 micrometers long and with cross-section of 40*40 micrometer, initially one phase is in the channel, then we inject another phase from inlet, and liquid can flow out from outlet.
my boundary condition is just the normal sets:
U

Code:

inlet  fixedValue (0.15 0 0)

outlet zeroGradient

p_rgh

Code:

inlet zeroGradient

outlet fixedValue 0

alpha

Code:

inlet  type            inletOutlet;

        value           uniform 0;

        inletValue      uniform 0;

outlet zeroGradient

But the calculated pressure is really strange,
As can seen, for the first time step t=0.0001s, the pressure is what we can expect, but at the second time step t=0.0002s, distribution and value is really strange: outlet pressure is even higher than inlet!:confused: And next time step it will return back to what we expect, then nonphysical again for the next step.

I have tried to refine the mesh, set initial velocity field in the channel, but it still happens. So does anyone has similar experience or has any hint for this?
Also the velocity in several cells near the inlet is really high, is this the reason ? How can we heal this effect ?
Thank you.

Dear all,

Considering maybe it is due to the boundary condition setting conflict for cells both at inlet and on the wall: non-zero inlet velocity, while no-slip at the wall. And this effect is significant in micro scale ???
So now maybe the proper statement is that how we set the ¨right¨ boundary condition to make the velocity in cells both at inlet and wall?
Any hints on this?
Thank you.

Hi there;

I am not really sure if this could be the problem but what are your top and bottom b.c's?

For velocity:
fixedValue (0 0 0) /*no outflow through top and bottom phases*/

For pressure:
fixedFluxPressure /*calculate the pressure gradient from the velocities.*/

As you are using 2 phases you always will have spurious currents generated at the interface between phases. You will need to get rid of them.

As per my initial runs I observe an alternative fluctuation of the U(one time is high and next time it falls and increases later. this is unphysical need to be solved). But also in some papers, this is neglected as it is not seen to influence the results too much.

Maybe the contact angle

Dear Saideep:

Thanks for your reply. But now I think that maybe it is due to the contact angle, if we have contact angle less than 45 degree, then we can have this problem.

Dear red.yxg,

I am simulating almost the same problem and observe some weird behavior at the outlet, as the one you showed, the fuild exist from just a portion of outlet patch.

I am wondering if you figured out a solution to that.
I am simulating a 2D flow confined between two walls (channel). I have single inlet and single outlet.

Please let me know if you were able to resolve the problem. Thanks.