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You have to set the same velocity profile on both inlet and outlet and then set for example a pressure on the lower left and right corner. The pressure difference decide the velocity and the pairing make it to a continous flow.

I have to correct myself. I have done a similar model before. You are right at setting periodic boundary condition but you have outlet as source and inlet as destination. For p you set p as a source and p+dp as destination but for other parameters source and destination are the same. dp then decide the velocity.

Thanks for your help!

One more question: Do I have to define dp by myself or is there any automatic determination?

Regards,

Nico

Hi

for me I would try "noslip" on the bottom "riple" surface, as I beleive this is more realistic, and open (no visquaos stress or f=p0=1[atm] for the top surface, for me it converges better.

And define p0=1[atm] in your constant and use that in the BC. Jut as well plot p-p0 (or perhaps use a gauge pressure of 0[atm]) to get the pressure changes

you have a Reynolds number up to 38000 too

Then your inlet velocity is interacting with the slip/noslip ripple surface boundary condition. I would rather use an average velocity or a volumic/surface density velocity, by having COMSOL defining the velocity distribution itself, only restraining the integral (or average) of the velocity over the inlet edge/surface

Finally, why not have periodic boundary conditions, I believe it should work too, but I'm always suspicious about those, so I like to simulate two periods (as you have) and I split the volume vertically in the middle to compare the natural continuity boundary in the middle of my simulation with the expected identical boundary variable at the periodic boundary, have a try.

Have fun Comsoling
Ivar

Hi Ivar,
thanks for your helpful hints. Another question, what do you mean with

I would rather use an average velocity or a volumic/surface density velocity, by having COMSOL defining the velocity distribution itself, only restraining the integral (or average) of the velocity over the inlet edge/surface

Do you think of a fixed pressure value on the boundary/edge or an Inlet velocity value, 0.5 m/s for example?

Thanks again for your help,
Nico

Hi

I have tried out different sequences for "fun" in V3.5a. I come to that if you enter (as input and output) a velocity profile as a Vx_ave*sqrt(2.24*(y-Y0)/length), where y is the vertical coordinate of the inflow edge (I was in 2D) Y0 the lower vertex where I expect Vx_ave=0 and length is the total inlet edge length, and the 2.24 is just to make the integrated value equal to the average, and then I pass over 5 identical ripples, I notice that my velocity profile is rather nice and periodic (if you exclude the inlet and outlet boundaries.

I noted that with "s" I got some funny velocity profil shapes, it does not seem to run from 0 to 1 ?

For this I also set the inlet pressure top vertex to p=p0=1[atm] and an initial value of the pressure to p0, and velocity initial condition Vx=Vx_ave. My Reynolds cell number wvere also more compliant with what I expected

Howevever, I failed to set up a "periodoc boundary condition" So obviosly , its easier to run over a few periodes of "ripples", and let the system stabilise. You can always then extract the velocity profile via a extrusion coupling variable into another geoemtry

Hope this helps
Good luck
Ivar

Hi
Im using a periodic flow in my Bc for a cube of porous medium sized 1.4 um the time of study is about 4 h and i didnt find the optimal mesh im worry that im wrong ! plz help me im in internship and still 1 month to finish the project!
the velocity field curve along a line is shown here
sorry but when i try to upload a file it says 'extension error ' pdf