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Pressure in Channel with simpleFoam and cyclic |
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#1 |
Senior Member
ArathoN
Join Date: Jul 2011
Posts: 137
Rep Power: 16 ![]() |
I've done some simulations over a channel using RANS models first with pimpleFoam however because of some problems i switched to simpleFoam (here the thread i created for pimple link)with cyclic Boundaries. I noticed:
Does any of you have an explanation about this p field? I'm really lost here. For the info on the flow i'll link the other thread link |
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#2 |
Senior Member
Philipp
Join Date: Jun 2011
Location: Germany
Posts: 1,297
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Hey,
I see the same for a periodic pipe, LaunderSharmaKE U_no_limiter.jpg p_no_limiter.jpg This is a cut through the (short) pipe. Upper profile is "U", flow goes in "x"-direction. X-direction is very poorly resolved by the mesh (see the lower pressure profile). Here you also see the wiggles.
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#3 |
Senior Member
ArathoN
Join Date: Jul 2011
Posts: 137
Rep Power: 16 ![]() |
I refined the mesh along x and y direction but the pressure still had that same behavior. I searched more on the forum and in the net but didn't find anything useful. Maybe The pressure gradient source is bugged with simpleFoam, I'll check my case with pimplefoam and report back.
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#4 |
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davide basso
Join Date: Jan 2012
Posts: 48
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This is what my residuals and middle plane profiles of velocity and pressure look like (simpleFoam, Re=44000 approx)
The inlet patch is at the bottom and it is mapped with the top outlet patch. I didn't use cyclic boundary conditions for inlet and outlet since it would have killed the pressure gradient between in and out. If you did maybe that's the reason for those strange behaviours. Infact especially in ArathoN's there is barely any pressure gradient at all |
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#5 |
Senior Member
ArathoN
Join Date: Jul 2011
Posts: 137
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Can you upload your /0 folder, I tried to use mappedBC but I had very bad residual. The mapped variable oscillates around 0.01-0.1 almost like your U. In my case I mapped all the field variables except for nut and I mapped to the nearest cell of the outlet (I've put the offset a Lil bit away from the inlet position, I've read that it can cause problems if you put it at the exact position of the outlet). I'll try to do the simulation again and I'll report, for now the u-profile is quite good.
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#6 |
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davide basso
Join Date: Jan 2012
Posts: 48
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There you go
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#7 |
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ArathoN
Join Date: Jul 2011
Posts: 137
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#8 |
Member
davide basso
Join Date: Jan 2012
Posts: 48
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I can't give you reference about the zero value for the average. To be honest since the thing worked I didn't pay much attention to it.
Regarding block mesh dictionary I used: sampleRegion region0; sampleMode nearestPatchFace; samplePatch top_end; |
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#9 |
Senior Member
ArathoN
Join Date: Jul 2011
Posts: 137
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Ah interesting didn't know you can directly specify the patch from which to sample. I usually used the offset option. Thanks I'll try tonight with mappedPatch and I'll report tomorrow.
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#10 | |
Senior Member
ArathoN
Join Date: Jul 2011
Posts: 137
Rep Power: 16 ![]() |
Quote:
So in the end the pressure field behavior with cyclic is a problem of how the fvOption works with the solver simpleFoam. In my opinion it is needed a pressure correction loop to reassess the continuity. P. S ah because I made the same error in blockmeshdict it is needed to set the offset value for mappedPatch otherwise it will not work. Moreover if setaverage is 0 there is no averaging. |
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#11 | |
Senior Member
M. Montero
Join Date: Mar 2009
Location: Madrid
Posts: 153
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Quote:
I am facing convergence problem in the pressure equation when using cyclic bc |
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