High Turbulent channel (duct) flow - a lot of problems

pao · August 5, 2022, 14:04

Hi guys! 1st post for me here at CFD-Online.
Great community , great people, thanks!

I'm currently trying to stabilize a simulation that doesn't want to "stay calm" -------- > EXPLOSION

I've a channel duct flow:

One inlet, air at 55 [m/s] (massflow = 1.5 [kg/s])
Reynolds at the inlet -> Re = 4.5e5
Two outlet where I'm imposing just the static pressure
Expected Reynolds at 1 of the 2 outlet -> Re= 8e5
At the inlet Ma<0.3 but in some inner regions of the domain it is reached and exceeded
So I'm using rhoSimpleFoam
kEpsilon with wall function

Are there some special BCs to impose to nut, T, p, U, etc. related to internal channel flow (compressible, very high turbulent) that I should use for this kind of problem?

Thanks
Pao

Santiago · August 7, 2022, 05:39

Quote:

Originally Posted by pao

[*]Expected Reynolds at 1 of the 2 outlet -> Re= 8e5

If you know the velocity at one of the two outlets, Why do you impose Neumann BC for velocity?

sudo_rm · August 8, 2022, 04:08

Hi,

Without additional information it's hard to say why your simulation crashes, so I can suggest some general things to check that might be the cause:

- Does it crash at the first few iterations or at a certain time?
- You could examine the log file, or monitor the residuals (https://doc.cfd.direct/openfoam/user...phs-monitoring) to find out which variable causes the problem (p,T,U etc.).
- Is your mesh fine? Are there any bad cells (use checkMesh)
- How did you calculate the BC for the turbulence model? You can estimate appropriate values e.g. at https://cfd-training.com/turbulent-b...ns-calculator/

Hope that helps, good luck!

August 5, 2022, 14:04	High Turbulent channel (duct) flow - a lot of problems	#1
pao New Member Join Date: Sep 2021 Posts: 1 Rep Power: 0	Hi guys! 1st post for me here at CFD-Online. Great community , great people, thanks! I'm currently trying to stabilize a simulation that doesn't want to "stay calm" -------- > EXPLOSION I've a channel duct flow: One inlet, air at 55 [m/s] (massflow = 1.5 [kg/s]) Reynolds at the inlet -> Re = 4.5e5 Two outlet where I'm imposing just the static pressure Expected Reynolds at 1 of the 2 outlet -> Re= 8e5 At the inlet Ma<0.3 but in some inner regions of the domain it is reached and exceeded So I'm using rhoSimpleFoam kEpsilon with wall function Are there some special BCs to impose to nut, T, p, U, etc. related to internal channel flow (compressible, very high turbulent) that I should use for this kind of problem? Thanks Pao

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August 8, 2022, 04:08		#3
sudo_rm New Member Join Date: Jul 2022 Posts: 6 Rep Power: 4	Hi, Without additional information it's hard to say why your simulation crashes, so I can suggest some general things to check that might be the cause: - Does it crash at the first few iterations or at a certain time? - You could examine the log file, or monitor the residuals (https://doc.cfd.direct/openfoam/user...phs-monitoring) to find out which variable causes the problem (p,T,U etc.). - Is your mesh fine? Are there any bad cells (use checkMesh) - How did you calculate the BC for the turbulence model? You can estimate appropriate values e.g. at https://cfd-training.com/turbulent-b...ns-calculator/ Hope that helps, good luck!