[shock77]

Hi foamers,


I have notices weird velocity fluctuations in my underexpanded jet. I have attached the velocity field and density field as images.


Those fluctuations occur only when I use second order schemes. I am using the solver rhoCentralFoam (openfoam4). I have tried reducing the Co-Number to 0.1 and the limiter schemes MinMod, vanAlbada and vanLeer. Only upwind seems to smear them out. I use the kOmegaSST turbulence model.



Does anyone ever had such an issue? I would be greatful for any advice.




Kind regards,
shock77

[IC01]

Originally Posted by shock77

Hi foamers,


I have notices weird velocity fluctuations in my underexpanded jet. I have attached the velocity field and density field as images.


Those fluctuations occur only when I use second order schemes. I am using the solver rhoCentralFoam (openfoam4). I have tried reducing the Co-Number to 0.1 and the limiter schemes MinMod, vanAlbada and vanLeer. Only upwind seems to smear them out. I use the kOmegaSST turbulence model.



Does anyone ever had such an issue? I would be greatful for any advice.




Kind regards,
shock77

Hi

I've had the same problem. I think they call it a chess board issue. Solutions that helped me: 1) I've added 0.1 m/s velocity field. 2) I started to use SimpleFoam instead of Pimple
Would be great to see if there are anything else that might help

Cheers

[shock77]

Hi,


thank you very much for your hints!


I am interested in the dynamic behavior, so rhoSimpleFoam is not an option for me.


I have already initiated my field with (1 0 0), becazse I knew it could lead to some problems initiating with (0 0 0). Since the flow is the 3D, I have tried (0.1 0.1 0.01) and... it worked! Those weird fluctuations disappeared! Thank you very much, that helped me a lot!



Kind regards,
shock77

[shock77]

They actually reappeared with a finer mesh.
Do you have an advice to solve that issue? I also tried reducing the timestep (Co= 0.2 and 0.1) but it didnt help.