interPhaseChangeFoam: velocity non zero at wall

alvariten · July 4, 2015, 19:05

Hi all,

I'm studying a cavitation phenomena in an axisymmetric nozzle. The point is, when I plot with paraview the velocity values at outlet (and in any section of the nozzle), I saw the velocity is not zero at wall. The velocity profile looks like a normal profile of a fully developed turbulent flow, with a high tendency to zero close to wall. But the value of the node in the wall is about 50 m/s (it being the maximum profile velocity is around of 300 m/s). I do not think the problem is due to the cavitation zone, as even under these conditions, the velocity imposed on the wall is zero (by definition at boundary).

Most likely this is due to the mesh, but I tried it with a very fine mesh and nothing... I ran the command "yPlusLES" and "yPlusLES -compressible" (as I saw in other thread) to see if the refined mesh was small enough, but doesn't work due to there are two phases defined in transportProperties (correct me if I'm wrong please).

Does anyone have any idea why this happens? And how I can be sure that my mesh is fine enough?

Any suggestion is welcome. Thanks.

Regards.

alexB · July 5, 2015, 17:33

Hi alvaro,

some time before I read about similar problems, when accidently have selected the internal mesh instead of the boundary.

regards
Alex

alvariten · July 6, 2015, 07:17

Hi Alex,
Thanks for your reply. When you say "accidently have selected the internal mesh instead of the boundary" what you mean exactly? What I understand due to your answer is when I select to plot over line in a determinate face in paraview, we select the internal face and we are not considering the patch wall values. So that could be why my velocity values are not zero, but clearly values tend to zero, and the difference between the maximun values of the velocity profile and the values at the walls of nozzle is about 2 or 3 orders of magnitude, then I can give as valid the results.
Regards.
Alvaro.

alexB · July 6, 2015, 10:02

Hi alvaro,

I thought you didn't meant plot, but the ordinary visualization of the mesh...

I tested the plot over line command right now... I think someone else more experienced with it could help you better

regards
Alex

July 4, 2015, 19:05	interPhaseChangeFoam: velocity non zero at wall	#1
alvariten Member alvaro Join Date: Apr 2015 Posts: 33 Rep Power: 11	Hi all, I'm studying a cavitation phenomena in an axisymmetric nozzle. The point is, when I plot with paraview the velocity values at outlet (and in any section of the nozzle), I saw the velocity is not zero at wall. The velocity profile looks like a normal profile of a fully developed turbulent flow, with a high tendency to zero close to wall. But the value of the node in the wall is about 50 m/s (it being the maximum profile velocity is around of 300 m/s). I do not think the problem is due to the cavitation zone, as even under these conditions, the velocity imposed on the wall is zero (by definition at boundary). Most likely this is due to the mesh, but I tried it with a very fine mesh and nothing... I ran the command "yPlusLES" and "yPlusLES -compressible" (as I saw in other thread) to see if the refined mesh was small enough, but doesn't work due to there are two phases defined in transportProperties (correct me if I'm wrong please). Does anyone have any idea why this happens? And how I can be sure that my mesh is fine enough? Any suggestion is welcome. Thanks. Regards.

July 5, 2015, 17:33		#2
alexB Member Alexander Bartel Join Date: Feb 2015 Location: Germany Posts: 97 Rep Power: 11	Hi alvaro, some time before I read about similar problems, when accidently have selected the internal mesh instead of the boundary. regards Alex __________________ Please note that I do not use the Friend-feature, so do not be offended, if I do not accept a request.

July 6, 2015, 10:02		#4
alexB Member Alexander Bartel Join Date: Feb 2015 Location: Germany Posts: 97 Rep Power: 11	Hi alvaro, I thought you didn't meant plot, but the ordinary visualization of the mesh... I tested the plot over line command right now... I think someone else more experienced with it could help you better regards Alex __________________ Please note that I do not use the Friend-feature, so do not be offended, if I do not accept a request.

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July 6, 2015, 07:17		#3
alvariten Member alvaro Join Date: Apr 2015 Posts: 33 Rep Power: 11	Hi Alex, Thanks for your reply. When you say "accidently have selected the internal mesh instead of the boundary" what you mean exactly? What I understand due to your answer is when I select to plot over line in a determinate face in paraview, we select the internal face and we are not considering the patch wall values. So that could be why my velocity values are not zero, but clearly values tend to zero, and the difference between the maximun values of the velocity profile and the values at the walls of nozzle is about 2 or 3 orders of magnitude, then I can give as valid the results. Regards. Alvaro.