Boundary Layer Inflation across a 90 degree bend

gill11a · September 23, 2014, 14:23

In my analysis, i need a boundary layer inflation across several 90 degree bends (corners) in my geometry. I am getting a good continuous mesh inside of a corner, but on the outside of a corner, the mesh is really bad ( as you can see in attached screenshots).
Any help will be much appreciated.
Thanks in advance.

hwet · September 23, 2014, 21:56

which software is this? you can just get away by making a curve instead of a sharp 90 degree bend, it should not make a big difference to the simulation.

hwet · September 23, 2014, 21:59

it also appears that you have different boundary layer inputs for the vertical and horizontal parts, or atleast they have different diameters which is resulting in the different growth rate of the inflation and hence the bad mesh. also you cant judge a mesh by how pretty it looks rather look at the mesh quality from the software and decide if it is good or bad.

R4RAHUL · September 24, 2014, 02:20

I agree with the hwet you can draw a small curve at the bend

gill11a · September 24, 2014, 12:56

Hi everyone,
Drawing a curve instead of 90 degree bend will not represent exactly whats happening in my physical model.
I am using ANSYS Mesher.
I need different sized layers in different surfaces because my throat is approximately 100 times smaller than the inlet and outlet. So to get enough elements at the throat, the size change is necessary.
I just have hard time figuring out why am i not able to get the same mesh in the two cases shown in the pictures above.

hwet · September 25, 2014, 03:49

rather than having smooth transition (which i believe you have done) you can control what you want the thickness of the inflation layer to be. you cant compare the inner side and the outer side as you have done above because the inner side belongs to the same part.
secondly saying it will not represent what is happening in you physical model is an exaggeration. cfd is all about approximation so it would not make a big difference to you simulation.
and check what the software itself has to say about your mesh, you cant judge a mesh by just looking at it and deciding it isn't looking pretty like that. The mesh in its current state would be fine as well depending on what accuracy you want.

gill11a · September 25, 2014, 11:50

hwet, i am not using smooth layer transition. I am using first layer height.

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September 23, 2014, 21:56		#2
hwet Senior Member Join Date: Mar 2014 Posts: 375 Rep Power: 13	which software is this? you can just get away by making a curve instead of a sharp 90 degree bend, it should not make a big difference to the simulation.

September 23, 2014, 21:59		#3
hwet Senior Member Join Date: Mar 2014 Posts: 375 Rep Power: 13	it also appears that you have different boundary layer inputs for the vertical and horizontal parts, or atleast they have different diameters which is resulting in the different growth rate of the inflation and hence the bad mesh. also you cant judge a mesh by how pretty it looks rather look at the mesh quality from the software and decide if it is good or bad.

September 24, 2014, 02:20		#4
R4RAHUL New Member rahul kumar Join Date: Jun 2014 Posts: 24 Rep Power: 12	I agree with the hwet you can draw a small curve at the bend

September 24, 2014, 12:56		#5
gill11a New Member Ravinder Gill Join Date: Sep 2014 Location: Windsor,ON Posts: 19 Rep Power: 12	Hi everyone, Drawing a curve instead of 90 degree bend will not represent exactly whats happening in my physical model. I am using ANSYS Mesher. I need different sized layers in different surfaces because my throat is approximately 100 times smaller than the inlet and outlet. So to get enough elements at the throat, the size change is necessary. I just have hard time figuring out why am i not able to get the same mesh in the two cases shown in the pictures above.

September 25, 2014, 03:49		#6
hwet Senior Member Join Date: Mar 2014 Posts: 375 Rep Power: 13	rather than having smooth transition (which i believe you have done) you can control what you want the thickness of the inflation layer to be. you cant compare the inner side and the outer side as you have done above because the inner side belongs to the same part. secondly saying it will not represent what is happening in you physical model is an exaggeration. cfd is all about approximation so it would not make a big difference to you simulation. and check what the software itself has to say about your mesh, you cant judge a mesh by just looking at it and deciding it isn't looking pretty like that. The mesh in its current state would be fine as well depending on what accuracy you want.

September 25, 2014, 11:50		#7
gill11a New Member Ravinder Gill Join Date: Sep 2014 Location: Windsor,ON Posts: 19 Rep Power: 12	hwet, i am not using smooth layer transition. I am using first layer height.