CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > General Forums > Main CFD Forum

The peak heat isn't located at the stagnation point of a 2D cylinder

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   January 11, 2023, 09:27
Default The peak heat isn't located at the stagnation point of a 2D cylinder
  #1
New Member
 
Dengke Li
Join Date: Dec 2022
Posts: 16
Rep Power: 3
Iniesta8 is on a distinguished road
Hello, everyone
Recently, I found that the heat flux results of a 2D laminar cylinder are mismatched with the fact. As we all know, for a hypersonic flow over a cylinder, the peak heat flux is located at the stagnation point. The true distribution of heat flux is like this But when I use some software or CFD codes to do the simulation, the result is that the peak heat flux is always a bit deviation to the stagnation point. The figure is attached. The grid is 2D and the height of the first layer is 1e-6m.

I don't know why the CFD results are wrong, can anyone give me some advice?
Many thanks!!!
Attached Images
File Type: jpg my.JPG (71.5 KB, 34 views)
Iniesta8 is offline   Reply With Quote

Old   January 12, 2023, 04:15
Default
  #2
Senior Member
 
Will Kernkamp
Join Date: Jun 2014
Posts: 343
Rep Power: 13
wkernkamp is on a distinguished road
The stagnation point will have the highest temperature if the wall has no heat flux. I suppose you gave the wall a fixed temperature. This means the wall is going to cool the flow near the stagnation point. At the stagnation point, there is very little fluid movement, so the cooling is more effective there relative to adjacent locations.
wkernkamp is offline   Reply With Quote

Old   January 12, 2023, 04:37
Default
  #3
New Member
 
Dengke Li
Join Date: Dec 2022
Posts: 16
Rep Power: 3
Iniesta8 is on a distinguished road
Quote:
Originally Posted by wkernkamp View Post
The stagnation point will have the highest temperature if the wall has no heat flux. I suppose you gave the wall a fixed temperature. This means the wall is going to cool the flow near the stagnation point. At the stagnation point, there is very little fluid movement, so the cooling is more effective there relative to adjacent locations.
Thanks for your reply,
Yes, I used an isothermal wall boundary for the cylinder wall. But in theories, the temperature gradient of the stagnation point is the highest and many experimental results prove that the stagnation point has a maximum heat flux. Here you can see a comparison of experimental and CFD results. experiment.JPG
Iniesta8 is offline   Reply With Quote

Old   January 18, 2023, 07:40
Default
  #4
New Member
 
Dengke Li
Join Date: Dec 2022
Posts: 16
Rep Power: 3
Iniesta8 is on a distinguished road
Quote:
Originally Posted by sellardsh View Post
I think you will be able to find the answer to this question using this link. The article exclusively deals with the Simulation of Conjugate Heat Transfer in Thermal Processes with Open Source CFD
That is not a link to the article!!! And my case is a pure fluid flow without the simulation of heat transfer in solid.
Iniesta8 is offline   Reply With Quote

Old   January 18, 2023, 09:46
Default
  #5
Senior Member
 
sbaffini's Avatar
 
Paolo Lampitella
Join Date: Mar 2009
Location: Italy
Posts: 2,163
Blog Entries: 29
Rep Power: 39
sbaffini will become famous soon enoughsbaffini will become famous soon enough
Send a message via Skype™ to sbaffini
What code did you use to get those results? Is it an immersed boundary code? If in house code, what method did you use?

Btw, you are right, higher heat flux should be at stagnation point for your fixed temperature bc. But the problem I see here is slightly different. The max heat flux seems shifted because of those oscillations that just seem to get worst at the stagnation point.

Give more details and we will try to help
sbaffini is offline   Reply With Quote

Old   January 18, 2023, 09:47
Default
  #6
Senior Member
 
sbaffini's Avatar
 
Paolo Lampitella
Join Date: Mar 2009
Location: Italy
Posts: 2,163
Blog Entries: 29
Rep Power: 39
sbaffini will become famous soon enoughsbaffini will become famous soon enough
Send a message via Skype™ to sbaffini
Also, I see you are postprocessing results in paraview? How were they written to file and processed?
sbaffini is offline   Reply With Quote

Old   January 18, 2023, 20:33
Default
  #7
New Member
 
Dengke Li
Join Date: Dec 2022
Posts: 16
Rep Power: 3
Iniesta8 is on a distinguished road
Quote:
Originally Posted by sbaffini View Post
Also, I see you are postprocessing results in paraview? How were they written to file and processed?
Hi
Thanks for your reply. The code I used is Hy2Foam, which is based on the OpenFoam framework. Now I think the reason for the unphysical result is that my mesh is not dense enough in the flow direction. But after refining the mesh, the peak heat is still located at a tiny distance from the stagnation point.
Iniesta8 is offline   Reply With Quote

Old   January 19, 2023, 04:09
Default
  #8
Senior Member
 
sbaffini's Avatar
 
Paolo Lampitella
Join Date: Mar 2009
Location: Italy
Posts: 2,163
Blog Entries: 29
Rep Power: 39
sbaffini will become famous soon enoughsbaffini will become famous soon enough
Send a message via Skype™ to sbaffini
This almost certainly excludes postprocessing issues and also the code is not IB. Have you maybe done some of the tutorials of the code, to see if the problem is there as well?
sbaffini is offline   Reply With Quote

Old   January 19, 2023, 04:37
Default
  #9
New Member
 
Dengke Li
Join Date: Dec 2022
Posts: 16
Rep Power: 3
Iniesta8 is on a distinguished road
Quote:
Originally Posted by sbaffini View Post
This almost certainly excludes postprocessing issues and also the code is not IB. Have you maybe done some of the tutorials of the code, to see if the problem is there as well?
Hi,
I have done some tutorials like a blunt cone. And the result is fine. This question just appears when I doing a 2D blunt body simulation. I also have done the simulation with some commercial software like fluent and CFD++. But it also needs a very dense grid to make the peak heat almost located at the stagnation point.
From my side, this mismatch with the fact can almost avoid via a very dense grid. And it will cost much more time to achieve convergence. I still want to know why it needs a so dense grid when doing 2D blunt body simulations.
Iniesta8 is offline   Reply With Quote

Old   January 19, 2023, 06:42
Default
  #10
Senior Member
 
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,683
Rep Power: 66
LuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura about
More than the peak heat not being at the center, there is the greater issue that the heat flux is not smooth anywhere. I suspect there is some c-grid shenanigans that doesn't go away no matter how you refine the mesh because the same skewed cells are messing you up every time. It doesn't happen in the tutorial because, well, you followed the tutorial instead of doing things on your own. There is a lot more amuck than the peak heat not being in the center, don't bury them under the rug.
LuckyTran is offline   Reply With Quote

Old   January 19, 2023, 07:08
Default
  #11
New Member
 
Dengke Li
Join Date: Dec 2022
Posts: 16
Rep Power: 3
Iniesta8 is on a distinguished road
Quote:
Originally Posted by LuckyTran View Post
More than the peak heat not being at the center, there is the greater issue that the heat flux is not smooth anywhere. I suspect there is some c-grid shenanigans that doesn't go away no matter how you refine the mesh because the same skewed cells are messing you up every time. It doesn't happen in the tutorial because, well, you followed the tutorial instead of doing things on your own. There is a lot more amuck than the peak heat not being in the center, don't bury them under the rug.
Hi
Thank you for the advice.
Yes, I know what you mean. But when I doing a sphere simulation, this mismatch will not take place. And the mesh is generated by myself. And the fluctuations always exist less or more because of the skewed cells. Could you tell me how to avoid these "c-grid shenanigans"?
Iniesta8 is offline   Reply With Quote

Reply

Tags
heat transfer laminar, hypersonic flow

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
How to implement time-varying boundary conditions in an enclosed cylinder Alejandro-FA OpenFOAM Pre-Processing 0 May 14, 2020 06:29
Domain Reference Pressure and mass flow inlet boundary AdidaKK CFX 75 August 20, 2018 05:37
Conjugate Heat transfer- Heat generating cylinder & natural convection sandymech OpenFOAM Running, Solving & CFD 6 July 3, 2018 13:40
Convection heat transfer at stagnation point canonical problem MachZero Main CFD Forum 9 March 15, 2018 06:49
Volumetric Heat generation in cylinder with natural convection conjugate heat transfe sandymech OpenFOAM Running, Solving & CFD 0 August 9, 2017 18:36


All times are GMT -4. The time now is 23:31.