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No turbulence in a turbulent case...!

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Old   October 1, 2007, 12:06
Default No turbulence in a turbulent case...!
  #1
Cyril
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Hi,

I'm simulating a plane (Mach=0.8) and the problem is that when i dsiplay the turbulences, I don't have anyturbulences around the fuselage (no recirculation)! I'm using the following settings:

3D, coupled implicit, rke, energy enabled, sutherland viscosity (air). velocity inlet: turbulent intensity and viscosity ratio=10, pressure outlet (gauge pressure=0) and operating conditions=0

I really need to display turbulences and recirculation vortices around my fuselage (as well as the thickness of the BL..)

Any help welcome!

Thanks
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Old   October 1, 2007, 12:57
Default Re: No turbulence in a turbulent case...!
  #2
JWilliams
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Have you tried changing your scale? It might be hidden in the blue area because your range is so broad.
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Old   October 1, 2007, 13:05
Default Re: No turbulence in a turbulent case...!
  #3
Cyril
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Thanks for your answer..!

Yeah, I tried to set the max value below the real max... It still appears like a laminar flow:



What do you think?

Is the turbulent viscosity ratio the best variable to see the turbulences?
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Old   October 1, 2007, 13:58
Default Re: No turbulence in a turbulent case...!
  #4
bart weisser
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What are your wall boundary conditions on the fuselage (Wall functions or "enchance treatment")? What about your grid density (how many CVs, and how dense it is around the wall)? If Ma = 0.8, it *might* be sensible to use wall functions to speed up calculations, and also to helps enforce a turbulent wall condition.

Another thing, if your CAD model drafted in units other than meters, you might want to check the scale on your fluent model. (Grid->Scale ...) This, I believe, may likely be your problem.
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Old   October 1, 2007, 14:48
Default Re: No turbulence in a turbulent case...!
  #5
Cyril
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Yeah, I scaled my model.. it is now in mm and goes to 14000mm (14m) which is correct.

As for the wall, i didn't touch anything.. the BC is wall with heat flux in thermal conditions (with default settings)

The near wall treatment is standard wall functions (with default settings).. Do you think I should switch to non equilibrium wall functions or enhanced wall treatment? why? should i also change the courant number (4 at the moment)?

Concerning the CV.. i don't know what this is.. but my mesh is as follows: I can't do smaller because of my machine performances (i'm working at school)

Thanks very much for your help !
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Old   October 1, 2007, 14:57
Default Re: No turbulence in a turbulent case...!
  #6
bart weisser
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The CV is okay. The image gave some ideas.

From the grid diagram it looks like you have defined a separate grid for boundary layer flow. Am I correct?

This I am not very familiar with, but how did you link the BL grid and the Tet grid together?

Methinks wall functions should be sufficient in this case.

Another thing I can think of ... what are values for ambient k and epsilon?

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Old   October 1, 2007, 15:04
Default Re: No turbulence in a turbulent case...!
  #7
Cyril
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In gambit, i defined a BL around the fuselage and then meshed the whole volume. The link is automatic betbeen the BL grid and the Tet Grid.

For k and epsilon..... I left the default values, and i don't know where and how to set them up..

Maybe I should change my velocity inlet BC... and put k and eps instead of turbulence intensity and turbulent viscosity ratio (both=10)
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Old   October 1, 2007, 15:06
Default Re: No turbulence in a turbulent case...!
  #8
Cyril
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Oh... i've just realzed that my static pressure was around 2000 Pa far from the fuselage...

It should be 101325Pa.... i'm a bit lost with all the gauge pressure... it is said in the fluent airfoil tutorial that the operating conditions should be=0 when M>0.2... so i maybe should imput 101325 in the velocity inlet and presure outlet gauge pressure ???
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Old   October 2, 2007, 09:16
Default Re: No turbulence in a turbulent case...!
  #9
PratiK Mehta
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of course
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