[GAMBIT] 2D turbulent flow in axisymmetric sudden expansion

Cesare88 · December 22, 2014, 09:06

hi guys,

I am a student in mechanical engineering . I'm working on a project for the cfd examination and I can not find a solution to the problem .
in particular I have to study the 2D turbulent flow of water in a pipe with a sudden expansion using the wall function approach and the near wall modeling approach and compare the results . Could someone explain how to create the mesh in gambit to obtain a valid results from the simulation ??? in particular I would like to know how to get the correct value of y + for the two different approaches . If you have any links to be attached that explains this i am very grateful .

have a nice evening

-mAx- · December 23, 2014, 01:06

For me: near wall modelling and wall function are linked
>>You will use a wall function for modelling effects near the walls

*y+ estimation --> http://www.cfd-online.com/Tools/yplus.php

*BL in Gambit --> https://www.sharcnet.ca/Software/Gam...tm#mesh_blayer

Cesare88 · December 23, 2014, 05:22

Hello max,

first of all thank you for responding to my question .
I do not know if I have to use to force the boundary layer or I can also use the MAP algorithm ?? I had divided the domain into four subdomains and using the map I made the mesh . I attach a photo of the mesh that I made so you can give me an opinion .
Thank You
have a nice day

-mAx- · December 23, 2014, 05:29

you can work with map, then your BL will be "integrated" within your mesh.
But if you want to adapt your BL, then it will give you some work.
If you create the BL, with the tool, then you will adapt it more easily

To convince you try to reduce your first cell's height with 50%

Cesare88 · December 23, 2014, 05:47

well thanks for the advice ...
Now another question :
I have to create the BL only in the region after the sudden expansion or even in the inlet region ??
Looking at the photo of the mesh that I have attached you think it might be a good start for the study ????
If the kind of discretization is ok now I will create the BL where it is appropriate , and follow that road...

-mAx- · December 23, 2014, 06:05

create the BL on each wall (not at inlet or outlet)

December 22, 2014, 09:06	2D turbulent flow in axisymmetric sudden expansion	#1
Cesare88 New Member cecè Join Date: Dec 2014 Posts: 3 Rep Power: 11	hi guys, I am a student in mechanical engineering . I'm working on a project for the cfd examination and I can not find a solution to the problem . in particular I have to study the 2D turbulent flow of water in a pipe with a sudden expansion using the wall function approach and the near wall modeling approach and compare the results . Could someone explain how to create the mesh in gambit to obtain a valid results from the simulation ??? in particular I would like to know how to get the correct value of y + for the two different approaches . If you have any links to be attached that explains this i am very grateful . have a nice evening

December 23, 2014, 01:06		#2
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	For me: near wall modelling and wall function are linked >>You will use a wall function for modelling effects near the walls y+ estimation --> http://www.cfd-online.com/Tools/yplus.php BL in Gambit --> https://www.sharcnet.ca/Software/Gam...tm#mesh_blayer Cesare88 likes this. __________________ In memory of my friend Hervé: CFD engineer & freerider

December 23, 2014, 05:29		#4
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	you can work with map, then your BL will be "integrated" within your mesh. But if you want to adapt your BL, then it will give you some work. If you create the BL, with the tool, then you will adapt it more easily To convince you try to reduce your first cell's height with 50% ghost82 likes this. __________________ In memory of my friend Hervé: CFD engineer & freerider

December 23, 2014, 06:05		#6
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	create the BL on each wall (not at inlet or outlet) __________________ In memory of my friend Hervé: CFD engineer & freerider

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December 23, 2014, 05:47		#5
Cesare88 New Member cecè Join Date: Dec 2014 Posts: 3 Rep Power: 11	well thanks for the advice ... Now another question : I have to create the BL only in the region after the sudden expansion or even in the inlet region ?? Looking at the photo of the mesh that I have attached you think it might be a good start for the study ???? If the kind of discretization is ok now I will create the BL where it is appropriate , and follow that road...