Surface Streamline and 3D streamline

AS_Aero · September 25, 2018, 05:56

Hi All

I am doing a quasi 2D simulation in CFX.

So my domain is 1mm thick in the z direction and when I check the streamlines along the center plane (2D Surface Streamline) I can see some recirculations and when I see the 3D streamlines I dont see them . Ofcourse in 3D streamlines I am saying the starting position as the flow inlet position. And within 1mm thickness do you think there will be difference in the flow pattern in the Z direction ? Why is the streamlines look different ? Which one can we trust then ? Or what is their significance ?

ghorrocks · September 25, 2018, 06:13

There is a recirculation in your 3D simulation. You just have not put a streamline in it. It looks pretty similar to the 2D results to me.

Whether there will be a difference in 2D and 3D results depends on which flow regime you are in. Have a look at flow over a cylinder - it goes through many flow regimes depending on the Reynolds number, going from 2D to 2D transient to 3D transient to 3D steady state.

Gert-Jan · September 25, 2018, 06:18

You should use the inlet AND the outlet as starting point for your streamlines. And then calculate 'Forward and backward'.

AS_Aero · September 25, 2018, 07:39

Ah ok now I see it ..So its the same for both surface streamline or the 3D streamline.
Thanks both of you..

September 25, 2018, 06:13		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,816 Rep Power: 144	There is a recirculation in your 3D simulation. You just have not put a streamline in it. It looks pretty similar to the 2D results to me. Whether there will be a difference in 2D and 3D results depends on which flow regime you are in. Have a look at flow over a cylinder - it goes through many flow regimes depending on the Reynolds number, going from 2D to 2D transient to 3D transient to 3D steady state. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

September 25, 2018, 06:18		#3
Gert-Jan Senior Member Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,885 Rep Power: 27	You should use the inlet AND the outlet as starting point for your streamlines. And then calculate 'Forward and backward'.

September 25, 2018, 07:39		#4
AS_Aero Senior Member Join Date: Mar 2013 Location: Germany Posts: 357 Rep Power: 14	Ah ok now I see it ..So its the same for both surface streamline or the 3D streamline. Thanks both of you..