Isosurface creation

Attesz · October 20, 2009, 04:33

Hi all,
I want to create isosurface with variable "velocity (value=0 m/s)" to study the detachments in the flow. But I can't see the results in cfx post because the generated surfaces are "behind" of the wall(where the velocity is zero). How can I plot the detachment zones?

Sorry for the beginner question

Thank you,
Attesz

mvoss · October 20, 2009, 05:54

hi,

When i am supposing your simulating a tube or smth. simillar... you could define a new variable via the "if"-command (if vel=0 AND diameter<max.Radius,...), if you´re using WB2.0/ CFX12.0
In CFX 11 try the same approach with the step-function.

neewbie

ghorrocks · October 20, 2009, 06:40

I think you will find that an isosurface of V=0 does not adequately show recirculations in 3D, even when you have removed the wall surface. There is plenty of research around about how recirculations are defined and how to find them in 3D - it is not as easy as it may first appear. Other variables which can be useful include vorticity, but it depends on a case by case basis.

I think CFX also has a new feature in V12 designed to detect vortex cores. I have never used it so have no idea how useful it is, but maybe you should consider it.

I would recommend looking at streamlines as the simplest approach, and having a read of the literature for a more complete discussion of the current thinking.

October 20, 2009, 04:33	Isosurface creation	#1
Attesz Senior Member Attesz Join Date: Mar 2009 Location: Munich Posts: 368 Rep Power: 17	Hi all, I want to create isosurface with variable "velocity (value=0 m/s)" to study the detachments in the flow. But I can't see the results in cfx post because the generated surfaces are "behind" of the wall(where the velocity is zero). How can I plot the detachment zones? Sorry for the beginner question Thank you, Attesz

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October 20, 2009, 05:54		#2
mvoss Senior Member Matthias Voß Join Date: Mar 2009 Location: Berlin, Germany Posts: 449 Rep Power: 20	hi, When i am supposing your simulating a tube or smth. simillar... you could define a new variable via the "if"-command (if vel=0 AND diameter<max.Radius,...), if you´re using WB2.0/ CFX12.0 In CFX 11 try the same approach with the step-function. neewbie

October 20, 2009, 06:40		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	I think you will find that an isosurface of V=0 does not adequately show recirculations in 3D, even when you have removed the wall surface. There is plenty of research around about how recirculations are defined and how to find them in 3D - it is not as easy as it may first appear. Other variables which can be useful include vorticity, but it depends on a case by case basis. I think CFX also has a new feature in V12 designed to detect vortex cores. I have never used it so have no idea how useful it is, but maybe you should consider it. I would recommend looking at streamlines as the simplest approach, and having a read of the literature for a more complete discussion of the current thinking.