CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > CFX

Vortical structure

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

Like Tree1Likes
  • 1 Post By ghorrocks

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   October 24, 2022, 10:28
Default Vortical structure
  #1
New Member
 
Join Date: Oct 2022
Posts: 7
Rep Power: 3
Dani125 is on a distinguished road
Dear CFX users,

I am trying to visualize the vortex core structure through iso-surfaces of the q-criterion but I'm not able to visualize it properly. The goal is to observe the vortex core region inside a volume. I would like to visualize the core vortex like the picture in attachment (cf. Figure 1). What I was able to achieve is the vortex structure that you can see in Figure 2.

Can someone help me obtain a proper vortex core iso-surface that allows me to visualize the vortex core region inside the volume ?

Screenshot.png

Screenshot2.jpg
Dani125 is offline   Reply With Quote

Old   October 24, 2022, 17:14
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,688
Rep Power: 143
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
What is wrong with what you have already done?
__________________
Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.
ghorrocks is offline   Reply With Quote

Old   October 25, 2022, 04:42
Default
  #3
New Member
 
Join Date: Oct 2022
Posts: 7
Rep Power: 3
Dani125 is on a distinguished road
I would like to evidence the direction of the vortex core from the center of the volume until the wall. It allows me to show that the vortex core does not follow a straight line inside the volume. As you can see on the following figure (attachment) the location of the vortex is well represented by the iso-surfaces but it should follow the yellow line. I would like to show that the vortex core follows the yellow line
Attached Images
File Type: jpg Capture.jpg (32.6 KB, 15 views)
Dani125 is offline   Reply With Quote

Old   October 25, 2022, 05:03
Default
  #4
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,688
Rep Power: 143
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
There are many ways of defining a vortex core - there is no universal definition. Have you had a look at the various options and read the literature to see how others have done it?

Alternately, do you know the mathematical function you want to plot?
__________________
Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.
ghorrocks is offline   Reply With Quote

Old   October 25, 2022, 05:24
Default
  #5
New Member
 
Join Date: Oct 2022
Posts: 7
Rep Power: 3
Dani125 is on a distinguished road
I have tried different methods available on CFD-Post and I have also looked in the literature and the most commonly used is the Q-criterion. In fact the first picture is extracted from a paper.

Here is the link : https://www.sciencedirect.com/scienc...21929015000998

I know the mathematical function of the Q-criterion but it is already implemented in CFD-Post. I'm not able to show it the way I want.
Dani125 is offline   Reply With Quote

Old   October 25, 2022, 06:17
Default
  #6
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,688
Rep Power: 143
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
Have you adjusted the isosurface value of the Q-criterion? What happens if you adjust it up and down?
__________________
Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.
ghorrocks is offline   Reply With Quote

Old   October 25, 2022, 07:57
Default
  #7
New Member
 
Join Date: Oct 2022
Posts: 7
Rep Power: 3
Dani125 is on a distinguished road
Yes I did. The first picture is level down and second picture is level up. The vortex core is still not well defined. When I decrease the value the curvature of the vortex center line is more visible but the volume covered by the isosurface is too big.
Capture2.jpg

Capture3.PNG
Dani125 is offline   Reply With Quote

Old   October 25, 2022, 17:38
Default
  #8
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,688
Rep Power: 143
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
And are you sure the vortex core actually is well defined? If your simulation has not given a well defined vortex core you cannot display one.
__________________
Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.
ghorrocks is offline   Reply With Quote

Old   October 26, 2022, 03:07
Default
  #9
New Member
 
Join Date: Oct 2022
Posts: 7
Rep Power: 3
Dani125 is on a distinguished road
Yes it should be well defined based on the first figure (velocity fields) and the second figure (streamlines and vortex core in black). On the second figure, based on the streamlines, you can see that the iso-surfaces can be reduced to a smaller vortex core.
Capture4.jpg

Capture5.jpg
Dani125 is offline   Reply With Quote

Old   October 26, 2022, 05:41
Default
  #10
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,688
Rep Power: 143
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
Have you looked at other ways of defining the vortex core, such as pressure or vorticity?
__________________
Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.
ghorrocks is offline   Reply With Quote

Old   October 26, 2022, 08:35
Default
  #11
New Member
 
Join Date: Oct 2022
Posts: 7
Rep Power: 3
Dani125 is on a distinguished road
I tried different mathematical expressions but the Q-criterion seems to be the more adequate. I even tried to identifies the vortex core by displaying iso-surfaces with different values of pressure and vorticity but it didn't get better than de Q-criterion.
By showing the vortex core my goal is to help the visualization of the flow inside the volume but it's not the main reason of my work. Therefore I won't dig too far in the mathematical expression of the vortex. I was just wondering if through Ansys it would have been possible in my case to quickly get a fairly accurate representation of the vortex core.
Thank you for your time.
Dani125 is offline   Reply With Quote

Old   October 26, 2022, 17:06
Default
  #12
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,688
Rep Power: 143
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
Looking at this more generally: There is no universal definition of a function to define a vortex core. Also, in 3D the exact definition of what is a vortex, a circulation, separation and so on because difficult. The result of this is than in 3D simulations there is no precise definition of a vortex. This means that if you want to visualise the vortices in a 3D flow you have to either compromise or use a specific definition which just happens to work in your case. Sometimes that could be pressure, vorticity, q, and there are others. It means it will take some time and experimentation to find what works best in your case.

It is starting to sound like the development work required to show what you ask for might not be worth the effort
Opaque likes this.
__________________
Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.
ghorrocks is offline   Reply With Quote

Old   October 27, 2022, 05:01
Default
  #13
New Member
 
Join Date: Oct 2022
Posts: 7
Rep Power: 3
Dani125 is on a distinguished road
Thank you for your answer.
It was just a question of visualization but it was not the main purpose of my work so indeed it is not worth the time and effort.
Dani125 is offline   Reply With Quote

Reply

Tags
cfd - post, q-criterion, vortex core region

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
Vortical Structure Capturing afrotimy OpenFOAM Programming & Development 1 March 9, 2015 13:37
New OpenFOAM Forum Structure jola OpenFOAM 2 October 19, 2011 06:55
vortical Structure in CFX Post simulationCFX CFX 1 December 28, 2010 03:00
New ANSYS forum structure, what do you think? Peter FLUENT 10 February 6, 2009 04:07
New ANSYS forum structure, what do you think? Peter CFX 5 February 4, 2009 11:59


All times are GMT -4. The time now is 08:35.