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

Wind Tunnel Blockage question

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   February 9, 2011, 12:47
Default Wind Tunnel Blockage question
  #1
New Member
 
Eric
Join Date: Feb 2011
Posts: 1
Rep Power: 0
ohma0043 is on a distinguished road
Hi all, I am trying to run a CFD test for an Inflatable Aerodynamic Decelerator (essentially a blunt body) in a wind tunnel. For this wind tunnel model, I have approximately 20% tunnel blockage. I will be looking for drag and turbulent flow characteristics around the decelerator. The question I have is, does CFX already incorporate tunnel blockage into its calculations or do I need to set it up to achieve accurate results. Any help towards this problem will be of great use.

Also, I will be running at low subsonic speeds, apprx. 38 m/s, and I will be using the K-Omega turbulence model. At the inlet I have a velocity boundary condition of 38 m/s and at the outlet I have a bound condition of 0 Pascal relative pressure. Along the walls I have used no-slip bound conditions.

To simplify the calculations required I have used a symmetry plane to cut the model in half. The wind tunnel is approximately 25 inches wide and 40 inches high. The model has a diameter of 16 inches.

Thanks,
Eric
Attached Images
File Type: jpg Model.jpg (35.2 KB, 23 views)

Last edited by ohma0043; February 9, 2011 at 13:38. Reason: Clearer Explanation of Problem
ohma0043 is offline   Reply With Quote

Old   February 9, 2011, 19:31
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 16,923
Rep Power: 132
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
Are you trying to model the thing in free air or reproduce a wind tunnel model? If free air then you should widen the domain. If a wind tunnel, then no, CFX does not have any blockage factor compensation built in. You should ask the wind tunnel people to give you the raw test results with no blockage factor compensation. Then you will be comparing CFD to the wind tunnel results and be doing a direct comparison.
ghorrocks is offline   Reply With Quote

Old   February 11, 2011, 06:42
Default
  #3
New Member
 
Join Date: May 2010
Posts: 14
Rep Power: 13
fastwave is on a distinguished road
Not quite true. If you model the WT size and use a wall condition on your boundaries the blockage is included in the simulation and can be compared to the WT results.

The choice of using slip or no-slip condition on the walls is a tradeoff betweeen simplicity and accuracy. If the boundary layer thickness is a small percentage of the overall WT dimensions then the effect on blockage is small. In small tunnel with thick WT wall boundaries it could be significant.
fastwave is offline   Reply With Quote

Old   February 11, 2011, 07:12
Default
  #4
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 16,923
Rep Power: 132
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
Quote:
Not quite true. If you model the WT size and use a wall condition on your boundaries the blockage is included in the simulation and can be compared to the WT results.
Isn't that what I said? It is at least what I tried to say.
ghorrocks is offline   Reply With Quote

Old   February 13, 2011, 10:12
Default like you
  #5
New Member
 
asan
Join Date: Jan 2011
Posts: 4
Rep Power: 12
asan09 is on a distinguished road
Hi
My name is Ghassan Sharraf.
I am a student in the 5th year of the mechanical engineering
I make a project about modeling a flow around bodies in the wind tunnel
I ask if you can help me to compare my results with experimental data
So if you can submit me from your knowledge
Note : my tool is Ansys
And thanks
my email : ghassan.s.a@hotmail.com
asan09 is offline   Reply With Quote

Old   June 16, 2018, 07:13
Default
  #6
New Member
 
Hamed
Join Date: Mar 2017
Location: Iran
Posts: 22
Rep Power: 6
hamed1983 is on a distinguished road
Quote:
Originally Posted by fastwave View Post
Not quite true. If you model the WT size and use a wall condition on your boundaries the blockage is included in the simulation and can be compared to the WT results.

The choice of using slip or no-slip condition on the walls is a tradeoff betweeen simplicity and accuracy. If the boundary layer thickness is a small percentage of the overall WT dimensions then the effect on blockage is small. In small tunnel with thick WT wall boundaries it could be significant.


Would you plz to introduce me a reference for that, perhaps in Tutorial or everywhere else?
hamed1983 is offline   Reply With Quote

Old   June 16, 2018, 07:14
Default
  #7
New Member
 
Hamed
Join Date: Mar 2017
Location: Iran
Posts: 22
Rep Power: 6
hamed1983 is on a distinguished road
Would you plz to introduce a reference for that?
hamed1983 is offline   Reply With Quote

Old   June 17, 2018, 08:02
Default
  #8
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 16,923
Rep Power: 132
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
Isn't it obvious? Why do you need a reference for that?
__________________
Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.
ghorrocks is offline   Reply With Quote

Old   June 17, 2018, 09:28
Default
  #9
New Member
 
Hamed
Join Date: Mar 2017
Location: Iran
Posts: 22
Rep Power: 6
hamed1983 is on a distinguished road
No unfortunately, I don't thing so, I couldn't find the relation between your explanation & the user named fastwave. I need a source in order to have more study on case. In my opinion your answer & fastwave's answer are quiet different.
hamed1983 is offline   Reply With Quote

Old   June 17, 2018, 20:19
Default
  #10
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 16,923
Rep Power: 132
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
fastwave said this, and my comment also said the same thing:

Quote:
If you model the WT size and use a wall condition on your boundaries the blockage is included in the simulation and can be compared to the WT results.
I cannot give you a reference for this as it is obvious.

fastwave also made comments about slip or no slip walls on the boundary - again these comments just come from a knowledge of the physics and seem obvious to me.
__________________
Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.
ghorrocks is offline   Reply With Quote

Reply

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
wind tunnel results vs fluent pixie Main CFD Forum 1 August 20, 2009 09:02
how to consider perforated wind tunnel wall in CFD simulation littlelz CFX 4 June 11, 2009 06:51
Simulating a G├Âttingen type wind tunnel in FLUENT Chris FLUENT 3 December 4, 2006 18:33
Virtual Wind Tunnel in FLUENT ND FLUENT 0 April 7, 2006 08:43
Air Flow within a Wind Tunnel Question Paul Kleinmeulman FLUENT 3 January 12, 2005 20:09


All times are GMT -4. The time now is 12:33.