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

Calculate the wind tunnel box size

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

Like Tree2Likes
  • 1 Post By ghorrocks
  • 1 Post By ghorrocks

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   October 26, 2018, 10:47
Default Calculate the wind tunnel box size
  #1
Member
 
tyw7's Avatar
 
Thu Win
Join Date: Apr 2017
Posts: 70
Rep Power: 9
tyw7 is on a distinguished road
I am running a CFX simulation on a wing about 40m in half span. What wind tunnel box size should I use? As this is for a university year 3 project, could you please provide references to back your answer.

Is there a formula I could use to calculate this?

I am testing the A380's wing at a cruise speed of Mach 0.8 and an altitude of 13136.88 meters

Pressure: 16157.9 Pascal [29]
Dynamic Viscosity: 0.0000143226
Density: 0.259814 kg/m3 [29]
Wind speed: 250.75 m/s
tyw7 is offline   Reply With Quote

Old   October 26, 2018, 20:49
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,862
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
You determine the boundary proximity by sensitivity analysis. You do a simulation with one proximity distance, and repeat with another proximity distance (say double the distance to the boundaries). Then you compare parameters of interest to you, which in your case are probably lift, drag and moment. If the parameters of interest to you do not change by a tolerance you are happy with then your boundary proximity is OK. If they are changing unacceptably then you double the boundary proximity distance again and rerun - and continue increasing the boundary proximity until the results converge to an accuracy you are happy to accept.

The concept of sensitivity analysis like this is fundamental to CFD. You should also do sensitivity analsyses of mesh size, convergence criteria and time step size (if transient). All these parameters are dependant on what you are modelling and how accurate you want to be, so need to be determined for your case.
aero_head 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 26, 2018, 21:07
Default
  #3
Member
 
tyw7's Avatar
 
Thu Win
Join Date: Apr 2017
Posts: 70
Rep Power: 9
tyw7 is on a distinguished road
Is there a rule of thumb sizing or is it more of a guess and test?
tyw7 is offline   Reply With Quote

Old   October 26, 2018, 21:16
Default
  #4
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,862
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
In general it is guess and test. If you can find other papers in the literature which have done similar analyses then that can give you a reasonable starting point.
__________________
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, 2018, 05:09
Default
  #5
Member
 
tyw7's Avatar
 
Thu Win
Join Date: Apr 2017
Posts: 70
Rep Power: 9
tyw7 is on a distinguished road
Should I start with one chord length and then increase cord lengths until the value converges.

Also how about the distance away from the wing, above the wing, below the wing, in front of the wing, and behind the wing?

My supervisor said to calculate via Reynolds number but I can't imagine how that would be.
tyw7 is offline   Reply With Quote

Old   October 28, 2018, 06:39
Default
  #6
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,862
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
You can start anywhere you like, but a better starting guess will mean you need to do less iterations. I would be thinking 5 chord distances is a better starting point and you will probably end up around 10 for a final figure, but that is just a guess.

You can do all the directions individually if you like running lots of sensitivity analyses or you can do them all together by doubling all those distances together for each iteration.

I do not know of any way to get this from Reynolds number. Maybe your supervisor can tell us and then we will all learn something.
aero_head 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

Reply

Tags
ansys 18.0, boxes, wind tunnel

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
[DesignModeler] change/increase model size box oewnce932c ANSYS Meshing & Geometry 5 April 8, 2022 02:37
Superlinear speedup in OpenFOAM 13 msrinath80 OpenFOAM Running, Solving & CFD 18 March 3, 2015 06:36
[How to obtain supersonic flow inside a supersonic wind tunnel ?] yx213 Siemens 1 September 17, 2014 14:52
defining velocity profile in a wind tunnel model Erdem FLUENT 0 June 20, 2006 14:00
Wind Tunnel Website now online Mike Worthey Main CFD Forum 0 June 6, 2000 03:27


All times are GMT -4. The time now is 15:13.