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

Low Reynolds NACA 0012 validation

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   March 5, 2019, 15:37
Default Low Reynolds NACA 0012 validation
  #1
New Member
 
Join Date: Mar 2019
Posts: 7
Rep Power: 7
35matt215 is on a distinguished road
Hi everyone,

I am modelling a NACA 0012 at 1.15 m/s, chord length = 1 m, 3 deg AoA, through air at 20 deg c and Re = 7000.

Using the SST turbulence model, I have obtained values for lift and drag coefficient being approx Cl = 0.13 and Cd = 0.015.

I am struggling to find validation for such a low Reynolds number, so I was wondering: would anyone be able to inform me if these values are accurate for this low Reynolds number?

Thank you in advance!

Last edited by 35matt215; March 25, 2019 at 16:56.
35matt215 is offline   Reply With Quote

Old   March 5, 2019, 17:19
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,728
Rep Power: 143
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
Didn't I post a link to a massive database of results for low Re airfoils? Why are you asking again?

If you can't find your exact airfoil in the database then just choose one which is close and model that as a validation.

By the way - I suspect that the airfoil at this Re is not turbulent. It will be either laminar, or transitions to turbulence mid-chord. That means you should be using a laminar flow model, or maybe SST with the turbulence transition model.
__________________
Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.
ghorrocks is offline   Reply With Quote

Old   March 5, 2019, 17:40
Default
  #3
New Member
 
Join Date: Mar 2019
Posts: 7
Rep Power: 7
35matt215 is on a distinguished road
Thank you for your reply.

Yes you did post that but I could not find the exact one and was not sure but now it is clear, so thank you for clarification.

I did try to run it as laminar but the Cl and Cd were not stable and RMS residuals did not converge and it seemed to converge quite well with SST. I have also tried the Gamma Theta SST model but it also did not converge too well however, I will play around with that further.

Thank you again.
35matt215 is offline   Reply With Quote

Old   March 5, 2019, 17:43
Default
  #4
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,728
Rep Power: 143
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
You select the physics models based on what the physics actually are, not what converges easily.
__________________
Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.
ghorrocks is offline   Reply With Quote

Old   March 17, 2019, 07:58
Default
  #5
New Member
 
Join Date: Mar 2019
Posts: 7
Rep Power: 7
35matt215 is on a distinguished road
I ran transitional turbulence model and seem to be getting quite good results when compared to published data.

I noticed there seems to be a laminar separation bubble that occurs near the trailing edge of the lower surface of the airfoil. However from reading papers, it seems that the separation bubble normally occurs at the top surface of the airfoil.

Can anyone maybe offer an explanation as to why I am getting this separation bubble on the bottom surface of the airfoil?

Thanks.
35matt215 is offline   Reply With Quote

Old   March 17, 2019, 08:17
Default
  #6
Senior Member
 
sheaker's Avatar
 
Oskar
Join Date: Nov 2015
Location: Poland
Posts: 184
Rep Power: 10
sheaker is on a distinguished road
Quote:
Originally Posted by 35matt215 View Post
I ran transitional turbulence model and seem to be getting quite good results when compared to published data.

I noticed there seems to be a laminar separation bubble that occurs near the trailing edge of the lower surface of the airfoil. However from reading papers, it seems that the separation bubble normally occurs at the top surface of the airfoil.

Can anyone maybe offer an explanation as to why I am getting this separation bubble on the bottom surface of the airfoil?

Thanks.

Dear Matt
Could You possibly share the case?


EDIT:
I am sorry. I thought it was an OPENFoam sub-forum.

Last edited by sheaker; March 18, 2019 at 00:50.
sheaker is offline   Reply With Quote

Old   March 17, 2019, 08:30
Default
  #7
New Member
 
Join Date: Mar 2019
Posts: 7
Rep Power: 7
35matt215 is on a distinguished road
Please see attached the images of this.

Last edited by 35matt215; March 25, 2019 at 16:57.
35matt215 is offline   Reply With Quote

Old   March 17, 2019, 16:55
Default
  #8
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,728
Rep Power: 143
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
It is because you are using a low angle of attack. Increase the AOA and the separation bubble will move to the top face.
__________________
Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.
ghorrocks is offline   Reply With Quote

Old   March 17, 2019, 17:31
Default
  #9
New Member
 
Join Date: Mar 2019
Posts: 7
Rep Power: 7
35matt215 is on a distinguished road
Thanks for replying.

I increased the AOA and it occurred on the top surface as you said.

Is this definitely a separation bubble and not recirculation? Is it okay if this 'bubble' occurs on the bottom surface?

Thank you.
35matt215 is offline   Reply With Quote

Old   March 17, 2019, 22:12
Default
  #10
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,728
Rep Power: 143
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
Separation bubbles and recirculations are the same thing. Just laminar separation bubbles are small, linked to the transition from laminar to turbulent flow and the flow generally reattaches afterwards. Recirculations are typically larger features and often do not re-attach but stay separated for the entire chord.

But there is no clear distinction between the two, large separation bubbles and small recirculations are the same thing.
__________________
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
how to use k-omega low reynolds number in phoenics? wilcox Phoenics 1 February 4, 2020 12:10
High reynolds number model and a low reynolds number model Ieg1995 Main CFD Forum 3 June 18, 2017 13:18
Low Reynolds 2D Airfoil simulation imoldschool FLUENT 0 December 23, 2016 15:38
Naca 0012 validation, Cd value is too high. Peter88 OpenFOAM 4 January 21, 2014 16:10
naca 0012 validation case: wrong Cd vaina74 OpenFOAM Running, Solving & CFD 5 July 15, 2011 11:50


All times are GMT -4. The time now is 03:36.