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

Aerofoil Simulation Agreement

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   June 2, 2014, 06:28
Default Aerofoil Simulation Agreement
  #1
New Member
 
Join Date: Sep 2013
Posts: 2
Rep Power: 0
Jansen is on a distinguished road
Hi all,

I am trying to simulate air flow over a NACA0021 aerofoil using k-omega SST(chord = 70mm, span = 50mm, planform area = 0.0035 square metres) at different angles of attack as to try and match another experiment conducted in a 0.5m x 0.5m wind tunnel at a Reynolds number of roughly 120,000, free-stream velocity 25m/s and turbulence intensity 0.8%. There is quite reasonable agreement with regards to the drag coefficient of the aerofoil but the lift coefficient does not match the experimental values nearly as well, even when considering general error and other differences.

From viewing the flow in paraview it appears that the aerofoil stalls in the simulation well before the point that it stalls in the experiment. The residuals also seem to plateau at quite a high value too. I have tried changing many things around but to no avail.

I feel that the problem of the early onset of separation may still lie in the boundary conditions but I am unsure of which ones to change and what to change them to.

I have attached the graphs, a plot of the residuals and the relevant OpenFOAM files.

Thanks in advance.

Ben
Attached Images
File Type: jpg Graphs.jpg (29.0 KB, 25 views)
File Type: jpg Residuals.jpg (29.8 KB, 19 views)
Attached Files
File Type: gz Aerofoil Files.tar.gz (5.6 KB, 15 views)

Last edited by Jansen; June 2, 2014 at 06:33. Reason: Files did not attach
Jansen is offline   Reply With Quote

Old   June 4, 2014, 01:56
Default
  #2
Senior Member
 
Join Date: Jun 2011
Posts: 163
Rep Power: 11
mechy is on a distinguished road
Hi
your problem is related to your mesh.

1- for freestream boundary condition, your farfield should be 20 times of chord. in your mesh the domain of solution is very small

2-for sst k-w you should refine the mesh on the airfoil (y+<10)
I advise you to use the Spalart-Allmaras model for this airfoil with 30<y+<300

3-your mesh has very cell numbers and I advise you to use the 2D model
mechy is offline   Reply With Quote

Old   June 4, 2014, 02:43
Default
  #3
New Member
 
Join Date: Sep 2013
Posts: 2
Rep Power: 0
Jansen is on a distinguished road
Hey, thanks for your reply

I have a couple of questions regarding the mesh
1- Does the (y+<10) mean that I should refine the mesh so that there are more cells at the airfoil?
2- Regarding your third point; does my mesh have too few cells?

As for using a 2D model, the next stage in my project once I validate the baseline is to add a sinusoidal leading edge to the airfoil. Would it still be beneficial to use a 2D model for the baseline?
Jansen is offline   Reply With Quote

Old   June 4, 2014, 03:21
Default
  #4
Senior Member
 
Join Date: Jun 2011
Posts: 163
Rep Power: 11
mechy is on a distinguished road
your mesh has very cell numbers and you should reduce it.
but you should use the inflation (grading) to refine the mesh on the airfoil.
if the sinusoidal leading edge is cover all of the span, I advise you to use the 2D model
mechy is offline   Reply With Quote

Reply

Tags
drag coefficient, k omega, lift coefficient, separation, stall

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
Huge file sizes when Running VOF simulation aarratia FLUENT 0 May 8, 2014 12:27
Supersonic Nozzle Exhaust Simulation mikeh FLUENT 0 May 1, 2014 21:28
Exporting data of transient simulation DURING a simulation, at user locations ? Milan2013 CFX 0 April 18, 2014 03:47
GUI crash and simulation engine still running RPJones FLOW-3D 2 November 9, 2010 08:18
Supersonic Simulation with a diamond aerofoil Boris Morton Phoenics 0 December 12, 2004 05:07


All times are GMT -4. The time now is 04:14.