CFD Online Logo CFD Online URL
Home > Forums > Main CFD Forum

Divergence problem when airfoil exceed pitch angle

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

LinkBack Thread Tools Display Modes
Old   March 11, 2007, 01:25
Default Divergence problem when airfoil exceed pitch angle
Posts: n/a

I've got a 2D FVM fractional step structured solver. It's used to simulate moving (oscillating, pitching) airfoil with grid deformation. Arc based TFI is used for the deforming of grids. It works well for pitch angle up to ~20deg. However, at higher angles or highly cambered airfoil, the results starts to diverge and the simulation has to be stopped. This divergence usually occur near the leading edge of the airfoil.

I've inspected the grid. It's deformed but it still seems ok (i guess). I wonder what can be done to prevent this from happening. Here's what I'm considering:

1. decrease time step 2. increase time step (avoid the high angle?) 3. increase grid no. 4. change deformation algorithm - suggestions?

I've done some initial testing but it's not too good. I wonder if there's other mtds available?

Thank you
  Reply With Quote

Old   March 12, 2007, 08:54
Default Re: Divergence problem when airfoil exceed pitch a
Posts: n/a
Before you jump into costly resolution studies I would try to diagnose the problem a little more. You say the grid looks ok even at the highest angle. Have you tried using this deformed grid to get a (quasi-) steady state solution at the high angle? This isn't a sufficient or even necessary condition for success, but it will help you sort out the effect of unsteadiness. In particular, you should take a look at the effect of the reduced frequency (choose a very small frequency of motion to get a quasi-steady solution, i.e. a solution that depends only on temporal angle of attack but not on rotational velocity of the airfoil).

And then, there's another revolutionary idea (wink): Look at the unsteady flow field (snap shots, movie) until the point when it starts to diverge. Also look at the unsteady pressure distribution. Do you see anything that stands out as a potential problem?

Furthermore, I would take out number 2 in your list of remedies as a very, very questionable (and probably useless) approach.
  Reply With Quote

Old   April 4, 2007, 04:22
Default Nice site
Posts: n/a
Hello, Your site is great. Regards, Valintino Guxxi
  Reply With Quote


Thread Tools
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 On
Pingbacks are On
Refbacks are On

Similar Threads
Thread Thread Starter Forum Replies Last Post
[GAMBIT] Meshing airfoil using .dat file problem creggie ANSYS Meshing & Geometry 10 June 27, 2010 19:24
Airfoil boundary condition Frank Main CFD Forum 1 April 21, 2008 18:36
Airfoil at stall angle cfd_newbie FLUENT 10 February 5, 2008 12:33
solving airfoil like square cylinder problem? zonexo Main CFD Forum 1 May 27, 2006 15:16
Oscillating airfoil problem ganesh Main CFD Forum 2 June 27, 2005 13:57

All times are GMT -4. The time now is 01:17.