CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > General Forums > Main CFD Forum

Vorticity Stream Function on Airfoil

Register Blogs Community New Posts Updated Threads Search

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   January 25, 2013, 04:47
Default Vorticity Stream Function on Airfoil
  #1
New Member
 
Mido
Join Date: Mar 2011
Posts: 25
Rep Power: 15
nw_ds is on a distinguished road
I am writing a code to solve the laminar flow over an airfoil for ( Re < 100000 ) in Generalized Coord using Stream function vorticity formulation
my code follows this algorithm

1 - Solve the StreamFunction using GS-SOR to tolerance 1e-8
2 - Calculate the Contravariant velocity
3 - Calculate the Vorticity Value at the Airfoil Surface
4- Advance the Vorticity Transport Equation one time step using ( Explicit Euler or ADI )
5- Check Vorticity Convergence else return to step 1

I use a C-grid of 257 x 129 with 129 points on the airfoil surface and min normal spacing of 1e-3 , the grid is Orthogonal on the airfoil surface points are clustered on near the LE ( to capture Circulation ) and TE to Capture seperation.
The values of SF and Vort. are updated on the Cut ( Wake ) by simple average up & down the Cut.

The Problem is that Convergence keeps stalling at points near the LE and I don't know what to do >
by Stalling , I mean that the Convergence of max residual doesn't go down beyond some value .this value changes with Re and time step.
I tried using finer grid but the solver becomes unstable and won't run and I tried using smaller time-step I solve still stalls at the LE




as you see in the second picture the max. Error in Vorticity is stuck at around 0.0035~0.0042 , near the LE ( x = 0.0 , y = 0.0 )
nw_ds is offline   Reply With Quote

Old   January 25, 2013, 07:30
Default
  #2
Senior Member
 
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,882
Rep Power: 73
FMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura aboutFMDenaro has a spectacular aura about
first, what do you physically expect from this simulation?
setting Re=O(10^5) while specifyng that the flow is laminar can be misleading... first, is your grid really able to take into account for the low molecular diffusion close to the wall? second, laminar flow can exhibit slowly time-dependent solution. Could you be sure your 2D solution must be really steady? third, check all the tolerances you are using to avoid errors cumulate during time integration
FMDenaro is offline   Reply With Quote

Old   January 25, 2013, 10:53
Default
  #3
Senior Member
 
Andrew
Join Date: Mar 2009
Location: Washington, DC
Posts: 211
Rep Power: 18
mettler is on a distinguished road
what is your BC for the vorticity at the LE. I know that that BC gets a little tricky at the corner of a backwards facing step.
mettler is offline   Reply With Quote

Old   January 26, 2013, 12:53
Default
  #4
New Member
 
Mido
Join Date: Mar 2011
Posts: 25
Rep Power: 15
nw_ds is on a distinguished road
I found the problem with my my code it turns that it doesn't like first order upwind scheme for convection ( very much ) , I tried second order upwind but I get a converged but in-accurate solution so I tried central differencing and it worked like magic I got an accurate converged solution. But I still want to use an upwind scheme so I am looking for suggestion >
nw_ds is offline   Reply With Quote

Reply

Tags
airfoil, streamfunction, vorticity


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
foamToTecplot360 thomasduerr OpenFOAM Post-Processing 121 June 11, 2021 11:05
How to approach calculating a stream function given a velocity profile on a grid ComFlu Main CFD Forum 1 October 25, 2009 14:25
Stream Function Jason T. FLUENT 2 February 28, 2007 15:43
HELP - stream function from the velocity field Fred Main CFD Forum 10 January 26, 1999 13:58
Stream function and vorticity for turbulence flow? Willard Lee Main CFD Forum 1 January 20, 1999 12:03


All times are GMT -4. The time now is 22:03.