CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM Running, Solving & CFD

2d aerofoil simpleFoam

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

Like Tree1Likes
  • 1 Post By plm

Reply
 
LinkBack Thread Tools Display Modes
Old   November 26, 2011, 14:34
Default 2d aerofoil simpleFoam
  #1
plm
New Member
 
RW
Join Date: Nov 2011
Posts: 22
Rep Power: 5
plm is on a distinguished road
Hi all,
I'm using simpleFoam to model turbulent flow over an aerofoil. When the angle of attack increases to a point where there is separation from the aerofoil, my model is unable to predict this.

Is this due to the use of the spalmartAllmaras turbulence model or is this a limitation of simpleFoam?

I've also read online about the use of DES which is potentially a better solver but I'm unsure how to set it up and would welcome any comments on it's effectiveness

plm
kiddmax likes this.
plm is offline   Reply With Quote

Old   November 28, 2011, 14:21
Default
  #2
plm
New Member
 
RW
Join Date: Nov 2011
Posts: 22
Rep Power: 5
plm is on a distinguished road
Is it even possible to run DES/LES cases in 2D?
Really would welcome any comments! Thanks!
plm is offline   Reply With Quote

Old   November 29, 2011, 06:39
Default
  #3
Member
 
wided
Join Date: Jul 2010
Posts: 54
Rep Power: 7
wiedangel is on a distinguished road
Quote:
Originally Posted by plm View Post
Is it even possible to run DES/LES cases in 2D?
Really would welcome any comments! Thanks!
Hi plm,

it is possible to run 2D cases using DES (Detached Eddy Simulation). I did it for a thick airfoil, you just need a fine enough mesh.
wiedangel is offline   Reply With Quote

Old   November 29, 2011, 07:20
Default
  #4
plm
New Member
 
RW
Join Date: Nov 2011
Posts: 22
Rep Power: 5
plm is on a distinguished road
Thanks wiedangel,
I have managed to run a DES case with a fine mesh but I'm still not predicting the stall condition - any ideas?
plm is offline   Reply With Quote

Old   November 29, 2011, 11:01
Default
  #5
Member
 
wided
Join Date: Jul 2010
Posts: 54
Rep Power: 7
wiedangel is on a distinguished road
Hi,

can you tell me which solver you are using? Are you simulating for each angle of attack individually or do you have some motion handling solver like pimpleDymFoam??

I am using pimpleFoam and no motion, I simulated pre- and post-stall situations and it seems to work.

Regards.
wiedangel is offline   Reply With Quote

Old   November 29, 2011, 11:45
Default
  #6
Senior Member
 
Vesselin Krastev
Join Date: Jan 2010
Location: University of Tor Vergata, Rome
Posts: 361
Rep Power: 10
vkrastev is on a distinguished road
1) before shifting to a new solver (e. g. transient pimpleFoam instead of steady-state simpleFoam) or a new turbulence model (e. g. k-omega SST instead of Spalart-Allmaras) you have to be sure that you have reached the maximum reasonable accuracy with your initial choices, and not simply change everything (solver+modeling) because of not satisfactory results...how about your mesh quality and solver tolerances? What is your wall treatment (and consequently the mesh near-wall spacing)? What about the numerical schemes?;

2) running a DES (or any kind of LES-like turbulence model) in 2D is not consistent with the vorticity dynamics, which is inherently three-dimensional (and unsteady): hence, if you want to keep a 2D modeling it will be better to try an unsteady RANS approach.

Best regards

V.
vkrastev is offline   Reply With Quote

Old   November 29, 2011, 14:36
Default
  #7
plm
New Member
 
RW
Join Date: Nov 2011
Posts: 22
Rep Power: 5
plm is on a distinguished road
Thank you for the instructive comments vkrastev and wiedangel

I have tried using both the steady state simpleFoam and transient pimpleFoam solvers, both with Spalart-Allmaras turbulence modelling.

I have had a DES running but from what vrakstev said will look to improve my unsteady RANS approach instead....

I have been using various wall functions and numerical schemes - is it likely that these may have an effect on whether I find stall or not?
plm is offline   Reply With Quote

Old   November 29, 2011, 14:58
Default
  #8
Senior Member
 
Vesselin Krastev
Join Date: Jan 2010
Location: University of Tor Vergata, Rome
Posts: 361
Rep Power: 10
vkrastev is on a distinguished road
Quote:
Originally Posted by plm View Post
I have been using various wall functions and numerical schemes - is it likely that these may have an effect on whether I find stall or not?
Yes, of course, but also solvers tolerances and, especially, boundary conditions and mesh quality and resolution (with respect to the particular near wall modeling) can have a large impact on the solution. To catch the stall phenomenon with a steady approach is quite hard, but what I'm saying is that simulating a case is not simply a mix of type of solver+type of turbulence model, and this is true whichever the solution approach. As I said before, for your particular case probably a well resolved unsteady-RANS simulation will be the best solution, but only with a proper combination of the factors cited above. Good luck for your work.

V.
vkrastev is offline   Reply With Quote

Old   November 29, 2011, 17:22
Default
  #9
Member
 
wided
Join Date: Jul 2010
Posts: 54
Rep Power: 7
wiedangel is on a distinguished road
Hi, plm. A good idea is also to check the previous work done by other researchers, there are some papers about the best practices when dealing with stall and turbulence modeling. Like vkrastev mentioned, sometimes one has to go for the simplest model and not just mix models and spring from one to another just because one did not work. I will be happy to send you some references if you are interested.

good luck with stall
wiedangel is offline   Reply With Quote

Old   November 29, 2011, 17:28
Default
  #10
plm
New Member
 
RW
Join Date: Nov 2011
Posts: 22
Rep Power: 5
plm is on a distinguished road
I'd definitely be interested in your references wiedangel, cheers!

I was jumping around a bit because I was unsure if the simple methods I am using can actually predict stall - at the moment they are simply predicting an increase in the predicted pressure distribution, as if stall has never occured.

I'll keep at it and see what I can come up with.

Thanks
plm is offline   Reply With Quote

Old   November 30, 2011, 08:36
Default
  #11
New Member
 
Join Date: Oct 2011
Posts: 4
Rep Power: 5
thinkagain is on a distinguished road
I am also intersted in your reference!
thinkagain is offline   Reply With Quote

Old   December 9, 2011, 05:36
Default
  #12
Member
 
wided
Join Date: Jul 2010
Posts: 54
Rep Power: 7
wiedangel is on a distinguished road
sorry for the delay in sending the references ... I could not find that post
here are some references about DES and the grid quality they have to satisfy:

http://books.google.de/books/about/D...sC&redir_esc=y

Spalart, P. R., Jou, W.-H., Stretlets, M., and Allmaras, S. R. (1997), "Comments on the Feasibility of LES for Wings and on the Hybrid RANS/LES Approach", Advances in DNS/LES, Proceedings of the First AFOSR International Conference on DNS/LES.

INVESTIGATION OF GRID RESOLUTION REQUIREMENTS FOR
DETACHED EDDY SIMULATION OF FLOW AROUND THICK AIRFOIL
SECTIONS
Jesper Madsen, Kaja Lenz, Pavitran Dynampally, Sudhakar P.
LM Glasfiber A/S, Denmark, LM Glasfiber R&D (India) Pvt. Ltd.

Profile Catalogue for Airfoil Sections
Based on 3D Computations
Franck Bertagnolio, Niels N. Sørensen and Jeppe Johansen

They helped me a lot, I hope it will help you.
wiedangel is offline   Reply With Quote

Old   December 9, 2011, 05:46
Default
  #13
plm
New Member
 
RW
Join Date: Nov 2011
Posts: 22
Rep Power: 5
plm is on a distinguished road
Thank you
plm is offline   Reply With Quote

Old   December 18, 2011, 05:58
Default Regarding results obtained for K-Ɛ, K-Omega and K-Omega SST
  #14
New Member
 
Nabil
Join Date: Oct 2011
Posts: 5
Rep Power: 5
nabilhaneef is on a distinguished road
Hi,

I have been running simulations on a simple 2D Nozzle guide vane. I have used different turbulence models and found out the results for the K-Ɛ and K-Omega SST were very close to each other for various points on the suction side and pressure side of the blade. The plot is for Velocity profile versus different points on the suction side. I am attaching a graph that i have plotted for the various turbulence models. Can someone guide me why is this is happening. Why K-Omega values are not close to the other models. I have my submission of my project report very close by and would highly appreciate if someone could guide me with the answers to why this is happening.
Attached Images
File Type: png Untitled.png (28.9 KB, 48 views)
File Type: png Untitled1.png (36.4 KB, 52 views)
nabilhaneef is offline   Reply With Quote

Old   April 11, 2012, 16:44
Default
  #15
New Member
 
Luca Bonfiglio
Join Date: Oct 2011
Posts: 9
Rep Power: 5
lucaBonfiglio is on a distinguished road
Hi plm,

I'm having the same problems simulating an hydrofoil naca0012 at Re 3e6, did you figure out something from the pimpleFoam solver??
I'm also trying the kklOmega turbolence model with the simpleFoam in order to reproduce laminar flow and the transition, but unfortunately with no success.
lucaBonfiglio is offline   Reply With Quote

Reply

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
Laminar simpleFoam and inviscid simpleFoam herenger OpenFOAM Running, Solving & CFD 7 July 11, 2013 06:27
simpleFoam ddt Euler ? Mo-ITB OpenFOAM Running, Solving & CFD 2 June 12, 2010 13:36
Naca0012 k-e mpirun gives fpe whereas simpleFoam not Pierpaolo OpenFOAM 1 May 8, 2010 03:08
Meshing an aerofoil with a plain flap Fatou FLUENT 0 November 15, 2005 15:24
2D Aerofoil Simulation StudentAndrew CFX 10 October 28, 2005 16:15


All times are GMT -4. The time now is 00:41.