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

Oscillating Airfoil - Dynamic meshing or user-defined velocity profile.

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   June 8, 2010, 04:09
Default Oscillating Airfoil - Dynamic meshing or user-defined velocity profile.
  #1
Member
 
Join Date: Sep 2009
Posts: 69
Rep Power: 16
DarrenC is on a distinguished road
Hello there esteemed CFD friends,

I am currently simulating a sinusoidal pitching NACA0012 airfoil in Fluent CFD using unsteady RANS. The two methods that I am considering is :-

1. Move the airfoil boundary as a rigid body and use remeshing and smoothing to deform/move the mesh according to the movement of the airfoil.

2. Keep the airfoil and mesh stationary and define a periodic boundary condition that will change the angle of attack of the inlet flow with respect to the stationary body at each timestep.

Now I have done method 1 and I seem to be able to get quite good results with it. Of course method 2 will be alot simpler and would apply better for large airfoil oscillations, but I am somehow skeptical about method 2 as I am not too familiar with the solver numerics.

Specifically my question is will the change in boundary condition flow at the start of each time step be convected throughout the computational mesh at the end of each time step. What I am worried here is that this is not the case and the flow solutions I am getting will somehow be lagging behind the movement of the airfoil.

I apologize if this is question is trivial, but I am trying to understand the numerics behind the two different methods better and I hope you CFD veterans will be able to shed some light for me on this matter.

Thanks!

Kind Regards,
Darren
DarrenC is offline   Reply With Quote

Old   June 17, 2010, 06:35
Default
  #2
Member
 
Join Date: Sep 2009
Posts: 69
Rep Power: 16
DarrenC is on a distinguished road
Hello again,

Can someone at least point me to the correct literature if its too long and time consuming to explain it here?

Regards,
Darren
DarrenC is offline   Reply With Quote

Old   July 12, 2010, 03:35
Default
  #3
Member
 
Join Date: Sep 2009
Posts: 69
Rep Power: 16
DarrenC is on a distinguished road
Hi there again,

I have done some digging around and have found some studies regarding this. In general i have seen a number of ways people normally compute dynamic stall of airfoil problems.

1. Moving the whole mesh as a rigid body
(Flow Prediction Around an Oscillating NACA0012 Airfoil at Re 1000000 by Frederich, Bunge, Mockett and Thiele)

2. Using the sliding mesh method, where there is a nonconformal interface between two different fluid domains and one will rotate against the other.
(Hybrid Grid Approach to Study Dynamic Stall by Reu and Ying)

3. Moving the airfoil boundary as a rigid body and deforming/remeshing the mesh around it accordingly.
(Unsteady Euler Airfoil Solutions Using Unstructured Dynamic Meshes by Batina)

However there hasn't been a detailed discussion about what happens to the transport variables at each of the grid points when they move. Will they be interpolated?

Also there hasn't been a comparison of the differences of each of those techniques (if there is any). Is anybody familiar with the differences care to explain?

Thanks

Cheers,
Darren
DarrenC is offline   Reply With Quote

Old   July 19, 2010, 08:54
Default
  #4
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,665
Rep Power: 143
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
Method 1 is best if you are modelling a free field.

Method 2 is best if you have objects away from the airfoil, eg wind tunnel walls, ground, aircraft body.... etc.

Method 3 is computationally slowest and hardest to get working properly, but it can handle more general motions than the previous 2.

But really you should be able to get any of the methods to work - and you have found literature in all approaches so that shows it.

The differences between the method is best appreciated by trying them all yourself. Run them all and don't forget to do a sensitivity study on all important parameters to make sure you are sufficiently accurate. They should all give the same answer within a numerical accuracy.

I think you will find the reason nobody has published a comparison is because nobody has done one before - and here is your chance to do something nobody has done before. That is always pretty cool.
ghorrocks is offline   Reply With Quote

Old   July 19, 2010, 20:45
Default
  #5
Member
 
Join Date: Sep 2009
Posts: 69
Rep Power: 16
DarrenC is on a distinguished road
Hi Glenn,

Thanks for the reply, greatly appreciated! By the way do you happen to know a good reference book that covers the numerics behind moving grids extensively? Im trying to understand the numerics behind it better and so far ive only come across a book by Ferziger and Peric with a small section in moving grids.

Thanks again,

Cheers,
Darren
DarrenC is offline   Reply With Quote

Old   July 19, 2010, 23:33
Default
  #6
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,665
Rep Power: 143
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
The numerics is best explained in the software documentation. Other then that you would have to look in the academic literature.
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
Velocity Profile Jeff FLUENT 1 November 24, 2008 09:21
Gradient of a User defined Variable Ramadas CFX 2 August 21, 2007 10:19
maintaining a logarithmic velocity distribution Morten Andersen CFX 1 January 8, 2007 12:37
Create hemisphere like velocity profile at inlet Nelson Main CFD Forum 3 July 27, 2005 13:05
CFX 5.5 Roued CFX 1 October 2, 2001 17:49


All times are GMT -4. The time now is 11:21.