CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > FLUENT > Fluent UDF and Scheme Programming

2D Pitching Airfoil

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   May 6, 2013, 01:51
Default 2D Pitching Airfoil
  #1
Member
 
samrat himvanth nanduri
Join Date: May 2012
Posts: 30
Rep Power: 13
samcfd is on a distinguished road
Dear all,

I'm using a UDF for pitching airfoil . The function i'm using is

omega[2] = 0.5 * pitchampl * (1-cos(w*time));

pitchampl = 25 * pi/180;

w = 2 * pi * 0.15;

when i use this function the airfoil is rotating 360 deg. i dont understand y..

but when i use omega[2] = 0.5 * pitchampl * sin(w*time); its pitching perfectly...

Could some1 pls tell me y this is happening.

thanks in advance,

regards,
sam
samcfd is offline   Reply With Quote

Old   May 6, 2013, 01:56
Default
  #2
Senior Member
 
Join Date: Aug 2011
Posts: 421
Blog Entries: 1
Rep Power: 21
blackmask will become famous soon enough
Note that omega is angular speed rather than the angle of attack. You angular speed is always non-negative so that your airfoil is always pitch in the same direction. You need something like
d 0.5 * pitchampl * (1-cos(w*time))
-----------------------------------
d time
which leads to
omega[2] = w*0.5 * pitchampl * sin(w*time);
blackmask is offline   Reply With Quote

Old   May 6, 2013, 02:13
Default
  #3
Member
 
samrat himvanth nanduri
Join Date: May 2012
Posts: 30
Rep Power: 13
samcfd is on a distinguished road
Quote:
Originally Posted by blackmask View Post
Note that omega is angular speed rather than the angle of attack. You angular speed is always non-negative so that your airfoil is always pitch in the same direction. You need something like
d 0.5 * pitchampl * (1-cos(w*time))
-----------------------------------
d time
which leads to
omega[2] = w*0.5 * pitchampl * sin(w*time);
Dear Blackmask,

Thanks for your reply. I really didnt get wat u were saying. I want the airfoil to pitch using

omega[2] = 0.5 * pitchampl * (1-cos(w*time));.

what changes do i make..


thanks in advance,
regards,
sam.
samcfd is offline   Reply With Quote

Old   May 6, 2013, 02:52
Default
  #4
Senior Member
 
Join Date: Aug 2011
Posts: 421
Blog Entries: 1
Rep Power: 21
blackmask will become famous soon enough
I assume that you can tell the difference between pitch angle, say beta, and angular velocity, say omega. And you should know they are related by
omega[2] = d (beta) / dt (#)
While
beta(t) = 0.5 * pitchampl * (1-cos(w*time))
is the pitch angle in the above equation (#) (so that beta is in the range [0, pitchamp]), what you need to specify in the UDF is the angular velocity. That is what I tried to tell you in the last post.
blackmask is offline   Reply With Quote

Old   May 31, 2013, 02:37
Default
  #5
Member
 
samrat himvanth nanduri
Join Date: May 2012
Posts: 30
Rep Power: 13
samcfd is on a distinguished road
Dear Blackmask,
How u keeping?? Hope all s gud.. I need a quick favor. Could u pls help me out on how to write a UDF for Rotating grid. Example: I have to circles one inside the otr n i need to rotate the inner circle at a particular RPM. mostly for turbine applications. could u help me..
thanks in advance...
samcfd is offline   Reply With Quote

Old   May 31, 2013, 03:56
Default
  #6
Senior Member
 
Join Date: Aug 2011
Posts: 421
Blog Entries: 1
Rep Power: 21
blackmask will become famous soon enough
Thanks, I am OK.

The sliding mesh is sufficient for your purpose. Use
Code:
DEFINE_TRANSIENT_PROFILE
for time varying rpm. Otherwise you do not need UDF at all.
blackmask is offline   Reply With Quote

Old   May 31, 2013, 04:00
Default
  #7
Member
 
samrat himvanth nanduri
Join Date: May 2012
Posts: 30
Rep Power: 13
samcfd is on a distinguished road
Thanks for your reply.. but wen i use sliding mesh the grid does not rotate at all..i cant see rotation in animation also...
samcfd is offline   Reply With Quote

Old   February 3, 2014, 15:25
Default
  #8
New Member
 
Rakesh
Join Date: Jan 2014
Location: Delft
Posts: 13
Rep Power: 12
rsarma is on a distinguished road
Dear Blackmask,

This is in continuation of the earlier message that I sent you. I tried adjusting sin by cos. But the problem still persists. Could you put forward any other suggestion. Here is my problem.
I am dealing with a pitching airfoil problem. I am using dynamic mesh with a udf.


My airfoil is pitching fine, but I see that there is some problem with the axis. It is pitching about the Z-axis. But it should have both positive and negative angles of attack. However my airfoil is either pitching above or below the zero angle of attack line. Could you kindly help me out?

Thanks.

Last edited by rsarma; February 5, 2014 at 12:23.
rsarma is offline   Reply With Quote

Old   February 22, 2014, 05:54
Default
  #9
New Member
 
Musa
Join Date: Mar 2012
Posts: 14
Rep Power: 14
fkanyako is on a distinguished road
Quote:
Originally Posted by rsarma View Post
Dear Blackmask,

This is in continuation of the earlier message that I sent you. I tried adjusting sin by cos. But the problem still persists. Could you put forward any other suggestion. Here is my problem.
I am dealing with a pitching airfoil problem. I am using dynamic mesh with a udf.


My airfoil is pitching fine, but I see that there is some problem with the axis. It is pitching about the Z-axis. But it should have both positive and negative angles of attack. However my airfoil is either pitching above or below the zero angle of attack line. Could you kindly help me out?

Thanks.
Hi
I am having the same problem, have you manage to solve it ? please share the solution with me.. Thanks
fkanyako is offline   Reply With Quote

Old   February 22, 2014, 09:26
Default
  #10
New Member
 
Rakesh
Join Date: Jan 2014
Location: Delft
Posts: 13
Rep Power: 12
rsarma is on a distinguished road
Dear Fkanyako,

Yeah it is solved now. I replaced sin by cos and it actually worked.
rsarma is offline   Reply With Quote

Old   February 25, 2014, 06:35
Default
  #11
New Member
 
Musa
Join Date: Mar 2012
Posts: 14
Rep Power: 14
fkanyako is on a distinguished road
How did you determine your time step size ?

I normally cal. this way
omega = 2*pi *frequency

and t = 1/freq.

Dt = t/300 or 400 or 500 it depends on how many time steps per circle I want. If this approach is wrong then please tell how to do it.

Thanks
fkanyako is offline   Reply With Quote

Old   February 25, 2014, 07:08
Default
  #12
New Member
 
Rakesh
Join Date: Jan 2014
Location: Delft
Posts: 13
Rep Power: 12
rsarma is on a distinguished road
Well, your approach is correct. It all depends on the number of points you want in each cycle. I typically was interested in about 20 points in a cycle for my application. So you can accordingly adjust that.

Good Luck!
rsarma is offline   Reply With Quote

Old   January 10, 2015, 14:14
Default
  #13
New Member
 
Join Date: Jan 2015
Posts: 2
Rep Power: 0
airbus is on a distinguished road
Hello everybody
I'm working on incompressible unsteady force measurement of two-dimensional naca0012 under pitch-up, hold and pitch-down motion at a constant velocity about 50 m/s

Recently I examined the model in static mode at various AOA in Fluent , but i've a problem for write a correct""UDF"" for Dynamic mode test that airfoil at defined AOA by specified HOLD time (h : holding factor) set in during motion as pitch up, HOLD , and return for different cases by different amplitude angular pitching rates

I'll so grateful to help me for doing this part
Thank you
airbus 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
Pitching Airfoil in FLUENT salihovic FLUENT 2 October 24, 2013 14:58
Airfoil pitching problem montag dp FLUENT 12 June 25, 2012 07:25
Airfoil Pitching sheth Fluent UDF and Scheme Programming 2 March 11, 2012 03:17
[ICEM] Dynamic mesh for a pitching airfoil bahram.raeisi ANSYS Meshing & Geometry 1 March 2, 2012 11:41
How to realize pitching airfoil with drooping nose calcualtion? zeitistgeld CFX 1 July 27, 2010 08:17


All times are GMT -4. The time now is 16:10.