# 2D Pitching Airfoil

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 May 6, 2013, 00:51 2D Pitching Airfoil #1 New Member   samrat himvanth nanduri Join Date: May 2012 Posts: 27 Rep Power: 6 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

 May 6, 2013, 00:56 #2 Senior Member   Join Date: Aug 2011 Posts: 315 Rep Power: 13 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);

May 6, 2013, 01:13
#3
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samrat himvanth nanduri
Join Date: May 2012
Posts: 27
Rep Power: 6
Quote:
 Originally Posted by blackmask 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);

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..

regards,
sam.

 May 6, 2013, 01:52 #4 Senior Member   Join Date: Aug 2011 Posts: 315 Rep Power: 13 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.

 May 31, 2013, 01:37 #5 New Member   samrat himvanth nanduri Join Date: May 2012 Posts: 27 Rep Power: 6 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...

 May 31, 2013, 02:56 #6 Senior Member   Join Date: Aug 2011 Posts: 315 Rep Power: 13 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.

 May 31, 2013, 03:00 #7 New Member   samrat himvanth nanduri Join Date: May 2012 Posts: 27 Rep Power: 6 Thanks for your reply.. but wen i use sliding mesh the grid does not rotate at all..i cant see rotation in animation also...

 February 3, 2014, 15:25 #8 New Member   Rakesh Join Date: Jan 2014 Location: Delft Posts: 10 Rep Power: 4 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.

February 22, 2014, 05:54
#9
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Musa
Join Date: Mar 2012
Posts: 14
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Quote:
 Originally Posted by rsarma 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

 February 22, 2014, 09:26 #10 New Member   Rakesh Join Date: Jan 2014 Location: Delft Posts: 10 Rep Power: 4 Dear Fkanyako, Yeah it is solved now. I replaced sin by cos and it actually worked.

 February 25, 2014, 06:35 #11 New Member   Musa Join Date: Mar 2012 Posts: 14 Rep Power: 6 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

 February 25, 2014, 07:08 #12 New Member   Rakesh Join Date: Jan 2014 Location: Delft Posts: 10 Rep Power: 4 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!

 January 10, 2015, 14:14 #13 New Member   Join Date: Jan 2015 Posts: 2 Rep Power: 0 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

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