# Airfoil pitching problem

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July 9, 2010, 11:50
Airfoil pitching problem
#1
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Hey,

I'm attempting to analyze a 2D airfoil in a pitch-plunge motion. I have done just plunging and now I want to incorporate pitching as well. I'm using a UDF as follows:

Quote:
 #include "udf.h" DEFINE_CG_MOTION(airfoil, dt, vel, omega, time, dtime) { real plungeampl, pitchampl, w, pi; pi = 3.14159265; /* define motion variables */ plungeampl = 0.0254; /* 1-inch plunge amplitude */ pitchampl = 45 * pi / 180; /* 45-degree pitch amplitude */ w = 2 * pi * 25; /* 25 Hz frequency */ /* define airfoil motion */ vel[1] = w * plungeampl * cos(w * time); /* y-component of velocity */ omega[2] = w * pitchampl * cos(w * time); /* z-component of angular velocity */ }
For some reason I can't see any rotation. Oddly enough, if I switch the angular speed to omega[0] or omega[1] for x or y rotation, it works fine, but that's not what I want to do.

Does anyone have any idea why the z-rotation isn't working?

Regards,
Dan

EDIT: I just realized there's a dedicated UDF programming sub-forum. If a moderator wants to move this there, that's ok.

Last edited by montag dp; July 9, 2010 at 12:06.

 July 9, 2010, 12:10 #2 Member   Join Date: Jul 2010 Posts: 38 Rep Power: 7 Figured out my own problem. The pitching motion is actually working but for some reason it doesn't show up when I use "display zone motion." It works with "preview mesh motion."

 July 16, 2010, 06:17 #3 Member   aerospain Join Date: Sep 2009 Location: Madrid, Spain Posts: 84 Rep Power: 8 Hi montag, I would appreciate it if you could answer me a couple of questions: When defininf a CG motion for pitch through a UDF, where do you define the centre of rotation? inside FLUENT when defining the Zone which is Moving? Is your UDF for deforming meshes, or did you have domains with sliding interfaces? Thanks

 July 16, 2010, 08:29 #4 Member   Join Date: Jul 2010 Posts: 38 Rep Power: 7 Hi aerospain, I'm using a dynamic (deforming) mesh. Inside the dynamic mesh menu is an input for CG location. This is the center of rotation. I have been using the 1/4 chord of the airfoil as the center. Then within that menu I select the airfoil as the moving zone and make sure that my UDF shows up in the motion profile selection box.

 July 16, 2010, 08:54 #5 Member   aerospain Join Date: Sep 2009 Location: Madrid, Spain Posts: 84 Rep Power: 8 Thanks for the quick answer montag. So, coming back to the picture I posted in my first message, can I define a motion for the intermediate subdomain as a moving mesh (which will move the small subdomain along with it) and a CG motion for the small subdomain for it to have a second motion (which is exclusive to it)? regards

July 16, 2010, 09:12
#6
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Quote:
 Originally Posted by aerospain Thanks for the quick answer montag. So, coming back to the picture I posted in my first message, can I define a motion for the intermediate subdomain as a moving mesh (which will move the small subdomain along with it) and a CG motion for the small subdomain for it to have a second motion (which is exclusive to it)? regards
I don't see the picture...Do you have domains inside each other, and you want the innermost one to move along with the intermediate one, but also have its own motion relative to the intermediate one?

Anyway, I don't know about moving meshes. Maybe someone else could chime in here?

July 16, 2010, 09:16
now with picture
#7
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aerospain
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Sorry about that, I had another post in mind.

Does it explain my problem?

cheers!
Attached Images
 2D_domain.jpg (78.5 KB, 88 views)

 July 16, 2010, 13:35 #8 Member   Join Date: Jul 2010 Posts: 38 Rep Power: 7 It does, unfortunately I don't really know about the sliding mesh. It seems like it should be possible, though, but you will probably have to define your airfoil motion relative to the global coordinate system and not the coordinate system of the domain it is directly inside.

August 3, 2010, 09:38
rotation about z axis
#9
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HI EVERYBODY...
i'm trying to rotate a small circle about z axis but i faced a problem,in 2 images that i sent u,u can see it,circle has been locked in its end points,how can i tell fluent that i want rotate small cylinder about center of bigger circle

it's kind of u if u think about it and help me out
Attached Images
 problem.JPG (22.7 KB, 49 views) problem 2.JPG (8.9 KB, 34 views)

August 4, 2010, 17:50
#10
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aerospain
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Quote:
 Originally Posted by almostafa67 HI EVERYBODY... i'm trying to rotate a small circle about z axis but i faced a problem,in 2 images that i sent u,u can see it,circle has been locked in its end points,how can i tell fluent that i want rotate small cylinder about center of bigger circle it's kind of u if u think about it and help me out
Hi almostafa,

1. Could you please explain a bit more your simulation? What "real world" situation are you trying to model?

2. How manu domains have you defined? Just the one shown in the pictures?

Regards

August 5, 2010, 01:49
#11
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Quote:
 Originally Posted by aerospain Hi almostafa, 1. Could you please explain a bit more your simulation? What "real world" situation are you trying to model? 2. How manu domains have you defined? Just the one shown in the pictures? Regards
i want to simulate peristaltic pump(http://www.randolphaustin.com/) and for this i need to rotate small circle about center of bigger circle,almost i could do this but faced a problem that explained befor,could u help me out?
thank you in advance

 June 10, 2012, 12:53 #12 New Member   srikanth Join Date: Jun 2012 Posts: 4 Rep Power: 5 Hi Montag, Can you please post the UDF.

 June 25, 2012, 06:25 #13 New Member   srikanth Join Date: Jun 2012 Posts: 4 Rep Power: 5 Opening library "libudf"... Error: open_udf_library: The system cannot find the file specified. Error Object: ()

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