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-   -   Airfoil pitching problem (http://www.cfd-online.com/Forums/fluent/78014-airfoil-pitching-problem.html)

montag dp July 9, 2010 11:50

Airfoil pitching problem
 
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.

montag dp July 9, 2010 12:10

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."

aerospain July 16, 2010 06:17

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

montag dp July 16, 2010 08:29

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.

aerospain July 16, 2010 08:54

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

montag dp July 16, 2010 09:12

Quote:

Originally Posted by aerospain (Post 267653)
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?

aerospain July 16, 2010 09:16

now with picture
 
1 Attachment(s)
Sorry about that, I had another post in mind.

Does it explain my problem?

cheers!

montag dp July 16, 2010 13:35

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.

almostafa67 August 3, 2010 09:38

rotation about z axis
 
2 Attachment(s)
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:confused:

it's kind of u if u think about it and help me out:o

aerospain August 4, 2010 17:50

Quote:

Originally Posted by almostafa67 (Post 270046)
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:confused:

it's kind of u if u think about it and help me out:o

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

almostafa67 August 5, 2010 01:49

Quote:

Originally Posted by aerospain (Post 270303)
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:)

srikanthgoli June 10, 2012 12:53

Hi Montag,
Can you please post the UDF.

srikanthgoli June 25, 2012 06:25

Opening library "libudf"...
Error: open_udf_library: The system cannot find the file specified.

Error Object: ()


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