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-   -   Meshing An airfoil with a simple plain flap (http://www.cfd-online.com/Forums/fluent/35548-meshing-airfoil-simple-plain-flap.html)

S. Kalam January 24, 2005 16:43

Meshing An airfoil with a simple plain flap
 
I am trying to mesh an airfoil and its boundary in GAMBIT. The airfoil has a plain flap on the end of it which rotates to different angles: 10/20/30/40 degrees.

I am having problems doing this...firstly as im not sure how to do it...I am a student.

Also when importing th airfoil into GAMBIT, the leading edge is not at coordinates 0,0 and seems to have enlargened itself.

The drawing are properley scaled and positioned in AutoCAD.

If required I can provide IGES (autocad) drawings of the airfoil and flap at different angles.

The whoe point of the project is too see how much lift is produced as the flap is lowerd to greater angles from 0 to 40 downwards.

Can anyone help me please.

My email is lazy_pervert_hermit@yahoo.co.uk


Jason January 24, 2005 17:23

Re: Meshing An airfoil with a simple plain flap
 
I'm assuming this is a 2D model...

The shift and enlargement are probably scaling. Most translators can put a units marker in the iges file, but Gambit's translator doesn't always recognize the marker, depending on the program you used to create the iges, your version of that program, your program of gambit, etc... If Gambit doesn't recognize a units marker, it assumes the units are meters (so if you exported a 10" wing, you might be importing it as a 10m wing).

As far as the model you're trying to build... The first step is to create a control volume around your wing and remove the solid body geometry from it (so there's a hole in your C.V. in the shape of your wing). In 2D, this is a flat plane larger than your wing profile (usually 5-10 chord lengths in every direction). The next step is to mesh your model. Then assign boundary conditions and export the mesh.

I recommend going through the gambit tutorials (since you are a student you might have to find your system admin to find out where those are) as well as the Fluent tutorials if you aren't familiar with that tool either.

This was just a quick overview of what you're going to have to do. Many of your sticking points have been discussed, and you can find them under the search function, but if you're still running into trouble, just let us know and someone will try to help.

Hope this helps, and goodluck Jason

S. Kalam January 30, 2005 11:06

Re: Meshing An airfoil with a simple plain flap
 
Thanks for the advice. I have managed to fix the scaling problem (turns out i didnt configure AutoCAD to define all units as mm and by default it had assumed them to be inches although during scaled 1:1 printing it printed them correctly- weird).

The second problem which i havent managed to fix is the positioning of the airfoil in the drawing. According to AutoCAD the airfoil leading edge foremost tip is at 0,0. But when converting to IGES, the airfoil has managed to move itself.

I don't have much time left for this project and am desperate to get this fixed. I am willing to send the dwg and igs files so anyone who can fix or move the airfoils leading edge to be at 0,0, so when i import the airfoils into gambit the airfoils leading edge will also be at 0,0.

If anyone could be kind enough to spare a few minutes to do this for me I would really appreciate it.

My email address is lazy_pervert_hermit@yahoo.co.uk


Jason January 30, 2005 13:32

Re: Meshing An airfoil with a simple plain flap
 
Why can't you move it once it's imported into Gambit? If there's a vertex at the leading edge of the airfoil, then you can get the vertex info (vertex->information) which will list the coordinates of the vertex. Then you can translate all of the edges (or faces, but I think you said before it's all edges) so that the leading edge is now at 0,0.

Goodluck, Jason

S. Kalam January 30, 2005 13:37

Re: Meshing An airfoil with a simple plain flap
 
Well i am trying to move the airfoil but its always off 0,0 by about y=4e-07 and gambit wont let me move it any closer....

Jason..if i sent the dwg files to u...or even the igs files to u- do u think you could try and move the airfoils leading edge to 0,0 if you dont mind. It would be more accurate this way.

Do you have yahoo or msn messenger? i could add you and type to u live on those...

mail me at: lazy_pervert_hermit@yahoo.co.uk

S. Kalam January 30, 2005 13:41

Re: Meshing An airfoil with a simple plain flap
 
what i meant is in AutoCAD it is already at 0,0. But the program that converts the dwg file into an IGS file moves the airfoil.

Maybe you have an program that can open and run IGS files- because I dont..(AutoCAD is rather lacking in this area)

S. Kalam January 30, 2005 17:45

Re: Meshing An airfoil with a simple plain flap
 
okay....iev moved the airfoil manually using that Informatin button...

Now my airfoil is made up lots (hundreds) of lines. I want to merge them so i can later split the airfoil it to four parts (surfaces) upper airfoil, upper flap, lower airfoil and lower flap.

But GAMBIT keeps saying: The edge list given including (among others) edges.318 and .319 does not form a single line (edges cant be merged or used for a face split).

This message come up for all lines no matter where they are on the airfoil or flap.

Any ideas Jason? Any one???

Let me know please

Thaaankkk Yooouuuu!!!!

Jason January 30, 2005 21:22

Re: Meshing An airfoil with a simple plain flap
 
Ok, merging the lines is going to create virtual geometry... if you go virtual you're going to have problems with working with the geometry (making faces, splitting faces, etc...). You might have to connect the vertices at the intersection of each line... another option would be to delete all the edges (making sure the delete lower geometry option is deselected), and reconnect all of the vertices with a variable curve (I think Gambit uses a nurbs line instead of a spline, but it's not a big difference). One other thing you can try is to create a face using all of the edges and subtract it from a larger face, instead of splitting the large face with the edges. If you send me the file (jason_at_bae@yahoo.com) I'll take a look at it for you as far as making/splitting the faces is concerned.

Jason


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