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Old   June 25, 2004, 07:14
Default Urgent!!!
  #1
Panos
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I've trying to calculate lift and drag forces over an airfoil. Can anyone tell me how to calculate lift and drag forces in a flow over an airfoil using starcd. Please help me because I have a deadline soon. Thank you!!
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Old   June 25, 2004, 08:01
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  #2
Jörn Beilke
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you can use the "acoe" command
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Old   June 25, 2004, 10:41
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Panos
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jrn I tried that but it sais that I have to load wall data. How do I do that? I have created a wall boundary over the surface of the airfoil so I think it can produce wall engineering data. Please help. Thanx!!
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Old   June 26, 2004, 05:19
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Anton Lyaskin
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First turn on writing forces for your wall boundary in engineering data. After simulation you'll get the file <your case name>.erd, containing forces for each iteration. The last three values in the last entry will be forces in X,Y,Z directions of Global Cartesian system. Just divide them to dynamic pressure and wing area. Note that you have to take area, not just chord length, because your model is 3D! Area should be taken in square meters, dynamic pressure in Pascales, cause the forces are always in Newtons. After this you'll get coefficients in body frame of reference, which can be then recalculated to lift and drag coefficients.
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Old   June 26, 2004, 10:26
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Panos
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Thanks Anton it works!! But how can I calculate the area of the airfoil? Thank you very much
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Old   June 26, 2004, 10:29
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  #6
Anton Lyaskin
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You need "plan projection" are - chord length multiplied by width of your model. You can select all verticies which belong to your wall boundary and use Utility->Geometric range->Vertex set to find out these dimensions
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Old   June 26, 2004, 10:56
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  #7
Panos
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The width of my model is the width in the z-direction right? The value is 0.85m. Can I change this value or is it by default when I generate the 3D mesh out of 2D mesh? Again I really appreciate it
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Old   June 26, 2004, 11:02
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  #8
Anton Lyaskin
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If you make it "automatically" then the answer is no - ProSTAR selects the size itself (something like 2 jr 5% of the largest dimension). That's why I usually make 3D mesh from 2D "manually" with vcextrude - to keep the width "round", like 1 meter.
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Old   June 27, 2004, 18:17
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  #9
Panos
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Anton something else. When I have ready my 2d model consisting of patces how can I generate the 3D mesh using the vextrude command? Could u please tell me how to use the above command more analytically? Again thanx a lot!!
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Old   June 28, 2004, 06:43
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4xF
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Have you tried the following?

!!! define the number of cell layers to be extruded *SET MYNC 1 !!! define the thickness of the cell layers to extrude *SET MYTH 1.0 !!! Select all patches CSET,NEWSET,SHELL !!! Extrude the shell (see also online help with F1) VCEX,MYNC,,CSET,,,NORMAL,MYTH

Hope it helps...
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Old   June 28, 2004, 10:20
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  #11
Panos
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Another thing I wanted to ask is that I keep getting the error that my mesh has small internal angles and cell has a greater aspect ratio. Are those errors importnant? Is there a way I can avoid them? Again I really appreciate it
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