# Help on induced drag in VLM

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 May 14, 2010, 13:44 Help on induced drag in VLM #1 New Member   Aneesh Goly Join Date: May 2010 Posts: 1 Rep Power: 0 Hello, I am doing analysis of ocean current turbine using vlm. i computed lift force and Can anyone please let me know how to calculate the induced drag (or any reference). Thanks Aneesh

 August 25, 2010, 05:07 #2 New Member   César Vecchio Join Date: Jul 2010 Location: Córdoba, Argentina Posts: 21 Rep Power: 9 If you where able to calculate lift force then induce drag is pretty much the same. I suppose you calculated the force on each panel by: Fi=gammai*rho*V*bi (Kutta's formula) Now, as Fi is a force it has three components in x,y,z respectively, usually in body axes. So: Fx=sum(Fxi) Fy=sum(Fyi) Fz=sum(Fzi) Then to convert those total components to wind axes simply apply a rotation matrix (Euler angles) which depends on attack and yaw angles solely: [Di,C,L]'=[rotation matrix]*[Fx,Fy,Fz]' Di is induced drag, C is lateral force and L is lift. To obtain coefficients divide each of them by q*S. If you're not happy with my answer, you can check the books by Jack Moran (provides sample VLM code) or the good ol' Katz & Plotkin. You can also check the source code of Tornado, AVL, VLMpc or VorStab, they are all open source VLM codes, and reliable.

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