[aaneesh]

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

[CAVT]

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.

[ZakBristol]

That would give you a force perpendicular to the freestream and you wont get drag force but thrust force,.