Is the lift and drag force on a wind turbine blade are responsible for torque development?
I understand that the torque and thrust are the decomposition of the net aerodynamic force on the turbine blade. and the net aerodynamic force is the vector summation of the lift and drag force. but are these two forces directly responsible for torque generation?
Yes. The blade of a wind turbine is like a wing. Air blowing over it generates life force, which pulls the wing "upward". The wing is oriented so the "upward" force pulls the blade around the propeller axis.
On the other hand, drag does not contribute a useful torque. Drag pulls the wing "backward", which is the direction the wind is blowing. This is parallel to the propeller axis. This generates a torque that tries to tip the wind turbine over, which is countered by a torque from the wind turbine structure that hold it upright. It is not the torque that generates electricity.
You might also check out this Veritasium video. Risking My Life To Settle A Physics Debate
The torque developed by a wind turbine blade is the horizontal component of the total Lift Force developed, but is only about 6% of the total as the blades normally operate at TSR's of 6 or more to prevent back winding of the blades by the ever present atmospheric turbulences. The balance of this Lift Force, its Normal component, is totally unused & wasted as static force trying to tip over the tower. Drag force is a very small component, mainly impeding the Tangential component of the Lift Force.
