Hi

I came across a paper that uses the thrust force and the side-force to calculate the aerodynamic forces and moment on the rotor when it is yawing. I know what a lift/drag force is and I know a bit obout thrust force but I have never heard of side-force. Can someone please explain to me what it is?

A thrust force depends on the thrust coefficient and similarly side-force depends on side-force coefficients. I have not been able to find how a side-force coefficient curve looks like either.

Dear Jamal,

I have never heard of a side-force coefficient. The forces that affect the rotor usually derive from the aggregate of the blade-element forces at various points along each blade. The relative wind speeds at many points on each blade are first computed and then some sort of rotor induction model (Blade-Element/Momentum, Generalized Dynamic Wake, etc.) is applied to the relative winds to affect them. The induced winds then produce a lift, drag, and (sometimes) pitching moment at each analysis point using basic aerodynamic equations. These forces and moments are then applied to the structural model to produce an aeroelastic response. The overall thrust coefficient can be computed integrating the forces over the entire rotor.

For simple performance analyses, one could use curves thrust and torque coefficients vs. wind speed, but I’ve never heard of anyone complicating such an analysis by using side forces.

Marshall

Hi

Thanks for your help.

In the paper both forces have been defined as:

Thrust force (which acts in the direction of the rotor axis normal to the rotor plane - Vcos(delta))

Side-force (which acts in the direction of the component of the wind velocity vector in rotor plane - Vsin(delta))

Maybe side-force name has been used instead of some other force like lift or torque? I hope this explanation makes more sense to you.

Dear Jamal,

I didn’t actually say I had never heard of the “side force” (it’s a common term), but that I had never heard of a “side-force coefficient.” I know of no work involving side-force coefficients, but there are a lot of things I do not know about.

Marshall