I’d like to follow up on a post dated June 27, 2016 to René where it was stated that ''c1" and “b1” refer to the orientation, not the origin, of the coordinate system by requesting a further clarification of the shaft (xs, ys, zs) and azimuth (xa, ya and za) coordinate systems. According to the FAST Users Guide, the shaft and azimuth coordinate systems are located at the origin, which is defined as the intersection of the yn-/zn-plane and the rotor axis. According to the diagrams shown, this intersection occurs at the yaw axis at the top of the tower. Many of the output variables indicate rotations about the ys, zs, ya and za axes. Examples include:
TeetVya: Rotor teeter angular velocity about the ya-axis
TeetAya: Rotor teeter angular acceleration about the ya-axis
LSSTipMya: Rotating LSS bending moment at the shaft tip (teeter pin for two-bladed turbines, apex of rotationfor three-bladed turbines) About the ya-axis
LSSTipMza: Rotating LSS bending moment at the shaft tip(teeter pin for two-bladed turbines, apex of rotation for three-bladed turbines) About the za-axis
LSSTipMys: Nonrotating LSS bending moment at the shaft tip (teeter pin for two-bladed turbines, apex of rotation
for three-bladed turbines) About the ys-axis
LSSTipMzs: Nonrotating LSS bending moment at the shaft tip (teeter pin for two-bladed turbines, apex of rotation
for three-bladed turbines) About the zs-axis
LSSGagMys: Nonrotating LSS bending moment at the shaft’s strain gage (shaft strain gage located by input ShftGagL) About the ys-axis
LSSGagMzs Nonrotating LSS bending moment at the shaft’s strain gage (shaft strain gage located by input ShftGagL) About the zs-axis
I have always assumed that the origin of the ys, zs, ya, and za axes would move along the xs axis to the designated position, e.g, shaft tip, teeter pin, strain gauge location, however I cannot find that stated in the FAST Users Guide and would appreciate your clarification. This interpretation would be consistent with the earlier post regarding “C1” and “b1” where the ys, zs, ya and za axes in the output variables listed above refer to the orientation, rather than the origin of the coordinate systems.
Yes, I agree with your understanding that the origin of the ys, zs, ya, and za axes would move along the xa / xs axis to the designated position, e.g, shaft tip, teeter pin, strain gauge location depending on the output parameter of interest.
Can I confirm the following points again for an upwind wind turbine? (check it together with the blade system in the following picture):
(1) NREL-5MW baseline wind turbine is an upwind wind turbine, and its blade rotation direction is clockwise.
(2) The aerodynamic lift that drives rotation has a component acting along negative y, which is opposite to the rotation tangential direction.
(3) Aerodynamic thrust acts along negative x.
Are the above statements correct? If they are correct, I can’t understand why the aerodynamic lift force points opposite to the blade rotation direction, could you explain the reason?
I agree with points (1) and (2), but point (3) and your picture are not correct. Regarding (3), the thrust for an upwind wind turbine should be directed along positive x. Regarding your picture, it would be correct if you rotate each blade 180 degrees around its z axis, such that x points downwind and the rotor spins clockswise (when looking downwind) opposite to the direction of y.
Thanks. So does it mean that a wind turbine always spins clockwise (looking downwind), no matter it is an upwind or a downwind turbine? Is this understanding correct?
