How to compute the non-tilted thrust coefficient?

Wind & Water Computer-Aided Engineering Software Tools
1

Hello,

I am running a FAST v8 simulation (using AeroDyn v14 :sweat_smile:) for a turbine with rotor shaft tilt but I need to report the non-tilted thrust value (i.e. in the inertial frame). The blades are rotating with a constant RPM but all other degrees of freedom for the blades/tower are disabled).

I am aware of the limitations of AeroDyn v14 such as not being able to output Aerodynamic quantities in contrast to AeroDyn v15.
My approach is to use the output of ElastoDyn instead to approximate the Aerodynamic thrust:

  • In ElastoDyn output: LSShftFxa ,LSShftFya, and LSShftFza . The force is then:
    F = LSShftFxa ⋅ e_xa + LSShftFya ⋅ e_ya + LSShftFza ⋅ e_za,
    where e_xa, e_ya, and e_za are the unit vectors in the axis coordinate system.
  • Project F in the x-direction of the inertial system, hence thrust : T = F ⋅ e_xi (dot product between the force F and the unit vector in x-direction of the inertial system, e_xi ).
  • Normalize T to find the thrust coefficient.

I appreciate your feedback on the approach above and point any mistakes/corrections to find the non-tilted thrust coefficient.

Best regards,

Y.Thiziri

2

Dear @Yoor.Thiziri,

Your equation will include the contribution of rotor weight, which you’ll have to subtract from ElastoDyn before rotating the coordinate system from a to i. Your equation will also include inertial effects from structural vibration, so, you should time-average the force if your goal is to estimate only the aerodynamic thrust.

Alternatively, you could compute the total aerodynamic thrust by outputting ForceN at each blade element (using the PRINT option) and summing across all elements and multiplying by the number of blades, then rotating this force from a to i.

Best regards,

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