We are currently going through a massive rewrite of the AeroDyn code and would like some feedback on how to best improve it. What do you like? what do you hate?..etc, etc… Please feel free to comment on documentation and usability issues as well.
Upon a brief scan of the aerodyn user’s manual, I am not clear whether pitch rate is an input to AeroDyn, and whether it is used in the correction for dynamic inflow. Could somebody clarify please?
The quick answer is: pitch rates are not a direct input into AeroDyn.
But, in the dynamic stall routines (is this what you mean by dynamic inflow? If not see below.) the rate of change of angle of attack is calculated between time steps. This will be affected by the blade motion (including pitch rate) and also the change in rotor speed, wind speed etc. The angle of attack change rate affects the predicted normal force coefficients through the Beddoes-Leishman model. So, in a way, pitch rate is accounted for indirectly in these routines. The smaller the time step, the closer to the true pitch rate being modeled.
Also, when we in the wind turbine community talk about dynamic inflow, often we are referring to generalized dynamic wake model (GDW) of Peters and He. Here, the induced rotor velocities are found using differential equations (in time) dependent on the incoming velocity and rotor loading. The rotor loading is dependent on the rate through the dynamic stall model indirectly as described above. There may be other higher order linkages between pitch rate and the GDW, but it would take some additional thinking on my part. There is no direct affect of pitch rate modeled by the GDW.
I believe that Burton et al may have derived direct corrections for pitch rate in blade element momentum theory, which we do not… if you’re curious.
Does this answer your question?
Thank you for your comments, and thank you for getting back so quickly. It is the GDW effects that I was meaning by ‘Dynamic Inflow.’ My question stems from a need to get the matrix elements corresponding to pitch rate states when linearizing a SymDyn model (I’m currently working at adding pitch as a dof to SymDyn). From your explanation, and from section 3.13.7 in the Wind Energy Handbook, it appears that the GDW does indeed account for pitch motion, but as jumps in angle of attack from one time step to another, not as an explicit product of pitch rate.
To get the linear-model matrix elements for the pitch rate state, I will therefore need to perturb the system with a pitch angle corresponding to the pitch angle that would be produced at the end of the time interval during which the rate perturbation acts. It seems like I should experiment with time intervals in the neighborhood of the characteristic time of the pitch actuators; it will also be interesting to see if there is an effect from dividing the time interval in the aerodynamic calculation (using multiple aerodynamic time steps to get to the characteristic actuator time).
Thank you for clarifying,