Induction factor flag (IndModel) off, sim problems

Hi everyone,

For my thesis I need to do a comparison between two aerolastic codes, one of them is FAST, I am interested on comparing the aerodynamic part of each codes and something weird happens when I have the following Aerodyn configuration:

SI SysUnits
BEDDOES StallMod
USE_CM UseCm
EQUIL InfModel
NONE IndModel
0.005 AToler
PRANDtl TLModel
PRANDtl HLModel

As you can see I’m interested on testing BEM method without Induction (a=0 and a’=0) this yields to a solution where the power output is greater than 5MW and the rotational speed goes further than 12.1rpm. My FAST input file has VSCONTROL = 1 and the wind input file is a steady wind field of Uwind = 11.4m/s constant

I hope you can put some light on this because when I simulate with induction it works as it supposed (5MW power output and 12.1rpm)

PD: as an extra question, does RotTorq depens only on the aerodynamic loads? As I understand Rotor Torque is the resulting torque of aerodynamic loads but I’m not sure on that and I hope you can help me

Dear Oriol,

I’m not really sure I understand your question. Is the result that the power is greater than 5 MW and the rotor speed is greater than 12.1 rpm not what you were expecting? The VSContrl = 1 (simple variable-speed control) option employs constant torque above rated, so, power will increase beyond 5 MW when the rotor speed increases beyond rated. If you switch to using the DISCON.dll supplied with the NREL 5-MW models, the torque controller employs constant power above rated, so, the power should remain at 5 MW regardless of the rotor speed beyond rated.

RotTorq is the same as LSShftTq and is discussed at length here.

Best regards,

Dear Jason,

First of all thank you for sharing that last post, was really helpful to understand the Rotor torque.

Regarding my first question, sorry if I didn’t express myself clear. I want to know why when I change between a model with induction flag ON, an a model with induction flag OFF (a=0 & a’=0), when the flag is OFF the power output and the rotor speed goes higher than 5MW and 12.1rpm respectively. In addition I was saying that I have set the VSControl to 1. What I expected with induction flag OFF is a constant rotor torque from the beginning.

Hope I express myself better this time

Kind Regards

Dear Oriol,

The VSContrl = 1 (simple variable-speed control) option results in constant generator torque above rated speed, but the rotor torque may still vary depending on the applied aerodynamic loads and acceleration/deceleration of the rotor. A constant torque control strategy may also result in variations of power above rated.

What have you enabled for blade-pitch control? It is common for the blade-pitch controller to regulate rotor speed above rated.

Again, I’m not sure why you are using VSContrl = 1 for the NREL 5-MW turbine, which includes a combined pitch and torque controller supplied as a DISCON.dll. But not using the proper controller may result in unexpected behavior.

Best regards,

Dear Jason,

Now I realised what you mean with the controller I didn’t understand that DISCON.dll was a compiled file already. So as I read your answer I went directly to try it. I downloaded a new version of FAST 7 from your repository: “FAST_v7.02.00d-bjj_AeroDyn_v13.00.02a-bjj_BladedDLLInterface.exe” as a WT i’m using the ONSHORE 5MW NREL wind turbine, while trying to run a simulation I obtained the following error message: “The DLL DISCON.dll could not be loaded”. I do not understand this I have my DISCON.dll file in the same folder as the .FST and the FAST executable. Do you know why is this happening? Using this controller will be a lot of help…

Regards,

Found it, I was missing the DFORRT.dll. Now I have rated power control. Thanks a lot.