Constant wind profile for WT_Perf

Wind & Water Rotor Aerodynamics
1

Dear all,

I’m currently evaluating the performance of different sized rotors under one sheared wind. The hub height of these rotors vary a lot, and wanted to asses them under one wind profile. I suspect when I set the wind shear exponent in the WT_Perf input file, the hub height is used as the reference height to model the atmospheric boundary layer, is this true? or is there a constant that is defined within the code? Could I have assess to make this reference height a constant?

I know this can be done using FAST as I could use a single wind file to perform the simulations, however I do not have the structural properties of these turbine.

I was wondering if there is a way to run AeroDyn without running FAST? or can I run FAST and gain the steady outputs from AeroDyn that are not influenced by FAST? i.e. I’m thinking of prescribing any false structural properties and turning off all the DOF for the simulations, is this the way to do it, in the FAST input file:
False FlapDOF1 - First flapwise blade mode DOF (flag)
False FlapDOF2 - Second flapwise blade mode DOF (flag)
False EdgeDOF - First edgewise blade mode DOF (flag)
False TeetDOF - Rotor-teeter DOF (flag) [unused for 3 blades]
False DrTrDOF - Drivetrain rotational-flexibility DOF (flag)
False GenDOF - Generator DOF (flag)
False YawDOF - Yaw DOF (flag)
False TwFADOF1 - First fore-aft tower bending-mode DOF (flag)
False TwFADOF2 - Second fore-aft tower bending-mode DOF (flag)
False TwSSDOF1 - First side-to-side tower bending-mode DOF (flag)
False TwSSDOF2 - Second side-to-side tower bending-mode DOF (flag)
True CompAero - Compute aerodynamic forces (flag)
False CompNoise - Compute aerodynamic noise (flag)

Is this is sufficient for the FAST code to not influence the AeroDyn results, or is there other flags/quantities I should change?

Any help is greatly appreciated,
Thank you,
Kind regards,
Kishore

2

Dear Kishore,

I apologize for taking so long to reply, but I’ve been out sick.

I’m not sure what you mean by “one wind profile.” Do you mean that turbines with different hub heights will all be sampling their own part of the same wind profile such that a smaller one will have a lower hub-height wind speed than a taller one will see, or do you want each turbine to have the same hub-height wind speed despite the fact that they have different hub heights?

It is true that the wind is sheared up and down from the hub height. There is no reference height that can be set differently than the hub height.

If you want to use just one wind profile for turbines of different sizes, you may just create one reference height and compute what the wind speed will be for different hub heights [WS(h)=WS_ref*(h/h_ref)^shear]. Use those wind speeds for the various turbines and they will each be sampling their portion of the single wind field.

If you want to use the same hub-height wind speed for each turbine, that’s quite trivial unless you want to have the same wind speed at the top and bottom of each rotor, too. If that’s the case, I suppose you would have to change the shear exponent.

Marshall

3

Dear Marshal,

Once again, I’m glad to say that you have successfully fixed my problem :slight_smile:

I wanted the turbines with different hub heights to be sampling their own part of the same wind profile such that a smaller one will have a lower hub-height wind speed than a taller one will see, and your method to evaluate and use the different wind speeds at the different hub heights for one reference height works great.

Thank you very much,
I hope you have recovered from your illness by now,
Kind regards,
Kishore