FAST.Farm

Sent.

Dear Jason,

I’m trying to simulate different scenarios from the one given in the example that you provided along with the pre-realease version of FAST.farm. In this case, I would like to simulate a row of 3 WTs separated 5D from each other. For wind speeds around 8 m/s or less, and setting Mod_AmbWind=2 and WindType=3, I’m getting the following error:

T3:FARM_UpdateStates:NearWakeCorrection:Local induction is high enough to invalidate the near-wake correction, i.e., m%a(i) >= 1.0_ReKi / p%C_NearWake.

I guess, one way to overcome this issue would be to reduce the value of C_NearWake from the default one. But in this case, I would be changing the value obtained from calibration. What would you suggest to solve this problem? Have you already simulated wind farms using wind turbines separation around 4-6D?

Best regards,
Bruno López

Dear Bruno,

We don’t have a lot of experience running FAST.Farm with 4-6D turbine spacings, but I don’t really that that would be problem either.

The current near-wake correction model of FAST.Farm is not valid under high-thrust conditions (C_T > 24/25). We are aware that the wake calculation of FAST.Farm will become unstable (indicated by a wide spreading of the wake) and eventually this error will be triggered under sustained high-thrust conditions.

My first question is why do you think you are getting such a high thrust? From my experience, often times this is controller related, e.g., commanding a rotor speed that is too high for the given mean wind speed. What conditions are you simulating and what is happening with the inflow and turbine response preceding this high thrust error?

FYI: We are currently working on an improved near-wake correction model applicable to such conditions, and hope to commit this improvement soon.

Best regards,

Dear Jason,

Thanks a lot for your quick reply. In order to simplify things I simulated the wind farm using WindType=1 (steady) and I got the same error. What I could see is that either decreasing the inflow wind speed or the wind turbine spacing I got the high thrust situation.

For example, I simulated a three turbine row, spacing the turbines at 600m each other and using HWindSpeed=8 at 90m and I got the error. But, when I simulated the same row layout using HWindSpeed=10 I did not get the error. I could also avoid the error using HWindSpeed=8 but spacing the turbines at 1000m each other (same layout provided in the example).

In terms of the controller, every time I got the error the turbine was operating in region 1 1/2, that is, generator speed was below 871 rpm. It is common to find higher thrust at the begining of the power curve, but I guess it should not be that high. As a consecuense of these high values of thrust, I am getting wake-velocity deficits at the rotor disk covering an area that at least doubles the rotor swept area.

I was looking at the output files but I could not find any clue about the error there. I share with you in the following link the output file of the 3rd wind turbine (the one that produces the error): drive.google.com/file/d/1YyGqmb … sp=sharing

Any suggestion would be very helpful! Thanks for your time.

Best regards,
Bruno

Dear Bruno,

Yes, I would guess it is the operation in Region 1.5 that is causing a high tip-speed ratio and high thrust.

It would be hard to see the effect from the OpenFAST *.out file. Instead, I would output a VTK slice (e.g., a XY plane through the hub), and you’ll clearly see the wake expand just before the near-wake correction error is displayed.

The improved near-wake correction model that we are working on now will resolve this problem. Until then, dropping C_NearWake is the only the solution that does not involve a source-code change.

Best regards,

Dear Jason,

I am very interested in Fast.Farm with the Super Controller for my PhD project. Could you please share with me the FAST.Farm pre-release version along with its documentation?

Thank you in advance.

Best regards,

Younes

Sent.

Dear Jason,

Yes, that’s is exactly what I tried to say in my previous post. The wake expansion doubles de rotor diameter when looking at a vtk slice just before the error occurs, which makes no physical sense.

Thanks for your suggestions! I look forward for updates regarding the near wake correction.

Best regards,
Bruno

Dear Jason,

Could you share with me the FAST.Farm pre-release version along with its documentation, please?

Thanks for your attenttion,

Sent.

Dear Jason,

I can run the 5.0 MW Baseline Wind Turbine with OC3 Monopile RF configuration, OC3 Hywind configuration and OC4-DeepCwind semi configuration in FAST.Farm successfully. But when I used the MIT-NREL TLP Configuration without any changes in FAST.Farm, it will have errors. So have the TLP configuration some special points that need to set in the primary files ? The errors as followings:

This error occurs in the initialization stage of the simulation, so I decided the cause may be improper domain specification, but why the other kinds of wind turbine have not this problem ?

And I also want to initialize the rotor speed and blade pitch to their expected values for the given mean hub-height wind speed, but I don’t know every wind speed correspond to the blade pitch ? Have it a table that we could reference ?

Best regards,

Jiaping.Cui

Dear Jason,

Using the example given in Fast.Farm, I always get issues of computation when I change the wind turbines positions (only by 20m in the Y direction), saying that it is out grid bounds (as you can see in the Matlab consol). But from the parameters given: NX_low=500; NY=200; dX_Low=10m; dY_Low=10m; the length of the boundaries are Lx=10.(500-1)=4990m and Ly=10.(200-1)=1990m, and the turbines in the Y axis are in 1020m;980m;1000m; which are inside the grid bounds. Maybe I missed something, but I can’t figure out the issue. Can you help me please?

Kindest regards

Younes

Dear Jiaping.Cui,

My guess is you are receiving the error about position = (0,0,0) because the tower aerodynamic analysis nodes in the AeroDyn v15 input file for the MIT/NREL TLP model extend down to ground level. To solve this problem, extend the FAST.Farm domain lower (to ground level), increase the lowest-most tower node in the AeroDyn v15 input file, or disable tower aerodynamics altogether.

Regarding the expected values of the rotor speed and blade-pitch angles for the NREL 5-MW baseline wind turbine as a function of mean hub-height wind speed, please see the following forum topic: http://forums.nrel.gov/t/nrel-5-mw-reference-turbine/257/7.

Best regards,

Dear Younes,

The error message you are getting is referring to the high-resolution domains, not the low-resolution domain. When you shifted the Y-locations of the wind turbines in FAST.Farm, did you also shift the location of the high-resolution domains?

Best regards,

Dear Jason,

I changed the high-resolution domain position and it works. Thank you so much!
I have another question: How the ambient wind is generated (the .vtk files)? Is it with TurbSim?
I would like to generate my own wind conditions and test my wind farm on it.

Kindest regards

Younes Oudich

Dear Younes,

The ambient wind in VTK format used by FAST.Farm (Mod_AmbWind = 1) is generated by a high-fidelity precursor simulation (CFD), e.g., SOWFA. You can use TurbSim to generate ambient wind using Mod_AmbWind = 2 or 3. See the draft FAST.Farm User’s Guide and Theory Manual for more information.

Best regards,

Dear Jason,

Could you please send to me the pre-release of the fast.farm software together with its documentation? I am interested to compare it with some of our internal tools.

Thank you in advance.

Kind regards,

Ertem

Sent.

Dear Jason,

I am trying to use InflowWind module with FAST.Farm, but I keep getting the following error:

T1:FARM_InitialCO:FWrap_t0:FAST_Solution0:CalcOutputs_And_SolveForInputs:SolveOption2:SrvD_CalcOut
put:Running with torque and pitch control of the NREL offshore 5MW baseline wind turbine from
DISCON.dll as written by J. Jonkman of NREL/NWTC for use in the IEA Annex XXIII OC3 studies.
T2:FARM_InitialCO:FWrap_t0:FAST_Solution0:CalcOutputs_And_SolveForInputs:SolveOption2:SrvD_CalcOut
put:Running with torque and pitch control of the NREL offshore 5MW baseline wind turbine from
DISCON.dll as written by J. Jonkman of NREL/NWTC for use in the IEA Annex XXIII OC3 studies.
T3:FARM_InitialCO:FWrap_t0:FAST_Solution0:CalcOutputs_And_SolveForInputs:SolveOption2:InflowWind_C
alcOutput:CalcOutput:IfW_4Dext_CalcOutput [position=(-5, 0, 90) in wind-file
coordinates]:Interp4D:Outside the grid bounds.
SolveOption2:SrvD_CalcOutput:Running with torque and pitch control of the NREL offshore 5MW
baseline wind turbine from DISCON.dll as written by J. Jonkman of NREL/NWTC for use in the IEA
Annex XXIII OC3 studies.
FWrap_t0:FWrap_CalcO

 Aborting FAST.Farm.

I changed X0_low and Y0_low to include this position (-5, 0, 90) but it didn’t solve the problem.
I am using the example file for FAST.Farm, all I changed was Mod_AmbWind to 2 (to use the inflow module)

Here is the relevant part of the inflow file

------- InflowWind v3.01.* INPUT FILE -------------------------------------------------------------------------
Sample InflowWind input file.
---------------------------------------------------------------------------------------------------------------
False         Echo           - Echo input data to <RootName>.ech (flag)
1   WindType       - switch for wind file type (1=steady; 2=uniform; 3=binary TurbSim FF; 4=binary Bladed-style FF; 5=HAWC format; 6=User defined)
0.0                PropagationDir - Direction of wind propagation (meteoroligical rotation from aligned with X (positive rotates towards -Y) -- degrees)
1   NWindVel       - Number of points to output the wind velocity    (0 to 9)
0   WindVxiList    - List of coordinates in the inertial X direction (m)
0   WindVyiList    - List of coordinates in the inertial Y direction (m)
90   WindVziList    - List of coordinates in the inertial Z direction (m)
================== Parameters for Steady Wind Conditions [used only for WindType = 1] =========================
16   HWindSpeed     - Horizontal windspeed                            (m/s)
90   RefHt          - Reference height for horizontal wind speed      (m)
0   PLexp          - Power law exponent                              (-)

Can you help me with this?

Thanks in advance

Dear Eduardo,

From the error message, it appears that turbine #3 falls outside of its corresponding high-resolution domain. How is the high-resolution defined relative to the location of turbine #3? Can you attach your FAST.Farm input file?

Best regards,