Wind farm modeling by using FAST and TurbSim

Discuss the effects of turbulence on wind turbines and its simulation.

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Goran.Mandic
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Wind farm modeling by using FAST and TurbSim

Postby Goran.Mandic » Sat Jan 15, 2011 10:26 pm

Hi,

I built a wind turbine model using FAST with Simulink for electrical part of the system and controls. I use TurbSim to generate wind profiles for this model.
Now, I want to simulate a whole wind farm. I plan to run simulations sequentially (i.e. one for each wind turbine) and to aggregate the power outputs to get the total power of the wind farm. However, I'm not sure what would be the best method to generate TurbSim wind profiles for such a simulation in order to obtain
results that are as close as possible to the realistic wind farm.
One idea would be to use the same TurbSim input file (same mean wind speed and turbulence level) and to generate a wind data file for each turbine.
Another method would be to slightly change mean wind speed and turbulence level for each wind profile.
Which one would be better for the purpose I described?
The number of turbines in the wind farm that I would like to simulate is 15-20. However, I would like to capture effects of space distribution of wind turbines,
rather than just scale up the output of one turbine.

Thanks,

Goran

Jason.Jonkman
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Re: Wind farm modeling by using FAST and TurbSim

Postby Jason.Jonkman » Mon Jan 17, 2011 10:55 pm

Dear Goran,

Unfortunately, FAST/AeroDyn and TurbSim are not currently set up to model interacting turbines in a wind farm.

The main influences of wind farm arrays are wake deficits, increased turbulence, and meandering wake impingement on the various turbines in the farm, which reduce overall power output and increase structural loads. NREL is currently working on developing an interface between FAST and CFD software, so that the wake and array effects can be modeled using CFD. We are also looking into adding a meandering wake model to FAST/AeroDyn. Until those tools are available, however, you are limited in what you can do with FAST/AeroDyn and TurbSim. The Frandsen model for increased turbulence in a wind farm described in Annex D of the IEC 61400-1 Ed. 3 wind turbine design standards could presumably be applied to derive an "effective turbulence" that could be input in TurbSim for use by FAST/AeroDyn, but NREL has not yet developed any scripts to automate this process.

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Daniel.Kim
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Re: Wind farm modeling by using FAST and TurbSim

Postby Daniel.Kim » Tue Feb 16, 2016 4:46 pm

Dear Dr. Jason.

Regarding the tower wake effect, I have a question.

I read the following from "Aerodyn theory manual"

"The influence of the wind turbine tower on the blade aerodynamics is also modeled in AeroDyn.
The tower influence model is based on the work of Bak, et al. (2001). This model uses a
potential flow solution around a cylinder as the base flow field along with a downwind wake
model dependent on tower drag coefficient (based on diameter), Cd, and a tower dam model for
upwind influence. The model provides the influence of the tower on the local velocity field at all
points around the tower, including increases in wind speed around the sides of the tower and the
cross-stream velocity component in the tower near flow field."


It seems that the existence of tower changes the original wind velocity field around the tower.
Does it mean that the velocity deficit and increase of TI caused by the wake effect of tower is implemented through Aerodyn?

Sincerely,
Daniel Kim.

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Re: Wind farm modeling by using FAST and TurbSim

Postby Jason.Jonkman » Wed Feb 17, 2016 10:35 am

Dear Daniel,

The tower-influence and tower-shadow models in AeroDyn augment the flow local to the blade based on the influence of the tower. While the tower-shadow model is purely a deficit, the potential-flow tower-influence model can include both a velocity deficit and a speed-up depending on where the blade is in the flow relative to the tower. However, neither model includes an increase of the turbulence intensity (TI).

Regardless, these tower models are entirely different from my post above dated Jan 17, 2011, which pertained to wake and array effects between turbines in a wind farm, which are dominated by rotor wakes and background turbulence (not tower effects).

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Daniel.Kim
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Re: Wind farm modeling by using FAST and TurbSim

Postby Daniel.Kim » Wed Feb 17, 2016 2:52 pm

Dear Dr. Jason.

Then, isn't the wind velocity deficit and increase of TI caused by rotor wake implemented in FAST?
In 2011, it looks impossible as shown in above posting. How about now? In the above posting, you wrote that NREL had the plan to add the meandering wake model.

I appreciate your help.

Sincerely
Daniel Kim.

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Re: Wind farm modeling by using FAST and TurbSim

Postby Jason.Jonkman » Wed Feb 17, 2016 3:00 pm

Dear Daniel,

Currently, FAST can be used to model wind farm wake and array effects (including wake velocity deficits and increased TI) when used in conjunction with SOWFA (high fidelity) or DWM (mid fidelity).

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Arash.HemmatiTopkanloo
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Re: Wind farm modeling by using FAST and TurbSim

Postby Arash.HemmatiTopkanloo » Mon Mar 07, 2016 3:57 pm

Dear Jason,

I am trying to produce full-filed wind profile (bts file) in Turbsim in order to use in FAST for finding Fatigue of Foundation. I am just generating aerodynamic loads without hydrodynamic loading ( I will include hydrodynamic loading later on in SESAM).

I have directionally scatter diagram and trying to change wind direction in Turbsim. Basically direction of my foundation is constant. I just need to analyse it for different wind directions. But I cant see any option in Turbsim to change wind direction. I have seen in Hyrdo.dyn I can change wave direction, but I can not find this option for wind loading.

I would be grateful if you could give me a hint. Thank you very much.

Best Regards,

Arash Hemmati,

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Re: Wind farm modeling by using FAST and TurbSim

Postby Jason.Jonkman » Mon Mar 07, 2016 4:38 pm

Dear Arash,

When using FAST/TurbSim, the wind direction is specified in FAST, not TurbSim; thus, the same wind file can be used for different wind directions. With the release of InflowWind v8 in FAST v8.12, the wind direction is specified within the InflowWind module (independently from the nacelle-yaw angle). In older versions of FAST, the wind direction was fixed at 0 degrees; instead, a yaw error (a wind direction not aligned with the rotor) could be defined by specifying a nacelle-yaw angle, rather than the wind direction.

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Arash.HemmatiTopkanloo
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Re: Wind farm modeling by using FAST and TurbSim

Postby Arash.HemmatiTopkanloo » Thu Mar 10, 2016 12:20 pm

Jason.Jonkman wrote:Dear Arash,

When using FAST/TurbSim, the wind direction is specified in FAST, not TurbSim; thus, the same wind file can be used for different wind directions. With the release of InflowWind v8 in FAST v8.12, the wind direction is specified within the InflowWind module (independently from the nacelle-yaw angle). In older versions of FAST, the wind direction was fixed at 0 degrees; instead, a yaw error (a wind direction not aligned with the rotor) could be defined by specifying a nacelle-yaw angle, rather than the wind direction.

Best regards,


Hi,

Thank you very much for your reply.

I started to use FAST v8.12 and I am changing wind direction in inflowWind input file. My question is that whether I need to change nacelle-yaw angle in the Elastodyn input file as well?

For example, when Wind is approaching from 30 degrees, do I need to change nacelle-yaw angle to 30 degree ?

I am specifying nacelle-yaw angle equal to wind propogation direction, but it gives me error whenever I specify nacelle-yaw angle to non-zero value.

I would be grateful if you could give me a hint.

Thank you,

Best Regards,

Arash Hemmati,
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Jason.Jonkman
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Re: Wind farm modeling by using FAST and TurbSim

Postby Jason.Jonkman » Thu Mar 10, 2016 2:50 pm

Dear Arash,

If you change the wind direction (PropagationDir) without changing the nacelle-yaw angle (NacYaw), then you'll introduce a yaw error (a wind direction not aligned with the rotor). Whether you want to do this or not depends on your analysis needs. Please note that PropagationDir and NacYaw have different sign conventions, so if you want to maintain zero error, you should set NacYaw = -PropagationDir.

Regarding the FAST error, when you changed NacYaw, did you also change YawNeut in the ServoDyn input file? While NacYaw is the initial yaw angle, YawNeut sets the neutral yaw position (the yaw angle where there would be no yaw moment). With the yaw degree-of-freedom (DOF) enabled and a large yaw spring (as set e.g. for the NREL 5-MW turbine), a large difference between NacYaw and YawNeut will generate a large yaw moment that will want to quickly move the nacelle back to the neutral angle, which would likely cause a problem with the model (as you are seeing). Thus, I recommend that you disable the yaw DOF or set YawNeut = NacYaw.

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Arash.HemmatiTopkanloo
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Location: Portugal

Re: Wind farm modeling by using FAST and TurbSim

Postby Arash.HemmatiTopkanloo » Thu Mar 10, 2016 3:18 pm

Jason.Jonkman wrote:Dear Arash,

If you change the wind direction (PropagationDir) without changing the nacelle-yaw angle (NacYaw), then you'll introduce a yaw error (a wind direction not aligned with the rotor). Whether you want to do this or not depends on your analysis needs. Please note that PropagationDir and NacYaw have different sign conventions, so if you want to maintain zero error, you should set NacYaw = -PropagationDir.

Regarding the FAST error, when you changed NacYaw, did you also change YawNeut in the ServoDyn input file? While NacYaw is the initial yaw angle, YawNeut sets the neutral yaw position (the yaw angle where there would be no yaw moment). With the yaw degree-of-freedom (DOF) enabled and a large yaw spring (as set e.g. for the NREL 5-MW turbine), a large difference between NacYaw and YawNeut will generate a large yaw moment that will want to quickly move the nacelle back to the neutral angle, which would likely cause a problem with the model (as you are seeing). Thus, I recommend that you disable the yaw DOF or set YawNeut = NacYaw.

Best regards,


Dear Jason,

Thank you very much for your reply.

I did based on your reply and now it is working. But which approach should I use? Disabling DOF or setting
YawNeut = NacYaw. I reckon the latter approach seems more realistic.

Thank you again.

Best Regards,

Arash Hemmati,

Jason.Jonkman
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Re: Wind farm modeling by using FAST and TurbSim

Postby Jason.Jonkman » Thu Mar 10, 2016 3:25 pm

Dear Arash,

Yes, the later is likely more realistic.

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Arash.HemmatiTopkanloo
Posts: 47
Joined: Mon Apr 20, 2015 3:35 am
Organization: University of Lisbon
Location: Portugal

Re: Wind farm modeling by using FAST and TurbSim

Postby Arash.HemmatiTopkanloo » Mon May 30, 2016 4:46 pm

Dear Jason,

I have a question about Meteorological Boundary Conditions in Turbsim.

I am trying run simulations for Fatigue and my wind data is turbulence intensity in percentage for each wind speed bin. As a compromise between IEC-3 and IEC-1, distribution of turbulence intensity is taken from a project (Noordzeewind OWEZ) that lies between IEC-3 and IEC-1 curves).

So, basically I need to change IECturbc (Turbulence intensity in percentage) and Uref (wind speed) (the only values and data I have)
But I am not sure about TurbModel. I dont know if I need to select "IECKAI"=Kaimal, "IECVKM"=von Karman,or none?


Thank you very much for your help.

Best Regards,

Arash,

Jason.Jonkman
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Re: Wind farm modeling by using FAST and TurbSim

Postby Jason.Jonkman » Wed Jun 01, 2016 1:54 pm

Dear Arash,

I'd recommend setting TurbModel to "IECKAI". The von Karman spectrum has lost favor in the IEC and is not included in newer editions of the standard.

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov


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