FAST Simulation in yawed flow conditions

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Piero.Mazza
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Joined: Fri May 31, 2019 12:13 am
Organization: TU Delft
Location: The Netherlands

FAST Simulation in yawed flow conditions

Postby Piero.Mazza » Sat Jun 01, 2019 1:18 am

To whom it may concern,
I need to run a FAST simulation in yawed flow conditions in order to see the resultant perturbations in the AoA. I tried to either change the parameter PropagationDir and HFlowAng in the InflowWind subfunction, but the former results in really large values while the latter has almost no influence, even with large yaw angles. I also tried to disable the YawDOF and setting a constant NacYaw value (in the ElastoDyn subfunction), but again, it seems to have no influence on the perturbations of the AoA. Could anybody please tell me how to perform such a simulation? Probably there is something i'm doing wrong.

with Kind Regards,
Piero.

Jason.Jonkman
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Location: Boulder, CO
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Re: FAST Simulation in yawed flow conditions

Postby Jason.Jonkman » Mon Jun 03, 2019 7:04 am

Dear Piero,

I would think all three of these changes would result in an oscillatory variation of AoA. So, I'm not sure why you are seeing "almost no influence" in two out of the three approaches. Are you rerunning FAST after changing each input and post-processing the correct output files?

Just one comment: It would better to change PropagationDir in InflowWind rather than HFlowAng in TurbSim. The former rotates the entire wind domain (full-field wind planes) while the latter only adds a transverse component to the wind vectors, leaving the full-field planes to march downwind at the zero-degree wind direction (the Taylor's frozen turbulence assumption is bit off when changing HFlowAng).

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

Piero.Mazza
Posts: 3
Joined: Fri May 31, 2019 12:13 am
Organization: TU Delft
Location: The Netherlands

Re: FAST Simulation in yawed flow conditions

Postby Piero.Mazza » Mon Jun 03, 2019 8:12 am

Dear Jason,
Thank you for the response. Yes, i am post-processing the correct output files. My problem is that by setting a PropagationDir value of 25 (which i am ssuming correspondent to a yaw misaligment angle of 25°) the standard deviation of the AoA (e.g. for a wind speed of 17 m/s) is around 13° for a radial position of r/R = 0.4 and about 4° at r/R = 0.95. By performing the difference between the Maximum AoA and the Minimum AoA over a revolution, the situation gets worst, because the values are around 35° for r/R = 0.4 and 11° for r/R = 0.95. Both cases with a descending trend in the intermediate radial positions.

These values seem to be large to me, can i please have your opinion? (I am running the NREL5MW wind turbine for 360s and i am excluding from the analysis the first 180s of outputs to avoid transient behavior)

On the other hand, by changing the HFlowAng and NacYaw values even with 45°, the standard deviation of AoA was less than 1°. This is why i am a bit confused of which value actually represents the Yaw Angle in the simulations and i feel there is something i am doing wrong.

Kind Regards,
Piero.

Jason.Jonkman
Posts: 4224
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: FAST Simulation in yawed flow conditions

Postby Jason.Jonkman » Mon Jun 03, 2019 10:54 am

Dear Piero,

I'm not sure what you are doing differently, but I just ran three 60-s cases of the land-based NREL 5-MW turbine as follows:
    1) Test18 unchanged (includes turbulence at 12 m/s mean wind speed, but without a mean yaw error)
    2) Test18 with PropogationDir = 20deg
    3) Test18 with YawDOF=False and NacYaw=-20deg

With these simulations, I get an AoA range of about 10deg for (1) and 18deg for (2) and (3) at about 40% span and an AoA range of about 8deg for (1) and 10deg for (2) and (3).

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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