Hi everyone, I’m investigating the relationship between blade tip deflection and wind speed under NTM load case of NREL 5 MW Onshore reference wind turbine with the SNL61p5m blade. I’m currently using OpenFAST v3.5.0 with ElastoDyn and AeroDyn v15.
Given each 10-min average wind speed U10 , I use TurbSim to generate wind field with a FIXED random seed. Then I use OpenFAST to perform 700s simulation, where the first 100s output is discarded to avoid start-up transient. The maximum value of “OoPDefl1” from ElastoDyn is used as the blade tip deflection.
In the initial condition of ElastoDyn, I modified the OoPDefl, IPDefl, BlPitch and RotSpeed according to the following figures referring from the document “Definition of a 5-MW Reference Wind Turbine for Offshore System Development”
I got the result in the following figure. It can be observed that for wind speed above 15 m/s, the relationship between tip deflection and wind speed is rather smooth. However, for wind speed below 15 m/s, this relationship becomes non-smooth and shows a little bit “chaos” . Does anyone know the reason or how to fix this?
Thanks in advance!
Tongzhou Zhang
Dear @Tongzhou.Zhang,
You mention that you are plotting the maximum value of OopDefl1, rather than mean value. If you plot the mean value, is the result smoother and more aligned with Figure 9-1 from the NREL 5-MW specifications report that you copied?
I would generally expect the mean value with turbulence to match reasonably well with the steady-state solution. The maximum value can be sensitive to specific conditions, and rather than looking at a single maximum, I would look at several maximums across different seeds to ensure that the overall maximum value is relatively converged.
Best regards,
Dear Jason,
Thank you for your kindly response. I plot the mean value in the following figure. It can be observed that the result is much smoother. However, the maximum average OoPDefl only reaches 2.593m in my figure, while in the Figure 9-1 from the NREL 5-MW specifications report, the maximum OoPDefl exceeds 5 m. The reason might be that I’m using the SNL 61p5m blade rather than the original blade in NREL 5-MW turbine, I guess.
I’m actually doing ultimate analysis of wind turbine blade, so it is the maximum OoPDefl rather than the mean value that I care about. I will try using different seeds to get an overall maximum, but it may take some time. I’ll come back when there is any result.
Best regards,
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Hi everyone,
I used 6 fixed seeds. For each seed, a maximum OoPDefl1 in 10-min simulation could be obtained. The six maximum OoPDefl1’s are averaged to get the final result, as plotted below.
It is much smoother compared with the originally posted result above.
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