Aerodynamic Drag Coefficient for 15MW Tower

Wind & Water Computer-Aided Engineering Software Tools
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Hello Forum Members,

I’m currently conducting numerical simulations using the 15MW Reference Wind Turbine (RWT), and I’ve encountered a question I hope to get your insights on.

Specifically, I am applying the 15MW RWT to a fixed-bottom offshore wind structure, and would like to clarify the appropriate aerodynamic drag coefficient for the tower.

As part of my parked condition simulations under a wind speed of 46.8 m/s, I tested two different aerodynamic drag coefficients for the tower: 1.0 and 0.5.

I observed that the maximum loads (Fx, Fy, Fz) and moments (Mx, My, Mz) at the tower base differed by approximately 1.5 times, depending on the coefficient used.

To clarify this, I referred to the DNV guidelines, which recommend using a drag coefficient of 1.0 for cylindrical structures.

However, when reviewing the OpenFAST 15MW IEA RWT model, I noticed that the aerodynamic drag coefficient applied to the tower is 0.5, as shown in the input files (AeroDyn15.dat).

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I would like to ask:

  • Is there a specific reason or reference behind using 0.5 in the 15MW RWT OpenFAST model?
  • What drag coefficient values do other users typically apply for tower aerodynamic loads in parked conditions?

Any insights or references would be greatly appreciated.

Thank you!
Jisu Lim.

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Hi Jisu Lim,
Cd of 0.5 and 0.6 are commonly used in aeroelastic models. This paper https://onlinelibrary.wiley.com/doi/pdf/10.1002/we.2703 is a good resource justifying these values. You are correct that if you have low Reynolds along your tower (a very skinny tower maybe?) then Cd can probably be higher. What Re do you measure?
Regards,
Pietro

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To Pietro Bortoloitti,

Thank you so much for your prompt response to my question.

The Reynolds number for the model I’m working on is approximately Re ≈ 3.1×10⁷.

Your reply was very helpful for modeling the numerical simulation.

The NREL forum has been an incredibly valuable resource for my offshore wind research.

Thank you again.

Jisu Lim

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