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IEAWindTask37 / IEA-15-240-RWT

15MW reference wind turbine repository developed in conjunction with IEA Wind
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Tower drag coefficient in AeroDyn15.dat #192

Closed maucollu closed 2 months ago

maucollu commented 6 months ago

Description

It is not so much as a bug, but a doubt about the value of the parametrt TwrCd in the Aerodyn15.dat file of the IEA15MW UMaine Semisub, section "Tower Influence and Aerodynamics".

The value is 0.5 for all the sections.

I suppose that the drag, evaluated quasi statically with a simple drag equation such as: D = 1/2 x air density x (relative wind velocity)^2 x reference area * C_d

where the reference area is the diameter of the tower multiplied by the height of the section of the tower considered.

If the above is correct, for a circular section, in post-critical regime, the C_d should be 1.0 (see, for example, DNV-RP-C205 (Sept 2021), Appendix E. Table E-1, geometry 14.

Have I misunderstood something?

Steps to reproduce issue

Please provide a minimum working example (MWE) if possible N.A.

Current behavior

TwrCd 0.5 in AeroDyn15.dat

Expected behavior

TwrCd 1.0 in AeroDyn15.dat

Code versions

N.A.

ptrbortolotti commented 6 months ago

Hello, Figure 6 here https://onlinelibrary.wiley.com/doi/pdf/10.1002/we.2703 suggests a value closer to 0.5 than 1.0

maucollu commented 6 months ago

Thanks a lot, @ptrbortolotti for the quick answer. Interesting study, indeed, the value seems to be lower than 1.0. I also noticed, though, that it states "Fortunately, most large downwind turbine will have large Reynolds numbers in the supercritical range, as shown by that for the SUMR-13, so that C_D = 0.7 is a good approximation". As far as I know, 0.7 is indeed the value at which it stabilises in post-critical regime, and some handbooks/recommended practices recommend to round it up to 1.0 as safety factor. Would you think that a value of 0.7 is more appropriate, based on the statement above?