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Re: NREL 5-MW reference turbine - CP, CQ, CT Coefficients

Posted: Thu Oct 24, 2019 4:16 am
by Jon.Martinez
Dear Jason,

Thank you very much for your anserwer.

Best regards,

Jon Martínez Rico

Re: NREL 5-MW reference turbine - CP, CQ, CT Coefficients

Posted: Thu Feb 27, 2020 3:14 am
by Chenxu.Zhao
Dear Jason,

I have some doubts about thrust of NREL 5MW given in this article [Definition-of-a-5-MW-reference-wind-turbine-for-offshore-system-development](Figure 9-1. Steady-state responses as a function of wind speed).

I used ORIGIN to obtain the data of RotThrust vs wind speed, and then it was easy to get the CT(coefficient of thrust, the black line) with the formula(air density=1.225, Ad=3.1415*63^2)

At the same time, I used FAST to calculate Ct in different average wind speed ranged from 3-25 m/s(the red line).

The strange things is that those 2 line has huge difference. Why has this happened? Is it normal Ct is as high as 2.5?

Best regards,
Chenxu.Zhao

Re: NREL 5-MW reference turbine - CP, CQ, CT Coefficients

Posted: Thu Feb 27, 2020 6:49 am
by Jason.Jonkman
Dear Chenxu.Zhao,

The FAST (ElastoDyn) output RotThrust is the reaction force transmitted from the rotor to the shaft, so, not only includes the applied aerodynamic forces, but also the forces resulting from rotor weight (and in transient analysis, rotor inertia); see related forum posts on this topic. So, normally, RotThrust is shifted upward relative to the aerodynamic applied Thrust. If you are using AeroDyn v15, you can output the aerodynamic applied rotor thrust via AeroDyn output RtAeroFxh.

Best regards,

Re: NREL 5-MW reference turbine - CP, CQ, CT Coefficients

Posted: Sun Mar 29, 2020 2:48 am
by Chenxu.Zhao
Dear Jason,

Thank you so much for your answer, sir! That had really solved most of my confusions.

But there is still one little problem. The red line was exactly caculated by using your method of getting 'RtAeroFxh' from FAST. And still when wind velocity equals 3m/s, the CT is somewhat higher than 1 as 1.1 . If this is the right way to do it, then what's the reason for this abnormal phenomenum? From the textbooks I have read, they told me that CT was not allowed to be more than 1.

Best regards,
Chenxu.Zhao

Re: NREL 5-MW reference turbine - CP, CQ, CT Coefficients

Posted: Mon Mar 30, 2020 6:28 am
by Jason.Jonkman
Dear Chenxu,

Actually, the aerodynamic thrust is able to exceed 1, but in this situation, flow will recirculate around the rotor and momentum theory no longer applies. At high thrust, AeroDyn uses Glauert’s empirical correction with Buhl’s modification in place of momentum theory.

Best regards,

Re: NREL 5-MW reference turbine - CP, CQ, CT Coefficients

Posted: Mon Mar 30, 2020 6:50 am
by Chenxu.Zhao
Dear Jason,

Thanks again! It turns out I need to do more researches about the theories used by FAST. Your guidence is really useful to me.

Best regards,
Chenxu.Zhao