Hello everyone,

I am running FAST simulations for the NREL 5 MW turbine model at a steady wind speed of 12 m/s with aerodyn parameters shown in the below table. It rotates at a speed of 12.1 rpm with a pitch angle of 2.74 degrees when I used aeordynamic coefficients calculated for the aerofoils using CFD simulations.

## AERODYN v15.03 input parameters

##
1 WakeMod - Type of wake/induction model (switch) {0=none, 1=BEMT}

2 AFAeroMod - Type of blade airfoil aerodynamics model (switch)

{1=steady model, 2=Beddoes-Leishman unsteady model}

True TipLoss - Use the Prandtl tip-loss model? (flag) [used only when WakeMod=1]

True HubLoss - Use the Prandtl hub-loss model? (flag) [used only when WakeMod=1]

True TanInd - Include tangential induction in BEMT calculations? (flag)

[used only when WakeMod=1]

True AIDrag - Include the drag term in the axial-induction calculation? (flag)

[used only when WakeMod=1]

True TIDrag - Include the drag term in the tangential-induction calculation? (flag)

[used only when WakeMod=1 and TanInd=TRUE]

When I run the NREL 5 MW onshore model (Test26 case) with above parameters, I get a distribution of Tangential force (to plane) per unit length along the Blade 1 (Using B1NjFy at 19 aero nodes as outputs in the Aerodyn file) as shown in the Figure 1 attached.

If I integrate this force distribution, I get a torque value of 1.3064e6 N-m.

Then its Rotor torque = 3*1.3064e6

= 3.9191e6 N-m

Rotor power = Rotor torque * omega

= 3.9191e6 * (2*pi*12.1/60)

= 4.9659 MW

I used ‘GenPower’ as an output from the Sevodyn file and ‘RotTorque’ as an output from the ElastoDyn_BDoutputs file, their values from the output file are given below.

GenPower = 5000 kW

RotTorque = 4200 kN-m

From the above output value of RotTorque, its rotor power can be calculated as

RotorPower = RotTorque * omega

= 4200*10^3 * (2*pi*12.1/60)

= 5.321 MW

This turbine generates its rated power at 12 m/s and as per the generator efficiency of 94.4% these values are correct.

I have following questions on the outputs from FAST simulations.

- When I enable the tip loss factor, I would expect a zero value for the tangential force at the tip something like shown in the atatched Figure 2. Are there any mistakes in my inputs ?

- Why there is a difference in the torque value computed from the integration of tangential force Fy output values from Aerodyn and torque value output from the Elastodyn_BDoutputs file ?

I attached Aerodyn, Servodyn, Elastodyn_BDoutputs, InflowWind files used for the simulations to this post.

Can anyone help me where exactly the issue is.

Thanks in advance

Sudhakar Gantasala

Input_files.zip (10.8 KB)