NREL 5-MW

This document details how the NREL 5-MW reference wind turbine is implemented in Ashes.

The data in the  Blade shape file  in Ashes is taken from the AeroDyn file available on GitHub ( https://github.com/OpenFAST/r-test/blob/84616202adc19515e08b5c78f92448aa848e5f12/glue-codes/openfast/5MW_Baseline/NRELOffshrBsline5MW_AeroDyn_blade.dat , accessed January 2023).

There is an almost one-to-one correspondance between the Ashes file and the AeroDyn file, summarised in the table below:

Column name in Ashes	Column name in AeroDyn	Comment
Position	BlSpn
PrebendOutOfPlane	BlCrvAC
PrebendInPlane	BlSwpAC	The value in Ashes is the opposite of that in AeroDyn
Curvature angle	BlCrvAng
Twist angle	BlTwist
Chord length	BlChord
Airfoil nickname	BlAFID	The nicknames for the airoils have to match the airfoil list

the data in the  Blade structure file  in Ashes is taken from the BeamDyn file available on GitHub ( https://github.com/OpenFAST/r-test/blob/84616202adc19515e08b5c78f92448aa848e5f12/glue-codes/openfast/5MW_Baseline/NRELOffshrBsline5MW_BeamDyn_Blade.dat , accessed January 2023)

The data in the BeamDyn input file is in matrix form, while the data in Ashes in presented as columns. The BeamDyn matrix definition can be found in the BeamDyn manual accessible here:  https://openfast.readthedocs.io/en/main/source/user/beamdyn/input_files.html#blade-input-file  (matrices 4.62 and 4.63, accessed January 2023). Each structural cross section is defined by two matrices: a stiffness matrix  and a generalised sectional mass matrix .

The correspondance between Ashes and BeamDyn is summarised in the table below:

Column name in Ashes	Parameter in BeamDyn	Parameter name
BMassDen	m	mass density per unit span
FlpStff	EIFlp	Flap stiffness
EdgStff	EIEdg	Edge stiffness
GJStff	GJ	Torsional stiffness
EAStff	EA	Extensional stiffness
FlpInerDistr	iFlp	Flap mass moment of inertia
EdgInerDistr	iEdg	Edge mass moment of inertia

In BeamDyn, the position along the balde for which the matrices are provided is given just before each pair of matrix. That parameter is equivalent to the BladeFraction  column in Ashes.

Note that the BeamDyn file does not provide the structural twist of the blade. When defining the blade in Ashes, we have assumed that the structural twist is equivalent to the aerodynamical twist, interpolated from the AeroDyn file.