Dear all,

I am currently modelling in OpenFAST a turbine where I have the blade geometry and aerofoil characteristics (polars and shapes).

However, I do not have the structural properties available. In order to perform aeroelastic simulations I plan on using the NREL 5MW structural properties from [1] for the tower and blade. The doubt I have is on the scaling method to use. The blade I have is 45m long and the rated power is 2MW.

Knowing that:

FlpStff = double integral of E(x,y) * x^2 dxdy

EdgStff = double integral of E(x,y) * y^2 dxdy

The stiffness seems to vary with the square of the surface. To define the scaled down stiffness coefficient I then used the ratio of the sectionnal areas, at the same r/R position, squared times the stiffness coefficient:

FlpStff_new_i = (Area_i_new_turbine / Area_i_NREL)^2 * FlpStff_NREL_i

Where:

FlpStff_new_i: is the scaled down flapwise stiffness coefficient for “my” turbine

i: is the same radial position (between 0 and 1) e.g. 50% span

Area_i_new_turbine: is the aerofoil cross sectional area in m^2 of “my” turbine

Area_i_NREL: is the aerofoil cross sectional area in m^2 of the NREL 5MW turbine

FlpStff_NREL_i: is the flapwise stiff corresponding to the spanwise position, e.g. 5% span.

The approach is then repeated for the edge stiffness and for the tower (since the tower diameter and height changes).

Using this approach I am able to ignore the issue of similarity in strains or stress, since I do not possess the targeted values. The aim was to use purely a geometrical approach.

Is this approach correct ? If so, is the ratio as defined above correct or should it be modified ?

Thanks for any help provided!

Best regards,

Thomas

[1] J. Jonkman, S. Butterfield, W. Musial, and G. Scott, ‘Definition of a 5-MW Reference Wind Turbine for Offshore System Development’, NREL/TP-500-38060, 947422, Feb. 2009. doi: 10.2172/947422.