I need to calculate the deflection of a 7m blade, and I've tried to simplify the blade as tapered beam and then derived deflection low for it , but this law gave deflection half of the experimental value.
Hello. If you give us more information what the simple model you use, we can discuss more clearly. :-)
Here, I link a NASA technical report. Moment-curvature relation is presented in Eq. (11-3). Using it, you can calculate displacement in y axis. Good Luck!
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20090029330.pdf
A proper wind turbine blade is tapered and also twisted. Its thickness varies along its longtudinal axis. Due to its aeorfoil cross section, its bening and torsion is coupled. Edgewise bending and flapwise bending often occur at the same time. To consider all these, there is no formula. You have to use a structural analysis software package to do the analysis, unfortunately.
My guess on why your theoretical result is poor is mainly due to bending-torsion coupling and neglect of twist and thickness variation.
Dear Huajiang,
I want to get deflection formula to use it in Buckinghum Pi theorem to get dimensionless ratio between the 7m blade and similitude of 0.30m ..
This can help me to predict the displacements of the larger blade by using this small similtude and hence validating the FE model of the large blade!
What do you suggest?
In addition with the fluctuating loads and the bending - torsion coupling, i think mass distribution also has to be taken into account. the spanwise ( along the chord length ) and the blade length wise. The coupling of the spanwise bending with the length wise bending would give different results than that of a simplified taper.
There is not such a thing as a "formula"... If you plan to model seriously the blade structural behavior you must use a numerical approach based on beam or shell finite elements, including composite material constitutive laws, aeroelasticity and multibody dynamics.
Tapered beams have a non trivial behavior and need accurate modeling. You can try with the model described in the attaced paper
Article Non-prismatic Beams: a Simple and Effective Timoshenko-like Model
- Badges
- Science topic