of computer simulation of airflows around a rotor blade ©
Risoe National Laboratory, Denmark
turbines engineers use techniques such as stall,
which aircraft designers try to avoid at all costs. Stall is
a very complex phenomenon, because it involves airflows in three
dimensions on wind turbine rotor blades. (e.g. the centrifugal
force will induce an airflow which makes the air molecules move
radially along the rotor blade from its root towards the tip
of the blade).
3D computer simulations of airflows are rarely used
in the aircraft industry, so wind turbine researchers have to
develop new methods and computer simulation models to deal with
Computational Fluid Dynamics, or CFD, is a group of
methods that deal with simulating airflows around e.g. rotor
blades for wind turbines.
The picture shows a computer simulation of
the airflows and pressure distributions around a wind turbine
rotor blade moving towards the left.
A number of technologies known from the aircraft industry
are increasingly being applied to improve the performance of
wind turbine rotors.
One example is vortex generators,
which are small fins, often only about 0.01 metre (0.4 inch)
tall, which are fitted to the surface of aircraft wings. The
fins are alternately slightly skewed a few degrees to the right
and the left. The fins create a thin current of turbulent air
on the surface of the wings. The spacing of the fins is very
accurate to ensure that the turbulent layer automatically dissolves
at the back edge of the wing.
this creation of minute turbulence prevents the aircraft wing
from stalling at low wind speeds.
Wind turbine blades are prone to stalling
even at low wind speeds close to the root of the blade where
the profiles are thick.
Consequently, on some of the newest rotor
blades you may find a stretch of one metre or so along the back
side of the blade (near the root) equipped with a number of vortex
(Picture © LM Glasfiber A/S).