13-11-2012, 06:06 PM
Wind rotor blade construction
blades_manual.pdf (Size: 331.67 KB / Downloads: 23)
This research on small wind energy systems for battery charging is the result of a
collaborative effort involving numerous contributors.
The project was managed by Intermediate Technology (known as The Intermediate
Technology Development Group or ITDG) under a contract to the UK Department for
International Development.
The overall international project was co-ordinated by Dr Smail Khennas, Senior
Energy Specialist from ITDG with support from Simon Dunnett. The field work in Peru
and Sri Lanka were respectively managed by Teodoro Sanchez and Rohan Senerath.
Teodoro Sanchez Campos (ITDG Peru), Sunith Fernando (Sri Lanka) and Hugh Piggott (a
UK technical consultant for the project), are the authors of this booklet on the rotor
blade manufacture.
The views expressed in this report are those of the authors and do not necessarily
represent the views of the sponsoring organisations, the reviewers or the other
contributors.
Introduction
The wind generator
This booklet is to assist manufacturers in make the blades, or ‘wind rotor’ for a small
wind generator. Another booklet tells how to build the permanent magnet generator
(PMG). The wind rotor will be fitted to the PMG. It turns the PMG, and the PMG
charges a battery.
The PMG and rotor blades have to be mounted on a ‘yaw bearing’ at the top of a tower
(usually made from steel pipe). The wind generator also needs a tail to make it face
the wind. The tail must also automatically turn the wind generator away from strong
winds to protect it from damage. The yaw bearing, tail and tower are not described
further in this booklet.
The two rotor designs
Here are the main features of the
two rotor designs described in this
booklet:-
SECTION
The ‘blade section’ is the shape of
the blade in cross-section (cut at
90 degrees). The NACA4412
section is made from two skins
with space between. The K2
section can be solid fibreglass
resin.
DIAMETER
The larger, 2.0 metre diameter rotor will sweep across more wind, and therefore it
can produce more power, in a given windspeed.
TIP SPEED RATIO
The ‘tip-speed-ratio’ is the speed at which the blade tip should run compared to the
windspeed. The shaft speed in revolutions per minute (rpm) depends on the tip speed
and the diameter.
Rpm = windspeed x tip-speed-ratio x 60 / (diameter x P)
The main reason why the two blade rotor can work at higher tip-speed-ratio is that it
only has two blades. The smaller, three bladed rotor will have a slower tip-speed, but
will run more smoothly because it has three blades.