Page 27 - Energize Issue 1 2023

TECHNICAL

common multiblade versions have three to five blades, but
experimental versions have been created with up to 18 blades in a
ring mounting (see Figure 5a - d).
By comparing various combinations of blades, it has been
shown that a three-bladed version gives the best results, and
5
examples of these are available on the market. A commercial unit Figure 5: Multiblade SWT 4
producing 5 kW has a diameter of 1 m and a height of 1 m.

Blade shapes
Various different shaped blades have shown to improve the
efficiency of the VAWT. Examples are shown in Figure 6.
Figure 6: Different blade shapes 7
Helical blade
The diameter of the SWT is limited by the restrictions on wing tip
speed, but this limitation is overcome by making the length of the
SWT much greater than the diameter. This also favours the helical
design and allows for a gradual helix. The helical blade version
was developed in an attempt to reduce torque ripple. The blade
is of a helical form, arranged so that there is always a blade edge
facing into the wind. (Figure 7). While the helical blade always
offers a drag surface facing into the wind, there is less drag due to
the angled surface so that the surface facing into wind is always
smaller than it appears. Typically designs are two-bladed, although Figure 7: The helical SWT 2
three-bladed versions are available, and the helical version has a
high length-to-width ratio.
Darrieus model
The Darrieus model uses aerodynamics to produce lift which turns
the rotor. The basic shape is given in Figure 8 for a two-bladed
version. The most common version for urban applications is the
H-configuration, which can be either straight- or helical-bladed.

The helical DWT
The helical configuration is perhaps the most interesting, since
it allows a longer aerofoil blade to be contained within the same Figure 8: Two-bladed Darrieus wind turbine 2
rotational area as a straight-bladed turbine, thereby capturing
more of the wind and increasing efficiency. The helical version is
the most common small Darrius turbine on the market.

Hybrid VAWT
There are several hybrid units on the market that combine drag
and lift principles, with a central multi-blade drag section and
outer lift section (see Figure 10).

Indirect powered wind turbine
A recent development does not use the wind directly but uses
an arrangement of aerofoil blades to create airflow in a manifold Figure 9: Helical 3-blade DWT 2
where a radial turbine generates electricity. The unit, designed
and manufactured by Aeromine, is shown in Figure 11. This design
provides an effective way to harness even moderate wind to
create energy for large, flat rooftop buildings such as warehouses,
data centres, office and apartment buildings. These could be used
to supplement solar panels on a flat-roofed building.
This technology does away with traditional wind turbine
blades by using a pair of vertically mounted aerofoils (or wings).
The turbine has two separate flow streams. The external aerofoils Figure 10: Hybrid VAWT 6

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