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For 2000 years, watermills and windmills have been employed to produce energy. This energy has been used to mill grain, pump water, saw wood and, since the late 1880s, to generate electricity. Industry and governments are currently seeking alternate sources of power, and wind energy is in high demand.
(Published on May 2008 – JEC Magazine #40)
ANDREW REKRET, PRESIDENT MASTERCORE SYSTEM LTD.
Mastercore has developed a ground-breaking unibody design for windmills or airmills which requires neither external frame nor internal strut.
As air flows over wings, it creates a boundary layer - a very thin layer of air lying over the surface of the wing. This layer is smooth as air begins to travel over the wing. As the boundary layer approaches the centre of the wing, however, it becomes more turbulent, creating drag and slowing the speed of airflow. The point at which this occurs is called the transition point (figure 1).
A smooth blade causes noise, instability, and can lead to a loss of energy. Mastercore has engineered its product to address the problem of turbulence by looking to nature for the solution.
Biomimicry is a new discipline that studies nature’s best inventions, and then imitates these designs and processes to solve human problems. The study of marine life and how water flows over various types of flippers can be applied in wind technology. Whales, for example, have tubercles on their flippers. As whales move through the water, the tubercles disrupt the line of pressure against the leading edge of the flipper. The row of tubercles sheers the flow of water and redirects it into the scalloped valley between each tubercle, causing swirling vortices that roll up and over the flipper to actually enhance lift properties.
Mastercore has further utilized biomimicry by carefully studying the world’s best flying machines: birds (figure 2). A superior blade has been developed by conducting engineering investigations, incorporating changes in the geometry, and analysing how the role of sculpture in leading edges and wing surfaces can improve lift and reduce drag. The owl’s feathers allow it to fly silently. It is the only bird whose plumage design has many small saw-toothed feathers protruding from the outer rim of their primary feathers. These saw-toothed, or “serration” feathers, generate small vortexes in the airflow, breaking up the larger vortexes that are noisier. As with all birds’ wings, the grooves and feather geometry keep air flow attached to the wing’s surface, which automatically reduces stall.
Blade shape and turbine design
Mastercore’s turbine consists of three vertical aerofoil blades which have a helical twist of 120 degrees similar to a DNA chain (figure 3). This design reduces drag since the wind pulls each blade around on both the windward and leeward sides of the turbine to spread the torque evenly over the entire revolution. The air flow is not disrupted and moves closer to the blade surface.
This design not only prevents destructive pulsations but the extra lift and reduced drag improve performance by as much as 30% compared with a similar smooth design. The blade not only gathers energy from the push on the front side but is actually pulled forward on the back side through a lift effect, similar to the principle that causes lift on a bird’s wing. The back pressure on the blades creates a vortex that pulls the blades around, turning the drag into positive forward movement.
Mastercore’s design allows the incorporation of multiple blades inside each other to take advantage of different air behaviour. The first layer of blades generates low pressure and channels the air flow to increase speed and in a specific direction. This flow pattern is directed with all its energy onto the second and any subsequent layer under low pressure. By using blades with this unique layered design, air is used much more efficiently thereby producing more energy (figure 4).
The essential feature of the Mastercore designed wind technology is the use of patented fibre reinforced skins with a structural foam core, which is a first in the wind energy market. A ground-breaking automated technology allows for the efficient, cost-effective mass production of complex 3D shapes and forms. The blades are made in pieces and joined together on site. The Mastercore design allows wind turbines to be scaled up easily in the installation process, resulting in much cheaper electricity (figure 5).
The foam core provides a microcellular structure that acts like a skeleton: highly distributing forces with an extremely efficient strength-to-weight ratio. The light weight of the foam core allows for the shaped blades and supports skins with complex 3D grooves, plates and segmented feather-like skin, where the plates overlap like the layers of a bird’s feathers.