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Propeller turbines convert fluid or gas flow into rotary motion, with wind and hydraulic propellers being the two main types. They are used to generate electricity and mechanical work, with wind turbines being horizontal or vertical axis. Water propeller turbines, such as the Kaplan turbine, are commonly used in hydroelectric plants. Propeller turbines are cost-effective and environmentally friendly, and advances in technology are making them more efficient and accessible.
A propeller turbine belongs to a group of machines that convert the energy of fluid or gas flow into rotary motion. As this description indicates, these machines fall into two basic categories: wind turbines or hydraulic propellers. The rotational force produced by these machines is most commonly used to generate electrical power and, to a lesser extent, to provide mechanical work. Common examples of mechanical working variants of the propeller turbine are windmills and some types of watermills. Due to the abundant, renewable and economical nature of the propeller turbine energy source, it is one of the most cost-effective and environmentally friendly methods of energy production ever devised.
A propeller turbine applies conventional propeller theory in reverse to harness the kinetic energy latent in gas and fluid streams. Propellers consist of a central shaft with a minimum of two opposed airfoil-shaped blades or vanes attached to it. These are usually spun by an external energy source to produce thrust by pushing or displacing air or liquid on the blades. In a propeller turbine, this principle is turned upside down; a stream or air or liquid moves the blades causing them to rotate the shaft.
Wind turbines are used extensively around the world to harness wind energy to generate electricity, run mills or pump water. Wind-driven propeller turbines can be horizontal or vertical axis. The most easily recognizable variant is the horizontal axis turbine which includes traditional windmills and wind generators with aircraft-type propellers. Equally effective are next-generation vertical-axis designs that feature flat or curved lugs that drive a vertical shaft. These include the curved Savonius blade, the Giromill flat blade and the distinctive Darrieus “egg beater” types.
Older horizontal turbines require the turbine head to always face the wind. In the case of smaller examples, a simple weather vane-style rudder turns the revolving turbine head. Larger turbines use a system of wind sensors and servo motors to keep the propeller turned into the wind. Most wind-driven propeller turbine designs use a gearbox to drive the generator or pump crank at the correct speed.
Water propeller turbines are commonly associated with large hydroelectric generating plants, although there are several smaller industrial and agricultural applications. These turbines function in the same way as their wind-powered sisters, although their basic design differs substantially. These machines are usually much larger and feature blade designs that are usually shorter than wind-driven variants. The most common of these larger water turbines is the Kaplan turbine. Kaplan turbines are low-head, high-flow reaction units used in most large hydroelectric plants.
The Kaplan variant features angle-adjustable blades resulting in efficiency levels typically in excess of 90% over a wide range of flow and water level conditions. Much of the efficiency is achieved through a carefully engineered water flow path that causes the outgoing fluid to decelerate. This deceleration leads to a transfer of the maximum amount of kinetic energy to the propeller mechanism. Kaplan turbines can produce outputs of 100 megawatts (100,000,000 watts) or more.
The propeller turbine taps into renewable sources of energy and is either free or extremely cheap compared to fossil fuel options. Advances in the technologies used in these devices are continually pushing the boundaries of their efficiency and capabilities and could prove to be a viable replacement for conventional fuel in the near future. Propeller turbine technology is also becoming more accessible, which further strengthens its role in a cleaner and greener energy supply scenario.
