Savonius wind turbine

A Savonius rotor, invented by Sigurd Savonius is a paddle-shaped wind turbine with two or more overlapping wings that are stretched along the axis of rotation mounted between circular end plates. With a vertical axis ( VAWT, vertical axis wind turbine ) does the Savonius rotor regardless of the wind direction. In its most common application, it serves as a drive fans to vehicles and fireplaces.

History

Anton Flettner filed in 1922, the idea for a patent that was at that time in the Aerodynamic Research Institute in Göttingen examined Magnus effect on rotating cylinders for the propulsion of ships to use with wind in order to save the crew to operate the conventional sails. He had to rebuild a three-masted schooner, the Buckau. The two rotors installed there cylindrical flettner had to be taken relative to the wind to achieve its maximum efficiency with a diesel-electric drive device to approximately four times the circumferential speed. Savonius ' idea it was, the cylindrical rotors modify so that they would be displaced by the wind itself in rotation. He shared the cylinder along and moved the halves against each other. In his wind tunnel, the first in Finland, he determined for various arrangements wing figures and profiles each of the curves of torque and ( Magnus ) lateral force on the tip speed ratio. At a converted boat he led attempts to propel ships through the Magnus effect on Savoniusrotor by, which were continued by his son. He noted that the strength of its rotor rather in the performance of work on the shaft, because lay idly in the use of the Magnus effect, and reported from December 1924 several applications for patents, including already a pumping plant whose rotor in (manual) off state was held by a wind vane in a convenient, low-drag position to the wind, and a (electronic ) " power station " with two 90 ° rotated stacked rotor stages and a speed control by centrifugal action in a pivotal wing. Also the rotor for the boat needed pivoting wing to change the direction of rotation while cruising. Under the first variant was the Savonius semi-cylindrical shape as the most suitable, favored later J-shaped wings, which extend parallel in the overlap region.

1931 died Savonius and Flettner acquired the German patent. Since then, his company manufactures fans, which are powered by Savonius rotors or consist of more bladed Savonius rotors.

Properties

The torque is relatively high, and the maximum is achieved in high-speed values ​​in the range 0.3 to 0.6. In principle, use at low wind speeds of about 2 m / s is thus already possible.

The specifications for the power coefficient vary from 0.15 to 0.26 at high-speed numbers close to 1, the performance level is significantly lower than that which can be achieved by Darrieus rotors or designs with horizontal rotor axis of rotation.

The rotor is driven independently of the wind direction. It is therefore no Yaw required. The result, in comparison to the horizontal construction that needs to be tracked to the wind, a good-natured attitude towards frequent wind direction changes.

Unrestrained, the tip speed ratio is only about 1.5. The offers in the no-load operation, eg in brake failure, some protection from damage due to excessive centrifugal forces. For the same reason a Savoniusrotor is relatively insensitive to deviations from the ideal shape and therefore, you build with simple means. While applications such as pumps are not dependent on a high speed, according to the construction of low-speed generators is more complex than that for high speeds. Alternatively, should the use of inexpensive standard generators additional gears are used, which is uneconomical for smaller rotors. For larger Savonius rotors, for which less fall, the friction losses associated with gear in weight, it is easy to unbalance by deformations of the rotor. The construction effort to build relatively large Savonius structures stable enough at the moment seems too big.

The large blade surfaces imply a high consumption of materials during construction. The evidence, first in high cost and high weight down. In addition, the large projection places a great burden on the storm. In a simple design with a single unidirectional stage not only the blades themselves large alternating loads through the ever-changing incident flow, but also the air force are subject to the total rotor varies greatly, both in wind direction and transverse to it. The average lateral force through the Magnus effect lies in the same order of magnitude as the flow resistance of the rotor. The load of the overall structure can be reduced by several twisted stages are used, or when the entire profile is helically rotated. However, the increased complexity and construction cost of the construction.

Applications

• Initially in shipbuilding for aeration of the crew and cargo spaces, later also in transport vehicles (railway wagons, vans, buses, etc.). Savonius rotors at the vent stack.
• Advertising medium.
• Water pumps, deep well, irrigation, swimming pool filters.
• Traction for Darrieus rotors. However, the power coefficient drops dramatically when the outcome to be in the picture, a nested arrangement. Combination of Darrieus rotor ( outdoor) and Savonius rotor ( near the axis)
• Toys: The Savonius rotor is also used for toys or sports or modeling. For example, in Dragon of the Magnus effect is used as a lift-generating application. Even in vehicles that can run against the wind head-on, there are built Savonius rotors. Here, however, not yet - or at least not primarily -. Using the Magnus effect, but by mechanical translation of the torque of the rotor on wheels or propellers

Variants

The aim of the construction in helix shape is to reduce problems with load changes. Again, this increases the design effort. Evidence that significant benefits consist of two 90 ° rotated levels are not known. Can operate the Savonius rotor and with a horizontally lying axis of rotation if, for example, concentrated at the roof edge flow occurs. Through this type of installation, however, you lose the advantage of the wind direction independence. If flow conditions are used for structures, also arises the issue of noise pollution occurring.