Savonius rotor

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Original drawing by Sigurd Savonius on the potential flow of the stationary rotor

A Savonius rotor , invented by Sigurd Savonius , is a wind turbine with two or more blade-shaped, overlapping blades , which are stretched along the axis of rotation and mounted between circular end plates. With the vertical axis (VAWT, V ertical A xis W ind T urbine ) of the Savonius wind turbine operates independently of the wind direction. In its most widespread use, it is used to drive fans on vehicles and chimneys.

history

Drawings from the Austrian patent specification by Savonius (1925)

In 1922, Anton Flettner submitted the idea for a patent that the Magnus effect on rotating cylinders, which was investigated at the aerodynamic research institute in Göttingen, could be used to propel ships with wind in order to save the crew from operating the conventional sails. He had a three-masted schooner, the Buckau , converted for this purpose. The two cylindrical Flettner rotors installed there had to be brought to around four times the circumferential speed relative to the wind with a diesel-electric drive device in order to achieve their maximum efficiency.

Savonius' idea was to modify the cylindrical rotors so that they would be set in rotation by the wind itself. He divided the cylinder lengthways and shifted the halves against each other. In his wind tunnel, the first in Finland, he determined the progression of the torque and the (Magnus) lateral force over the high speed number for various arrangements, numbers of blades and profiles . On a converted boat, he carried out experiments to propel ships using the Magnus effect on the Savonius rotor, which his son continued.

He found that the strength of his rotor was doing work on the shaft rather than using the Magnus effect when it was running freely. From December 1924 he applied for a patent for various possible applications, including a pump system whose rotor was (manually) switched off and held in a favorable, low-resistance position to the wind by a wind vane and an (electrical) "power station" with two at 90 Degree rotated one above the other arranged rotor stages and a speed control by centrifugal effect on swiveling blades. The rotor for the boat also needed swiveling blades to change the direction of rotation when cruising. Among the first variants, Savonius found the semi-cylindrical shape to be the most suitable; later he favored J-shaped wings that run parallel in the overlap area.

Savonius died in 1931 and Flettner acquired the German patent. Since then, his company has been producing fans that are driven by Savonius rotors or consist of multi-bladed Savonius rotors.

properties

Savonius Windspiel in front of the UDX high-rise in Akihabara . Depending on the wind strength, a different number of LEDs light up on the wing edges of the three counter-rotating, three-winged rotors.

The torque is comparatively high, the maximum being reached with high-speed numbers in the range 0.3 to 0.6. In principle, it can be used at low wind speeds from around 2 m / s.

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

The rotor is driven regardless of the wind direction. No wind direction tracking is therefore required. Compared to the horizontal construction, which has to follow the wind, this results in a more good-natured behavior towards frequent changes of wind direction.

Unbraked, the high-speed speed is only around 1.5. In operation without a load, for example in the event of a brake failure, this offers a certain degree of protection against destruction by excessive centrifugal forces. For the same reason, a Savonius rotor is relatively insensitive to deviations from the ideal shape and can therefore be built with simple means. While applications such as pumps do not depend on high speeds, the construction of correspondingly slow-running generators is more complex than those for high speeds. Alternatively, a gearbox would also have to be used for the use of inexpensive standard generators, which is uneconomical with smaller rotors. With larger Savonius rotors, for which the friction losses of a gear are less important, unbalance can easily occur due to deformation of the rotor. The constructive effort to build relatively large Savonius constructions stable enough seems to be too great.

The large shovel areas mean high material consumption during construction. This is reflected in both high costs and high weight. In addition, the large projection surface means a great deal of stress in a storm. In the case of a simple design with a single unidirectional step, not only are the blades themselves subject to large alternating loads due to the constantly changing flow, but the air force on the rotor as a whole fluctuates greatly, both in the direction of the wind and across it. The mean transverse force due to the Magnus effect is in the same order of magnitude as the flow resistance of the rotor. The load on the overall structure can be reduced by using multiple twisted steps or by turning the entire profile into a helix. However, this increases the complexity and construction costs of the construction.

Applications

  • Initially in shipbuilding to ventilate the crew and cargo spaces, later also in transport vehicles (railway wagons, delivery vans, buses, etc.)
    Savonius rotors on the exhaust chimney
  • Advertising medium
  • Water pumps, deep wells, irrigation, swimming pool filters
  • Starting aid for Darrieus rotors. The performance coefficient drops significantly if a nested arrangement is selected, as shown in the figure.
    Combination of Darrieus rotor (outside) and Savonius rotor (near the axis)
  • Toys: The Savonius rotor is also used for toys or in sports or model making. In kites , for example , the Magnus effect is used as a lift-generating application. Built-in Savonius rotors can also be found in vehicles that can drive head-on against the wind. So far, however, not - or at least not primarily - using the Magnus effect, but by mechanically translating the torque of the rotor onto wheels or propellers.

variants

The aim of the helical design is to reduce problems with load changes. Here, too, the construction effort increases. Evidence that there are significant advantages to two levels rotated by 90 degrees is not known. The Savonius rotor can also be operated with a horizontal axis of rotation, if, for example, there is a concentrated flow at roof edges. With this type of installation, however, the advantage of being independent of the wind direction is lost. If flow conditions are used in structures, the problem of noise emissions also arises.

literature

  • Sigurd J. Savonius: The wing-rotor in theory and practice. Helsingfors 1926 ( online as PDF; 11.8 MB).
  • Felix von König: Wind energy in practical use - wheels, rotors, mills and wind power plants. Pfriemer, Munich 1976, ISBN 978-3-7906-0062-9 .
  • Heinz Schulz: The Savonius rotor. Ökobuch, Staufen 2002, ISBN 3-922964-48-6 .

Web links

Commons : Savonius rotor  - collection of images, videos and audio files
Wiktionary: Rotor  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ^ Sigurd Savonius: The wing-rotor in theory and practice. Helsingfors 1926 ( online as PDF; 12.4 MB).
  2. ↑ Various posters with various images from Savonius' life ( online as PDF; 4.9 MB; Finnish).
  3. ↑ Sigurd Savonius: Rotor. Austrian patent , filed in 1925.
  4. ↑ Sigurd Savonius: Wind turbine with two hollow blades, the inner edges of which reveal a central wind passage gap and overlap. German patent , filed in 1927.
  5. ↑ Video of the Akihabara Greyhound
  6. ↑ R. E. Sheldahl, B. F. Blackwell, L. V. Feltz: Wind Tunnel Performance Data for Two- and Three-Bucket Savonius Rotors. J. Energy (United States), Vol. 2, 1978, pp. 160-164; Preprint: Sandia Report SAN D76-0131 ( Memento of the original dated August 15, 2011 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 2.9 MB). @1@ 2Template: Webachiv / IABot / www.wrapwind.com
  7. ↑ M. A. Kamoji et al .: Experimental investigations on single stage modified Savonius rotor. Applied Energy , Vol. 86, 2009, pp. 1064-1073, doi : 10.1016 / j.apenergy.2008.09.019 ( online as PDF; 1.1 MB).
  8. ↑ M. A. Kamoji et al .: Performance tests on helical Savonius rotors . Renewable Energy , Vol. 34, 2009, pp. 521-529, doi : 10.1016 / j.renene.2008.06.002 .
  9. ↑ James F. Manwell et al .: Wind Energy Explained - Theory, Design and Application. Wiley, 2009, ISBN 978-0-470-01500-1 .
  10. ↑ Tsutomu Hayashi, Yan Li, Yutaka Hara and Katsuya Suzuki: Wind Tunnel Tests on a Three-stage Out-phase Savonius Rotor. JSME International Journal, Vol. 48, 2005, pp. 9–16 ( PDF  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice .; 381 kB).@1@ 2Template: Dead Link / www.wrapwind.com  
  11. ^ Sezai Taskin, Bahtiyar Dursun, Bora Alboyaci: Performance Assessment Of A Combined Solar And Wind System. In: The Arabian Journal for Science and Engineering. Vol. 34, 2009 ( PDF ; 257 kB).
  12. ↑ Md. Nahidul Islam Khan, M. Tariq Iqbal, Michael Hinchey: Submerged Water Current Turbines. OCEANS 2008, pp. 1-6, IEEE, 2008.
  13. ^ U. K. Saha, M. Jaya Rajkumar: On the performance analysis of Savonius rotor with twisted blades. In: Renewable Energy . Vol. 31, 2006, pp. 1776-1788.
  14. ↑ John A. C. Kentfield: The Fundamentals of Wind-Driven Water Pumpers. Overseas Publishers, Amsterdam 1996, ISBN 2-88449-239-9 , limited preview in Google Book Search.
  15. ↑ Yusaku Kyozuka: An Experimental Study on the Darrieus-Savonius Turbine for the Tidal Current Power Generation. J. Fluid Sci. Tech. 3, 2008, pp. 439-449, doi : 10.1299 / jfst.3.439 .
  16. ↑ photos and descriptions of toy dragons that use the Magnus effect (English)
  17. ↑ photos and descriptions of toy dragons that use the Magnus effect (English)
  18. ↑ Amateur video of a model ship with a Savonius rotor
  19. ↑ Photo of a so-called headwind vehicle with a Savonius rotor