Darrieus wind turbine analysis - Home

Brief website contents:

• Technical introduction to wind turbine here
• Predicting and analysing Darrieus rotor performance here
• Testing performance of Darrieus rotor model in laboratory here
• Designing and building a small Darrieus rotor test model here
• About the website, the author, and his hometown wind data here
• Darrieus rotor patent, commercial unit, and research prototype below

What is a Darrieus wind turbine?

The Darrieus rotor is a vertical axis type of wind turbine or VAWT. It’s powered by the lift forces generated from a set of airfoil blades so it can reach blade speed much higher than the blowing wind speed. Its equivalent horizontal axis or HAWT counterpart will be the propeller type wind turbine. Another well-known VAWT is the Savonius rotor, which differ a lot from the Darrieus rotor as it used mainly drag force for propulsion thus moving at vane speed not much higher than the incoming wind speed.

The creator of this modern wind turbine

The Darrieus rotor was named upon its France creator Georges Jeans Mary Darrieus. The patent was submitted in 1931 at US as shown in the picture above. The patent shows the proposed (later became common) eggbeater shape configuration (Fig. 3), or the skipping rope, or the troposkien shape, which eliminates or minimise the bending stress in the blades. The second configuration is the straight bladed or the squirrel cage configuration (Fig. 1, 2, 6) with circular plates above and below for supporting the blades. In the patent, the Darrieus rotor is not only intended for wind energy use but also for the use in hydropower.

Examples of commercial and prototypes Darrieus rotor

A picture will provide more info than pages of text in most cases. Here are links to some of the online pictures of Darrieus wind turbine around the world.

<The biggest eggbeater Darrieus, the nearly 100m height 60m diameter 4MW rated gigantic eggbeater EOLE, as shown in the left picture, located at Cap-Chat, Quebec, Canada. The giant was operated at lower speed now to ensure ‘longevity’ thus output reduced to 2.5MW. Another Eole picture is here.

The 42m height 34m diameter 625kW Sandia Laboratory prototype was built specially for research at Bushland, Texas. It can be identified easily from the fat column with ‘USDA’, ‘DOE’, and an eagle logo on it.

Large scale installation of Darrieus wind turbine in California was done by FloWind Corporation which went bankrupt in 1997. The company's newer Flowind model, the EHD model has the obvious Extra Height to Diameter ratio, needed less area for its guy wires support.

Some of the large straight bladed Darrieus rotor are:
Heidelberg-Rotor with the small but numerous support arm struts. Too bad Musgrove big single large arm H-rotor was not there to contrast one and another.
Kirk-Lazauskas 3kW prototype giromill utilising pitch change (not cyclically but rpm) using weight's centrifugal force and spring.
McDonnell Aircraft giromill will look thin and frail compare to the peers above.

Specifications of some small scale straight bladed Darrieus rotor

Large scale straight bladed Darrieus rotor always seems to be limited to the research stage only although large eggbeater Darrieus wind turbine had reach the market commercially already (before disappearing away later). However, in the small scale wind turbine market, the simple straight bladed Darrieus seems to be more cost effective than the eggbeater Darrieus as few companies had marketed this type of wind turbine before, i.e. the Pinson/Asi cycloturbine (this one disappear too) which utilise an end tail for changing pitch. This giromill model was stated in the Drees (1978) research paper of having a 3.6m diameter and 2.4m height. With 3 blades at chord length of 29cm, the rotor has solidity Nc/D of 0.24.

Currently, the only commercial small scale straight bladed Darrieus with more complete information in the web is this 3m diameter and 2.5m height model by Solwind company in New Zealand. This Darrieus rotor was designed to cut in at wind speed of 1.5m/s only and seems to be starting without any assistance, so we can expect a high solidity rotor. For a two bladed rotor, chord length of 48cm will therefore produce solidity Nc/D of 0.32.

In one of Musgrove (1978) research paper, a comparable sized rotor (2.7m diameter and 1.2m height with chord length of 40cm) with solidity of 0.60 was reported to be able to self start without assistance and the ability retained even after removing 2 of the 4 blades which effectively halves the solidity to 0.3. However, the important testing wind speed was not stated.

Another pitch changing research prototype was built by Grylls (1978). It has diameter of 2.4m and height of 1.6m. Using 3 blades with chord length of 14.5cm only, the rotor has solidity Nc/D of 0.18. Wind tunnel result for this prototype indicate the rotor was able to self start at wind speed of 3.5m/s provided that the pitch angle change is larger than plus minus 4degree.

Pattern search on Darrieus rotor

A brief patent search at US Patent Office on 'wind turbine' or 'windmill' resulted with numerous innovative or creative but sometimes time impractical and repetitive idea. The Savonius alike rigid vane mainly drag rotor tops the list, followed by collapsible type sail VAWT and flip off plank type, straight bladed Darrieus, vane or shrouded or augmented type, some eggbeater, and finally some crosswind type.

P. J. Musgrove patented his speed (rotor rpm) control method in US patent 4,087,202. The modified fixed pitch Darrieus rotor, termed variable geometry VAWT, has blades which are attached to one solid support arm while the second support was a extensible wire. The wire lengthen when the rpm or centrifugal load increase. So when the wind speed is turning high the rotor will rotate faster causing the blades to open up which in turn reduce the propulsion and limit the rotor rpm in return.

US patent 6.320,273 clearly mentioned a cyclic pitch change mechanism using end tail and push or pull rod. Darrieus did patented this feature too (as shown in the top Fig. 1) in his patent but the implementation in the figure was using an eccentric bearing on a squirrel cage. For a real cyclic pitch change rotor, look at this serious DIY enthusiast model

Cyclic pitch change is also possible using the aerodynamic moment on the airfoil as patented in 4,435,124. The concept does look feasible theoretically when the rotor is already rotating at high speed. But during startup and low rpm period, different propulsion method will be needed. Till now, have not seen a real working model of this type.

A much direct pitch change method we might first think of will be attaching a mass which will pitch depending on the rotor rpm and not cyclically. A real example of rpm pitch change this will be the previous Kirk-Lazauskas prototype of course.

Some more interesting straight bladed Darrieus rotor patents are listed here:
4052134, 4130380, 4204805, 4247253, 4274809, 4430044, 4456429, 4483657, 4525124, 4979871, 5518367, 6394745

Links to some selected wind turbine website

Sandia National Laboratory (the lab where most VAWT researches were done) freely available online research papers
Micheal Selig UIUC Airfoil Data Site for airfoils coordinate and data, which might be applicable for your rotor blades
NACA airfoil reports, available at Nasa server, are also available free for download or browsing directly
Leo Lazauskus develops pitch changing straight bladed Darrieus rotor. A very handy digitised set of NACA airfoil data is available.
Berlin Technical University wind turbine group has some straight bladed Darrieus pictures but u won’t find much information into it from its old website. Paul Gipe articles are available there if u search from search engine
Danish 3 bladed propeller manufacturers website with load of general and technical information (not research paper type of information)
American Wind Energy Association prefers to place their information in FAQ, so go straight to that section for load of consumer info.
UPSTO provides the patent information on various form of windmill you could ever imagine.
Google Groups archived alt.energy.homepower, alt.energy.renewable, and sci.energy.* newsgroups where the DIY enthusiasts discussion took place. A lot info on alternator, generator/motor, howto build, beginner...
Awea-wind group, a Yahoo public group, is frequented by quite a few authors of wind energy book and some industry expert seems to be hanging around too. They bashed off quite a few wind turbine company with product alleged more efficient than Betz 59%.
Hugh Piggott the well-known wind turbine DIY author provides blade carving and generator building information in his informative website.
Bergey, a manufacturer of small propeller wind turbines. Their product information in pdf specification sheet and excel sheet provide a complete power curve and wind distribution calculation
Sustainable Energy Technologies seems like a new (and the only one) VAWT company with a commercial eggbeater described in their brochure.

Last updated at November 6, 2002
Comments are welcomed