The Magnus Effect and Wind Power
The Magnus effect, first described by German physicist Heinrich MAGNUS in 1852, is what makes a baseball or golf ball curve in flight. It's similar to the Bernoulli effect of wind passing over an airfoil causing lift.
When a rotating sphere or cylinder moves through a fluid (like air or water), one side of the round shape is moving forward and the other side backwards, relative to the motion of the object. This means that the airspeed is higher on the side spinning forward, and lower on the side spinning backwards.
What happens is that the round shape experiences a sideways force, like lift, pushing from the forward side to the rearward side. http://www.youtube.com/watch?v=l9OV-UQPb6M&feature=related
This effect has been used in many ways, including propelling boats by a cylindrical rotating sail http://www.youtube.com/watch?v=ao8RfUermdw&feature=related , and in a lighter-than-air vehicle with a spherical lifting envelope, rotated to produce more or less lift http://www.youtube.com/watch?v=szXSr3vD2cc&feature=related
The effect is applicable to the generation of wind power via a wind turbine, and has several great advantages over using wings (airfoil blades) as in a normal windmill turbine.
Firstly, an airfoil turbine has to be designed to cope with wind in a specific range of windspeeds. Wind below the starting speed does not turn the turbine. Wind over the rated speed could cause damage, so the windmill must "furl" or spill air to avoid turning too fast. Most simple turbines foil automatically by a trick of geometry in their construction.
A wind turbine constructed with Magnus-effect rotors instead of blades would be able to capture wind over a very great range of windspeeds. The rotors would be constructed of light-guage sheet metal, and cold be very very strong for their weight. Compared to airfoil blades, the construction and geometry would be much simpler and cheaper.
A problem faced by Magnus-effect rotors is that the "blades" must be rotated before they can capture the wind. For this reason, some Magnus-effect wind turbines have electrical motors which rotate the blades, while the wind power causes rotation of the entire turbine, extracting more net energy than the input to spin up the rotors. http://www.youtube.com/watch?v=RC8Qe--wB1c&feature=channel
Instead of using an external power source to rotate the individual rotors, it is possible to design them in such a way that the wind itself spins them, producing the necessary rotation to cause the Magnus effect to turn the turbine. Anton FLETTNER suggested a standard windmill blade array on the tip of each rotor to make them spin. I've seen a Japanese product which uses a spiral auger blade on each rotor to capture wind and spin up the rotors. http://www.youtube.com/watch?v=UA1t2_EPkro&feature=channel http://www.mecaro.jp/eng/products.html
These spiral ridges would automatically start the rotor from stall as soon as the wind picks up enough, with a standard vane aiming the turbine into the wind.
It seems to me that this approach has very great potential, though the actual geometry required will have to be determined to produce the best results for the greatest efficiency and least amount of material and cost.
Further, instead of cylindrical rotors, it is worth investigating whether conical rotors would extract more energy, by placing more surface area in contact with the wind. http://www.youtube.com/watch?v=xC9DYd_LVaQ&feature=channel
If all the rotors are geared together in mesh, then they can be braked together with a single braking system. This braking system could use a mechanical governor to slow the turbine to it's safe speed in very high winds, or to stop the rotors entirely. Remember that if the rotors don't rotate, there's no Magnus effect to turn the turbine, so the whole turbine should be safe in even very high storm winds.
But I'm thinking that a strong welded construction for the rotors should lead to a VERY high top speed, and with a charge-controller with an adequately designed dump-load, should be able to produce a great deal of average power across the entire range of wind speeds.
Another point I want to mention is that there is no reason why a wind turbine has to be designed to produce electrical power. Electricity is hard to store, requiring expensive batteries, or a grid-tied system to give you net metering where the power company buys your power production and charges you for your usage.
Instead, how about storing energy as compressed air in air tanks buried underground? In the right area, large underground chambers could be dug by a small tunnel boring machine (TBM) and sealed in shotcrete. These chambers would act as pressure vessels and act as air springs for storing energy mechanically. Remember that a steam engine is a pressure engine and can be designed to run just as happily off compressed air as steam.
Another advantage of compressed air storage is that any source of energy can compress the air in the storage system, and any kind of system can extract that air for use later. It's cross-compatible. For example, you can pipe compressed air to your workshop via a regulator, to provide "shop air" for air tools such as impact wrenches and die grinders. At the same time you could have an air-powered "steam turbine" generator for making electricity when you need it. The same compressed air powers both mechanical and electrical power-output.
When a rotating sphere or cylinder moves through a fluid (like air or water), one side of the round shape is moving forward and the other side backwards, relative to the motion of the object. This means that the airspeed is higher on the side spinning forward, and lower on the side spinning backwards.
What happens is that the round shape experiences a sideways force, like lift, pushing from the forward side to the rearward side. http://www.youtube.com/watch?v=l9OV-UQPb6M&feature=related
This effect has been used in many ways, including propelling boats by a cylindrical rotating sail http://www.youtube.com/watch?v=ao8RfUermdw&feature=related , and in a lighter-than-air vehicle with a spherical lifting envelope, rotated to produce more or less lift http://www.youtube.com/watch?v=szXSr3vD2cc&feature=related
The effect is applicable to the generation of wind power via a wind turbine, and has several great advantages over using wings (airfoil blades) as in a normal windmill turbine.
Firstly, an airfoil turbine has to be designed to cope with wind in a specific range of windspeeds. Wind below the starting speed does not turn the turbine. Wind over the rated speed could cause damage, so the windmill must "furl" or spill air to avoid turning too fast. Most simple turbines foil automatically by a trick of geometry in their construction.
A wind turbine constructed with Magnus-effect rotors instead of blades would be able to capture wind over a very great range of windspeeds. The rotors would be constructed of light-guage sheet metal, and cold be very very strong for their weight. Compared to airfoil blades, the construction and geometry would be much simpler and cheaper.
A problem faced by Magnus-effect rotors is that the "blades" must be rotated before they can capture the wind. For this reason, some Magnus-effect wind turbines have electrical motors which rotate the blades, while the wind power causes rotation of the entire turbine, extracting more net energy than the input to spin up the rotors. http://www.youtube.com/watch?v=RC8Qe--wB1c&feature=channel
Instead of using an external power source to rotate the individual rotors, it is possible to design them in such a way that the wind itself spins them, producing the necessary rotation to cause the Magnus effect to turn the turbine. Anton FLETTNER suggested a standard windmill blade array on the tip of each rotor to make them spin. I've seen a Japanese product which uses a spiral auger blade on each rotor to capture wind and spin up the rotors. http://www.youtube.com/watch?v=UA1t2_EPkro&feature=channel http://www.mecaro.jp/eng/products.html
These spiral ridges would automatically start the rotor from stall as soon as the wind picks up enough, with a standard vane aiming the turbine into the wind.
It seems to me that this approach has very great potential, though the actual geometry required will have to be determined to produce the best results for the greatest efficiency and least amount of material and cost.
Further, instead of cylindrical rotors, it is worth investigating whether conical rotors would extract more energy, by placing more surface area in contact with the wind. http://www.youtube.com/watch?v=xC9DYd_LVaQ&feature=channel
If all the rotors are geared together in mesh, then they can be braked together with a single braking system. This braking system could use a mechanical governor to slow the turbine to it's safe speed in very high winds, or to stop the rotors entirely. Remember that if the rotors don't rotate, there's no Magnus effect to turn the turbine, so the whole turbine should be safe in even very high storm winds.
But I'm thinking that a strong welded construction for the rotors should lead to a VERY high top speed, and with a charge-controller with an adequately designed dump-load, should be able to produce a great deal of average power across the entire range of wind speeds.
Another point I want to mention is that there is no reason why a wind turbine has to be designed to produce electrical power. Electricity is hard to store, requiring expensive batteries, or a grid-tied system to give you net metering where the power company buys your power production and charges you for your usage.
Instead, how about storing energy as compressed air in air tanks buried underground? In the right area, large underground chambers could be dug by a small tunnel boring machine (TBM) and sealed in shotcrete. These chambers would act as pressure vessels and act as air springs for storing energy mechanically. Remember that a steam engine is a pressure engine and can be designed to run just as happily off compressed air as steam.
Another advantage of compressed air storage is that any source of energy can compress the air in the storage system, and any kind of system can extract that air for use later. It's cross-compatible. For example, you can pipe compressed air to your workshop via a regulator, to provide "shop air" for air tools such as impact wrenches and die grinders. At the same time you could have an air-powered "steam turbine" generator for making electricity when you need it. The same compressed air powers both mechanical and electrical power-output.