Online references from which some of this Online references from which some of this material was obtained:material was obtained: www.windpower.org/en/tour/design/index.htm www.eere.energy.gov/windandhydro/wind_how.htmlwww.eere.energy.gov/windandhydro/wind_how.html

Basic Designs and Design Issues of Basic Designs and Design Issues of Wind TurbinesWind Turbines

Basic Designs of Wind TurbinesBasic Designs of Wind Turbines

One convenient categorization is the following:One convenient categorization is the following: ““Horizontal” Axis MachinesHorizontal” Axis Machines ““Vertical” Axis MachinesVertical” Axis Machines

The words “horizontal” and “vertical” are normally The words “horizontal” and “vertical” are normally used, but we are really referring to rotors with axes used, but we are really referring to rotors with axes that are either parallel (horizontal) or perpendicular that are either parallel (horizontal) or perpendicular (vertical) to the local wind velocity.(vertical) to the local wind velocity.

Each type has certain advantages and disadvantagesEach type has certain advantages and disadvantages

Wind Turbine ClassificationWind Turbine Classification

Horizontal Axis Machines: Machines with Horizontal Axis Machines: Machines with rotors that move in a plane perpendicular to rotors that move in a plane perpendicular to the direction of the wind.the direction of the wind. A farmers windmill, for example.A farmers windmill, for example.

Vertical Axis Machines: Machines that have Vertical Axis Machines: Machines that have the working surfaces traveling in the direction the working surfaces traveling in the direction of the wind.of the wind. These machines are sometimes called These machines are sometimes called

“panemones.”“panemones.”

Examples of Horizontal Axis Examples of Horizontal Axis MachinesMachines

Examples of Vertical Axis MachinesExamples of Vertical Axis Machines

Advantages of Vertical Axis Advantages of Vertical Axis MachinesMachines

The generator and gearbox can be placed on The generator and gearbox can be placed on the groundthe ground

The structure is usually simpler. The structure is usually simpler. You do not need a yaw (pointing) mechanism You do not need a yaw (pointing) mechanism

to turn the rotor against the wind.to turn the rotor against the wind. These are easier for hobbyists to build – little These are easier for hobbyists to build – little

detailed knowledge of aerodynamics is needed detailed knowledge of aerodynamics is needed for simple designs.for simple designs.

Disadvantages of Vertical Axis Disadvantages of Vertical Axis MachinesMachines

These structures are low to the ground, where wind These structures are low to the ground, where wind speeds are lowest.speeds are lowest.

The overall efficiency is much lower than horizontal The overall efficiency is much lower than horizontal axis machines. axis machines.

Most vertical axis machines are not self starting. Most vertical axis machines are not self starting. Many vertical axis machines require guy wires which Many vertical axis machines require guy wires which

greatly increase the structural footprint. greatly increase the structural footprint. Maintenance is usually more difficult.Maintenance is usually more difficult.

For example, replacement of the generator typically For example, replacement of the generator typically requires disassembly of the entire machine.requires disassembly of the entire machine.

Current Status of Vertical Axis Current Status of Vertical Axis MachinesMachines

The only commercially available vertical axis The only commercially available vertical axis machine that was built in large quantities was machine that was built in large quantities was the Darrieus rotor, built by Flowind Inc.the Darrieus rotor, built by Flowind Inc.

Flowind declared bankruptcy in 1997.Flowind declared bankruptcy in 1997. There are several vertical axis concepts that There are several vertical axis concepts that

are being studied.are being studied. They all face the same challenges that scuttled They all face the same challenges that scuttled

previous efforts. previous efforts.

Darrieus Wind Turbine at SNL, Darrieus Wind Turbine at SNL, Early 1980’s?Early 1980’s?

VAWT that are Under DevelopmentVAWT that are Under Development

Other VAWT DesignsOther VAWT Designs

Other VAWT Designs Other VAWT Designs (continued)(continued)

Other VAWT Designs Other VAWT Designs (continued)(continued)

Early VAWT – The Savonius Rotor.Early VAWT – The Savonius Rotor.(A very simple design!)(A very simple design!)

Advantages of Horizontal Axis Advantages of Horizontal Axis MachinesMachines

The efficiency is higher than that of vertical The efficiency is higher than that of vertical axis machines.axis machines.

They are easier to mount high enough to avoid They are easier to mount high enough to avoid much of the ground effect.much of the ground effect.

They are self starting.They are self starting. They are less expensive.They are less expensive. The technology is better developed.The technology is better developed. They are available commercially.They are available commercially.

Disadvantages of Horizontal Axis Disadvantages of Horizontal Axis MachinesMachines

Many of the important parts that require Many of the important parts that require maintenance are high off the ground.maintenance are high off the ground.

A yaw mechanism must be in place to turn the A yaw mechanism must be in place to turn the turbine into the wind.turbine into the wind.

Current Status of Horizontal Axis Current Status of Horizontal Axis MachinesMachines

Virtually all grid connected wind turbines in Virtually all grid connected wind turbines in operation today (fall 2005) are propeller type operation today (fall 2005) are propeller type designs mounted on a horizontal axis.designs mounted on a horizontal axis.

Some of these machines have the ability to Some of these machines have the ability to pitch up and down to face the wind as directly pitch up and down to face the wind as directly as possible.as possible. Instructor - make sure everyone knows the aircraft Instructor - make sure everyone knows the aircraft

terminology of “pitch,” “yaw,” and “roll” axes!terminology of “pitch,” “yaw,” and “roll” axes! These designs are being improved on. These designs are being improved on.

Variations of HAWT Designs – Variations of HAWT Designs – Upwind DesignsUpwind Designs

Upwind Machines: The front rotor faces the Upwind Machines: The front rotor faces the wind.wind. This avoids interference with the wind from the This avoids interference with the wind from the

structure. structure. The rotor must be very stiff and placed far enough The rotor must be very stiff and placed far enough

from the structure to avoid contact/interference from the structure to avoid contact/interference problems.problems.

A yaw control mechanism is necessary. A yaw control mechanism is necessary. Most wind turbines in operation are of this design.Most wind turbines in operation are of this design.

Example of Upwind Design – 3.6 Example of Upwind Design – 3.6 MW GE Wind TurbineMW GE Wind Turbine

The rotor is placed on the downwind (lee) side of the The rotor is placed on the downwind (lee) side of the structure.structure. An advantage is that, at least in principle, yaw control is An advantage is that, at least in principle, yaw control is

not necessary.not necessary. This is not always realized in practice since a mechanism still must This is not always realized in practice since a mechanism still must

exist to prevent the machine from continuously rotating!exist to prevent the machine from continuously rotating! In principle, the rotor blades can be much more flexible In principle, the rotor blades can be much more flexible

with these designs.with these designs. Both upwind and downwind machines have a power Both upwind and downwind machines have a power

fluctuation as the blades pass in front of or behind the fluctuation as the blades pass in front of or behind the structure. However, this is much more pronounced with structure. However, this is much more pronounced with downwind designs. downwind designs.

Variations of HAWT Designs – Variations of HAWT Designs – Downwind DesignsDownwind Designs

Example of Downwind Design – Example of Downwind Design – from The Wind Turbine Companyfrom The Wind Turbine Company

www.windturbinecompany.com/technology/index.htmlwww.windturbinecompany.com/technology/index.html

Number of Blades and “Solidity”Number of Blades and “Solidity”

The property called “solidity” is important in turbine (and The property called “solidity” is important in turbine (and compressor) design.compressor) design.

Solidity is defined as the fraction of the swept area that is Solidity is defined as the fraction of the swept area that is occupied by a working blade.occupied by a working blade.

A farmers windmill is a high-solidity device, while a single A farmers windmill is a high-solidity device, while a single blade rotor, illustrated earlier, is a low solidity device.blade rotor, illustrated earlier, is a low solidity device.

An efficient turbine must interact with as much of the wind An efficient turbine must interact with as much of the wind passing through the swept area as possible.passing through the swept area as possible.

As the solidity decreases, the rotor speed must increase for this As the solidity decreases, the rotor speed must increase for this to happen. to happen. Therefore, as the number of blades decrease, the required speed for Therefore, as the number of blades decrease, the required speed for

maximum efficiency must increase.maximum efficiency must increase.

How Many Blades?How Many Blades?

Two-blade designs are problematic because they can Two-blade designs are problematic because they can lead to structural instability for stiff structures.lead to structural instability for stiff structures. This is because as one blade passes the wind shade of the This is because as one blade passes the wind shade of the

tower, generating its minimum lift, the other blade is above tower, generating its minimum lift, the other blade is above the tower generating its maximum lift.the tower generating its maximum lift.

Three blade designs avoid this problem, and are able Three blade designs avoid this problem, and are able to rotate slower.to rotate slower. This is more or less the standard design right now – and is This is more or less the standard design right now – and is

called (at least by the Danes) the “Classical Danish Design.”called (at least by the Danes) the “Classical Danish Design.” This terminology also refers to certain control and power take off This terminology also refers to certain control and power take off

schemes.schemes.

Windbelt

• An alternative to wind turbines• A taut membrane fitted with a pair of magnets that oscillate between wire coils.• Prototypes have generated 40 milliwatts in 10-mph winds • Can be 10 to 30 times as efficient as the best wind microturbines.

One blade concepts have also been tried.One blade concepts have also been tried. An Illustration of these three types is given by An Illustration of these three types is given by

the following hyperlink:the following hyperlink: www.windpower.org/en/tour/design/concepts.htm

How Many Blades? (continued)How Many Blades? (continued)

Noise Issues with Wind Turbine Noise Issues with Wind Turbine DesignDesign

There have been complaints concerning noise There have been complaints concerning noise generated by wind turbines.generated by wind turbines.

They are really not very loud, but the noise they do They are really not very loud, but the noise they do put out is pretty much constant!put out is pretty much constant! There are stories of homesteading settlers, driven insane by There are stories of homesteading settlers, driven insane by

the constant west Texas wind, running out of there homes the constant west Texas wind, running out of there homes and across the plains, never to be seen again!and across the plains, never to be seen again!

The noise level doesn’t bother most people, but we The noise level doesn’t bother most people, but we should probably avoid instigating insanity among should probably avoid instigating insanity among even a small portion of the populace.even a small portion of the populace.

Mechanical Noise in Wind TurbinesMechanical Noise in Wind Turbines

Mechanical noise emanates from moving parts Mechanical noise emanates from moving parts such as gearboxes and Shafts.such as gearboxes and Shafts. Gearboxes can be designed for quite operation, Gearboxes can be designed for quite operation,

and insulated to reduce noise.and insulated to reduce noise. Certain gear designs (hard surface, softer interior, for Certain gear designs (hard surface, softer interior, for

example) are quieter than others.example) are quieter than others. Unstable vibrations of turbine blades and Unstable vibrations of turbine blades and

structures can emit sound. structures can emit sound. This problem has largely been eliminated through the This problem has largely been eliminated through the

use of finite element analysis and other modern use of finite element analysis and other modern structural design tools.structural design tools.

Sources of Aerodynamic NoiseSources of Aerodynamic Noise ““Singing” and “Whistling” from sharp corners, etc.Singing” and “Whistling” from sharp corners, etc.

Similar phenomena to that used by many musical instruments.Similar phenomena to that used by many musical instruments.

Vibrations induced by Aerodynamic effects may be in the Vibrations induced by Aerodynamic effects may be in the audible range.audible range.

A portion of the irreversible losses that occur as the wind A portion of the irreversible losses that occur as the wind transfers energy to the blade results in the “Whishing” sound.transfers energy to the blade results in the “Whishing” sound.

Acoustic principles tell us that this emission goes as generally the fifth Acoustic principles tell us that this emission goes as generally the fifth power of the rotor blade speed relative to the surrounding wind.power of the rotor blade speed relative to the surrounding wind.

Just as with mechanical noise, these effects can all be Just as with mechanical noise, these effects can all be minimized through the use of modern design tools.minimized through the use of modern design tools.

Aerodynamic Noise in Wind Aerodynamic Noise in Wind TurbinesTurbines

Structural and Mechanical Design Structural and Mechanical Design Issues with Wind TurbinesIssues with Wind Turbines

Components of Wind Turbines that are under considerable Components of Wind Turbines that are under considerable stress:stress: Propeller Blades and Hub.Propeller Blades and Hub. Mechanical PowertrainMechanical Powertrain Support TowerSupport Tower

Loads are both static and dynamicLoads are both static and dynamic Structural vibrations due to both propeller motion and wind loads must Structural vibrations due to both propeller motion and wind loads must

be accounted for.be accounted for. Fatigue failures have been a problem on some designs.Fatigue failures have been a problem on some designs. Wind gusts are very common.Wind gusts are very common.

Contingencies for extreme winds must be made.Contingencies for extreme winds must be made. For example, feathering and locking the propeller.For example, feathering and locking the propeller.

Structural design and analysis will be the subject of a Structural design and analysis will be the subject of a subsequent lecture.subsequent lecture.