Field Engineering Sciences
Wind Storage (MEC453)
Lecture 3
Dr : Aly Soliman
Date : 22 /10 /2024
DRAG DEVICES
• Drag devices are inherently limited in efficiency because the speed of the device or blades
cannot exceed the wind speed.
• The wind pushes on the blades of a drag turbine, forcing the rotor
to turn on its axis.
Examples of drag devices are cup anemometers, vanes, and paddles that are shielded from
the wind or change parallel to the wind on half the rotor cycle
WE 5.3
LIFT DEVICES
Most lift devices use airfoils similar to propellers or airplane wings for
blades, but other concepts have also been used.
Using lift, the blades can move faster than the wind and are more efficient in terms of
aerodynamics and amount of material needed.
The tip speed ratio is the speed of the tip of the blade divided by the wind speed.
At the point of maximum efficiency for a rotor, the tip speed ratio is
around 7 for a lift device and 0.3 for a drag device.
The ratio of amount of power per material area for a lift device is
around 75, again emphasizing why wind turbines using lift are used to
produce electricity.
The optimum tip speed ratio also depends on the solidity of the rotor.
Solidity is the ratio of blade area to rotor swept area
ORIENTATION OF ROTOR AXIS
Wind turbines are further classified by the orientation of the axis of the
rotor to the ground: horizontal axis wind turbine (HAWT) and vertical
axis wind turbine.
The rotors on HAWTs must be kept perpendicular to the flow of the
wind to capture maximum energy.
This rotation of the unit or rotor about the tower axis (yaw) is
accomplished by tails on upwind units (small turbines up to 10 kW
although some 50-kW units had tails), by coning on downwind units, or
by electric motors or wind-propelled fan tail rotors to drive the unit
around the yaw axis. Coning means the blades are at an angle from the
plane of rotation.
VAWTs have the advantage of
accepting wind from any direction.
However, the Darrieus wind turbine
is not reliably self-starting because
the blades have to be moving faster
than the wind to generate power.
SYSTEM DESCRIPTION
» A total system consists of the
wind turbine and load. A
typical wind turbine consists
of the rotor (blades and hub),
speed increaser (gearbox),
conversion system, controls,
and tower.
» The nacelle is the covering or
enclosure. The output of the
rotor
(rotational
kinetic
energy) can be converted to
electrical, mechanical, or
thermal energy. Generally, the
choice is electrical energy, so
the conversion system is a
generator
LARGE TURBINE
DIAGRAM
ANEMOMETER
NACELLE
GENERATOR
MAIN
BEARING
MAIN
SHAFT
BLADE
OIL COOLER
GEAR BOX
TOWER
HUB
WTAMU
WE 5.9 S2
AERODYNAMICS
The moving blades of a wind
turbine convert part of the
power in the wind to
rotational power.
Wind Power and Turbine Efficiency
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Tips speed ratio (TSR):
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Wind Turbine Power
𝜼𝜼𝒐𝒐𝒐𝒐𝒐𝒐𝒐𝒐𝒐𝒐𝒐𝒐𝒐𝒐 = 𝑪𝑪𝑷𝑷 × 𝑵𝑵𝒃𝒃 × 𝑵𝑵𝒈𝒈
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Rotor Solidity
• The wind turbine efficiently intercepts the wind energy flowing
through the entire swept area even though it has only two or three
thin blades with solidity between 5 to 10 percent.
• The solidity is defined as the ratio of the solid area to the swept area of the
blades. The modern 2-blade turbine has low solidity ratio. Hence, it
requires little blade material to sweep large areas.
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To calculate the rotational speed: “ 𝝎𝝎”
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Solved Examples
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