Blade Tip Speed of a Wind Turbine: Quiz and Flashcards

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Questions and Answers

Theoretical maximum rotor efficiency Cp is _____%

59.3

Under the best operating conditions, about _ to _ percent efficiency can be achieved in converting the power in the wind into the power of a rotating generator shaft

If the rotor turns too slowly, the efficiency drops off since the blades are letting too much wind pass by _____

unaffected

If the rotor turns too fast, efficiency is reduced as the turbulence caused by one blade increasingly affects the blade that _____

follows Signup and view all the answers

The usual way to illustrate rotor efficiency is to present it as a function of its tip-speed _____ (TSR)

ratio Signup and view all the answers

The tip speed ratio is defined as the speed of the blade at its tip divided by the speed of the _____

wind Signup and view all the answers

In stall control method of speed control, when the wind speed exceeds the safe limit, the blades are shifted into a position such that they _____

stall Signup and view all the answers

Theoretical maximum rotor efficiency Cp is usually illustrated as a function of its tip-speed _____ (TSR)

ratio Signup and view all the answers

If the rotor turns too slowly, the efficiency drops off since the blades are letting too much wind pass by the _____

blade Signup and view all the answers

Under the best operating conditions, about _ to _ percent efficiency can be achieved in converting the power in the wind into the power of a rotating generator shaft

35, 45 Signup and view all the answers

The friction coefficient α for ground with shrubs and hedges is estimated to be ______.

0.20 Signup and view all the answers

The wind speed at 50 m will be ______ the wind speed at 10 m.

higher than Signup and view all the answers

The power density at 50 m will be more than two and one-half times as much power as the ______ available at 10 m.

76.5 W/m2 Signup and view all the answers

The ratio of power at the top of the blade swing (65 m) to that at the bottom of its swing (35 m) will be ______.

45% higher Signup and view all the answers

This illustrates an important point about the variation in wind speed and power across the face of a spinning ______.

rotor Signup and view all the answers

TIP SPEED RATIO: video Tip speed = π D N / 60 where N is the rotor speed (rpm) , D is the rotor diameter (m); and v is the wind speed (m/s) upwind of the ______.

turbine Signup and view all the answers

The optimum ______ is found in rows 5 to 9 rotor diameters apart in the wind direction, and 3 to 5 rotor diameters apart in the crosswind direction.

spacing Signup and view all the answers

The wind shear at ground surface causes the the wind increase with height in accordance with the expression where V1 = wind measured at the reference height h1 V2 = wind __ estimated at height h2, and α = ground surface friction coefficient.

speed Signup and view all the answers

Given the nonlinear relationship between power and , we can’t just use average speed to predict total energy available, as the following example illustrates.

wind Signup and view all the answers

With steady 6 m/s, Energy (6 m/s) = 1/2 ρAv3t = 12 · 1.225 kg/m3 ·1m2 · (6 m/s)3 · 100 h = 13,230 Wh b.

energy Signup and view all the answers

The tip-speed-ratio is the speed at which the outer tip of the blade is moving divided by the ______ speed

wind Signup and view all the answers

At what rpm does the rotor turn when it operates with a TSR of ______?

4.0 Signup and view all the answers

If the generator needs to turn at 1800 rpm, what gear ratio is needed to match the rotor speed to the generator ______?

speed Signup and view all the answers

What is the efficiency of the complete wind turbine (blades, gear box, generator) under these ______?

conditions Signup and view all the answers

Using the data of a Vesta V90 – 3.0 MW turbine (diameter = 90 m), find the turbine’s efficiency for a) just above the cut-in speed (5m/s), b) the average speed (15 m/s).c) Why does the power output level off at 3,000 ______?

kW Signup and view all the answers

Turbulence (also referred to as ______) prevents the lifting force of the rotor blade from acting on the rotor when the wind is too high.

stall Signup and view all the answers

As the angle of the wind increases, the lift also increases until the wind can no longer smoothly travel over the upper surface of the ______.

blade Signup and view all the answers

The wind begins to tumble over the top of the rotor which destroys the low pressure area created by the smooth flowing air over the top of the rotor ______.

blade Signup and view all the answers

Each turbine has a maximum operating efficiency defined by a particular tip speed ______.

ratio Signup and view all the answers

Tip speed ratios typically between 4 – 8 for low solidity ______.

turbines Signup and view all the answers

Wind speed = 5 m/s, Diameter of the turbine = 90 m, Actual power output = 250 kW. Input power, P= ½ ρAv3 = ½ x 1.2 x 3.14x 45x45 x 5 x 5 x 5 = 477,125 W = 480 kW. Efficiency = Output Power / Input Power = 250kW / 480kW = 52%. Theoretical maximum rotor efficiency Cp is _____%

52 Signup and view all the answers

Wind speed = 15 m/s, Diameter of the turbine = 90 m, Actual power output = 3,000 kW. Input power = P = 13,000 kW. Efficiency = 23.2%. Under the best operating conditions, about _ to _ percent efficiency can be achieved in converting the power in the wind into the power of a rotating generator shaft

23.2 to 52 Signup and view all the answers

World's Biggest Wind Turbine: The Vestas V164 has a rated capacity of 8 MW, later upgraded to 9.5 MW. The wind turbine has an overall height of 220 m (722 ft), a diameter of 164 m (538 ft), is for offshore use, and is the world's largest-capacity wind turbine since its introduction in 2014. The usual way to illustrate rotor efficiency is to present it as a function of its tip-speed _____ (TSR)

ratio Signup and view all the answers

Study Notes

Rotor Efficiency

Theoretical maximum rotor efficiency Cp is 59.3%
Under the best operating conditions, about 45 to 50 percent efficiency can be achieved in converting the power in the wind into the power of a rotating generator shaft

Factors Affecting Efficiency

If the rotor turns too slowly, the efficiency drops off since the blades are letting too much wind pass by
If the rotor turns too fast, efficiency is reduced as the turbulence caused by one blade increasingly affects the blade that follows

Tip-Speed Ratio (TSR)

The usual way to illustrate rotor efficiency is to present it as a function of its tip-speed ratio (TSR)
Tip-speed ratio is defined as the speed of the blade at its tip divided by the speed of the wind
Tip-speed ratio typically ranges between 4 to 8 for low solidity rotors

Wind Speed and Power

The wind speed at 50 m will be 1.5 times the wind speed at 10 m
The power density at 50 m will be more than two and one-half times as much power as the power available at 10 m
The ratio of power at the top of the blade swing (65 m) to that at the bottom of its swing (35 m) will be 4.5

Turbine Design

The optimum spacing is found in rows 5 to 9 rotor diameters apart in the wind direction, and 3 to 5 rotor diameters apart in the crosswind direction
The wind shear at ground surface causes the wind speed to increase with height in accordance with the expression where α is the ground surface friction coefficient

Calculating Efficiency

The formula to calculate power is: P = ½ ρAv³
Efficiency is calculated by: Output Power / Input Power

Real-World Examples

The Vesta V90 – 3.0 MW turbine has an efficiency of 52% at 5m/s wind speed and 23.2% at 15m/s wind speed
The Vestas V164 has a rated capacity of 8 MW, later upgraded to 9.5 MW, and is the world's largest-capacity wind turbine

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Test your knowledge on turbine blade tip speed with this quiz. Explore concepts like tip speed, centrifugal force, and tip speed ratio.

Turbine Blade Tip Speed Quiz

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Questions and Answers

Theoretical maximum rotor efficiency Cp is _____%

Under the best operating conditions, about _____ to _____ percent efficiency can be achieved in converting the power in the wind into the power of a rotating generator shaft

If the rotor turns too slowly, the efficiency drops off since the blades are letting too much wind pass by _____

If the rotor turns too fast, efficiency is reduced as the turbulence caused by one blade increasingly affects the blade that _____

The usual way to illustrate rotor efficiency is to present it as a function of its tip-speed _____ (TSR)

The tip speed ratio is defined as the speed of the blade at its tip divided by the speed of the _____

In stall control method of speed control, when the wind speed exceeds the safe limit, the blades are shifted into a position such that they _____

Theoretical maximum rotor efficiency Cp is usually illustrated as a function of its tip-speed _____ (TSR)

If the rotor turns too slowly, the efficiency drops off since the blades are letting too much wind pass by the _____

Under the best operating conditions, about _____ to _____ percent efficiency can be achieved in converting the power in the wind into the power of a rotating generator shaft

The friction coefficient α for ground with shrubs and hedges is estimated to be ______.

The wind speed at 50 m will be ______ the wind speed at 10 m.

The power density at 50 m will be more than two and one-half times as much power as the ______ available at 10 m.

The ratio of power at the top of the blade swing (65 m) to that at the bottom of its swing (35 m) will be ______.

This illustrates an important point about the variation in wind speed and power across the face of a spinning ______.

TIP SPEED RATIO: video Tip speed = π D N / 60 where N is the rotor speed (rpm) , D is the rotor diameter (m); and v is the wind speed (m/s) upwind of the ______.

The optimum ______ is found in rows 5 to 9 rotor diameters apart in the wind direction, and 3 to 5 rotor diameters apart in the crosswind direction.

The wind shear at ground surface causes the the wind ______ increase with height in accordance with the expression where V1 = wind ______ measured at the reference height h1 V2 = wind ______ estimated at height h2, and α = ground surface friction coefficient.

Given the nonlinear relationship between power and ______, we can’t just use average ______ speed to predict total energy available, as the following example illustrates.

With steady 6 m/s, Energy (6 m/s) = 1/2 ρAv3t = 12 · 1.225 kg/m3 ·1m2 · (6 m/s)3 · 100 h = 13,230 Wh b.

The tip-speed-ratio is the speed at which the outer tip of the blade is moving divided by the ______ speed

At what rpm does the rotor turn when it operates with a TSR of ______?

If the generator needs to turn at 1800 rpm, what gear ratio is needed to match the rotor speed to the generator ______?

What is the efficiency of the complete wind turbine (blades, gear box, generator) under these ______?

Using the data of a Vesta V90 – 3.0 MW turbine (diameter = 90 m), find the turbine’s efficiency for a) just above the cut-in speed (5m/s), b) the average speed (15 m/s).c) Why does the power output level off at 3,000 ______?

Turbulence (also referred to as ______) prevents the lifting force of the rotor blade from acting on the rotor when the wind is too high.

As the angle of the wind increases, the lift also increases until the wind can no longer smoothly travel over the upper surface of the ______.

The wind begins to tumble over the top of the rotor which destroys the low pressure area created by the smooth flowing air over the top of the rotor ______.

Each turbine has a maximum operating efficiency defined by a particular tip speed ______.

Tip speed ratios typically between 4 – 8 for low solidity ______.

Wind speed = 5 m/s, Diameter of the turbine = 90 m, Actual power output = 250 kW. Input power, P= ½ ρAv3 = ½ x 1.2 x 3.14x 45x45 x 5 x 5 x 5 = 477,125 W = 480 kW. Efficiency = Output Power / Input Power = 250kW / 480kW = 52%. Theoretical maximum rotor efficiency Cp is _____%

Study Notes

Rotor Efficiency

Factors Affecting Efficiency

Tip-Speed Ratio (TSR)

Wind Speed and Power

Turbine Design

Calculating Efficiency

Real-World Examples

Studying That Suits You

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Under the best operating conditions, about _ to _ percent efficiency can be achieved in converting the power in the wind into the power of a rotating generator shaft

Under the best operating conditions, about _ to _ percent efficiency can be achieved in converting the power in the wind into the power of a rotating generator shaft

The wind shear at ground surface causes the the wind increase with height in accordance with the expression where V1 = wind measured at the reference height h1 V2 = wind __ estimated at height h2, and α = ground surface friction coefficient.

Given the nonlinear relationship between power and , we can’t just use average speed to predict total energy available, as the following example illustrates.