Wind Energy
For each increment of wind speed, energy produced at this wind speed is obtained by multiplying?
# of hours X corresponding turbine power @ this speed ->(km/h)
Wind velocity (v) varies from?
0 to 8.71m/s in 24 hours
What is rotational power (P) after 2003 =
0.000195D^2.156
What is rotational power (P) =
0.06D^2.42
Betz limit is=?
0.593 or 59.3% (theoretical)
Wind turbine efficiency depends on what four factors?
1)ambient air velocity 2)rotational design speed 3)type of wind turbine 4)size of wind turbine(or blade diameter)
Name 5 VAWT disadvantages
1)cyclic load on tower 2)lower efficiency 3)some are limited in height(structural issues) 4)unable to produce sufficient aerodynamic starting torque 5)not economically competitive
How much power a wind turbine produces depends on?
1)its wind speed power curve 2)wind speed frequency distribution at the site
Name 5 environmental impacts of wind turbines?
1)noise (mechanical/aerodynamic) 2)electrmagnetic interference 3)aviatuoncrelated issues 4)wild life 5)public attitudes, planning
List 4 controls of wind turbine output:
1)passive stall control 2)active pitch control 3)active stall control 4)yaw control
Turbine power curve can be influenced by? (name 12)
1)rotor swept area 2)choice of aerofoil 3)# of blades 4)blade shape 5)optimal tip speed ratio 6)speed of rotation 7)cut-in wind speed 8)rated wind speed 9)cut-out wind speed 10)Aerodynamic efficiency 11)gearing efficiency 12)generator efficiency
What does a power generating system comprise of? (6 things)
1)tower(30-50m high) 2)yaw bearing 3)yaw brakes 4)rotor blades 5)gear box 6)generator
Air density is :
1.225kg/m^3 @ P(atm)15 degrees Celsius
Knot is equal to? (in km/h)
1.852
Wind speed is recorded by weather stations as average constant velocity for how long?
10 minute intervals
How long must wind records be analyzed before it's deemed feasible to install a wind turbine?
10 years of records
How many 'average constant velocity' results are calculated in 24 hours?
144 results
HAWT has how many blades?
2 or 3,or more
How many blades on a turbine for optimal efficiency?
3
Meteorological stations measure wind velocity at what height?
30ft(10-12m)above ground
Velocity profile of wind flattens at what hight?
40 meters
Power extracted from the wind by turbine is (> or <) available power of wind?
< available power of wind
Drag forces are in line with?
Air stream
Lift forces are perpendicular to?
Air stream
V variable:
Air velocity (m/s)
The angle at which the air is directed toward the aerofoil is called?
Angle of attack
What is the stall angle?
Angle of attack at which the aerofoil exhibits stall behavior(loss of lift)
What direction can VAWT harness wind from without repositioning the rotor?
Any direction
What is variable A
Area swept by turbine blades
Assume solar power at inlet and outlet is:
Atmospheric
What is variable D
Blade diameter
R or D variable:
Blade radius or diameter
The line straight through the aerofoil is called?
Chord line
Assume density of air is:
Constant
What is Betz limit?
Conversion of air flow kinetic energy into mechanical energy
Tip speed ratio is?
Correlates rotor speed to wind speed (U/V) =(WR/V) =[(pi*n*D)/(60V)]
Wind speed is measured in:
Cup-anemometers with wind vanes.
Lift forces on a flat plate is minimal when?
Direction of the air stream is at zero angle to the flat surface of the plate
At a small angle of attack, low pressure is created on the...
Downstream side of the plate as a result of increased air velocity on that side
Cd=
Drag coefficient
Fd=
Drag force
Wind velocity vs height is___ and what is the formula?
Exponential (V1/V2)=(Z1/Z2)^(1/7)
Turbulence is caused by?
Friction between air flow and earth's surface.
Drag and lift forces depend on.
Geometrical shape
Lower pressure means...
Higher lift
Aerofoils: Arching a flat plan results in?
Higher lift forces
What is HAWT stand for
Horizontal axis wind turbine
The front of the aerofoil is called?
Leading edge
Cl=
Lift coefficient
Fl=
Lift force
The principal force that drives wind turbines is?
Lift force
U variable:
Linear turbine tip speed
Faster air flow means...
Lower pressure
Fluctuation of air velocity over a short period of time can cause?
Negative effect on turbine rotor
Pressure above aerofoil is called?
Negative preasure(suction)
To convert all available wind power to electricity, wind would have to leave the turbine with?
No Ke(kinetic energy)
The two wind classifications are?
Planetary, local
Pressure below the aerofoil is called?
Positive pressure
Name 4 major winds trends :
Prevailing, NE trade, SE trade, polar easterners(south & north), westerlies.
How are wind patterns created?
Rise of hot air creates a small pressure differential, cold air gets in.
w variable:
Rotational speed (rads /sec)
n variable:
Rotational speed of the engine(rpm)
Damping in yaw brakes does what?
Slows rotational motion
Wind is a by product of what?
Solar energy
Objects designed to minimize drag forces are described as?
Streamlined
The total energy produced in a given period is equal to:
Sum of the energy produced at all wind speed within the operating range of the turbine.
What is the scavenged area
Swept area
The back of the aerofoil is called?
Trailing edge
Define -> cut-out speed:
Velocity at which the turbine stops generating power.
Define -> Cut-in wind speed:
Velocity at which wind turbine begins to generate power
Define -> rated wind speed :
Velocity at which wind turbine generates it's rated power
What is VAWT stand for?
Vertical axis wind turbine
What is power density?
Wind average potential of location
Output power of wind turbine varies with?
Wind speed
Wind energy sources are based on which two factors?
Wind speed and direction, wind power density(wind energy potential of the location)
What is variable V?
Wind speed/velocity
What would happen if you increase down stream pressure?
Wind would stop the turbine and no long produce any power.
What is the capacity factor (CF) of a wind turbine=
average power produced annually / rated power