06-08-2011, 10:11 AM
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Wind Power and Wind Turbines
Pressure
Wind – what causes it?, cont.
Pressure differences cause the flow of fluids (gases and liquids)
pressure is always measured relative to some reference pressure
Sometimes relative to vacuum absolute
Sometimes relative to atmospheric pressure
Prevailing Winds
Wind – what causes it?, cont.
Weather Processor Symbols
WXP Legend
Review Question 1
What causes wind?
Air pressure
Weight of the atmosphere
Pressure difference in atmosphere
Low pressure
High pressure
Review Question 2
What are the units of pressure?
Force/Area
Pascals (Pa)
Pounds per square inch (psi)
Millirads
B and C
Wind Energy and Power
Atmospheric pressure differences accelerate and impart kinetic energy into the air
Wind energy conversion machines (WEC) convert wind energy into electrical or mechanical forms
How much power can we extract?
Wind Power - Example
Wind Power – Example, cont.
Wind Turbine Size-Power Comparison
Wind Turbine Configurations
Configuration Tradeoffs
Factors
Efficiency
Power produced per unit cost
Directionality
Support configuration
Speed of rotation
Reliability
Cost
Maintainability
Common HAWT Construction
Aerodynamics of Wind Turbine Blades
Forces are transmitted from a moving fluid to an object in the flow stream
Lift = the force component perpendicular to the original flow direction
Drag = the force component in line with the original flow direction
Two Types of Turbine Designs
Drag Designs
Savonius
Lift Designs
VAWT Darrieus
Most HAWT designs
Aerodynamics of HAWT Blade
Aerodynamics of HAWT Blade, cont.
Design of HAWT Turbine Blade
Design of HAWT Turbine Blade, cont.
Number of blades
Increasing the number of blades tends to increase the aerodynamic efficiency
Increasing the number of blades increases the cost (material and manufacturing
Turbines with fewer blades tend to run most efficiently at lower tip speed ratios (ratio of tip speed to wind speed)
Review Question 3
The lift force on a wing or turbine blade is:
In line with the relative wind direction
Perpendicular to the relative wind direction
Somewhere between in line and perpendicular to the relative wind direction
Varies
A and B
