Aerodynamics 1: Energy Conversion

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Aerodynamics 1: Energy Conversion - PowerPoint PPT Presentation

Aerodynamics 1: Energy Conversion. References: NREL (Pat Moriarty, Tony Jimenez). Wind Turbine Components. Courtesy: Alternative Energy Institute. Energy and Power. Energy is the ability to do work Energy = Force * Distance Electrical energy usually measured in kWh Power = Energy / Time

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Aerodynamics 1: Energy Conversion

References:

NREL (Pat Moriarty, Tony Jimenez)

Wind Turbine Components

Courtesy: Alternative Energy Institute

Wind Energy

Energy and Power
• Energy is the ability to do work
• Energy = Force * Distance
• Electrical energy usually measured in kWh
• Power = Energy / Time
• Electrical power usually measured in kW

Wind Energy

Kinetic Energy
• Kinetic energy (KE) is the energy of motion
• Air molecules have mass, and wind is moving air. Thus, wind has kinetic energy.
• Wind turbines convert the wind’s kinetic energy into mechanical kinetic energy (spinning the rotor).
• Mass = density * volume:
• What is the kinetic energy of a 1m cube of air moving at 5 m/s in Colorado (r = 1 kg/m3)?

Wind Energy

Energy Conservation and Energy Conversion
• When the turbine extracts kinetic energy from the wind, the speed of the wind is reduced.
• Some of the wind’s kinetic energy is converted into mechanical kinetic energy, i.e., the rotation of the turbine rotor.
• Some of the wind’s kinetic energy remains in the wind (conservation of energy).
• What would happen if all of the wind’s kinetic energy were converted?

Wind Energy

Power
• Power available in the wind
• r = air density
• v = wind speed
• A = cross sectional area swept by rotor (“swept area”)

Wind Energy

Energy and Power – II
• Consider the units of the kinetic energy equation:and the units of the power equation:
• Recall: Power = (Energy) / (Time) and Mass = (Density)*(Volume)

Wind Energy

Power Coefficient
• Power coefficient Cp is a measure of the aerodynamic efficiency of the wind turbine
• Q = turbine’s aerodynamic torque
• W = rotor rotational speed
• Betz limit - theoretical maximum

Wind Energy

Tip-Speed Ratio
• Ratio of the linear speed of the tip of the blade to the wind speed
• Linear speed of a rotating object is angular speed times distance from center of rotation
• l = tip-speed ratio