Wind Turbine Aerodynamics Vocabulary

Vocabulary flashcards related to Wind Turbine Aerodynamics.

Aerodynamics

Deals with the motion of air and the forces/moments acting on bodies in motion relative to the air.

Incompressible flow

Air density (ρ) is constant.

Inviscid flow

Effects due to viscosity are ignored; forces on blades are due to pressure, not skin friction.

Steady flow

Conditions do not change with time (but not necessarily position).

Linear Momentum

velocity × mass = 𝑈 × 𝑚

Force

Pressure × Area = 𝑝 × 𝐴

Energy/work done

Force × distance = 𝐹 × 𝑑

Power

Energy/Time, also: Force × Velocity = 𝐹𝑈

Mass flow rate

𝜌 × 𝑈 × 𝐴 = 𝜌𝑈𝐴

Momentum flux

𝑚ሶ × 𝑈 = 𝑚ሶ𝑈

Momentum principle (Newton’s 2nd Law)

External force on a body due to fluid flow equals the rate of change of momentum of the flow. F = Δ𝑈𝑚

HAWT

Horizontal Axis Wind Turbine

VAWT

Vertical Axis Wind Turbine

Darrieus turbine

A type of VAWT where blades are attached to the top and the bottom of the vertical axis

Actuator Disc (AD) theory

Simplest model of a wind turbine used to estimate power output and wind thrust force on the rotor, by simply considering the power extraction process.

Streamtube

A closed pattern of 3D streamlines within which the flow is confined

Axial induction factor (a)

The fractional decrease in wind velocity between the free stream and disc plane.

Betz Limit

The maximum achievable value for the power coefficient of an ideal wind turbine, approximately 0.593.

Thrust force

Force on the disc/turbine due to airflow, developed in the stream-wise wind direction, resulting from the pressure difference/jump across the disc.

Power coefficient (Cp)

A way to characterise the ability of a wind turbine to capture wind energy, defined as the ratio of the extracted power divided by the available power.

Wake rotation

The rotation of air in the wake, in the opposite sense of blade rotation.

Tangential (or azimuthal) induction factor (a’)

Related to the angular velocity of the air flow in the wake.

Blade Element Momentum (BEM) Theory

Method used to determine wind turbine blade performance by combining the equations of momentum theory and blade element theory

Chord line

The straight line joining the leading and the trailing edges of an aerofoil.

Angle of attack (AoA)

The angle between the chord line and the incoming flow direction.

Stall

Condition where lift decreases sharply and drag increases rapidly after a critical angle of attack is reached.

Dynamic stall

Due to sudden changes in inflow velocity direction, causing rapid unsteady variations in the angle of attack.

Tip Speed Ratio (TSR)

Ratio of blade tip speed to the mean wind speed.

Winglet

Small wings on blade tips to reduce tip vortices.

Solidity

Ratio of blades area to rotor swept area

SPL

Sound pressure level.