Wind Turbine Aerodynamics Flashcards

This is a set of vocabulary flashcards for the Wind Turbine Aerodynamics lecture.

Aerodynamics

Deals with the motion of air and the forces/moments acting on bodies in motion relative to the air. It allows quantitative predictions of forces and moments on a turbine blade.

Incompressible Flow

Air density (ρ) is constant.

Inviscid Flow

Effects due to viscosity are ignored, meaning terms containing dynamic viscosity (μ) or kinematic viscosity (ν) are ignored. Forces are purely due to pressure, not skin friction.

Steady Flow

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

Linear Momentum

velocity × mass = 𝑼 × 𝑚 = 𝑈𝑚 [𝑘𝑔𝑚𝑠 −1]

Force

Pressure × Area = 𝑝 × 𝐴 = 𝑝𝐴 [𝑁]

Energy/Work Done

𝐹𝑜𝑟𝑐𝑒 × 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 = 𝐹 × 𝑑 = 𝐹𝑑 [𝐽]

Power

𝐸𝑛𝑒𝑟𝑔𝑦 / 𝑇𝑖𝑚𝑒 also: 𝐹𝑜𝑟𝑐𝑒 × 𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦 = 𝐹𝑈 [𝑊]

Mass Flow Rate

𝑚ሶ = 𝜌 × 𝑈 × 𝐴 = 𝜌𝑈𝐴 [kg/s]

Momentum Flux

𝑚ሶ × 𝑈 = 𝑚ሶ𝑈 [N]

Change in Momentum Flux

Δ𝑈 × 𝑚ሶ = Δ𝑈𝑚ሶ [N]

Momentum Principle

The external force on a body due to fluid flow is equal to the rate of change of momentum of the flow or is equal to the change in momentum flux. 𝐹 = Δ𝑈𝑚ሶ

Rotating Lift-Based Machines

Power is generated due to lifting forces on the rotating blades when the wind passes over them (HAWT or VAWT).

Rotating Drag-Based Machines

Drag based Savonius turbines, where the drag difference on the blades creates a rotating moment or torque and thus power (usually low efficiency).

Flying Lift-Based Machines

A flying kite that pulls a cable which is attached to an electric generator that is mounted on the ground.

Flow-Induced Vibrations Machines

Energy is extracted from the flow induced vibrations as wind passes over a structure such as a foil.

Horizontal Axis Wind Turbine (HAWT)

A turbine whose shaft/rotational axis is mounted horizontally parallel to the ground.

Vertical Axis Wind Turbine (VAWT)

A turbine that has its shaft normal to the ground.

Darrieus Rotor

A type of VAWT mainly used for small power applications.

Streamtube

A closed pattern of 3D streamlines within which the flow is confined starting far upstream of turbine and expands continuously as it goes through rotor and into downstream region.

Actuator Disc (AD)

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. Replace real rotor with a permeable, non-rotating 'disc' of equivalent area to real rotor.

Axial Induction Factor (a)

The fractional decrease in wind velocity between the free stream and disc plane (U∞ - Ud = aU∞).

Betz Limit

The maximum achievable value for an ideal turbine (approximately 0.593 or 59.3%). It is independent of turbine design.

Power Coefficient (Cp)

Ratio of extracted power divided by available power. CP = Power / (0.5 * ρ * A * U∞^3)

Thrust Coefficient (CT)

A coefficient that defines Thrust force: CT = T / (0.5 * ρ * U∞^2 * A)