Wind Turbine Blade Analysis Flashcards Preview

NM969 - Renewable Marine Energy Systems > Wind Turbine Blade Analysis > Flashcards

Flashcards in Wind Turbine Blade Analysis Deck (10)
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1
Q

Which two methods of examining wind turbine operation does the Blade Element Momentum Theory adopt?

A
  1. Momentum balance on a rotating annular stream tube passing through a turbine.
  2. Examine forces generated by aerofoil lift and drag coefficients at various sections along blade.
2
Q

What are the equations for the coefficient of thrust?

A

Ct=T/(0.5ρAv^2)=4a(1-a)

3
Q

What are the equations for the coefficient of power?

A

Cp=P/(0.5ρAv^3)=4a(1-a)^2

4
Q

How are the maximum values of Ct and Cp determined?

A

Differentiate eqns and set equal to 0, factorise for value of a and sub into original equation

5
Q

What is the name for the theoretical maximum value of Cp and what is this value?

A

The Betz Limit, Cp = 0.593

6
Q

What are the two key assumptions made with the Blade Element Momentum Theory?

A
  1. There are no aerodynamic interactions between different blade elements.
  2. The forces on the blade elements are solely determined from the lift and drag coefficients.
7
Q

Why must the overall performance characteristics of a turbine blade be determined via numerical integration along the blade span?

A

Along the span of the blade, slightly different flow is experienced due to differences in the rotational speed (Ωr), chord length (c) and angle of twist (γ).

8
Q

What is the equation for the local tip speed ratio at a specific point along a blade element?

A

λr=(Ωr/v)

9
Q

What is the equation for local solidarity at a specific point along a blade element?

A

σ’=Bc/2πr

10
Q

Under what theoretical conditions could the value of Cp be greater than the Betz Limit?

A

When the tip losses and drag coefficient of the blade are assumed to be zero.