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Blade Element Theory - Wind Engineering - Lecture Slides, Slides of Environmental Law and Policy

These are the Lecture Slides of Wind Engineering which includes Governing Equations for Flow, Preliminary Remarks, Conservation of Mass, Continuity Equation, Area of Boundary, Speed Incompressible Flow, Angular Velocity of Fluid etc. Key imporatnt points are: Blade Element Theory, Turbine Data, Calculation of Angle of Attack, Lift and Drag, Functions of Angle, Induction Factor, Tangential Induction Factor, Sectional Forces, Lift and Drag Coefficients

Typology: Slides

2012/2013

Uploaded on 03/21/2013

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Wind Engineering
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Blade Element Theory
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Wind Engineering

Module 4.

Blade Element Theory

Recap

• In Module 1, we looked at an overview of the

course objectives, syllabus, and deliverables. We

also reviewed history of wind technology,

nomenclature, and case studies.

• In Module 2, we looked at the wind turbine as an

actuator disk, and established the theoretical

maximum for power that may be captured.

• In module 3, we reviewed airfoil aerodynamics,

and discussed how to compute lift and drag

coefficients. We also reviewed airfoil design

issues.

Blade Element Theory

  • We look at a reference blade from a multi-blade system (typically 2 or 3).
    • Blade, geometry, wind speed, blade RPM, and blade pitch angle are assumed to be known or chosen.
  • We divide the blade into strips, aka blade elements.
  • On each strip/element
    • We find the local section angle of attack.
    • We look up the corresponding lift and drag coefficients from a table of airfoil characteristics.
    • We correct these for tip losses, root losses, stall delay, swirl losses as needed.
    • We find lift and drag forces.
    • We find the propulsive force (in the plane of rotation)
    • We find the torque contribution of that strip.
  • Sum up the toque contribution over all strips to find torque for one blade.
  • Multiply by the number of blades, B.
  • Vary the wind speed and compute the entire performance map.

Calculation of Angle of Attack

  • The figure on the right is from

AeroDyne Theory manual, found

in the resource section.

  • β is pitch angle (known from from blade geometry)
  • U∞ is wind speed
  • a is the axial induction factor (axial induced velocity v divided by wind speed), discussed later.
  • a’ is a tangential induction factor (tangential induced velocity divided by ωr), discussed later.
  • λr is the local speed ratio Ωr/ U∞