Basic Aerodynamics
Which condition ensures that the pressure on the top and bottom side of an airfoil are the same at the trailing edge?
Kutta condition
What are the two main components of CFRP?
Carbon fiber and a matrix material (e.g. Epoxy)
What is the most common way of aerodynamic power control on a wind turbine?
Blade pitch control towards feather
Where do you expect the main stresses induced by the bending moment: top&bottom or nose&tail?
top&bottom
If the rotor radius of an ideal wind turbine is doubled, how does its power output change?
It quadruples based on quadrupled swept area
How does the boundary layer affect the lift slope?
It decreases the lift slope
Which theory can be used to calculate the stresses of a multi-layer composite (MSV)??
Classical Laminate Theory
Why is a larger number of blades advantageous for the start-up behavior of a rotor?
Higher torque, proportional to number of blades and blade solidity
In addition to the mean wind speed and cross winds, name another air force that influences the total load on the rotor!
Vertical wind shear
What is the decisive characteristic of the so-called "Danish wind turbine", a three-bladed and initially very successful wind turbine type?
Stall-regulated rotor
Which relationship is described by the Joukowski equation?
Lift as function of circulation and translatory flow velocity
Which basic mechanical properties (elasticity) do you have to determine for a unidirectional (UD) layer in the plane stess case?
E_11; E_22; G_12; v_12
What is the maximum power coefficient that can theoretically be achieved and what is its name?
16/27 or 0.5926, Betz limit
Name one mass force to which the rotor is subjected!
Gyroscopic forces
Deadweight force
Centrifugal forces
What is the maximum diameter of currently built wind turbine rotors?
220m, Haliade-X from GE
How is the principle called that a 2D airfoil in subsonic inviscid flow that produces lift does not generate any drag?
Paradox of d'Alembert
What are the basic failure types that can occur in fibre composites?
fibre failure;
interfiber failure;
Delaminations
What is the main difference between airfoils that were optimized for low speed airplanes and those optimized for wind turbines?
Robust performance also for rough surface
What other criterion do you have to pay attention to in structural dimensioning besides strength and stiffness?
(very high cycle) fatigue
What is the order of magnitude of the number of load cycles over the lifetime of today's wind turbines?
108 to 109
Based on momentum theory, how much is the axial velocity far downstream of the rotor disk reduced compared to the wind speed for an axial induction factor of a=0.25?
By 50%, V0(1-2a)
Into which two categories can the failure hypotheses of fibre composites be fundamentally divided?
global criteria
fracture type criteria
Does the number of rotor blades have a larger or smaller influence on obtainable power coefficient for a badly designed airfoil?
Larger influence
What rule of thumb should you follow when designing upwind rotors with regard to the clearance between the rotor and the tower?
distance should be ~ 1 D_tower
Name a typical manufacturing process of rotor blades made of fibre composite material.
Vacuum injection or recently "IntegralBlade"