Load attenuating passively adaptive wind turbine blade

a passive adaptive, wind turbine technology, applied in passive/reactive control, vessel construction, marine propulsion, etc., can solve the problems of changing loads and affecting output power, affecting fatigue life throughout the system, and small twisting angles that can have significant impa

Inactive Publication Date: 2003-01-07
SANDIA NAT LAB
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

Whenever the blades on a wind turbine are twisted, the twist directly influences the blade's angle of attack, thereby changing loads and affecting output power.
When the pitch changes are sufficiently rapid, they can affect not only average rotor loads and turbine power, but vibratory loads as well, influencing fatigue life throughout the system.
Even quite small angles of twist can have significant impact.
The conclusion was that perfect regulation is very difficult to achieve, and that even less than perfect regulation is a challenge.
As .alpha. becomes increasingly positive, the blade bends and twists toward stall, increasing angle of attack and also loads, and this reduces the divergence stability margin.
Results for the constant speed stall-controlled case indicated that twist / coupling toward stall produces significant increases in fatigue damage, and for a range of wind speeds in the stall regime apparent stall flutter behavior is observed.
There are limits to the amount of coupling that can be achieved with asymmetric fiber lay-ups.

Method used

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  • Load attenuating passively adaptive wind turbine blade
  • Load attenuating passively adaptive wind turbine blade
  • Load attenuating passively adaptive wind turbine blade

Examples

Experimental program
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Effect test

example 1

The analysis for the bending-twist coupled blade according to the invention was carried out within the confines of beam finite element theory. The coupling terms for the beam elements are generated starting with beam "stress- strain" relations. For bending-twist coupling the "stress-strain" relations at a point along the blade span are given by Equation 1: ##EQU1##

Here, .theta.=.delta..upsilon. / .delta.x is the flapwise slope of the blade, .upsilon. is the flapwise displacement, M.sub.b is the flapwise bending moment, .psi. is the blade twist, and M.sub.t is the twisting moment. The material parameters E and G are the Young's modulus and the shear modulus respectively; I represents the moment of inertia of the cross section and K the torsional moment of inertia (equal to the polar moment of inertia for circular sections). The quantity g, is the coupling term, and has a value of zero for the standard beam where no coupling is present. In order for this system to be positive definite (...

example 2

The present invention includes improved bending twist-coupled blades in rotors that use different power-control strategies. In confirming these alternative embodiments, a constant speed type stall-controlled rotor was included in the simulation as a baseline. Two of the more commonly accepted control strategies, variable speed stall-control and variable speed pitch-control, were used. The blades of each of these alternative embodiment rotors were first optimized mized by setting the pretwist such that a desirable twist distribution is achieved at rated power. In each case this procedure produced power curves for the twist-coupled rotors that were nearly identical to those of the uncoupled rotors to which they were compared.

A separate study for the variable speed stall-controlled rotor was performed wherein the twist-coupled rotor efficiency was compared to that of the uncoupled one in a steady wind environment. The peak rotor efficiency was determined at each windspeed by optimally ...

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Abstract

A method and apparatus for improving wind turbine performance by alleviating loads and controlling the rotor. The invention employs the use of a passively adaptive blade that senses the wind velocity or rotational speed, and accordingly modifies its aerodynamic configuration. The invention exploits the load mitigation prospects of a blade that twists toward feather as it bends. The invention includes passively adaptive wind turbine rotors or blades with currently preferred power control features. The apparatus is a composite fiber horizontal axis wind-turbine blade, in which a substantial majority of fibers in the blade skin are inclined at angles of between 15 and 30 degrees to the axis of the blade, to produces passive adaptive aeroelastic tailoring (bend-twist coupling) to alleviate loading without unduly jeopardizing performance.

Description

BACKGROUND OF THE INVENTION1. Field of the Invention (Technical Field)The present invention relates to rotor blades, particularly wind turbine rotor blades, and specifically to an aeroelasticly tailored turbine blades.2. Background ArtWhenever the blades on a wind turbine are twisted, the twist directly influences the blade's angle of attack, thereby changing loads and affecting output power. Classic pitch control used in not only wind turbines, but in rotors of all types, directly exploits these principles. When the pitch changes are sufficiently rapid, they can affect not only average rotor loads and turbine power, but vibratory loads as well, influencing fatigue life throughout the system. Even quite small angles of twist can have significant impact.The general concept of rotor blades that passively adapt to the incident wind loading is not new. Mechanisms that adjusted blade angle of attack in response to the thrust loading were quite popular in the early days of the modem wind ...

Claims

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Application Information

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Patent Type & Authority Patents(United States)
IPC IPC(8): F03D1/00F03D7/02F03D1/06F03D7/00
CPCF03D1/0675F03D7/0224F05B2270/1095F05B2270/402Y02E10/72
Inventor VEERS, PAUL S.LOBITZ, DONALD W.
Owner SANDIA NAT LAB
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