STRUCTURAL REPAIR METHODOLOGY FOR WIND TURBINE BLADES Rikard B. Heslehurst, PhD Heslehurst & Associate P/L University of NSW, ADFA Canberra ACT Composites Australia and CRC – ACS Australian Composite Conference 2015 Gold Coast, Queensland April 2015 Wind Turbine Environment
16
Embed
Composites Australia and CRC – ACS Australian Composite ... · METHODOLOGY FOR WIND ... Canberra ACT Composites Australia and CRC – ACS Australian Composite Conference 2015 Gold
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
STRUCTURAL REPAIR METHODOLOGY FOR WIND
TURBINE BLADES
Rikard B. Heslehurst, PhDHeslehurst & Associate P/LUniversity of NSW, ADFA
Canberra ACT
Composites Australia and CRC – ACS Australian Composite Conference 2015
Gold Coast, QueenslandApril 2015
Wind Turbine Environment
INTRODUCTION
• Turbine blade damage requires the application of simple repairs given the physically difficult task
• The typical operational damage is surface impact and aging.
• Other damage due to debris of bird and high wind collected object impact, or the propagation of manufacturing anomalies.
• The repairs need to be simple for ease of installation and enhanced success of retaining the blade structural integrity and operational effectiveness.
Aim
• To provide recommendations for damage repair zoning of the wind turbine blade and
• Simplifying the installation of repairs to the blade surface.
• Only considering solid laminate blade surface damage.
BACKGROUNDAerodynamic Loading of Wind Turbine Blades
Propeller Spanwise Resultant Force Profile at a Moderate Angle of Attach
0%10%20%30%40%50%60%70%80%90%
100%
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Rel
ativ
e F
orce
per
Un
it S
pan
Percentage Distance Hub-to-Tip of Blade
70%
Laminar Flow and Boundary Layer
Aeroelasticity of Wind Turbine Blades
• The interaction between aerodynamic forces structural stiffness.
• A key parameter is torsional divergence (the more common problem in high aspect ratio aerofoils)
• The resultant lift force is at the aerodynamic centre (ac) of the blade and is approximately 25% chord length from the blade leading edge.
• The shear centre is approximately 34.5% of the chord length from the leading edge (for a uniformly distributed material blade cross section of typical aerofoil shape).
• The importance of not adding significant weight behind the shear centre is crucial.
tmax
0.25c
acShear Centre
0.3c0.345c
0.345c
Blade Repair Zoning
1
2
34
Blade Repair Zoning
Zone 1. For both for aerodynamic and structural purposes. The blade leading edge and requires the mould line (D-nose shape) to be maintained for the laminar boundary layer. Zone 1 is from the 20% to 100% span length and to 25%-30% of the local chordline. Zone 1 will always require a flush repair.
Zone 2. For aeroelastic purposes. Not add significant weight to the blade for blade mass balance, but is not a major structural region of the blade. The repair needs to be an aeroelastic semi-structural repair.
Zone 3. Primarily for aeroelastic purposes. Not necessarily need to be flush for airflow aerodynamics, but must not add significant weight behind the shear centre position. Trailing edge repair are typically flush for the aeroelastic requirements.
Zone 4. Not required to be aerodynamically smooth, but may need to the semi-structural or structural based on the severity of the damage and the location of the damage to the main load bearing region of Zone 4 (i.e. spar cap). Because of the large enclosed area of the blade in Zone 4 the torsional rigidity is much higher than locations in Zone 3, hence aeroelastic requirements are not necessarily critical. However, significant damage to Zone 4 training edge may need a flush semi-structural repair.
REPAIR FUNCTIONAL SPECIFICATION
• The basic functional specification requirements are a combination of the customer requirements and engineering specification.
• Utilizing the Quality Functional Deployment (QFD) approach develop a functional specification
Typical Customer Requirements(not necessarily an exhaustive list)
• Fast repair application
• Quick return to operational usage
• Low cost repair
• Structurally efficient repair
• Repair application safety
• In-situ repair
• Low impact on operational efficiency
• Negligible impact on blade aeroelastic balance
Notable Engineering Specifications(not necessarily an exhaustive task list)
• Number of personnel required to undertake the repair.
• Cure time of the repair resin system
• Time to undertake the repair process
• Total downtime of the turbine
• Repair in precipitation (Yes/No)
• Allowable maximum wind speed to conduct the repair
• On-site power (Yes/No)
• Blade removable (Yes/No)
REPAIR METHODOLOGYSTEP 1 – Damage Assessment
• The damage is identified (usually visually)
• Conduct an NDI survey to determine the damage type and extent.
• The NDI survey will require in-situ positioning of the NDI equipment.
REPAIR METHODOLOGYSTEP 2 – Damage Type/Category
The damaged area is zoned and damage type categorized:
• Intralaminar Matrix Cracks
• Interlaminar Matrix Cracks (Delaminations)
• Fibre Fracture (Holes)
Delamination
Cut Fibres
Matrix Cracks
REPAIR METHODOLOGYSTEP 3 – Damage Stress State
Engineering evaluation of the repair requirements is based onblade zone and damage type will determine the repair schemetype.