Optimization of core grove geometry for the manufacture and operation of composite sandwich structures in wind turbine blades
Topic(s) : Manufacturing
Co-authors :
Maksim LARIONOV (DENMARK), Md Tusher MOLLAH (DENMARK), Jon SPANGENBERG , Robert PIERCE (DENMARK)Abstract :
As modern wind turbine blades continue to grow in scale, there is also a significant need to reduce weight and improve manufacturing reliability for greater efficiency in both the operation and production respectively. Large regions of the blade structure consists of composite sandwich panels, with a lightweight core material surrounded by Non-Crimp glass fiber fabric skins, that is manufactured by large-scale Vacuum Assisted Resin Infusion (VARI). While the main purpose of lightweight core materials is to increase the stiffness of sandwich panel, many special grooves are also machined into the core materials to facilitate improved forming or infusion behavior. The design of such features is still reliant on the empirical experience of blade manufacturers. However, significant research into the optimization of groove dimensions and spacing has been little work, despite the potential improvements in manufacturing speed and reliability or reductions in total resin uptake and a reduction of overall blade mass. This work specifically focuses on the design of shallow resin infusion channels, investigating the optimization of cross-sectional shape on resin flow and uptake by analytical, numerical, and experimental means.
The performance of different channel designs can be quantified by an equivalent permeability, dependent on the shape and dimensions of the channel cross-section and the permeability properties of the adjacent fabric . These channels are typically rectangular, however Figure 1a shows that circular or square cross sections can offer better flow performance. Additionally, the total embedded resin weight from different designs can be determined from the combined contributions of the direct resin weight within the channel volume and the absorbed resin weight (uptake) by the porous core material (based on channel surface area). This again supports the use of a square (or circular) cross-section for the least resin uptake. Balancing resin flow and weight, this work demonstrates how a 1.5x3 mm2 rectangular groove can be replaced by a 2x2 mm2 square groove for a 9.3% increase of equivalent permeability and a 14.9% reduction in resin weight.
The analysis of the core channel design has also been validated both experimentally and numerically, using FEM (PAM-Composites) and FVM (Flow-3D) infusion models. These have allowed for a more thorough investigation into the significance of lead/lag behavior in the channels and adjacent reinforcement fabrics that make up the composite skins, which can significantly affect infusion quality and the potential for dry spots. Ultimately this work prepares a number of recommendations for optimizing channel designs in core materials to best balance their infusion performance and resin uptake.
The performance of different channel designs can be quantified by an equivalent permeability, dependent on the shape and dimensions of the channel cross-section and the permeability properties of the adjacent fabric . These channels are typically rectangular, however Figure 1a shows that circular or square cross sections can offer better flow performance. Additionally, the total embedded resin weight from different designs can be determined from the combined contributions of the direct resin weight within the channel volume and the absorbed resin weight (uptake) by the porous core material (based on channel surface area). This again supports the use of a square (or circular) cross-section for the least resin uptake. Balancing resin flow and weight, this work demonstrates how a 1.5x3 mm2 rectangular groove can be replaced by a 2x2 mm2 square groove for a 9.3% increase of equivalent permeability and a 14.9% reduction in resin weight.
The analysis of the core channel design has also been validated both experimentally and numerically, using FEM (PAM-Composites) and FVM (Flow-3D) infusion models. These have allowed for a more thorough investigation into the significance of lead/lag behavior in the channels and adjacent reinforcement fabrics that make up the composite skins, which can significantly affect infusion quality and the potential for dry spots. Ultimately this work prepares a number of recommendations for optimizing channel designs in core materials to best balance their infusion performance and resin uptake.