The forces of nature put super heavy wind turbine blades to the test. The longest blades are 100 metres long and achieve a rotation speed of around 250 km/h when the wind hits the hardest. Even though the blades are built to withstand the rigours of nature, even the smallest production errors can have major impact—at worst, the blades may break. However, the defects usually result in expensive repairs or that the blades must be discarded.
Manufacturing the massive blades is an extensive process, and even though the blade is hollow, it consists of many tonnes of load-bearing material. The largest wind turbine blades are cast in moulds more than 100 metres long, which are moved around the huge production halls using gantry cranes.
One of the biggest challenges in manufacturing is avoiding air pockets when moulding the blade.
Air pockets that weaken
When a wind turbine blade is produced, many layers of carbon fibre or fibreglass cloth are placed on top of each other with other material in a mould. Liquid resin (a form of hardening plastic) is then added through a so-called vacuum infusion. The resin spreads between the layers and binds the components together. However, if the resin flows too quickly in parts of the process, air can get trapped, creating air pockets that weaken the bond between the materials.
"It's hard to monitor what's happening inside the casting. If the resin does not saturate the fibres sufficiently, air pockets will occur, weakening the blade and—at worst—leading to it breaking. It's very expensive for a manufacturer to discard what is easily many tonnes of material," says Philipp Ulrich Haselbach, Associate Professor at DTU Wind.
He has participated in the AIOLOS project to develop sophisticated production methods that enable simulations with 'digital twins' to predict exactly where air pockets risk occurring before the actual casting begins.
"We simulate the casting process to identify better infusion strategies and modifications that can prevent air pockets and other errors from occurring," explains the associate professor.
By testing alternative methods digitally, manufacturers can optimize resin flow through the materials before they even touch the physical raw materials.
The innovative methods are developed in close interaction between computer and reality. At DTU Risø Campus, the researchers use ComponentLab, which is a key facility in the process, making it possible to cast and produce the researchers' own 12.6-metre-long wind turbine blades under controlled conditions.
