HAWT blade erosion

Wind turbine blade leading edge (LE) erosion has become a critical technical and cost issue in the wind energy industry. The problem is particularly serious in the case of offshore wind farms including hundreds of large horizontal axis wind turbines (HAWTs), because the large rotor size, unavoidably, forces higher tip speeds to reduce loads on the drivetrain and also the mass of the blades. This higher tip speed results in higher relative kinetic energy of rain droplets and hailstones impacting the blade leading edge region, an occurrence which accelerates the blade LE erosion process.

HAWT blade LE erosion results in surface state alterations (roughness), and, at more advanced erosion stages, more significant airfoil geometry alterations due to increased material loss, for example delamination. These geometric alterations reduce the aerodynamic performance of HAWT rotors and, thus, their power with respect to the design intent, yielding lower annual energy production (AEP). Moreover, blade LE repair or reinforcement can be very costly, due to the harsh marine environment and downtimes. Both AEP losses and repair costs contribute to lowering and making uncertain the levelized cost of energy (LCOE) of the power plant, with the uncertainty arising primarily because of the difficulties of determining the power loss associated with specific patterns and depths of LE erosion, and also predicting the site-dependent progression of the erosion process. An introductory and cross-disciplinary overview of the blade LE erosion problem in offshore wind is provided in the presentation delivered for the Institution of Mechanical Engineers in July 2020 [1].

The research we are conducting on blade LE erosion focuses both on investigating the aerodynamics of the eroded blades of offshore HAWT blades and developing experimentally validated simulation-based technologies for the rapid and reliable estimate of wind turbine and wind farm AEP losses due to observed blade LE erosion. With this mindset, we have started by making a first demonstration of the AEP loss prediction system (ALPS) technology for the case of advanced blade LE erosion resulting in LE delamination [2]. ALPS combines Navier-Stokes (NS) Computational Fluid Dynamics (CFD), the blade element momentum theory (BEMT), and artificial neural networks (ANNs) to obtain very rapidly reliable estimates of the AEP loss due to delamination. The particular blade damage considered in [2] is a simplified representation of a severe delamination state of comparable depth and chordwise extension. The modular structure of the ALPS technology is depicted in the figure below. A brief summary of the ALPS technology is also available in a presentation made at the Technical University of Denmark in February 2020 [3].

We are presently also working on generalizing the damage modeling functionalities of ALPS by including in the digital model of the eroded blade also the pits and gouges encountered in the earlier stages of the delamination process [4], leading to blade strip geometries of the type reported in the figure below.

This research is being conducted in collaboration with the Department of Mechanical and Aerospace Engineering of Strathclyde University, Glasgow, UK and the School of Engineering of Universita' della Basilicata, Potenza, Italy. The work has received support from Helispeed Ltd., the UK Engineering and Physical Sciences Research Council and the European Union through the Centre of Global Eco-innovation of Lancaster University.

1. M.S. Campobasso, Accounting for Uncertainty in Offshore Wind Economics: the Case of Blade Leading Edge Erosion, Institutions of Mechanical Engineers, webinar, 1 July 2020. Download presentation (1.7 MB).

2. M.S. Campobasso, A. Cavazzini, E. Minisci, Rapid Estimate of Wind Turbine Energy Loss due to Blade Leading Edge Delamination Using Artificial Neural Networks, ASME Journal of Turbomachinery, Vol. 142, no. 7, 2020. DOI: 10.1115/1.4047186.

3. M.S. Campobasso, L. Cappugi, A. Cavazzini, E. Minisci, ALPS: CFD and Machine Learning for Real-time Estimates of HAWT AEP Loss due to Blade Leading Edge Erosion, International Symposium on Leading Edge Erosion of Wind Turbine Blades, Risoe, Technical University of Denmark, Roskilde, 4-6 February 2020. Download presentation (1.6 MB).

4. A. Castorrini, L. Cappugi, A. Bonfiglioli, M.S. Campobasso, Assessing wind turbine energy losses due to blade leading edge erosion cavities with 3D computer-aided engineering, TORQUE Conference, Delft, The Netherlands, 2020. Under review.