Establishing the optimal conditions for rotating arm erosion testing, materials characterisation and computational modelling of wind turbine blade rain erosion

This thesis was previously held under moratorium from 5th August 2020 until 5th August 2022.Leading edge erosion is a growing issue within the wind industry; impacting upon blade performance and efficiency. Even with the wide range of research being conducted, there are currently no apparent foolproof material solutions for the issue. The research presented here looks to develop a better understanding of lead edge erosion: firstly through the development and characterisation of an erosion test rig; then by conducting a range of parametric studies, both numerically (finite element) and experimentally, to explore the key factors and damage mechanisms associated with leading edge erosion. This work shows the importance of characterising a test rig before starting any experimental tests, through this work specifically the most optimal operating conditions can be established. Consistent results are key to transferring knowledge from the test rig to real-world applications, and this repeatability can only be reached with proper understanding of the operating conditions and aerodynamics of an erosion test rig. Reliable results were achieved at rotational speeds around 1100 and 1200rpm rather than the fastest rotational speeds, speeds greater than 1200rpm resulted in an increase in droplet breakup and less repeatable results. The development of modelling techniques alongside experimental testing allows for the physics associated with droplet impacts to be fully explored. Sub-surface imagery, through XCT scans, showed that any defects near the surface of a sample can lead to stress concentrations at the damaged area. The XCT imagery also showed that voids near the composite interface did not affect the erosion initiation or location. Subsequent modelling work also revealed that stress concentrations were the main differing factor between undamaged and damaged samples undergoing erosion, rather than a change in the peak stresses. The peak compressive and shear stresses remained similar regardless of the state of the sample, however, the stress waves became concentrated centrally, around the damaged area, once erosion had initiated. An investigation of a variety of different samples showed that currently industry struggles to find a balance between performance and consistency. Mass loss curves were established for each of the different materials tested, with the affect of number of impacts and kinetic energy also explored. Different failure mechanisms were observed: delamination causing severe damage and brittle failure most common amongst samples. Interesting work is being undertaken where coatings are optimised for certain operating conditions; showing that there is an understanding of the failure mechanisms present, though the level of understanding has not reached the stage where a significant improvement in blade lifetime can be achieved. Future work and research development aimed at further understanding the issues of blade leading edge erosion are also identified, discussed and recommendations given.Leading edge erosion is a growing issue within the wind industry; impacting upon blade performance and efficiency. Even with the wide range of research being conducted, there are currently no apparent foolproof material solutions for the issue. The research presented here looks to develop a better understanding of lead edge erosion: firstly through the development and characterisation of an erosion test rig; then by conducting a range of parametric studies, both numerically (finite element) and experimentally, to explore the key factors and damage mechanisms associated with leading edge erosion. This work shows the importance of characterising a test rig before starting any experimental tests, through this work specifically the most optimal operating conditions can be established. Consistent results are key to transferring knowledge from the test rig to real-world applications, and this repeatability can only be reached with proper understanding of the operating conditions and aerodynamics of an erosion test rig. Reliable results were achieved at rotational speeds around 1100 and 1200rpm rather than the fastest rotational speeds, speeds greater than 1200rpm resulted in an increase in droplet breakup and less repeatable results. The development of modelling techniques alongside experimental testing allows for the physics associated with droplet impacts to be fully explored. Sub-surface imagery, through XCT scans, showed that any defects near the surface of a sample can lead to stress concentrations at the damaged area. The XCT imagery also showed that voids near the composite interface did not affect the erosion initiation or location. Subsequent modelling work also revealed that stress concentrations were the main differing factor between undamaged and damaged samples undergoing erosion, rather than a change in the peak stresses. The peak compressive and shear stresses remained similar regardless of the state of the sample, however, the stress waves became concentrated centrally, around the damaged area, once erosion had initiated. An investigation of a variety of different samples showed that currently industry struggles to find a balance between performance and consistency. Mass loss curves were established for each of the different materials tested, with the affect of number of impacts and kinetic energy also explored. Different failure mechanisms were observed: delamination causing severe damage and brittle failure most common amongst samples. Interesting work is being undertaken where coatings are optimised for certain operating conditions; showing that there is an understanding of the failure mechanisms present, though the level of understanding has not reached the stage where a significant improvement in blade lifetime can be achieved. Future work and research development aimed at further understanding the issues of blade leading edge erosion are also identified, discussed and recommendations given