Abstract
Top coating are usually moulded, painted or sprayed onto the wind blade Leading-Edge surface to prevent rain erosion due to transverse repeated droplet impacts. Wear fatigue failure analysis based on Springer model has been widely referenced and validated to quantitatively predict damage initiation. The model requires liquid, coating and substrate speed of sound measurements as constant input parameters to define analytically the shockwave progression due to their relative vibro-acoustic properties. The modelling assumes a pure elastic material behavior during the impact event. Recent coating technologies applied to prevent erosion are based on viscoelastic materials and develop high-rate transient pressure build-up and a subsequent relaxation in a range of strain rates. In order to analyze the erosion performance by using Springer model, appropriate impedance characterization for such viscoelastic materials is then required and represents the main objective of this work to avoid lack of accuracy. In the first part of this research, it is proposed a modelling methodology that allows one to evaluate the frequency dependent strain-stress behavior of the multilayer coating system under single droplet impingement. The computational tool ponders the operational conditions (impact velocity, droplet size, layer thickness, etc.) with the appropriate variable working frequency range for the speed of sound measurements. The second part of this research defines in a complementary paper, the ultrasonic testing characterization of different viscoelastic coatings and the methodology validation. The modelling framework is then used to identify suitable coating and substrate combinations due to their acoustic matching optimization and to analyze the anti-erosion performance of the coating protection system.
Highlights
Rain erosion damage, caused by repeated droplet impact on wind turbine blades, is a major cause for concern, even more so at offshore locations with larger blades and higher tip speeds, see Figure 1.In most cases, since the surface protection plays a decisive role in the blade manufacture and overall performance, it has been identified as an area where a solution may be obtained
Numericalasand analytical models have used in this work wear surface erosion performance
The modelling description offers a guidance in the analysis based
Summary
Rain erosion damage, caused by repeated droplet impact on wind turbine blades, is a major cause for concern, even more so at offshore locations with larger blades and higher tip speeds, see Figure 1. Φ defines the relative where a portion of the stress wave is reflected back into theofcoating and the remaining is transmitted where the mass loss mdefined produced given number droplets n, can bepart estimated once impedance parameter on by thealiquid-coating interface andimpacts φ on the substrate-coating one.the to the substrate Due to this reflection a new wave is advancing in the coating with a different incubation of the coating slope of the erosion rate on the coating are identified. As we have previously stated from [13] in order to predict the incubation time and the mass removal rate, the stress history in the coating and in the substrate has to be identified analytically or numerically It is affected by the shockwave progression due to the vibro-acoustic properties of each layer, and by the time interval of the repeated water droplet impacts.
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