Raindrop Erosion of Composite Materials: Some Views on the Effect of Bending Stress on Erosion Mechanisms

Abstract

This paper represents the investigation of rain erosion on wind turbine blade materials under load in the simulation of onshore and offshore environmental conditions. The experimental work was carried out on a whirling arm rig with the material under a static 3 point bend to simulate large multi-megawatt wind turbine blades flexing during operation. This experiment was run with both fresh water and salt water to simulate onshore and offshore turbines. The results showed that the effects of a pre-stress on the samples resulted in a higher degradation rate following rain drop erosion. The microscopic analysis of the samples exposed to pre-stress identified distinctive surface features which has been termed a surface impact circular deformation. These features showed signs of cracking which enhanced the erosion rate. The pre-stressed samples also encountered a larger crossover in erosive mechanisms of abrasion and direct impacts; this was theorised to be due to the material being close to its yield stress and more likely to plastically deform.

Rain Erosion Maps for Wind Turbines Based on Geographical Locations: A Case Study in Ireland and Britain

“…A damaged blade will require a higher airflow or blade angle to produce the same output [20]. This has been proved experimentally within the literature which considered the drag coefficients of compromised blades [21] and also the microscopy of material subject to rain droplets at high velocities [22].…”

A Study of Raindrop Impacts on a Wind Turbine Material: Velocity and Impact Angle Effects on Erosion MAPS at Various Exposure Times

“…There are many ways to recreate the conditions of a wind turbine blade in the field within laboratory conditions and there have been some issues with cross referencing results from different methodologies [4,11,12]; however, the technique that replicates the conditions closest would be a whirling arm erosion rig (WARER) as stated by the DNVGL recommended practice [13]. The rig that was used for this investigation was built in the University of Strathclyde in the tribology laboratory to artificially simulate turbine blade conditions [14,15]. This was achieved with a water tank connected to the peristaltic pump through tubing, then connected to 16 droplet needles of the chosen gauge (23 G).…”

Some Thoughts on Modelling Hail Impact on Surfaces

“…Another aspect that could be tackled using a modelling approach is the effect of bending loads on the simulated material damage during ice impact. Bending stresses have been shown experimentally to affect the rain erosion properties of glass fibre-reinforced composites [19], and so adding a constant load in order to simulate the stress caused by the blade rotational motion should be considered, as it may have a large effect on the material predicted response to solid particle impact. This effect will assume more significance in turbine blades with larger diameters, and so will become more important as turbine manufacturers seek to produce turbines with greater power output.…”