Droplet impact modelling to predict the rain-induced Erosion of wind turbine blades

Research output: Contribution to conferencePresentation

Abstract

The wind turbine industry has grown rapidly since the last decade progressing towards manufacturing giant
offshore turbines with larger blades. Lengthy wind blades result in high tip speed whereas the impact of rain
droplets is significant in blade erosion, especially at the leading edge (Leading Edge Erosion-LEE) [1]. Eroded
blades degrade the turbine performance, reducing the Annual Energy Production (AEP) by up to 5% [2,3]. Periodic
repairing and new coating solutions for the leading edge of wind blades are the main precautions against rain
erosion [4].
To achieve the precautions strategies, the most fundamental stage of erosion, the liquid droplet impact should
be studied and analysed having reliable accuracy. Experimental observation on droplet impact is limited due to
capturing the nano-second scale impact. Analytically, the approximation value for the peak impact pressure of a
single droplet was developed by modifying the water-hammer pressure.
On the other hand, numerical studies are significantly useful to study the liquid droplet impact phenomenon by
not only calculating the peak pressure but also the pressure distribution on the surface throughout the impact time.
Therefore, the current research trend is led by CFD (Computational Fluid Dynamic) and FSI (Fluid Structure
Interaction) studies on droplet impact observing the detailed picture of this nano-scale incident. Following the
trend this research was conducted to understand the droplet impact using the CFD analysis, as a preliminary step
for estimating the repair frequencies and exploring the new coating systems.
Typical rain generally consists of 1-5 mm droplets, whereas this study focused on the single impact of a 2 mm
drop. The droplet impact speed was approximately determined as 100 m/s considering the average terminal
velocity of rain and the general tip speed of the blade. The next section of this extended abstract explains the
modelling and the simulation procedure of the single droplet impact followed by the mesh and time-step
convergence tests. The result and discussion section compares the peak pressure of the current study with analytical
and previous CFD studies while discussing the impact pressure variation on the surface and the water velocity
behaviour inside the droplet during the impact.
Original languageEnglish (Ireland)
Publication statusPublished - 06 Sep 2023

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