Analysis of the Impact of Leading Edge Surface Degradation on Wind Turbine Performance

Abstract

Over time it has been reported wind turbine power output can diminish below manufacturers promised levels. This is clearly undesirable from an operator standpoint, and can also put pressure on turbine companies to make up the difference. A likely explanation for the discrepancy in power output is the contamination of the leading edge due to environmental conditions creating surfaces much coarser than intended. To examine the effects of airfoil leading edge roughness, a comprehensive study has been performed both experimentally and computationally on a NACA 633 − 418 airfoil. A description of the experimental setup and test matrix are provided, along with an outline of the computational roughness amplification model used to simulate rough configurations. The experimental investigation serves to provide insight into the changes in measurable airfoil properties such as lift, drag, and boundary layer transition location. The computational effort is aimed at using the experimental results to calibrate a roughness model that has been implemented in an unsteady RANS solver. Furthermore, a blade element momentum code was used to assess the impact on the performance of a turbine as whole due to discrepancies in clean vs. soiled airfoil characteristics. The results have implications in predicting the power loss due to leading edge surface roughness, and can help to establish an upper bound on admissible surface contamination levels.

High-Resolution Structure-from-Motion for Quantitative Measurement of Leading-Edge Roughness

“…As the shape of wind turbine blades is specifically designed to achieve maximum energy efficiency [3], this increased leading-edge roughness (LER) may lead to a reduced annual energy production of the wind turbine. Through CFD modelling, several studies have found that even a small degree of LE erosion can lead to 2-5% loss in annual energy production [4][5][6]. Severely eroded blades with high levels of LER can experience losses from 8% and up to 25% [4,7,8].…”

On the role of surface roughness in the aerodynamic performance and energy conversion of horizontal wind turbine blades: a review

“…The annual energy losses for the heavy erosion cases with pits, gouges and delamination can reach up to 25%. On the other hand, Langel et al [27] predicted the power loss because of insect accumulation is roughly 5%.…”

“…Second, a comparison between the experimental results and computational roughness model was presented by Langel et al [27]. They used a NACA 63 3 -418 airfoil model to study the effect of different roughness patterns on its aerodynamic performance.…”

Wind tunnel experiments on a NACA 633‐418 airfoil with different types of leading edge roughness

“…Thus, in recent years, the performance of wind turbines with LER has been investigated in more detail. Examples of such investigations are found in work by Sareen et al., 13 Gaudern, 14 Ehrmann et al., 15 and Langel et al 16 …”