Emil Brink Kruse Olsen

Quantifying leading edge roughness on wind turbine blades

Increasing focus on wind turbine performance has led to the need for a deeper understanding of the impact of blade erosion and degradation on the aerodynamic properties of wind turbine blades. To accomplish this task, the LER project has been established. 

The project consortium consists of the Technical University of Denmark (DTU), Aalborg University (AAU) and the Danish National Meteorology Institute (DFM) with Power Curve as project manager. The LER project is partially funded by the Energy Technological Development and Demonstration Program (EUDP). Turbine operators experience decreases in AEP over time. Among other things, this is caused by LER. The ability to better quantify and estimate the losses is relevant to establish a reliable business case for a retrofit solution, aiming at regaining lost energy production.

There are two novel ideas in this project. The first one is to develop the roughness models in DTU’s EllipSys CFD software. The second one is to scan the LER directly on a wind turbine blade with a UAV/Drone.

Abstract

The project goal is to quantify leading edge roughness (LER) on wind turbine blades in order to estimate the aerodynamic penalty and hence the decrease in AEP, which can provide a basis for more qualified repair/retrofit solutions. The estimations are done in CFD, and methods are to be validated in the National Wind Tunnel. The quantification of LER on a given turbine is done by means of 3D reconstruction of the blade surface using a UAV with a high-resolution camera.

Current results

The main findings at the time of writing arethat there seems to be no correlation, within a certain limit, between the size of a cavitation and the lift and drag penalties. It seems that the edges of a cavitation as well as the location on the aerofoil is of more critical character.

The preliminary results for geometrical changes simulated in CFD can be seen in figures 1 and 2. Zigzag tape has been used to trip the boundary layer and emulate LER. Two heights, 0.4 and 0.8 mm, were used in the Stuttgart tunnel measurements. The drag in figure 1 is estimated quite well considering these are the first simulations. However, the simulated lift penalty seems inaccurate. The lift penalty in the simulation of 0.8 mm zigzag tape corresponds to the measured 0.4 mm zigzag tape. 

The results are currently being investigated, and the zigzag tape is being simulated by a roughness model without geometrical changes to the aerofoil.

The deviation may be due to the dimensional differences – The LER tape is a 3D pattern but the CFD simulations are made in 2D. It is possible that the simulation is unable to capturesome of the critical vorticities.

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