Calculation of the power output loss based on thermographic measurement of the leading edge condition

Due to operation under harsh conditions, rotor blades suffer from soiling and erosion of the leading edge, which causes a premature laminar-turbulent transition of the boundary layer flow. A quantification of both the extent of the contamination and the impact on wind turbine performance is difficult and calculations are based on estimates. A new method for assessing the power output loss due to leading edge contamination is presented. The method is based on thermographic flow measurements along the rotor blade and the automated determination of the laminar-turbulent transition location. A comparison with the expected natural transition of the clean rotor blade position enables the extent of the leading edge contamination to be quantified. Measurements on a multi-MW rotor blade indicate a contamination level of up to 90.4 % in the given highly contaminated example. This information is then used in a blade element method (BEM) model to calculate the annual energy production (AEP) for both a clean and a contaminated case. Results indicate that for this particular case, the measured contamination level leads to a decrease in annual energy production of 4.7 % to 2.7 % for the investigated average wind speeds of 6 m/s to 9 m/s.