Realistic Leading-Edge Roughness Effects on Airfoil Performance
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abstract
Wind farm operators observe power production decay over time, with the exact cause unknown and dificult to quantify. A likely explanation is blade surface roughness, as wind turbines are continuously subjected to environmental hazards. Dificulty arises in understanding and quantifying performance degradation. Historically, wind turbine airfoil families were designed for the lift to be insensitive to roughness by simulating rough- ness with 2D trip strips. Despite this, roughness is still shown to negatively affect airfoil lift performance. Experiments have also illustrated that random-distributed roughness is not properly simulated by trip strips. Therefore, to better understand how real rough- ness effects performance, field measurements of turbine-blade roughness were made and simulated on an airfoil section in a wind tunnel. This data will serve to validate and cal- ibrate a one-equation, computational roughness amplification model that interacts with the Langtry-Menter transition model. The observed roughness contains 2D steps, heavy 2D erosion, pitting, insects, and repairs. Of these observations, 2D steps from paint chips were characterized and recreated for this particular wind tunnel entry. The model was tested at chord Reynolds numbers up to 3:6 106. Measurements of lift, drag, and pitch- ing moment were made with and without roughness contamination. Transition location was acquired with infrared thermography and a hotfilm array. The paint roughness yields a consistent increase in drag compared to the clean configuration. Numerical simulations are only compared to the clean configuration and match well to lift, drag, and transition for Rec = 1:6 106. However, drag is overpredicted at Rec = 3:2 106.
