Effects of Grit Roughness and Pitch Oscillations on the S815 Airfoil

    Research output: NRELSubcontract Report


    Horizontal axis wind turbine rotors experience unsteady aerodynamics due to wind shear when the rotor is yawed, when rotor blades pass through the support tower wake, and when the wind is gusting. An understanding of this unsteady behavior is necessary to assist in the calculation of rotor performance and loads. The rotors also experience performance degradation due to surface roughness. Thesesurface irregularities are caused by the accumulation of insect debris, ice, and/or the aging process. Wind tunnel studies that examine both the steady and unsteady behavior of airfoils can help define pertinent flow phenomena, and the resultant data can also be used to validate analytical computer codes. An S815 airfoil model was tested in The Ohio State University Aeronautical andAstronautical Research Laboratory (OSU/AARL) 3x5 subsonic wind tunnel (3x5) under steady flow with both stationary model conditions and pitch oscillations. To study the extent of performance loss due to surface roughness, a standard grit pattern, leading edge grit roughness (LEGR), was used to simulate leading edge contamination. After baseline cases were completed, the LEGR was applied for bothsteady state and model pitch oscillation cases. The Reynolds numbers for steady state conditions were 0.75, 1, 1.25, and 1.4 million, while the angle of attack ranged from -20 deg. to +40 deg. With the model undergoing pitch oscillations, data were acquired at Reynolds numbers of 0.75, 1, 1.25, and 1.4 million, at frequencies of 0.6, 1.2, and 1.8 Hz. Two sine wave forcing functions were used, atmean angles of attack of 8 deg., 14 deg., and 20 deg.
    Original languageAmerican English
    Number of pages154
    StatePublished - 1996

    Bibliographical note

    Work performed by The Ohio State University, Columbus, Ohio

    NREL Publication Number

    • NREL/TP-442-7820


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