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Christian Bak – One of the best experts on this subject based on the ideXlab platform.

  • Development of the Risø wind turbine Airfoils
    Wind Energy, 2004
    Co-Authors: Peter Fuglsang, Christian Bak

    Abstract:

    This paper presents the wind turbine airfoil development at Ris�.\nThe design method is\n\ndescribed together with our target characteristics for wind turbine\nAirfoils. The use of the\n\nCFD code Ellipsys2D for prediction of final target characteristics\nis described together with\n\nthe VELUX wind tunnel testing setup. Three airfoil families were developed;\nRis�-A1, Ris�-P\n\nand Ris�-B1. The Ris�-A1 airfoil family was developed for rotors of\n600 kW and larger. Wind\n\ntunnel testing and field testing showed that this airfoil family is\nwell suited for stall and\n\nactive stall control. However, sensitivity to roughness was higher\nthan expected. Field tests\n\nof a 600 kW active stall wind turbine showed an estimated reduction\nin blade fatigue\n\nloading of up to 15% at the same annual energy yield and at the same\ntime reduced blade\n\nweight and blade solidity. The Ris�-P Airfoils were developed to replace\nthe Ris�-A1 Airfoils\n\nfor use on pitch controlled wind turbines. Improved design objectives\nshould reduce the sen-sitivity to roughness, but measurements are\nnot yet available. The Ris�-B1 airfoil family was\n\ndeveloped for variable speed operation with pitch control of large\nmegawatt sized rotors.\n\nWind tunnel testing verified the high maximum lift for these Airfoils,\nand the Airfoils were\n\nfound to be very insensitive to leading edge roughness. Performance\nwith vortex genera-tors and Gurney flaps in combination was found\nto be attractive for the blade root part.\n\nField testing of a 1�5 MW rotor is in progress. Copyright � 2004 John\nWiley & So

Anya R. Jones – One of the best experts on this subject based on the ideXlab platform.

  • Reynolds Number Effects on Airfoils in Reverse Flow
    53rd AIAA Aerospace Sciences Meeting, 2015
    Co-Authors: Andrew H. Lind, Luke R. Smith, Joseph Milluzzo, Anya R. Jones

    Abstract:

    This work is aimed at providing an improved understanding of the impact of the radial Reynolds number distribution that exists in the reverse flow region of a helicopter operating at high advance ratios. Time-averaged sectional airloads and flow fields were measured experimentally for four Airfoils in forward and reverse flow at Reynolds numbers between 3.3× 10 and 1.0× 10. Two Airfoils with a sharp geometric trailing edge (NACA 0012 and NACA 0024) and two Airfoils with a blunt geometric trailing edge (a 24 % thick elliptical airfoil, and a 26 % thick cambered ellipse airfoil) were tested. This work shows that the airloads for a NACA 0012 in reverse flow (a “thin” airfoil with a sharp aerodynamic leading edge) are insensitive to Reynolds number due to early flow separation. The airloads of thicker Airfoils are found to be more sensitive to Reynolds number. In reverse flow, a NACA 0024 airfoil exhibits a decrease in the magnitude of the airloads with increasing Reynolds number for −3 ≤ −αrev ≤ 15deg. The lift curve of an elliptical airfoil becomes more linear with increasing Reynolds number. The character of the lift curve for the cambered ellipse airfoil in both forward and reverse flow changes drastically for Re ≥ 3.3 × 10. This includes a large shift in the zero-lift angle of attack. These results give insight to the design of high-speed helicopter rotor blades by examining the sensitivity of airloads to the range of Reynolds numbers encountered in the reverse flow region.

  • Time-Averaged Aerodynamics of Sharp and Blunt Trailing-Edge Static Airfoils in Reverse Flow
    AIAA Journal, 2014
    Co-Authors: Andrew H. Lind, Jonathan N. Lefebvre, Anya R. Jones

    Abstract:

    Two-dimensional wind-tunnel experiments have been conducted on three Airfoils held at static angles of attack through 360 deg at a Reynolds number of Re=1.1×105 to evaluate the influence of trailing-edge shape on time-averaged force and flowfield measurements. The present study focuses on airfoil performance in reverse flow to advance the understanding of this flow regime for high-speed helicopter applications. It is shown that the drag of a NACA 0012 airfoil in reverse flow is more than twice as large compared to forward flow due to early flow separation, similar to a flat plate. Two blunt trailing-edge Airfoils are considered in this work: an elliptical airfoil and the DBLN-526. Both Airfoils exhibit a rapid increase in lift at low angles of attack in both forward and reverse flows. The drag of the elliptical airfoil in reverse flow is significantly lower than the NACA 0012 for 5

  • time averaged aerodynamics of sharp and blunt trailing edge static Airfoils in reverse flow
    AIAA Journal, 2014
    Co-Authors: Andrew Lind, Jonathan N. Lefebvre, Anya R. Jones

    Abstract:

    Two-dimensional wind-tunnel experiments have been conducted on three Airfoils held at static angles of attack through 360 deg at a Reynolds number of Re=1.1×105 to evaluate the influence of trailing-edge shape on time-averaged force and flowfield measurements. The present study focuses on airfoil performance in reverse flow to advance the understanding of this flow regime for high-speed helicopter applications. It is shown that the drag of a NACA 0012 airfoil in reverse flow is more than twice as large compared to forward flow due to early flow separation, similar to a flat plate. Two blunt trailing-edge Airfoils are considered in this work: an elliptical airfoil and the DBLN-526. Both Airfoils exhibit a rapid increase in lift at low angles of attack in both forward and reverse flows. The drag of the elliptical airfoil in reverse flow is significantly lower than the NACA 0012 for 5<αrev<17  deg. Lift was calculated via a circulation box method applied to time-averaged flowfield measurements and compared t...

Peter Fuglsang – One of the best experts on this subject based on the ideXlab platform.

  • Development of the Risø wind turbine Airfoils
    Wind Energy, 2004
    Co-Authors: Peter Fuglsang, Christian Bak

    Abstract:

    This paper presents the wind turbine airfoil development at Ris�.\nThe design method is\n\ndescribed together with our target characteristics for wind turbine\nAirfoils. The use of the\n\nCFD code Ellipsys2D for prediction of final target characteristics\nis described together with\n\nthe VELUX wind tunnel testing setup. Three airfoil families were developed;\nRis�-A1, Ris�-P\n\nand Ris�-B1. The Ris�-A1 airfoil family was developed for rotors of\n600 kW and larger. Wind\n\ntunnel testing and field testing showed that this airfoil family is\nwell suited for stall and\n\nactive stall control. However, sensitivity to roughness was higher\nthan expected. Field tests\n\nof a 600 kW active stall wind turbine showed an estimated reduction\nin blade fatigue\n\nloading of up to 15% at the same annual energy yield and at the same\ntime reduced blade\n\nweight and blade solidity. The Ris�-P Airfoils were developed to replace\nthe Ris�-A1 Airfoils\n\nfor use on pitch controlled wind turbines. Improved design objectives\nshould reduce the sen-sitivity to roughness, but measurements are\nnot yet available. The Ris�-B1 airfoil family was\n\ndeveloped for variable speed operation with pitch control of large\nmegawatt sized rotors.\n\nWind tunnel testing verified the high maximum lift for these Airfoils,\nand the Airfoils were\n\nfound to be very insensitive to leading edge roughness. Performance\nwith vortex genera-tors and Gurney flaps in combination was found\nto be attractive for the blade root part.\n\nField testing of a 1�5 MW rotor is in progress. Copyright � 2004 John\nWiley & So