Performance analyses of low Reynolds number airfoils for small-scale horizontal axis wind turbines

• Main Author: Chua, John Christian T.
• Format: text
• Language: English
• Published: Animo Repository 2017
• Subjects: Wind turbines; Aerofoils
• Online Access: https://animorepository.dlsu.edu.ph/etd_masteral/5705
• Institution: De La Salle University

Research on low Reynolds number has become a promising topic of interest in wind turbine studies. The wind turbine performance is greatly dependent on the rotor blade configuration as defined by airfoils. Airfoils employed for this type of application could experience performance degradation caused by the formation of separation bubbles. Similarly, wind turbines subjected to turbulent environment could likely affect the performance of airfoils and the efficiency of rotor blades. This study aims to investigate the aerodynamic characteristics of several thin and thick airfoils intended for small horizontal axis wind turbines considering the impacts of moderate turbulence intensity and transitional separation bubble using Xfoil. Numerical results were validated against published experimental data and exhibited favorable agreement more specifically in attached flow conditions within the Reynolds number range of 300 x103 to 500 x103. Surface pressure and skin friction drag coefficient plots show that the upstream migration of the separation bubble is associated with decrease in its stream wise extent as angle of attack is increased. With increasing Reynolds number and turbulence intensity, separation bubble length is likewise reduced due to postponement of laminar separation and immediate reattachment of the separated shear layer as a turbulent boundary layer. The reduction of bubble length due to amplification of turbulent mixing in the unstable laminar region is fairly associated with the increase of lift-to-drag ratio, which is more pronounced in low angles of attack and Reynolds numbers around 200 x103. Additionally, separation bubble tends to disappear at higher values of Reynolds number and turbulence intensity but the improvement in lift-to-drag ratio is compromised due to occurrence of pre-trailing-edge separation that tends to expand with increasing incidence. The effect of Reynolds number and turbulence intensity on separation bubble length appears to be similar but exhibit a few differences in terms of variations in lift-to-drag ratio. Consequently, output numerical data were also used to perform statistical analyses that yielded predictive models for multiple response variables. It was learned that interaction effects could likewise have significant influence on the aerodynamic properties of airfoils and characteristic length of the enclosure.+