Aerodynamic Characteristics of Airfoils with Blunt Trailing Edge

Abstract

23 técnica #24 revista de ingeniería. Universidad de los Andes. rev.ing. ISSN. 0121-4993. Noviembre de 2006 PALABRAS CLAVE Aerodinámica, Perfiles Aerodinámicos, CFD, Energía Eólica, Aerogeneradores. RESUMEN El siguiente trabajo estudia de manera com-putacional el comportamiento de las características aerodinámicas de perfi les NACA (National Advisory Committee for Aeronautics, hoy conocido como NASA), con modifi caciones en el borde de salida. Las modifi ca-ciones consisten en remover secciones del borde de fuga del perfi l. La investigación realizada estudia 39 perfi les diferentes de la familia NACA de 4 dígitos, con modelos teóricos sencillos para explicar los fenómenos. Los re-sultados muestran los cambios en las características de sustentación y arrastre del perfi l, y cambios en cuanto a la entrada en pérdida del mismo. ABSTRACT This paper is a computational study of the behaviour of aerodynamic characteristics of NACA (National Advisory Committee for Aeronautics, today known as NASA) profi les with tailored trailing edges. 39 different profi les 4-digit NACA family were studied du-ring the research. A computational research was made, using simple theoretical models to explain and to un-derstand the results. The results describe the changes in lift and drag characteristics and changes in stall angle of attack. Recibido 13 de marzo de 2006, aprobado 1 de junio de 2006. Traditionally, airfoil geometries are such that they have a rounded leading edge and a sharp trailing edge. It would be useful in some cases, to use airfoil geometries which are thicker, in order to attain better structural performance. The following paper studies the effects on the aerodynamic performance caused by modifications made to the trailing edge of subso-nic profiles, intended for use in wind turbines. The type of modifications proposed can be summarized as cutting off the trailing edge perpendicular to the chord line of the profile at different positions along the chord. In the early 1950's, NACA (National Advi-sory Committee for Aeronautics) undertook a series of investigations to conclude about the benefits of tailoring the trailing edge of supersonic and transo-nic profiles [1-4]. The conclusions of these studies can be summarized as an increase in the maximum lift coefficient, and increase in profile drag, and an increase in the lift coefficient slope. The following paper studies similar results for subsonic profiles. The results found include an increase of maximum lift coefficient, a delay in stall and an increase in pro-file drag. This paper describes how the C l , C d , and C l /C d curves change as modifications to the trailing edge are made. Delay in stall of the airfoil could be advantageous for applications such as acrobatic flight, where high an-gles of attack are needed before the profile stalls. For wind turbines, the fact that higher angles of attack can be reached before entering stalled conditions means that some unsteady effects can be avoided. Namely, when wind gusts or sudden change of wind direc-tion occur, some sections of the wind turbine can stall. This happens mainly in the inboard region of