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    AN EXPERIMENTAL STUDY OF PERPENDICULAR ACOUSTIC DISTURBANCES EFFECT ON FLOW OVER AN AEROFOIL AT LOW REYNOLDS NUMBERS
    (Amer Soc Mechanical Engineers, 2013) Genc, M. Serdar; Akpolat, M. Tugrul; Acikel, H. Hakan; Karasu, Ilyas
    In this study, the effect of perpendicular acoustic excitation on laminar separation bubble over a NACA2415 aerofoil and stall characteristics of the aerofoil was investigated experimentally at low Reynolds numbers (50000 and 75000) and various angles of attack on the aerofoil using force measurement, pressure measurement and smoke-wire flow visualization techniques. The experiments of resonance characteristics of test section of the wind tunnel showed that the frequencies used for acoustic control were not equal to the peak (resonance) frequencies of the wind tunnel test section. The experimental results of acoustic control showed that when acoustic excitation of a certain frequency was applied, the length of the laminar separation bubble was shortened owing to the energy added to the flow by acoustic excitation. Because of the shortened laminar separation bubble, coefficient of lift was increased. Furthermore, at the stall angles the separated flow was forced to reattach to the surface of the aerofoil, so the stall angle was increased from 12 degrees to 17 degrees and maximum coefficient of lift was increased from 1.16 to 1.24 at Re=50000 and from 13 degrees to 18 degrees and maximum coefficient of lift was increased from 1.18 to 1.34 at Re=75000.
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    An experimental study on aerodynamics of NACA2415 aerofoil at low Re numbers
    (Elsevier Science Inc, 2012) Genc, M. Serdar; Karasu, Ilyas; Acikel, H. Hakan
    This study is a detailed experimental investigation on aerodynamics of a NACA2415 aerofoil by varying angle of attack from -12 degrees to 20 degrees at low Reynolds number flight regimes (0.5 x 10(5) to 3 x 10(5)d). For this investigation, pressure distributions over the aerofoil were measured using a system including a pitotstatic tube, a scanivalve unit and a pressure transducer. Moreover, time-dependant lift and drag forces and pitch moment of the aerofoil were obtained by using an external three-component load-cell system. Velocity measurements at different points over the aerofoil were carried out by using a hot-wire anemometer, and oil flow visualization method was used to photograph the surface flow patterns. The experimental results showed that as the angle of attack increased, the separation and the transition points moved towards the leading edge at all Reynolds numbers. Furthermore as the Reynolds number increased, stall characteristic changed and the mild stall occurred at higher Reynolds numbers whereas the abrupt stall occurred at lower Reynolds numbers. The stall angle varied with Re number due to the viscous effects and decreased with decreasing Re number. By the decreasing of the Re number, short bubble burst at higher angles of attack, which caused long bubble to occur. (C) 2012 Elsevier Inc. All rights reserved.