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Öğe An experimental study of acoustic disturbances effect on laminar separation bubble and transition over an aerofoil at low reynolds number(2012) Hakan Açikel, H.; Serdar Genç, M.; Tu?rul Akpolat, M.; Karasu, IlyasIn this study, the effect of parallel acoustic excitation on laminar separation bubble over NACA2415 aerofoil and stall characteristics of the aerofoil were investigated at Re=50x103 and at various angles of attack. A sound source connected to a signal generator and an audio amplifier was placed in front of the wind tunnel to be parallel to the aerofoil. The amplitude of the sinusoidal sound wave was kept constant at 60 dB to determine the effects of varying frequencies from 70 Hz to 1100 Hz. In the experiments, an external three component load-cell system for force measurements, a scanivalve unit and a pressure transducer for pressure measurements and smoke-wire technique for flow visualization were used. The pressure measurement experiments showed that at the range of 200 Hz to 850 Hz the separated flow was reattached at the angle of attack of 15° and the laminar separation bubble was shortened at the angle of attack of 8° The shortened laminar separation bubble was seen clearly from some-wire flow visualization photos. Furthermore, the stall angle was delayed from ?s=12° to ?s=16° and CLmax was increased from 1.2 to 1.56 with acoustic excitation of 350 Hz. © 2012 by the American Institute of Aeronautics and Astronautics, Inc.Öğe 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, IlyasIn 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.Öğe An experimental study on aerodynamics of NACA2415 aerofoil at low Re numbers(Elsevier Science Inc, 2012) Genc, M. Serdar; Karasu, Ilyas; Acikel, H. HakanThis 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.Öğe An experimental study on laminar separation bubble and transition over an aerofoil at low reynolds number(American Institute of Aeronautics and Astronautics Inc., 2012) Karasu, Ilyas; Genç, MMustafa Serdar; Açikel, H. Hakan; Akpolat, M. Tu?rulLaminar separation bubble over NACA2415 aerofoil at Re=50,000 and different angles of attack was investigated in detail by performing force, pressure, hot-wire and flow visualization via smoke wire technique. From the experiments, the flow separation, the reattachment and forming the laminar separation bubble were clearly seen. From the experimental results, it was indicated that the point of separation moved towards the leading edge as the angle of attack increased. Moreover, the flow visualization results showed that as the angle of attack increased further, at the angle of attack of 13o the bubble burst and the separated flow was not able to reattach to the aerofoil surface, which indicated the stall. © 2012 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.Öğe A review on wind energy and wind-hydrogen production in Turkey: A case study of hydrogen production via electrolysis system supplied by wind energy conversion system in Central Anatolian Turkey(Pergamon-Elsevier Science Ltd, 2012) Genc, Mustafa Serdar; Celik, Muhammet; Karasu, IlyasStudies about investigation of hydrogen production from wind energy and hydrogen production costs for a specific region were reviewed in this study and it was shown that these studies were rare in the world, especially in Turkey. Therefore, the costs of hydrogen, hydrogen production quantities using a wind energy conversion system were considered as a case study for 5 different locations of Nigde, Kirsehir, Develi, Sinop and Pinarbasi located in the Central Anatolia in Turkey. Annual wind energy productions and costs for different wind energy conversion systems were calculated for 50 m, 80 m and 100 m hub heights. According to wind energy costs calculations, the amounts and costs of hydrogen production were computed. Furthermore, three different scenarios were taken into account to produce much hydrogen. The results showed that the hydrogen production using a wind energy conversion system with 1300 kW rated power had a range from 1665.24 kgH(2)/year in Nigde at 50 m hub height to 6288.59 kgH(2)/year in Pinarbasi at 100 m hub height. Consequently, Pinarbasi and Sinop have remarkable wind potential and potential of hydrogen production using a wind-electrolyzer energy system. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.
