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Permanent URI for this collectionhttps://ada.atilim.edu.tr/handle/123456789/19

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Browsing Scopus by Author "Akpolat, Muhiddin Tuğrul"

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    Book Part
    Citation Count: 9
    Acoustic control of flow over NACA 2415 aerofoil at low reynolds numbers
    (Springer International Publishing, 2016) Serdar Genç,M.; Karasu,İ.; Hakan Açıkel,H.; Tuğrul Akpolat,M.; Özkan,G.; Airframe and Powerplant Maintenance
    Within the concept of this study, first low Reynolds number flow phenomena, including laminar separation bubble (LSB) and stall were explained. Then a literature review on the acoustic flow control was presented in three categories: flow control with constant frequency, flow control with constant amplitude, and flow control with variable frequency and amplitude. Aside from the review part, results of a comprehensive experimental study on the effects of acoustic flow control at low Reynolds numbers were presented. Within the scope of this experimental study, the effects of both parallel and perpendicular acoustic flow control were examined by means of pressure measurements, force measurements, hot-wire anemometry, flow visualization, and particle image velocimetry (PIV). In order to establish a baseline data, all of the measurements were first applied for the no control case. The effects of acoustic control were examined especially on the characteristics of LSB and stall. It was found that the acoustic excitation can be employed to decrease the height and length of LSB leading to increased lift coefficient and decreased drag coefficient. Also, acoustic flow control increased the angle of stall. It was also seen that the effective excitation frequency increases also, but the range of Zaman number (St/Re0.5) based on effective frequency still is approximately same with increasing Reynolds numbers. Finally, it was shown that the general aerodynamics performance of an aerofoil at low Reynolds numbers can easily be enhanced by employing acoustic flow control, and the parameters of the acoustic flow control can easily be adjusted in order to keep up with the changing conditions of flow. © Springer International Publishing Switzerland 2016.
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    Article
    Citation Count: 27
    Acoustic Control of Flow over NACA 2415 Airfoil at Low Reynolds Numbers
    (Asce-amer Soc Civil Engineers, 2016) Genc, M. Serdar; Acikel, H. Hakan; Akpolat, M. Tugrul; Ozkan, Gokhan; Karasu, Ilyas; Airframe and Powerplant Maintenance
    In this study, the effects of acoustic excitation frequency on flow over an NACA 2415 airfoil were determined, and all of the experiments were done both with and without the presence of the acoustic excitation. The acoustic excitation was applied for a range of angles of attack (0 degrees-25 degrees) and Reynolds numbers of 50,000, 75,000, 100,000, 150,000, and 200,000. To examine the effects of acoustic excitation on the flow, force measurements, pressure measurements, hot-wire anemometry, smoke-wire flow-visualization, and particle image velocimetry techniques were employed. The results indicated that for stall and some limited poststall angles of attack of the acoustic excitation having a frequency in a certain range forced the separated shear layer to reattach to the surface of the airfoil. As the Reynolds number increased, the effective excitation frequency increased, but the range of Zaman number [St/(R-1/2)] was the same. With the acoustic excitation, the stall angle was delayed from 12 degrees to 16 degrees at R = 50,000, and there was a 30% and 50% increase on the maximum value of the lift coefficient and the ratio of the lift and drag forces, respectively. Moreover, the stall angle was delayed from 13 degrees to 17 degrees at R = 75,000, from 15 degrees to 18 degrees at R = 100,000, from 15 degrees to 17 degrees at R = 150,000. Furthermore, it was concluded that acoustic excitation shrunk laminar separation bubble, and an effect of the acoustic control on the separation bubble decreased as the Reynolds number increased. (C) 2016 American Society of Civil Engineers.
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    Conference Object
    Citation Count: 0
    Design and optimization of a notional scramjet by means of stream thrust analysis and design of experiments
    (American Institute of Aeronautics and Astronautics Inc., 2014) Akpolat,M.T.; Toker,K.A.; Genç,M.S.; Airframe and Powerplant Maintenance
    Within the scope of this study, a 0-dimensional code is developed by using Stream Thrust Analysis in order to evaluate scramjet cycle performance with respect to selected performance parameters (specific impulse, overall efficiency) and combustion chamber exit temperature. By using the results of this code an analysis employing "Design of Experiments" (DoE) is performed to determine the most effective input parameters and/or interactions on the scramjet performance. The results showed that most effective input parameter for all of the selected parameters is fuel/air ratio. Selected parameters are evaluated first individually then simultaneously. The purpose of evaluating the performance parameters simultaneously is to determine the input parameter set which gives the highest values of specific impulse and overall efficiency while giving the lowest value of combustion chamber exit temperature. As a result the input parameter sets for different cases are determined.