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Öğe Buji plazma sentetik jet aktüatörünün pem yakıt pili performansı üzerine etkisinin incelenmesi(Niğde Üniversitesi / Fen Bilimleri Enstitüsü, 2015) Seyhan, Mehmet; Akansu, Yahya ErkanBu yüksek lisans tez çalışması iki ana kısımdan oluşmaktadır. Bunlardan birincisi, Buji Plazma Sentetik Jet diye adlandırılan yeni bir aktuatör geliştirmek ve bu geliştirilmiş yeni aktuatörü kızgın tel anemometresi kullanarak durgun havada karakterize etmektir. İkincisiyse, PEM yakıt pili performansı üzerine BPSJ aktuatörün etkilerini deneysel olarak araştırmaktır. BPSJ aktuatör üzerinde farklı yüksek voltaj güç kaynaklarının, farklı hacimlere sahip olan başlıkların, farklı h/d oranlarının, duty cycle’ın ve frekansın etkisi yaklaşık olarak jet hızının büyüklüğünü belirlemek için kızgın tel anemometresi kullanılarak incelenmiştir. BSPJ aktuatör ile 120 m/s’nin üzerinde anlık jet hızı elde edilebilmiştir. Duman tel akış görüntüleme deneyleri düz plaka üzerinde gelişen sınır tabakayı BPSJ aktuatörün nasıl etkileyebildiğini görselleştirmek için gerçekleştirilmiştir. Oluşan sentetik jetin düz plaka etrafında gelişen sınır tabakayı bozarak sınır tabakanın üzerindeki kayma tabakalarını etkileyecek kadar güçlü olduğunu göstermektedir. Maksimum normalize hız beklendiği gibi h/d=4’de elde edilmiştir. BPSJ aktüatör yakıt pilinin katot kısmına uygulandığında, akım ve güç yoğunluğu yakıt pilinin düşük voltaj değerleri için az oranda artış sağlanmıştır. Fakat bu artış deneysel ölçüm belirsizliği içerisindedir. Bu yüzden BPSJ aktüatörün, PEMYP performansı üzerine önemli bir etkinin olmadığı gösterilmiştir.Öğe EFFECT OF ATTACK ANGLE ON FLOW AROUND A SQUARE PRISM WITH A SPLITTER PLATE(2018) Seyhan, Mehmet; Sarıoğlu, Mustafa; Akansu, Yahya ErkanLift and drag forces on a square prism with a (splitter) plate are experimentally investigated byforce measurements with a load cell. Results showed that drag and lift coefficients are independent ofReynolds number for Re = 9700 – 36500 at 0°, 45°, 90°, 135° and 180°. Drag coefficient at 0? is obtainedas 2.02 for the square prism alone, and 1.04 for the square cylinder with splitter plate. Maximum dragreduction for the square cylinder with the plate is 50% as compared to the square cylinder at 0? and 15.For ? < 30° and ? > 114°, drag coefficient of a square prism with splitter plate is smaller than that of thesquare prism alone. At Re = 20000, lift and drag coefficients significantly change with increasing attackangleÖğe Effect of attack angle on the flow around adjacent circular and rectangular prisms(2021) Seyhan, Mehmet; Sarıoğlu, Mustafa; Akansu, Yahya ErkanAn experimental investigation has been carried out to clarify the flow structure around adjacent circular and rectangular prisms. The measurements of hot-wire for Re= 4.1 x 103, 9.0 x 103 and 1.5 x 104, lift and drag force for Re = 1.0 x 104, and in addition the flow visualization experiments for Re = 2.3 x 103 have been performed in the range of 0° ? ? ? 180°. The adjacent bodies consist of a circular cylinder having 9.5 mm diameter and a rectangular prism having 6 mm x 10 mm cross-section attached to the circular cylinder from its short side in all the cases. The hot wire measurement results showed that the Strouhal number has Reynolds number independence for Re = 4.1x103, 9.0x103, and 1.5x104. Sudden peaks in St and lift coefficients are obtained for a similar reason that is reattachment of the separated shear layer in the vicinity of ? = 60? and 174?. For the adjacent bodies compared with the bare circular cylinder, 40%, and 25% drag reduction is obtained at ? = 0? and 174?, respectively. The obtained results show that the variations of lift coefficient, drag coefficient, and Strouhal number are strictly subjected to the attack angle.Öğe Effect of signal modulation of dbd plasma actuator on flow control around NACA 0015(Turk Isı Bilimi ve Teknigi Dernegi, 2018) Güler, Adem Arif; Seyhan, Mehmet; Akansu, Yahya ErkanEffects of DBD plasma actuator driven by six different type modulated signals on flow around NACA 0015 airfoil are experimentally investigated for lift augmentation. One actuator attached to the upside of the airfoil at x/c = 0.1 is used. Force measurement and smoke wire flow visualization are performed in a low speed wind tunnel. For Re= 3.6x104, the actuator is driven with six different signal modulations among which frequency modulation, amplitude modulation, excitation frequency and duty cycle at ? = 10°. SM4 including amplitude modulation is indicated to have better performance than the other signal modulations. Signal modulations provide energy savings while generating plasma to increase the lift coefficient. The obtained results indicate that as the dimensionless excitation frequency (F+) is 1 at low duty cycle, a better lift coefficient is obtained in comparison with the other F+ values. For Re= 3x104, the lift coefficient is proportionally increased with driving voltage and frequency due to increasing induced flow at ? = 10°. Flow visualization results showed that the separated shear layer at the leading edge gets closer to the (suction) surface of the airfoil by increasing the driving voltage from 6 kVpp to 8 kVpp which confirms the driving voltage effect. © 2018 TIBTD Printed in Turkey.Öğe Effect of the duty cycle on the spark-plug plasma synthetic jet actuator(E D P SCIENCES, 2016) Seyhan, Mehmet; Akansu, Yahya Erkan; Karakaya, Fuat; Yesildag, Cihan; Akbiyik, Hurrem; Dancova, P; Vesely, MA promising novel actuator called Spark-Plug Plasma Synthetic Jet (SPSJ) has been developed in Atmospheric Plasma Research Laboratory at Nigde University. It generates electrothermally high synthetic jet velocity by using high voltage. SPSJ actuator can be utilized to be an active flow control device having some advantages such as no moving parts, low energy consumption and easy to integrate the system. This actuator consists of two main components: semi-surface spark plug (NGK BUHW) as an anode electrode and a cap having an orifice as a cathode electrode. The cap, having a jet exit orifice diameter of 2 mm, has diameter of 4.4 mm and height of 4.65 mm. This study presents the characteristics of SPSJ actuator by using the hot wire anemometer in order to approximately determine jet velocity in quiescent air. Peak velocity as high as 180 m/s was obtained for f(e) = 100 and duty cycle 50%. The flow visualization indicated that the actuator's jet velocity is enough to penetrate the developed boundary layer.Öğe Influence of Leading-Edge Tubercle with Amplitude Modulation on NACA 0015 Airfoil(Amer Inst Aeronautics Astronautics, 2021) Seyhan, Mehmet; Sarioglu, Mustafa; Akansu, Yahya E.Flow around a NACA0015 airfoil with leading-edge tubercles was investigated using force measurements and flow visualization at 0 deg <= alpha <= 30 deg. The experiments were carried out at a low Reynolds number of Re = 6.3 x 10(4), where the transition to turbulent flow still occurred on the suction side of the airfoil. The leading-edge patterns of the models were produced by using only either one wave function or one superposition of two wave functions. Two tubercle models with uniform distribution and nine more realistic biomimicked airfoil models with amplitude modulation in tubercle geometry were tested in experiments. Force measurements showed that when compared to the baseline model, models with tubercles did not experience a sudden loss of lift and have higher lift coefficients in the poststall regime, irrespective of the model. It was found that the W15 model performs best in terms of maximum lift coefficient, stall angle, aerodynamic performance (C-L/C-D) in the poststall regime; as well as in terms of the minimum fluctuating lift coefficient C-L' in both pre- and poststall regimes. Enhancement of aerodynamic performance is due to the presence of stall cell formation with the counter-rotating vortex pairs and three-dimensional spanwise flow pattern initiated by leading-edge tubercles at the poststall regime.Öğe Performance prediction of PEM fuel cell with wavy serpentine flow channel by using artificial neural network(Pergamon-Elsevier Science Ltd, 2017) Seyhan, Mehmet; Akansu, Yahya Erkan; Murat, Mirac; Korkmaz, Yusuf; Akansu, Selahaddin OrhanEffects of serpentine flow channel having sinusoidal wave at the rib surface on performance of PEMFC having 25 cm(2) active area are investigated at different flow rates, three different amplitudes changing from 0.25 mm to 0.75 mm and three different cell operation temperatures. A proton exchange membrane fuel cell (PEMFC) is modeled for the prediction of the output current by using artificial neural network (ANN) that is utilized the aforementioned experimental parameters. Effect of hydrogen and air flow rate, the fuel cell temperature, amplitude of channel is tested. The results indicated that model C1 having lowest amplitude is enhanced maximum power output up to 20.15% as compared to indicated conventional serpentine channel (model C4) for 0.7 SLPM H-2 and 1.5 SLPM air and also model C1 has better performance than C2, C3 and C4 models. The maximum power output is augmented with increasing the cell temperature due to raising the fuel and oxidant diffusion ratio. Cell temperature, amplitude, H2 and air flow rate and input voltage is used as input variables in train and test of the developing ANN model. MAPE of training and testing is determined as 239 and 2.059, respectively. Prediction results of developed ANN model including two hidden layer shows similar trend with experimental results. Developed ANN model can be used to both decrease the number of required experiments and find the optimum operation condition within the range of input parameters. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Öğe THE IMPROVEMENT OF DRAG FORCE ON A TRUCK TRAILER VEHICLE BY PASSIVE FLOW CONTROL METHODS(TURKISH SOC THERMAL SCIENCES TECHNOLOGY, 2016) Akansu, Yahya Erkan; Bayindirli, Cihan; Seyhan, MehmetIn this study, the drag force measurements were carried out for a 1/32 scaled heavy vehicle model, consisted of truck and trailer, placed in the wind tunnel. The wind tunnel tests were also performed for 9 different free stream velocities in the range of Reynolds number between 113 000 and 453 000. The drag coefficients (CD) of the truck and trailer combination were experimentally determined. In the experimental studies, kinematic similarity was provided except moving road and blockage effect is ignored due to the small blockage ratio of 3%. The independence of Reynolds number was used for the dynamic similarity condition. The regions forming aerodynamic resistance on the truck trailer were determined and aerodynamic improvement was obtained with passive flow control methods. In the case of model 1 of truck and trailer, the aerodynamic improvement is obtained as % 15,71 by improving geometry of spoilers. % 22,46 aerodynamic improvements is also obtained by using passive air channel with a spoiler for the case of model 2. For the case of model 3, by adding a redirector to the model 2, the improvement is reached to % 25,58.
