Yazar "Akbiyik, Hurrem" seçeneğine göre listele

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    Aerodynamic performance changes of an airfoil modified with biomimetic spiky-vortex generators
    (AIP Publishing, 2025) Kaya, Fatih; Akbiyik, Hurrem
    An experimental study was conducted to investigate the aerodynamic characteristics and surface flow topologies of spiky-vortex generators (Spiky-VGs) placed on the National Advisory Committee for Aeronautics (NACA0012) airfoil. Within the scope of this study, aerodynamic force measurement and titanium-dioxide (TiO2) surface oil experiments were performed at a Reynolds number (Re) of 1.5 x 10(5). Moreover, TiO2 surface oil and three-dimensional (3D) smoke-wire flow visualization techniques were applied to Spiky-VG having a certain scale. According to the aerodynamic force measurement results, it was observed that model 1 (M1) Spiky-VGs increase the maximum lift coefficient (C-Lmax) by 7.6% compared to the base NACA 0012 airfoil. It was observed that model 2 (M2) increased the lift coefficient (C-L) by 9.9% at an angle of attack slightly above the stall angle of the baseline airfoil (alpha = 11 degrees) and delayed the onset of stall by approximately 1 degrees. Furthermore, the drag coefficient (C-D) of model 2 (M2) is lower than that of the base wing model and is about 14.5%, indicating improved aerodynamic performance. It was observed that the presence of Spiky-VGs leads to significant alterations in surface flow topology over the wing model, primarily owing to their geometric configuration. The findings demonstrate that Spiky-VGs, functioning as vortex generators, contribute to enhanced aerodynamic performance by modifying surface flow topology and improving flow characteristics. Hence, they can be considered as effective passive flow control devices for airfoil applications.
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    An experimental investigation on the flow control of the partially stepped NACA0012 airfoil at low Reynolds numbers
    (Pergamon-Elsevier Science Ltd, 2024) Seyhan, Mehmet; Akbiyik, Hurrem
    An experimental study of flow control around a NACA0012 airfoil modified with fully and partially step geometry was conducted at Reynolds numbers of 6 x 104 and 1.2 x 105. Partially step geometries, the location of the step on the airfoil, and Reynolds number are varied to show their effect on aerodynamic performance and flow structures on the airfoil. Experimental results show that fully and partially step geometries are effective for flow control around the airfoil and aerodynamic performance enhancement. The maximum increase in lift coefficient is approximately 46%, and the stall angle is shifted about 1 degrees by the SM4 model at Re of 6x104 while the step geometry is on the pressure side. For a Reynolds number of 1.2 x 105, the highest increase in the lift-to-drag ratio of the airfoil is observed about 17.1 at an angle of attack of 6 degrees by the SM2 model when step geometry is placed on the pressure side of the airfoil. In the event of partially or fully stepped at the pressure side of the model, step flow structures, including the reattachment line, recirculation zone, and corner eddy, are obtained. However, even though the step geometry is at the suction surface of the model, the formation of a laminar to turbulent transition is observed. The overall results suggest that the partially stepped geometry length, Reynolds number, and step location side on the airfoil have an important role in flow control to improve aerodynamic performance for various angles of attack.
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    Investigation of the effects of bioinspired vortex generators on aerodynamic performance of a NACA0015 airfoil
    (IOP Publishing Ltd, 2025) Kaya, Fatih; Akbiyik, Hurrem
    An experimental study was carried out to investigate the effects of biomimetic vortex generators (biomimetic-VGs) on the aerodynamic performance of the NACA0015 airfoil. Aerodynamic force measurements and titanium dioxide (TiO2) based flow visualization technique experiments were performed for test models at Re = 1.2 x 105. Aerodynamic force measurement experiments were carried out in the wind tunnel at angles of attack of 0 degrees-18 degrees with an increment of 1 degrees. As a result of the experiments, it was revealed that the lift coefficient (CL) increased and the drag coefficient (CD) decreased by using the seaconchshell structure as a VG for the wing model. In addition, it has been observed that biomimetic models (BMs) shifted the stall angle of the airfoil by 1 degrees. In the surface oil flow visualization experiment results, the flow structure around the NACA0015 airfoil of BMs was revealed and interpreted. Moreover, it has been revealed that the aerodynamic performance of the airfoil increases as a result of the use of BMs. It is also revealed that the seaconchshell structure, which has not been studied before in the literature and which is the subject of this study, can be used as an effective flow control device.
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    Low-cost saw/sinus-tooth-shaped circular microstrip patch antenna for in-space and satellite applications
    (Iop Publishing Ltd, 2024) Aydin, Emine Avsar; Akbiyik, Hurrem
    Antennas operating in S and C bands are crucial in space satellite applications due to their high bandwidth, which facilitates the swift transmission of large data volumes from space vehicles to Earth. These bands are less affected by atmospheric disturbances and exhibit lower noise levels, ensuring uninterrupted and reliable communication between spacecraft and Earth centers. They are essential for satellite-based remote sensing, analyzing surface properties, transmitting high-resolution images, scientific data, and other information. Additionally, they are used for spacecraft control and navigation, enabling precise mission operations. This study emphasizes user-friendly production antennas with different geometries and distinct feeding techniques, demonstrating various design implementations using CST Microwave Studio software. Innovative manufacturing methods such as 3D printing PLA substrates and using copper tape for antenna elements were explored to optimize costs and production processes. Precise cutting of antenna radiation geometries was achieved using the Cricut machine. Experimental validation through reflection coefficient (S11) measurements with a handheld vector network analyzer confirmed the practical application of theoretical foundations. The study's novelty lies in examining unconventional materials like PLA filament for antenna substrates, exploring fractalization theory for enhancing bandwidth, and discussing advancements in material science with flexible filaments like TPU. These contributions offer insights into user-friendly antenna production, innovative manufacturing techniques, and theoretical explorations in antenna design, enhancing the efficiency and effectiveness of space satellite communication systems.
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    The effect of cavity modified stepped geometry on aerodynamic performance of an airfoil at a low Reynolds number
    (AIP Publishing, 2025) Akbiyik, Hurrem
    An experimental investigation was conducted to elucidate the effect of modified stepped region on a National Advisory Committee for Aeronautics (NACA) model NACA0012 airfoil surface at Reynolds number (Re) of 1 x 10(5). Force measurements as well as titanium dioxide ( TiO2)-based flow visualization experiments and velocity measurements were carried out to evaluate aerodynamic performance change, to gain insight into flow structures, and to show the changes in wake region. The angle of attack ( alpha) of the airfoil was chosen to lie between 0 degrees and 30 degrees with 1 degrees intervals for force measurements. The attack angles were chosen as 0 degrees, 6 degrees, and 12 degrees considering pre-stall and post-stall cases for velocity measurements and surface oil visualization. In the light of force measurement experiments, it was concluded that a fully step model and all modified models had a higher lift coefficient ( C-L) value than the base model (BM). It is observed that the D2 model results in 13.22% improvement in the C-L value at alpha = 12 degrees compared to the BM. The drag coefficient of the D3 model shows less increase compared to the other modified models, with a value about 0.113 at alpha = 11 degrees. However, there were no improvements in drag reduction when the base airfoil was modified. Velocity measurements showed that the effect of stepped modifications in the pressure surface provides the wake width changes and the wake width centerline shifts. TiO2-based surface oil visualizations were provided to enlighten the new flow structures as cavity-based induced flow structure, step-based induced flow structure, wavy shape reattachment line and wavy shape recirculation region.
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    The effect of leading-edge tubercle on a tapered swept-back SD7032 airfoil at a low Reynolds number
    (Pergamon-Elsevier Science Ltd, 2022) Seyhan, Mehmet; Akbiyik, Hurrem; Sarioglu, Mustafa; Kececioglu, Sevda Ceren
    An experimental study is performed to research the effect of the implemented leading-edge tubercles on the tapered swept-back SD7032 airfoil at Re of 5.5 x 104 and 1.1 x 105. In this study, along with a baseline model with no tubercles (T0), in total four different configurations are used for analysis of the aerodynamic charac-teristics. In the other three models (T1, T2, T3) mainly different amplitude and wavelength modulations are studied. In all experimental studies, force measurements are performed by using a six-axis load cell force measurement device. To achieve detailed information on the flow field of all models, surface oil flow visuali-zation technique is used for visualization purposes at Re = 1.1 x 105. The geometric specifications of the model are the sweep angle of 300, the tip chord of 37.5 mm, the root chord of 112.5 mm, and the span of 300 mm. Airfoil models with the LE tubercles significantly improve lift curve at almost all AoAs as compared to the baseline model. The streamwise vortices are positioned together more closely leading to interaction with each other. Consequently, these interactions lead to an increase in turbulence. This increase in turbulence may lead to a better mixing and increase in momentum exchange in the boundary layer. Amongst the models (T1-T3), the best airfoil model is determined as T3, having a1 = 0.06c, lambda 1 = 0.5c, a2 = 0.015c, and lambda 2 = 0.125c parameters, in terms of lift, drag and CL/CD ratios.
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    The effects of ice accretion on aerodynamic performance of NACA 2415 airfoil at low Reynolds number
    (Springer, 2025) Yilmaz, Remzi Can; Akbiyik, Hurrem
    This paper deals with the effects of three distinct ice accumulations on the aerodynamic performance of the NACA 2415 airfoil. The experiments are carried out for the base airfoil as well as glaze (GIA), rime (RIA), and horn ice (HIA) accumulated airfoils at Re = 1.2 x 105. For this study, force and velocity measurements are taken. Additionally, the oil and smoke-wire flow visualization techniques were performed. The selected range of angle of attack for force measurements is defined as -7 degrees to 23 degrees. In addition, considering the results of force measurements, seven distinct angle of attack values including 0 degrees, 4 degrees, 8 degrees, 13 degrees, 14 degrees, 17 degrees and 20 degrees are chosen for velocity measurements and flow visualization experiments. Experimental results showed that CLmax of ice accreted airfoils are decreased as expected. 20%, 23% and 88% of decrease in maximum lift coefficient are observed in the GIA, RIA and HIA models, respectively. Increases in drag coefficients at alpha = 0 degrees for the GIA, RIA and HIA airfoils are observed to be around 14%, 4% and 307%, respectively. A sudden increase in lift coefficient of the GIA airfoil is observed at post-stall. Moreover, a double-peak behavior is noted for the GIA and RIA airfoil, and also for the base airfoil in velocity measurements.