Yazar "Doğan, Sercan" seçeneğine göre listele
Listeleniyor 1 - 8 / 8
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe Comparison of Flow Characteristics of Different Sphere Geometries Under the Free Surface Effect(E D P SCIENCES, 2013) Özgören, Muammer; Doğan, Sercan; Okbaz, Abdulkerim; Aksoy, Muharrem Hilmi; Şahin, Beşir; Akıllı, HakanComparison of the experimental results of turbulent flow structures between a smooth sphere and a sphere with a vent hole, roughened, and o-ring is presented in the presence of a free-surface. Dye visualization and particle image velocimetry (PIV) techniques were performed to examine effects of passive control methods on the sphere wake for Reynolds number Re = 5000 based on the sphere diameter with a 42.5mm in an open water channel. Instantaneous and time-averaged flow patterns in the wake region of the sphere were examined from point of flow physics for the different sphere locations in the range of 0 <= h/D <= 2.0 where h was the space between the top point of the sphere and the free surface. The ratio of ventilation hole to sphere diameter was 0.15, o-ring was located at 55 degrees with a 2 mm from front stagnation point of the sphere and roughened surface was formed by means of totally 410 circular holes with a 3 mm diameter and around 2 mm depth in an equilateral triangle arrangement. The flow characteristics of instantaneous velocity vectors, vorticity contours, time-averaged streamline patterns, Reynolds stress correlations and streamwise and cross-stream velocity fluctuations for both the smooth and passively controlled sphere were interpreted.Öğe Experimental and Numerical Investigation of Flow Structures around Cylindrical Bluff Bodies(E D P SCIENCES, 2015) Yağmur, Sercan; Doğan, Sercan; Aksoy, Muharrem Hilmi; Canlı, Eyüb; Özgören, MuammerThe understanding and quantitative prediction of velocity and pressure fluctuations in turbulent flows around such bluff bodies have been evolving over the years. The main aim of the present work is to investigate experimentally and numerically the flow field in the wake region of different bluff bodies such as circular, square and triangle cross section cylinders placed horizontally perpendicular to the uniform flow. The experimental studies were performed by Particle Image Velocimetry (PIV) method in an open water channel at Reynolds numbers 5000 and 10000 defined according to the characteristic lengths of the cylinders in the facilities of Selcuk University of Advanced Technology Research and Application Center in Turkey. The experimental results are compared to the numerical results obtained by means of transient simulation with LES turbulence model of ANSYS-Fluent Software. It is shown that the numerical and experimental results have a good agreement in respect of the instantaneous and time-averaged flow field patterns of vorticity, velocity component streamwise direction and streamline topology. In addition, drag coefficient of the geometries were also numerically calculated. For all geometries the wake length in x and y directions and size of the foci of the streamlines are decreasing by increasing Reynolds numbers in time-averaged results. The time-averaged flow patterns of both experimental and numerical results have considerable symmetry with respect to the centerline of each cylinder. Contours of the time-averaged stream wise velocity for Re=10000 demonstrate that the stagnation point around the symmetry plane moves further upstream for all cylinders in accordance with Re=5000. The maximum drag coefficient value was yielded for the square cross-section cylinder as 1.78 due to the sharp-edged geometry.Öğe Experimental Performance Investigation of Photovoltaic/Thermal (PV-T) System(E D P SCIENCES, 2013) Özgören, Muammer; Aksoy, Muharrem Hilmi; Bakır, C.; Doğan, SercanPhotovoltaic solar cells convert light energy from the sun into electricity. Photovoltaic cells are produced by semi-conducting materials to convert the energy into electricity and during this process heat is absorbed by the solar radiation. This heat causes a loss of electricity generation efficiencies. In this study, an experimental setup was designed and established to test two separate photovoltaic panel systems with alone PV and with water cooling system PV/T to examine the heat effect on PV systems. The absorbed heat energy behind the photovoltaic cell's surface in insulated ambient was removed by means of a water cooling system and the tests for both systems were simultaneously performed along the July 2011. It is found that without active water cooling, the temperature of the PV module was higher during day time and solar cells could only achieve around 8% conversion efficiency. On the other hand, when the PV module was operated with active water cooling condition, the temperature dropped significantly, leading to an increase in the efficiency of solar cells as much as 13.6%. Gained from absorbed solar heat and maximum thermal conversion efficiencies of the system are determined as 49% and 51% for two different mass flow rates. It is observed that water flow rate is effective on the increasing the conversion efficiency as well as absorption and transition rates of cover glass in PV/T (PV-Thermal) collector, the insulation material and cell efficiency. As a conclusion, the conversion efficiency of the PV system with water cooling might be improved on average about 10%. Therefore, it is recommended that PV system should be designed with most efficient type cooling system to enhance the efficiency and to decrease the payback period.Öğe An experimental test set-up with the ANSI / AMCA 210-16 standard for performance analysis of axial fans(Selçuk Üniversitesi, 05.01.2021) Güven, Türker Burak; Altun, Aziz Hakan; Doğan, SercanThe fact that fans are used in a large variety and wide areas today requires them to have a certain performance and quality. The test set-up to be used to determine the performance values of the fans should also be prepared and verified in accordance with standards such as ISO, ANSI / AMCA. In this study, a test set-up was designed and established in accordance with the ANSI / AMCA 210-16 standard. In order to ensure the accuracy of this test set-up, the static pressure values for different flow rates of the AXI500-5-25 model axial fan produced in a fan manufacturer company in Konya were measured, and data were obtained. The static pressure-flow rate performance curve obtained from the tests was compared with the manufacturer's catalog data. As the most important result in comparison, it was seen that the experimental and the catalog data were quite compatible. The highest difference between experimental and catalog data was obtained at the points where the flow rate is minimum and maximum. However, this difference was determined to be around 5%. With the results obtained in the study, it was determined that the accuracy of the experimental set-up designed and set up according to ANSI/AMCA 210-16 standard was ensured and it was suitable to be used for testing.Öğe Investigation of flow characteristics around a sphere placed in a boundary layer over a flat plate(ELSEVIER SCIENCE INC, 2013) Özgören, Muammer; Okbaz, Abdulkerim; Doğan, Sercan; Şahin, Beşir; Akıllı, HüseyinFlow characteristics around a sphere located over a smooth flat plate were experimentally investigated using dye visualization and PIV technique. The sphere was embedded in a turbulent boundary layer with a thickness of 63 mm which was larger than the sphere diameter of D = 42.5 mm. Instantaneous and time-averaged flow patterns in the wake region of the sphere were examined from the point of flow physics for different sphere locations in the range of 0 <= G/D <= 1.5 where G was the space between the bottom point of the sphere and the flat plate surface. Reynolds numbers with a range of 2500 <= Re <= 10000 based on the free-stream velocity while the velocity distributions over the plate surface are the developed turbulent boundary layer condition attained by using a tripwire. Distributions of velocity fluctuations, patterns of sectional streamlines, vorticity contours, velocity fields, turbulent kinetic energy and corresponding Reynolds stress correlations are obtained using PIV data. It was found that a jet-like flow stimulated the flow entrainment between the core and wake regions as a function of the sphere locations. The gap ratio has a strong influence on the flow structure of the wake-boundary layer interaction and the variation of the reattachment location of the separated flow from the plate surface. The time-averaged flow patterns yield asymmetric structures downstream of the sphere due to the effect of the boundary layer flow distribution. (C) 2012 Elsevier Inc. All rights reserved.Öğe Küre serbest yüzey etkileşimiyle oluşan akış yapısı ve kontrolünün deneysel incelenmesi(Selçuk Üniversitesi Fen Bilimleri Enstitüsü, 2013-06-10) Doğan, Sercan; Özgören, MuammerBu tez çalışmasının amacı küre etrafındaki akış yapısı ve bu akış yapısının serbest yüzeyle etkileşiminin nicel ve nitel olarak deneysel araştırılmasıdır. Serbest yüzey akışı etkisi altında yerleştirilen pürüzsüz bir küre ve pasif akış kontrolü uygulanmış üç farklı küre modeli için açık bir su kanalı içerisinde deneyler yapılmıştır. Serbest yüzey ile küre art izinin etkileşimi sonucu meydana gelen akış yapısını Parçacık Görüntülemeli Hız Ölçme (PIV) metodu ile nitel ve boya akış görüntüleme yöntemi ile nicel olarak incelemek için Reynolds sayısı 2500?Re?10000 aralığında ve küre alt noktası ile serbest yüzey arasındaki daldırma oranı 0.25?h/D?3.0 arasında 0.25D aralıkla değiştirilmiştir. PIV ve boya görselleştirme deneylerinden elde edilen sonuçlar pürüzsüz küre durumu ve bunun pasif akış kontrolü uygulanmış kürelerle karşılaştırılması olmak üzere iki aşamada değerlendirilmiştir. Anlık ve zaman ortalaması hesaplanmış hız çalkantıları, akım çizgi yapıları, girdap eş düzey eğrileri, hız alanları, türbülans kinetik enerji ve Reynolds gerilmesi eş düzey eğrilerinin dağılımları PIV verileri kullanılarak elde edilmiş ve karşılaştırılmalı olarak sunulmuştur. Pasif akış uygulamalarının etkisini araştırmak için akışa paralel olarak art izini enerjilendirmek için küre merkezine küre çapının %15' i oranında delik açılmış (d/D=0.15) delikli küre, akış ayrılmasını geciktirmek için akışın durma noktasından itibaren küre yüzeyi üzerine 55° de o-ring yerleştirilen o-ringli küre ve küre yüzeyine işlenen 410 adet 3mm çaplı silindirik pürüzlülük elemanına sahip pürüzlü küre modelleri kullanılmıştır. Elde edilen sonuçlar pürüzsüz küre sonuçlarıyla karşılaştırılarak değerlendirilmiştir. Serbest su yüzeyinin akış yapısına etkisinin daldırma oranına bağlı olarak değiştiğini göstermek için akım çizgileri modelleri incelenmiştir. Küre yüzeyinden ayrılan akışın yüzeyle birleşme noktası R'nin değişimi, art izinde hızların sıfır olduğu S düğüm noktasının daldırma oranının değişmesiyle küre sırtına doğru yaklaşması ve art izinde meydana gelen odak noktalarının boyutundaki değişimler yorumlanmıştır. Pasif akış kontrolü uygulanan 2mm çapa sahip o-ringli küre durumunda art izi boyutunda diğer küre modellerine göre önemli derecede bir azalma meydana gelmiştir. Delikli küre modelinde ise küre üzerindeki delikten gerçekleşen momentum transferi yüksek akış art izi bölgesinde bir hareketlenmeye neden olmuştur. Ayrıca, bu jet akış etkisinden dolayı alt ve üst serbest kayma tabakasındaki odak noktalarından farklı olarak küre sırtına yakın kısımda iki adet odak noktası daha oluşmuştur. Yüzeyi pürüzlü şekilde işlenen küre deneyi sonuçlarının, düşük Reynolds sayısı nedeniyle pürüzsüz küreden çok farklı olmadığı gözlemlenmiştir. Pürüzlü art izi kısalması haricinde önemli bir kontrol etkisi gözlemlenmemiştir. Serbest su yüzeyi etkisinin h/D=1.5 daldırma oranına kadar devam ettiği PIV deneylerinden elde edilen anlık ve zaman ortalaması alınmış sonuçlardan anlaşılmaktadır. Daldırma oranı h/D=1.1 olduğu duruma kadar kürenin sadece alt kısmından akış ayrılması olmaktadır ve dolayısıyla sadece alt kayma tabakasında akış hareketliliği meydana gelmiştir. Serbest kayma tabakasının yüzeyle birleşme noktası içinde kalan bölgede şiddeti yüksek dönümlü girdaplar oluşmaktadır. Daldırma oranı h/D=2.0 değerine ulaştığında küre art izi akış karakteristiklerinin serbest akım şartlarına benzer bir görünüm elde edilmiştir.Öğe Turbulent Shear Flow Downstream of a Sphere with and Without an O-Ring Located Over a Plane Boundary(E D P SCIENCES, 2012) Özgören, Muammer; Okbaz, Abdulkerim; Doğan, Sercan; Şahin, Beşir; Akıllı, HüseyinFlow-structure interaction of separated shear flow from the sphere and a flat plate was investigated by using dye visualization and the particle image velocimetry technique. Later, a passive control method was applied with 2mm o-ring located on the sphere surface at 55 degrees from front stagnation point. The experiments were carried out in open water channel for Reynolds number value of Re=5000. Flow characteristics have been examined in terms of the 2-D instantaneous and time-averaged velocity vectors, patterns of vorticity, streamlines, rms of velocity fluctuations and Reynolds stress variations and discussed from the point of flow physics, vortex formation, lengths of large-scale Karman Vortex Streets and Kelvin-Helmholtz vortices depending on the sphere locations over the flat plate. It is demonstrated that the gap flow occurring between the sphere bottom point and the flat plate surface has very high scouring effect until h/d=0.25 and then unsymmetrical flow structure of the wake region keeps up to h/D=1.0 for smooth sphere. For the sphere with o-ring, the wake flow structure becomes symmetrical at smaller gap ratios and reattachment point on the flat plate surface occurs earlier. Moreover, o-ring on the sphere diminishes peak magnitudes of the flow characteristics and thus it is expected that the flow-induced forces will be lessened both on the sphere and flat plate surface. Vortex formation lengths and maximum value occurring points become closer locations to the rear surface of the sphere with o-ring.Öğe Wake structures of two side by side spheres in a tripped boundary layer flow(E D P SCIENCES, 2014) Canlı, Eyüb; Özgören, Muammer; Doğan, Sercan; Aksoy, Muharrem Hilmi; Akıllı, HüseyinTwo independent spheres were placed in a side by side arrangement and flow structure in the wake region of the spheres was investigated with a Particle Image Velocimetry (PIV) system when the spheres were in a boundary layer over a flat plate as a special case. Reynolds number was 5000 based on the sphere diameter which was 42.5 mm. Boundary layer was tripped 8mm away from the leading edge of the flat plate with a 5 mm trip wire. The thickness of the hydrodynamically developed boundary layer was determined as 63mm which was larger than the sphere diameter of D=42.5mm. Wake region of the spheres was examined from point of flow physics for the different sphere locations in the ranges of 0 <= G/D <= 1.5 and 0 <= S/D <= 1.5 where G and S were the distance between the spheres and the distance between the bottom point of the spheres and the flat plate surface, respectively. Depending on the different sphere locations, instantaneous and time averaged vorticity data, scalar values of time-averaged velocity components and their root mean square (rms) values and time averaged vorticity data are presented in the study for the evaluation of wake region of the spheres. It is demonstrated that the gap between the two spheres and the interaction between the gap and the boundary layer greatly affects flow pattern, especially when spheres are located near to the flat plate surface, i.e. S/D=0.1 for 0 <= G/D <= 1.5. Different distances between the spheres resulted in various flow patterns as the spheres were approached to the flat plate. The distance S/D=0.1 for all gap values has the strongest effect on the wake structures. Beyond G/D=1.0, the sphere wakes tend to be similar to single sphere case. The instantaneous vorticity fields of the side by side arrangements comprised wavy structures in higher level comparing to an individual sphere case. The gap flow intensifies the occurrence of small scale eddies in the wake region. The submersion rate of the spheres actually determines the characteristics of the wake region and is affected from boundary layer flow in a gradually decreasing manner.
