LEE- Isı Akışkan Lisansüstü Programı- Yüksek Lisans
Bu koleksiyon için kalıcı URI
Gözat
Yazar "Çadırcı, Sertaç" ile LEE- Isı Akışkan Lisansüstü Programı- Yüksek Lisans'a göz atma
Sayfa başına sonuç
Sıralama Seçenekleri
-
ÖgeAerodynamic shape optimization of the DLR-F6 wing by using openfoam as CFD solver integrated with rsm(Graduate School, 2023-06-15) Buluş, Halil ; Çadırcı, Sertaç ; 523201122 ; Heat FluidAerodynamic shape optimization plays a critical role in aerospace engineering as it allows designers to enhance aerodynamic performance by altering the shape of a body. The ability to optimize the shape of structures like aircraft wings, wind turbine blades, and rockets can lead to increased efficiency, reduced fuel consumption, and minimized emissions. Given the pressing need to address climate change and the exponentially escalating global crisis, it's essential to prioritize sustainable solutions in every aspect of design, including minimizing the impact of aircraft emissions. This requires a primary focus on decreasing the drag and increasing the lift on the airplane, which is one of the most significant factors affecting aerodynamic performance and range. As air traffic continues to grow, the importance of aerodynamic shape optimization in reducing emissions and increasing fuel efficiency becomes increasingly clear. This thesis on the aerodynamic shape optimization of the DLR-F6 wing demonstrates an effective and a comprehensive way of an optimization process that can contribute to the ongoing research in this field. The DLR-F6 wing is a common benchmark for aerodynamic research due to its complex geometry and challenging flow characteristics. By optimizing the shape of the wing, it is aimed to improve its performance and contribute to ongoing research in this field. To ensure that the structural strength of the wing is not compromised, the optimization process also involves some considerations on various design constraints like modal frequency and mass of the wing. In the optimization process, different chord slices at various locations along the span has been taken and twisted some angles by taking their aerodynamic centers as reference. The work focuses on to determine the best improved angle sets which let the better performance on L/D value without sacrificing its structural integrity. The optimization model tree was constructed using ModeFRONTIER software, which integrated different software tools and automated the optimization process. The construction involved four main stages. Firstly, Pointwise software was used to create a new wing database by twisting at the six sliced chords with angles determined by the software. The software automatically executed all the steps to twist, create a new database, make surface mesh, and create a pre-meshed geometry for Abaqus, with the help of a journal. In the second stage, volume meshes were prepared using ANSYS Fluent Meshing, which automatically executed all the meshing processes controlled by optimization software. Thirdly, CFD analysis was conducted using OpenFOAM as the CFD solver to simulate the flow around the wing. The volume mesh created by Fluent Meshing was used as the solution cells. With the help of a function, OpenFOAM can convert a fluent mesh to foam format. To make the optimization process faster and well talent based, the HPC (High Performance Computer) was used to run in OpenFOAM. ModeFRONTIER makes an automatic connection with HPC systems based on SSH protocol and with a Linux bash script, aerodynamic analysis had been conducted. After the simulation was done, a file storing all the forces at each iteration was transferred to the host computer, and lift, drag and L/D values were computed using an inner MATLAB stage. The L/D value and lift value were set as design objectives. The purpose was the maximize these values. Since the twisting rotation angles were set as the input values, the optimization tool organizes and selects the best input values to succeed the design objectives. Lastly, Abaqus software was used to perform structural analysis to ensure the strength of the wing, with the pre-meshed geometry file directly transferred after the first stage. With an Abaqus journal, for each different design mass and modal frequency are calculated and processed with another MATLAB stage. These were selected as another design objective, with the goal being to minimize the mass and maximize the frequency value. However, 'Lift' and 'L/D' objectives were prioritized to make the optimization processes easy to go on. The optimization process was streamlined through these main stages, with simultaneous file transfers and evaluation of results made in intermediate steps. About 220 DoE (Design of Experiments) were created and evaluated. Due to the expensive CFD simulations, direct optimizations were not feasible to proceed. Therefore, RSM (Response Surface Methodology) was used to reproduce more experiments in an inexpensive way. RSM, also known as Surrogate Models, are a collection of statistical and mathematical techniques used to create, model, and analyze the relationships between input variables and output responses. By using RSM, the number of experiments needed can be reduced to obtain optimal results, saving time and resources in the optimization process. The direct optimization results were used to train the data set to build a good quality RSM. After using good RSM strategies, 1000 more experiments were created. After selecting the best design, a real analysis was conducted and showed that the RSM predicted the design output very well. The results of the optimization process were evaluated using a set of performance metrics, including the L/D ratio, maximum lift, minimum drag. Since the mass and modal frequency objectives were required to assure the structural integrity of the new design, they were not included as optimization performance metrics. The modified DLR-F6 aircraft was then compared with the original DLR-F6 aircraft using these performance metrics. The results show that the modified aircraft had a 13.15% improvement in L/D ratio and 2.24% improvement in lift compared to the original aircraft. A 3DOF flight simulation was done using MATLAB Simulink tool, with two aerodynamic databases created by sweeping 2 Mach numbers and 13 angle of attacks. One was for the airplane with the original wing, and the other was for the airplane with the optimized wing. Overall, the thesis demonstrates the effectiveness of using a multi-disciplinary optimization approach to improve the performance of complex aerodynamic shapes such as the DLR-F6 wing. The optimized wing not only shows a significant improvement in its aerodynamic performance but also maintains its structural strength. Although the flow chart may seem complex, it helps make the optimization process comprehensive and efficient. The optimization process and methodology used in this research can be applied to other complex aerodynamic shapes to improve their performance as well.
-
ÖgeDelta kanat hücum kenarı eklentilerinin boylamsal ve yanal stabiliteye etkilerinin incelenmesi(Lisansüstü Eğitim Enstitüsü, 2024-06-13) Ece Yalaz, Ayşe Sibel ; Çadırcı, Sertaç ; 503201127 ; Isı AkışkanBu tez çalışmasında savaş uçaklarında sıkça tercihe edilen delta kanat yapısına hücum kenarı eklentilerinin (strake) eklenmesi ile hava aracında meydana gelen boylamsal ve yanal stabilite etkilerinin incelemeleri yapılmıştır. İncelemeler kapsamında üç farklı referans geometri modelinde değişen hücum açısı, değişen beta açısı ve değişen aileron, flap ve rudder kontrol yüzeyi açılmalarında HAD analizleri koşturulmuş, sonuçlar üzerinde akış topoloji değerlendirmeleri ve stabilite analizleri gerçekleştirilmiştir. Şimdiye kadar üzerinde az oranda araştırma yapılmış olan strake geometrilerinin hava aracındaki kontrol yüzeyi verimliklerindeki etkisini araştırmak, stabilite ve kontrol stratejileri hakkında sonuçlar üretmek bu tezin ana amaçları arasında yer almaktadır. Çalışmalar birebir ölçekte kullanılan savaş uçağı modelinin (Lamar ve Frink, 1981) rüzgâr tüneli verileri ile doğrulanması olarak başlamıştır. Gerçekleştirilen bütün HAD analizleri sıkıştırılabilir akış kabulündeki üç boyutlu tam ölçekli modelde koşturulmuş ve RANS denklemleri hücre merkezli sonlu hacimler yöntemi ile çözülmüştür. Stabilite analizleri kapsamında, aynı zamanda tasarım parametresi olan strake referans alanının yarıya düşürülmesinin aerodinamik ve stabilitedeki etkileri de incelenmiştir. Analizler üç farklı geometri versiyonunda yapılmış olup, model üzerindeki kontrol yüzeyleri literatür referans alınarak tasarlanmıştır. Bu tez çalışmasında hava koşulu deniz seviyesi (0 ft), ideal gaz tanımlanmış ve serbest akım hızı (Ma=0.5) giriş bölgesi sınır şartı olarak verilmiştir. S0 strakesiz geometri modelini, S1 AD-14 isimli strake yapısına sahip geometri modelini ve S2 ise AD-14 strake yapısının referans alanı yarıya düşürülmüş geometri modelini içermektedir. Sonuçlar ilk olarak akış topolojisinin değerlendirilmesi üzerine kurulmuştur. Hücum açısı analizleri incelendiğinde; S0 versiyonunda ɑ=24° ve üstünde akım ayrılmalarının gittikçe şiddetlendiği ve kanat üzerinde taşıma kayıplarının yaşandığı gözlemlenmiştir. S1 ve S2 versiyonlarında ɑ=16°'den ilerideki hücum açılarında strake başlangıç bölgesinden gelişen girdabın kanat yüzeyindeki girdap ile birleştiği, kanat yüzeyindeki negatif basınç bölgesini arttırdığı görülmüştür. Strake alanının küçülmesi ile girdap şiddetinde azalma meydana geldiği görülmüştür. Beta açısının değişiminin incelendiği analizlerde strakeli versiyonların ɑ=32° ve β=10° açısındaki koşulunda strake girdabı rüzgârı önden alan bölümünde daha güçlü şekilde gelişmekte, rüzgâr arkasında kalan bölümde ise yüzeyden ayrıldığı görülmüştür. S2 versiyonu için sağ kanattaki akım ayrılmalarının S1 versiyonuna göre daha fazla olduğu gözlemlenmiştir. Ayrıca S0 versiyonunda olduğu gibi S1 ve S2 versiyonlarında da kanattan ayrılan akım, kuyruk bölgesindeki düzenli akımı gölgelemiş ve o bölgede kararsız akış rejimlerinin oluşmasına sebebiyet vermiştir. Kontrol yüzeylerinden flap ve aileronun strake entegresindeki aerodinamik etkileri incelendiğinde; kontrol yüzeyi etkinliklerinin S0 için ɑ=24° koşulunda oldukça verimsiz olduğu görülmektedir. Strake entegresi oluşan girdap gelişimi ile flap ve aileron kontrol yüzeyindeki akımın yeniden tutunduğu ve kanat yapısındaki taşımayı arttırdığı gözlemlenmiştir. Betalı koşulda rüzgârı arkadan alan kanattaki aileron yüzeyinin üzerindeki taşımanın arttığı gözlemlenmiştir. Strake referans geometrisindeki artış ile ɑ=24° hücum açısında aileron etkinliğinde artış gözlemlenmiştir. Strake geometrisinin eklenmesi ile kuyruk ve rudderdaki yanal düzlemde taşımanın artması sağlanmış, ɑ=24° ve β=10° koşulunda rudder kontrol yüzeyinde verimlikte artış sağlandığı görülmüştür. Versiyonların boylamsal stabilite analizleri yapıldığında, S0 boylamsal kararlı, S1 ɑ=0° ila ɑ=16° aralığında nötr stabilitede, ɑ=16° ila ɑ=32° aralığında ise yüksek seviyelerde boylamsal kararsız, S2 ise ɑ=0° ila ɑ=16° aralığında boylamsal kararlı durumda olduğu görülmüştür. Flap kontrol yüzeyinin ɑ=24° hücum açısında getirdiği yunuslama moment değişimi incelenecek olursa, S1 versiyonunda S0'a göre %50 artış, S2 versiyonunda ise %25 artış görülmüştür. Son olarak yüksek hücum açısındaki burun aşağı moment otoritesinin sağlanması için strake referans alanında azalma yoluna gidilebileceği gözlemlenmiştir. Versiyonların yanal stabilite analizleri yapıldığında ise aileron etkinliği S0 ile karşılaştırıldığında ɑ=24°'de S1 aileron verimi %34 oranında artarken, S2 aileron verimi yaklaşık %16 civarında artış göstermiştir. β=0° koşulunda S1 ve S2'nin rudder verimliliğinde bütün hücum açıları aralığında S0'e göre oldukça fazla iyileşme görülmüştür. Fakat beta açısının artması ile kanat girdaplarındaki kararsız yapı kuyruk akımını etkilemiş, yüksek hücum açısında rudder etkinliğinde kayıplara yol açmıştır. Strake geometrisinin kullanımı ile yanal stabilitede ɑ=24° hücum açısına kadar artış sağlanmıştır. Fakat girdap bozunmaya uğradığı ɑ=32°'de strake girdapları düzensiz yapıya bürünmüştür.
-
ÖgeImproving the aerodynamic characteristics of the gap between the cabin and trailer of heavy-duty commercial vehicles(Graduate School, 2023-09-14) Çil, Utku ; Çadırcı, Sertaç ; 503201121 ; Heat Fluid
-
ÖgeNumerical investigation of double layer microchannel heatsinks and performance assessment based on Taguchi method(Graduate School, 2022-06-14) Demirsöz, Mustafa ; Çadırcı, Sertaç ; İliş Gediz, Gamze ; 503191117 ; Heat-FluidIn this study, the performance of double-layer microchannel heat sinks was investigated by Computational Fluid Dynamics Analysis using the Taguchi Experimental Design Method. Selected parameters are Reynolds number, microchannel material, width of upper and lower channels, distance between these channels and heat flux. The effect of these parameters on the on-chip thermal resistance, the total thermal resistance and the pumping power requirement were investigated. The influence of the selected factors was investigated based on the average of the signal-to-noise (SN) ratios and the response table for the signal-to-noise ratios. Except for the total thermal resistance in the counterflow configuration, the Re number was found to be the most important factor for all other cases. Copper gives the best results due to its thermal dissipation characteristic. For the counterflow configuration, the effect of the heat flux on the thermal resistances is negligible except for the total thermal resistance. The effect of the width of the lower channel on the thermal resistances is more dominant than the upper channel. The lower and upper channel widths are equally important in terms of the required pumping power. There is an inverse relationship between channel width and required pumping power. The distance between the lower and upper channels is insignificant in terms of the required pumping power. If this distance is lower in a parallel flow configuration, on-chip thermal resistance is minimal. On the other hand, the total thermal resistance increases with this distance. As the channel widths increase, the average velocity in the channel decreases, so an increase in thermal resistance is observed.
-
ÖgeNumerical investigation of inertial focusing of micro andnanoparticles in curvilinear microchannels(Graduate School, 2022-01-21) Aldemir, Ahmet Turan ; Çadırcı, Sertaç ; 503181126 ; Heat FluidRecently, microfluidic systems have been preferred more than conventional methods due to their ease of production, economic advantages, high precision processing capabilities and ease of operation. These systems are in a situation where many disciplines such as physics, chemistry and engineering are intertwined. Microfluidic systems aim to provide manipulation of fluids moving in microchannels and to control the flow field. With the provision of this control, important developments are experienced in fields such as biomedical engineering and medicine. As an important area, there have been serious improvements in the separation of particles of different diameters in microfluidic systems recently. In the studies carried out, particles of different diameters are sent into the microchannel through from source (like a pump) and can be collected in separate beams from the channel exit. This has become an important step in the early diagnosis of deadly diseases such as cancer. The concept of separating particles of different diameters from each other in the microfluidic systems has accelerated with the developments in Lab on a Chip (LoC) and MEMS systems. Many different mechanisms have been developed for the separation of particles. Separation of particles in the microfluidic systems can be achieved either by active separation techniques, where external forces act, or passive separation techniques, where an external force is not used. In active separation, many different sources such as electrical systems, sound, optics can be used to create an external force. On the other hand, passive separation techniques use dynamics within the microchannel to separate particles. Inertial focusing, which is an important area in passive focusing, still continues to develop. The logic of inertial focusing is that forces acting on a particle moving in a fluid, either from flow, from interaction with the walls of the microchannel, or from effects at the molecular level. The most important of these forces is the lift force, which directs the particle to a certain equilibrium position. Lift force is divided into two as wall interacting lift force and shear stress lift force. The most important difference of these forces emerges when determining the equilibrium position of the particles. The lift force arising from the wall interaction pushes the particles towards the center, while the shear stress lift force directs the particles from the center towards the walls. As a result, when these forces reach equilibrium, the equilibrium position of the particle is determined. The magnitude of these forces is highly dependent on the particle diameter, so they cause the particles with different diameters to line up in different equilibrium positions, thus allowing the particles to be separated from each other. In inertial focusing, the addition of curvature to the microchannels adds a secondary effect to the flow. This phenomenon is due to the formation of eddies in the curved regions within the channel. This flow effect also causes a force called the Dean force to be added to the particles. In the studies carried out, it was observed that the focusing mechanisms of the particles improved thanks to this effect. Microchannel geometry is an important parameter that affects the mentioned forces. By changing the geometry and dimensions, it is possible to design a particle separation mechanisms that works with higher efficiency. In this context, different microchannel designs such as straight microchannel, spiral microchannel, serpentine microchannel have been studied, and detailed studies have been carried out on these effects. Studies in the field of separation of microparticles are mostly carried out using synthetic particles in order to better understand how blood and cancer cells interact with each other. Particle separation is affected by many different parameters such as flow rate, type of fluid used, particle diameter, as well as microchannel geometry. Therefore, it is very important to best understand the physics of inertial focusing in order to design the most efficient decomposition. In this study, the concept of inertial focusing is examined. Computational Fluid Dynamics (CFD) analyzes were performed on microchannels with different geometries, parametric analyzes affecting focusing were completed and the effects were examined. Within the scope of the study, flow and particle analyzes of the sunflower geometry obtained by adding serpentine regions to a conventional spiral microchannel geometry and the importance of this geometry were discussed.
-
ÖgeNumerical investigation on hub effects of hubless-rim driven propeller(Graduate School, 2022-12-16) Aşçı, Ali Burak ; Çadırcı, Sertaç ; 503191132 ; Heat and FluidSince the beginning of humanity, various methods have been developed for the interaction of countries with each other. Therefore, people have developed various methods of transportation in order to strengthen political and economic relations, explore new places and access resources in new places. Maritime transportation is one of these prominent methods to create interactions among countries. Thanks to the developments in the field of maritime transport, humanity has made significant progress in numerous fields. Ships have been a widely used vehicles for transportation and ships are generally driven by the shaft-propeller mechanism. Energy occurred from fuel, nuclear or electrical is transferred to propeller via a transmission mechanism. During this drive movement, undesirable problems such as increased fuel consumption, reduced mechanical efficiency and noise may occur and these problems may cause irreversible damage to the shaft mechanism. Besides the effects of climate change dramatically continue to increase and marine transportation sector is one of the causes to emit more CO2 in the world. Therefore, hubless Rim Driven Propellers (RDP) has been developed and used for various marine vehicles in order to prevent above-mentioned problems. The working principle of RDP can be summarized as an electric motor driving the propeller with the help of the rim. However, since hubless RDP technology is a new field of marine researches, information on how changing the dimensions of the hub affects the hydrodynamic performance of the propeller is scarce. In this master's thesis, analyzes were made for hubless RDP design with five different hub ratios (0.05, 0.1, 0.15, 0.167, 0.25) by means of various dimensionless parameters to monitor the performance effects of the propeller. Ka4-70 propeller was selected for these five designs. They were solved numerically benefiting from Unsteady Reynolds Averaged Navier-Stokes equations (URANS) and Shear Stress Transform (SST) k-ω turbulence transport equations. Numerical operations were handled on the finite volume method solver Simcenter STAR-CCM+ solver, using the Rigid Body Motion (RBM) approach. The Computational Fluid Dynamics (CFD) results have been conducted in terms of non-dimensional parameters such as thrust coefficient (KT), torque coefficient (KQ), and efficiency (η) ranging from 0.1 to 0.6 advance ratio (J) for 600 rpm. It was monitored that KT, KQ, and η increased as the hub ratio increased under a certain rotation speed until the hub ratio =0.167. Due to no experimental data for hubless RDP, validation studies were able to conduct with hub type propeller. Accordingly, an ideal propeller configuration can be determined by comparing numerical results and experimental data.