LEE- Uçak ve Uzay Mühendisliği Lisansüstü Programı

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http://hdl.handle.net/11527/19473

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Konu "aeroakustik" ile LEE- Uçak ve Uzay Mühendisliği Lisansüstü Programı'a göz atma
  • Öge
    Aeroacoustic investigations for a refrigerator air duct and flow systems
    (Graduate School, 2022-02-16) Demir, Hazal Berfin ; Çelik, Bayram ; 511181186 ; Aeronautics and Astronautics Engineering
    Noise has become an important public health problem with industrialization, and has become a crucial design problem for engineering. For this reason, noise reduction studies have became the focus, especially in the white goods, automotive and aviation sectors, which requires interaction with human. Among the vehicles and products in the aforementioned sectors, the refrigerators, unlike the others, are located in the center of the living area and work throughout the day. Therefore, possible sound problems are observed more quickly by the users and are found to be disturbing. At this point, the investigation and reduction of the acoustic propagation of existing products by various numerical and experimental methods is a valuable contribution to both industry and literature. Within the scope of this thesis, the freezer compartment of a refrigerator with a No frost cooling system was investigated from an aeroacoustic perspective. The freezer compartment consists of three drawers where food will be placed, an axial fan that provides air flow, an evaporator cover that separates the evaporator pipes and the interior volume, and plastic walls surrounding them. The main source of air flow noise in the system is the axial fan. For this reason, in the first step of the study, solo aeroacoustic examination of the axial fan was made. Afterwards, the entire freezer volume was examined and the study was completed with three different model proposals in which acoustic emission was reduced. The flow field analysis of the axial fan with an operational speed of 1200 rpm was carried out with commercial software ANSYS Fluent. In this numerical model, Shear Stress Transport 𝑘 – 𝜔 turbulence model was used. Governing equations was solved under three-dimensional, transient, viscous, incompressible flow assumptions. The rotation of the fan was defined by the sliding mesh method. The numerical flow solution was validated with experimental volumetric flow rate data. According to the numerical and experimental results, the flow rate of the axial fan under the specified conditions was determined as 19 L/s. A hybrid aeroacoustic model is created by giving the pressure outputs of the flow solution as input to the acoustic model. For the acoustic solution, Ffowcs Williams & Hawkings (FW-H) model defined in ANSYS Fluent was used and the result of the solution was compared with the sound pressure data collected in the full anechoic acoustic room. Although there is some difference between the numerical and experimental sound pressure curves, it was observed that the hybrid model established to understand the general trend and to catch the blade passing frequency was successful. It was predicted that the difference between experimental and numerical measurements occurred for two reasons. The first is absence of the fan motor in the numerical analysis. Another reason is that the acoustic propagation resulting from the excitation of the air flow to the system structures cannot be predicted with this model. In the second step of the study, the model validated with axial fan solutions was applied to the freezer compartment. The aim here is to reveal the air flow distribution in the freezer volume and to identify the regions where turbulence effects increase. In the numerical model, the axial fan was rotated at an operational speed of 1200 rpm and this rotation was achieved by the sliding mesh method. As a result of the analysis, it was seen that the turbulence formation started at the wing tips as observed in the solo fan analyses, and the vortices coming out of the trailing edge tips were especially concentrated in the region between the upper wall of the freezer volume and the upper two drawers. In addition, a turbulent area was detected at the bottom of the evaporator cover (which is the fan suction area). As a result of the hybrid aeroacoustic model solution, the sound pressure data collected from 1 meter away from the front, rear and side surfaces of the freezer and the sound pressure data collected from the same locations in the full anechoic acoustic room were compared. When the total sound pressure in the range of 10-10000 Hz is compared, it is seen that there is a difference of 3-7 dBA between the numerical model and the experimental results. As a result of the investigations of the axial fan in the solo and freezer volume, three different freezer models have been proposed to improve air flow, reduce turbulence and reduce the resulting noise caused by air flow. In the fist suggested model, the bottom part of the evaporator cover has changed and the acostic propagation has decreased 0.24 dBA at 1200 rpm rotational speed. The position of the axial fan and its distance from the structures in the suction and discharge directions are the parameters affecting the acoustic propagation. In the second model, it is aimed to provide acoustic gain by changing the fan position. In this context, the fan was moved on the shaft by 5 mm and brought closer to the blowing region. With this modification, total sound power level was decreased 2.18 dBA. The final model is the superposition of the first two models. Here, it was aimed to see the combined effect of two mentioned model. At 1200 rpm rotational speed, 3.27 dBA gain was achived by the third model.
  • Öge
    Development of a nonlinear sonic boom propagation code
    (Graduate School, 2023-01-24) Demiroğlu, Yusuf ; Nikbay, Melike ; 511191144 ; Astronautics and Aeronautics Engineering
    Civil supersonic flight is still one of the most challenging research topics in the aerospace industry. Since Concorde's last flight in 2003, researchers tried to find efficient solutions to make supersonic flights more affordable and reliable. Meanwhile, with the advance of computational power, computational fluid dynamics (CFD) has been implemented in advanced optimization studies involved in elevating supersonic aircraft design processes with given operational criteria and requirements. However, reducing the cost of a supersonic flight by increasing aerodynamic efficiency is not the only concern in civil supersonic transport. The second most important factor for a supersonic aircraft is the noise produced on land due to the shock waves that propagate through the atmosphere to the ground. This phenomenon is called sonic boom which is addressed in this thesis study. A sonic boom generated by a supersonic aircraft can cause very loud noise on the ground that may exceed 100 decibels. This loudness value is not acceptable due to its effects on people's daily life. Therefore, to enable civil supersonic flight over land, sonic boom loudness must be eliminated or reduced below a certain level. This effort is called sonic boom minimization and there are several methodologies that are provided in this study. Lots of studies for sonic boom minimization utilize optimization algorithms that call sonic boom prediction tools along with the CFD solvers. Therefore, to reduce sonic boom loudness, a sonic boom propagation code that accurately predicts sonic boom loudness is essential for the multidisciplinary design optimization of civil supersonic aircraft. In this regard, a new nonlinear sonic boom prediction code, named ITUBOOM, is developed in-house to be incorporated into our design optimization studies to achieve a low-boom aircraft geometry. ITUBOOM is developed in Python programming language for ease of implementation for design studies. A sonic boom calculation process can be broken down into three main steps; a near-field solution with CFD to generate an initial acoustic signal, atmospheric propagation with acoustics methods, and loudness calculation. Unlike other sonic boom codes, ITUBOOM can also be used to generate a near-field pressure directly from CFD outputs by surface slicing or in-flow signature extraction. Then, it can be used to perform atmospheric propagation by taking into account nonlinear effects such as molecular relaxation and thermoviscous attenuation. Results of ITUBOOM are validated against NASA Langley Research Center's well-known sBOOM code for different conditions on benchmark problems and presented in this thesis in detail.
  • Öge
    Helikopter ana rotor uç geometrisinin aeroakustik açıdan optimizasyonu ve rotor hareketlerinin aeroakustik etkilerinin incelenmesi
    (Lisansüstü Eğitim Enstitüsü, 2024-05-31) Öztürk, Tuğrul Teoman ; Aslan, Alim Rüstem ; 511122109 ; Uçak ve Uzay Mühendisliği
    Helikopter hem mekanik hem de aerodinamik açıdan karmaşık bir uçan makinedir. İtki/taşıma üretiminin dönel doğası, helikopterleri daha yüksek güç ihtiyacıyla birlikte çok titreşimli ve gürültülü hale getirir. Bir helikopter tasarlanırken genel maliyetin yanı sıra güç talebi, titreşim ve gürültünün de en aza indirilmesi gerekir. Dolayısıyla bu dört parametre, helikopter tasarımının en temel Araştırma ve Geliştirme etkenleri olarak değerlendirilebilir. Helikopterlerin yük ve yolcu taşımacılığında sivil amaçlı kullanımı, gelişen sosyal ve ticari ihtiyaçlar çerçevesinde özellikle büyüyen metropol şehirlerde hızlı bir artış göstermiş, buna bağlı olarak çevre için önemsenebilir bir gürültü kaynağı olmaya başlamıştır. Helikopterlerin şehir kullanımındaki artışı , yönetmeliklerde tanımlanan kabul edilebilir gürültü seviyelerini sağlamasını gerektirmektedir . Ayrıca helikopterler, hareket kabiliyetleri dolayısı ile nokta hedefler için kritik öneme sahip olduklarından, askeri amaçlı kullanım için de vazgeçilmezdir. Askeri amaçlı kullanımda, gerek intikal gerek boşaltmada helikopterin genel gürültü seviyesinin gizlilik unsuru için bozucu bir etkiye sahip olduğu da temel bir gerçektir. Bu iki durumdan hareket ile helikopterin asıl gürültü kaynaklarından biri olan ana rotorun, gerek askı durumunda gerekse ileri uçuşta rotor uç geometrisinin gürültüye katkısının incelenmesi ve düşük gürültü yaratacak geometrinin tahmini, gürültü kirliliğini azaltma anlamında büyük önem taşımaktadır. Bu gerçeklik, ABD ve Avrupa Devletlerini yeni gürültü yönetmelikleri oluşturmaya, DNW (Alman Nederland Rüzgar Tüneli) ve Onera (Fransa) gibi Deneysel Araştırma Kurumlarına yeni araştırma projeleri için yatırımlar yapmaya teşvik etmiştir. Rotor tarafından üretilen gürültünün kaynakları; kalınlık gürültüsü, yükleme gürültüsü, yüksek hızda atım gürültüsü, kanat-girdap etkileşimi gürültüsü, geniş bant gürültüsü olmak üzere çeşitlilik arz eder. Bu sebeple helikopter tasarım çalışmalarında, rotor araç akış alanının ve buna bağlı gürültünün doğru sayısal analizi hala çok zorlu bir iştir. Aeroakustik tahminler, deneysel ölçümlerle eşleşen kabul edilebilir gürültü rakamlarına ulaşmak için on milyonlarca veya daha fazla sayıda akışkan ağ örgüsü ve yüksek kapasiteli bilgisayar altyapısı gerektirir ki bu durum tasarım çalışmalarının süresini uzatmakta ve sonuca ulaşmayı zorlaştırmaktadır. Yapılan bu çalışmalara ait detaylar 1.2. Literatür Araştırması bölümünde ayrıntılı olarak ele alınmıştır. Tez kapsamında, bir helikopterin ana rotor uç geometrisinin rotor kaynaklı gürültüye etkisinin incelenmesi ve rotor ucu şeklinin en az gürültüyü yaratacak biçimde optimize edilmesi ve rotor hareketlerinin yaratılan gürültüye etkisini tahmin etmek üzere matematik model ve sayısal çözümün oluşturulması hedeflenmiştir.
  • Öge
    Passive control of aeroacoustic noise generation in transonic cavity flow via cylindrical rod
    (Graduate School, 2025-01-27) Yılmaz, Murat ; Zafer, Baha ; 511201176 ; Aeronautics and Astronautics Engineering
    Cavity flow is a phenomenon that is encountered in many applications in various industries. The flow over a cavity generates highly turbulent and complex flow structures which produce a significant level of noise. The noise generation is undesirable for several concerns depending on the application. Weapon bay of a modern fighter is one of the most important instances of cavity flow in aerospace industry. High amplitude tonal pressure fluctuations occurred within a weapon bay may cause damage on sensitive avionic devices or the stores. Additionally, the noise in the weapon bay increases the detectability of aircraft, which means that the primary purpose of internal store carriage is compromised. Therefore, control of cavity flow noise is a crucial issue for a modern fighter aircraft. In the present study, a numerical investigation was carried out about noise generation in transonic cavity flow and its passive control by a cylindrical rod. First of all, the numerical method was validated by an available experimental data in the literature namely, the M219 cavity case which involves transonic flow over a cavity with a length to depth ratio of 5. CFD analysis of the reference case was performed by Star-CCM+ using Detached Eddy Simulation (DES) model and the methodology was validated by comparing with the experimental data. High amplitude tonal noise was observed within the M219 clean cavity. Subsequently, several designs were developed for the aim of noise reduction by introducing a cylindrical rod with different diameters and positions around the leading edge. Using the same CFD methodology, each design was analyzed numerically and their attenuation performance was evaluated by comparing with the clean cavity. Overall sound pressure levels are examined at both cavity floor and rear wall. OASPL distribution is also calculated over the cavity symmetry plane. Moreover, frequency spectrum of the sound pressure level at the rearmost probe was calculated to determine mode frequencies and evaluate tonal noise reduction. Furthermore, the SPL spectrum was computed not only for a single point, but also for entire symmetry plane of the cavity, hence, SPL fields for discrete frequencies are also available. Therefore, unlike previous studies about the topic, the present study provides detailed spectral examination of cavity flow by providing the SPL fields at the mode frequencies. Additionally, Spectral Proper Orthogonal Decomposition method was utilized to reveal dynamically important flow structures that developed coherently in both time and space. Besides, pressure coefficient distributions on the cavity floor are examined to consider the designs also in perspective of loads on the store. The numerical results of each design are compared and their performances are discussed based on different aspects.