Hangar kenar modifikasyonu ile basitleştirilmiş fırkateyn modeli hava izinin iyileştirilmesi
Improvement of ship airwake of a simplified frigate model with hangar edge modification
- Tez No: 916865
- Danışmanlar: PROF. DR. UĞUR ORAL ÜNAL
- Tez Türü: Yüksek Lisans
- Konular: Gemi Mühendisliği, Havacılık ve Uzay Mühendisliği, Savunma ve Savunma Teknolojileri, Marine Engineering, Aeronautical Engineering, Defense and Defense Technologies
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2025
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Lisansüstü Eğitim Enstitüsü
- Ana Bilim Dalı: Gemi İnşaatı ve Gemi Makineleri Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Gemi İnşaatı ve Gemi Makineleri Mühendisliği Bilim Dalı
- Sayfa Sayısı: 105
Özet
Gemilerde konuşlandırılan operasyonel elemanlar için; geminin direnç, stabilite ve mukavemet gibi ana hesap unsurlarının yanı sıra harici hesaplara ihtiyaç duyulabilmektedir. Bunlardan biri olan helikopter güverteleri için, helikopterlerin güvenli iniş ve kalkış sınırlarını belirleyen uçuş zarfı hesaplarını yapmak önem arz etmektedir. Uçuş zarfı hesaplarının temelinde gemiye ait hava izinin modellenmesi yer almaktadır. Kaba yapılı süreksiz gövde tasarımlarına sahip gemiler, etraflarında türbülanslı yapıda hava akımı oluşturmaktadırlar. Helikopter güvertesinin kıçta olduğu bu tür gemilerde üst yapı aerodinamiğinin şekillendirdiği hava izi, helikopter operasyon bölgesinde daha karmaşık, asimetrik ve türbülanslı bir forma ulaşmakta, bahse konu türbülanslı ortam helikopter iniş kalkış manevralarında pilot kontrolünü zorlaştırmaktadır. Operasyonel verimliliğin artması, oluşabilecek kaza-kırımın önlenebilmesi ve pilot iş yükünün azaltılabilmesi amacıyla uçuş bölgesinde oluşan türbülansın doğru değerlendirilmesi önem arz etmektedir. Bu çalışmada bir basit fırkateyn şekli (SFS2) üzerinde oluşan akış rejiminin helikopter güvertesi bölgesine olan etkisi güncel Ölçek-Çözümlü Simülasyonlar (SRS) kullanılarak hesaplamalı akışkanlar dinamiği (HAD) ile incelenmiştir. Sonuçlar literatürde yer alan deney verileri ile kayda değer bir uyum göstermiştir. Kullanılan yöntemin hava izi hesaplamalarında öncelikli olarak kullanılabileceği değerlendirilmektedir. Askeri gemilerde üst yapı, aerodinamik kaygılar yerine düşük radar görünürlüğü öncelenerek tasarlanmaktadır. Gemilerin gizlilik kabiliyetini artırmak için eski üstyapı tasarımlarının yerini eğimli, düz yapılı, kaba tasarımlar almıştır. Bu yapılar gemi hava direncini artırırken helikopter güvertesi bulunan gemilerde uçuş bölgesindeki hava izini de karmaşıklaştırmaktadırlar. Gizlilik özelliklerinin yanında direnç ve hava izi iyileştirmelerinin sağlanabilmesi için ön dizayn aşamasında aerodinamik optimizasyon uygulanması önem arz etmektedir. Aerodinamik optimizasyon bütün üstyapıya uygulanabileceği gibi bölgesel olarak da uygulanabilir. Bu çalışmada gemi hava izi yapılanmasına odaklanıldığından, uçuş bölgesi civarında bir iyileştirme öngörülmüş ve Coanda etkisinden esinlenilerek hangar dış kenarlarına 5 farklı tipte yapı elemanı eklenmiştir. Uygulanan modifikasyonlar öncesinde sunulan aynı hesaplama yöntemi ile çözümlenerek sonuçlar yalın geometri ile karşılaştırılmıştır. Tüm modifikasyonlar hava izi türbülansını azaltmış, en iyi sonucu veren modifikasyon nihai karşılaştırmada sunulmuştur.
Özet (Çeviri)
Ships may need external calculations when it comes to operational structures deployed, in addition to the calculations such as resistance, stability and strength. One of these structures is the helicopter deck. It is important to make flight envelope calculations that determine the safe recovery and launch limits of helicopters. The basis of the flight envelope calculations is the modeling of the ship's airwake. The airwake shaped by the superstructure aerodynamics generates a complex, asymmetrical and highly turbulent form in the helicopter operation area. Within the helicopter operations, the turbulent area makes pilot control more difficult. It is vital to accurately evaluate the turbulence occurring in the relevant region in order to increase operational efficiency, prevent possible accidents and reduce pilot workload. In this study, the effect of the flow regime in the flight deck airborne on a Simple Frigate Shape (SFS2) has been examined with Computational Fluid Dynamics (CFD) using Scale-Resolving Simulations (SRS) including brand new Stress-Blended Eddy Simulation (SBES). The results have been exhibited a remarkable agreement with the experimental data, and it has been agreed that the solution method could be a priority in ship airwake calculations. In military ships, the superstructure is designed with a priority on low radar visibility rather than aerodynamic concerns. To enhance the stealth capabilities of the ships, sloped, flat and bluff body designs have replaced the older superstructure designs. While these structures increase the ship's air resistance, they also complicate the airwake in the flight area of ships with helicopter decks. In addition to stealth features, aerodynamic optimization during the pre-design phase is important for improving both drag and airwake characteristics. Aerodynamic optimization can be applied to the entire superstructure or regionally. Since this study focuses on ship airwake structuring, an improvement around the flight area has been envisioned, and five different types of structural elements were added to the outer edges of the hangar, inspired by the Coanda effect. The modifications were analysed using the same computational method presented above, and the results were compared with the main geometry. All modifications reduced airwake turbulence, and the best-performing modification was presented in the final comparison. In ship construction, aerodynamic design is often overlooked due to the relatively lower contribution of air resistance to the overall resistance of the vessel. While aerodynamic considerations are more critical for yachts, they are not typically prioritized for commercial and military ships. In modern military ship design, the superstructures are primarily shaped to minimize radar visibility, with less emphasis on aerodynamic efficiency. These enclosed, bluff-body designs significantly impact the ship's air resistance and have a considerable influence on the flow characteristics over the vessel. In ships with helicopter decks, such as large naval ships, mega yachts, research ships, and drilling platforms; besides considering the air resistance, calculation of the airwake over the flight deck are of great importance. Particularly in ships with stern flight decks, the airflow, shaped by the superstructure, directly influences the flight operations by forming a complex turbulent wake over the deck. The relative airflow over the flight deck, created by the ship's own motion and the external wind flow, is the main factor driving the airwake formation. Additional elements, such as the thermodynamic effects of air temperature and exhaust gases, contribute to the complexity of the airwake. These bluff superstructures, along with various systems and equipment mounted on them (such as antennas, radars, funnels, and weapon systems), further complicate the already asymmetric flow regime. This turbulent environment, characterized by various multi-directional vortices, causes sudden pressure differences at both low and high frequencies, which result in a significant increase in the pilot's workload. Especially within the ratchet frequency range of 2-3 Hz, helicopter control becomes difficult. In bad weather and sea conditions, these situations unfortunately can lead to crashes. Given the high intensity of flight operations on naval ships and the importance of manoeuvre efficiency and time, it is extremely important to include airwake calculations during the design phase and implement related aerodynamic structural improvements. Given the presence of high vortices and turbulence over a simple ship form, the resulting airwake becomes complex, and each ship exhibits distinct flow characteristics, making airwake interpretation a challenging task. To date, the interpretation of airwake has been conducted using in situ measurements taken on ships, low-speed wind tunnel experiments, and flow-resolving simulations. In light of this information, accurately assessing turbulence in the flight region is essential for improving operational efficiency, reducing pilot workload, and preventing potential accidents and damage. Accordingly, this study focuses on calculating the ship airwake, which represents the initial step in ship-helicopter interaction studies, and aims to establish a foundation for airwake calculations using CFD. Based on previous research, it has been concluded that SRS offer an effective approach to resolving the turbulent structures generated by bluff bodies, such as ship superstructures, which induce significant flow separations. However, a review of the literature reveals that the critical computational steps necessary for accurately capturing flow structures, particularly turbulence intensity, using different SRS techniques have not been clearly defined. Thus, this study aims to present a comprehensive computational strategy for effectively and reliably conducting ship airwake simulations using advanced SRS methods. In addition to the commonly employed SRS models, this study incorporates the Stress-Blended Eddy Simulation (SBES) model, which has been introduced in recent studies but has not yet been applied to ship airwake calculations. By comparing the computational results with experimental data available in the literature, this study demonstrates the predictive capabilities of these methods for complex separated flows characterized by high levels of vorticity and turbulence. It serves as a roadmap for researchers interested in advancing this field. In this study, a comprehensive computational analysis strategy has been presented for the effective and accurate calculation of ship airwakes. Within the scope of the study, various Scale-Resolving Simulation (SRS) techniques, which have become relatively widespread in recent years, were examined and compared with experimental studies available in the literature to evaluate their predictive capabilities in detail. Additionally, the research focused on accurately interpreting the turbulence over the flight deck and investigated the reduction of turbulence intensity in the flight region by employing modified SFS2 ship geometries with modified hangar edges. Detailed comparisons revealed that SRS methods demonstrated significantly superior results in terms of velocity magnitudes and turbulence intensity levels compared to Unsteady Reynolds-Averaged Navier-Stokes (URANS). It was observed that SRS methods produced close results for velocity magnitude calculations, with relative errors of less than 1% between them. However, their turbulence intensity predictions differed by ~1–4%, depending on the simulation technique. These discrepancies are attributed to the differences in the formulation of the respective simulation techniques. The Delayed Detached-Eddy Simulation (DDES) and Stress-Blended Eddy Simulation (SBES) models predicted turbulence intensity in the flight region with deviations of approximately ~15% and ~16% from experimental results, respectively. In spectral analyses, which are critical for flight envelope calculations, the SBES method showed better agreement with experimental results. Particularly at high frequencies, which are crucial to accurately capturing experimental data, SBES outperformed DDES by approximately ~50%. This success of SBES is attributed to its formulation, which accelerates the transition to the Large Eddy Simulation (LES) solution compared to other methods. Detailed comparisons also demonstrated that SRS methods are highly effective in modelling turbulence in regions of significant flow separation, particularly in ship geometries with discontinuous superstructures. It was determined that increasing grid resolution in the flight region could further improve the results by enabling more detailed modelling of turbulent structures. By adopting a simplified approach to the boundary layer without compromising simulation accuracy, computational studies of ship airwakes were significantly relieved from excessive computational loads. It was also shown that the use of optimal values for time steps eliminates the need for an additional time convergence study. It was proven that ship airwake analyses, which form the basis for flight envelope calculations, can achieve more efficient results with relatively fewer computational resources. The SBES model, which has only recently been encountered in the literature and used in various analyses, is considered a priority choice for ship airwake calculations. Inspired by the Coanda Effect, hangar edge extensions applied to discontinuous superstructures successfully redirected the airwake, reducing turbulence in the flight region and providing improved aerodynamic performance. However, it was found that the CSAW geometry, which was designed to mimic the winglets of birds that reduce noise and wingtip losses, is not effective in reducing turbulence in ship airwake studies. The modified geometry named CS90 reduced turbulence intensity in the flight region by approximately 15% compared to the unmodified SFS2 geometry. It was concluded that extensions like those used in this study, which can be applied to hangar edges during or after ship design, can significantly improve operational performance in the flight region.
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