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Öğe Design and optimization of the hydrokinetic turbine blades using statistical approaches(Pergamon-Elsevier Science Ltd, 2026) Kale, Fatih Mehmet; Yilmaz, Naz; Bademlioglu, Ali Husnu; Sokmen, Kemal Furkan; Shi, WeichaoIn this study, the design and optimization of Horizontal Axis Hydrokinetic Turbine (HAHT) blades were carried out using statistical approaches. Taguchi and ANOVA analyses were employed as the statistical methods. Initially, experimental and detailed computational analyses were conducted to predict the hydrodynamic performance of a HAHT. Subsequently, Taguchi and ANOVA analyses were performed to investigate the effects of design parameters such as thickness ratio (t/c), pitch angle (phi) and twist angle (theta) on the hydrodynamic performance of HAHT blades for different r/R blade sections 0.4, 0.6 and 0.8, and the optimal design parameters were identified. The study aims to investigate the effect of the design parameters, which are the most important in HAHT designs, on the power coefficient (CP) and to obtain the maximum CP for the existing HAHT as a result of changes proposed by the Taguchi and ANOVA optimization method. For the optimal HAHT geometry, the CP increase is observed between 2 % and 6 % at different TSR values. As a result of the analyses, the maximum CP was obtained as 0.4499 for the optimal design parameters. Additionally, it was concluded that the pitch angle was the most influential parameter on CP. Overall, the optimized blade provided a maximum 6 % increase in CP at TSR 5 compared to the initial design, and the pitch angle affected more than 96 % of this improvement compared to other parameters.Öğe Experimental and numerical investigations of hydrodynamic performance for horizontal-axis hydrokinetic turbines(Univ Zagreb Fac Mechanical Engineering & Naval Architecture, 2025) Kale, Fatih Mehmet; Yilmaz, Naz; Sokmen, Kemal Furkan; Shi, WeichaoThis paper presents both experimental and numerical investigations of the hydrodynamic performance of Horizontal-axis Hydrokinetic Turbines (HAHTs) using experimental methods and Computational Fluid Dynamics (CFD) approaches, respectively. The innovative aspect of this study lies in the consistency of the results, achieved by aligning the method used in the CFD analyses for Hydrokinetic Turbines (HKTs) and airfoil profiles with experimental data. For this purpose, 2-D CFD analyses were first conducted with blade section geometries (Eppler 395 and S1210), which are commonly used in HKT designs. The aerodynamic characteristics (CL and CL/CD) of these blade sections were computed and compared with the experiments. Subsequently, a three-dimensional (3-D) turbine geometry, featuring three different pitch angles (PAs), was simulated using CFD, and the results were compared with experimental data obtained under the same operating conditions in the Emerson Cavitation Tunnel (ECT) at Newcastle University. The comparisons showed good agreement while the maximum relative error was calculated less than 10 % for the power coefficient (CP) of the turbine with a PA of 0 degrees. For the other PA (8 degrees), the maximum relative error was 11 % for CP and 14 % for the thrust coefficient (CT). The CFD investigations of HKTs revealed that the Detached Eddy Simulation (DES) model has less relative errors compared to the other turbulence models at the same Tip Speed Ratio (TSR) values, while the Sliding Mesh (SM) method describing rotation gives more consistent and closer results to the experiments, with the investigation of y+ point of view.Öğe Gemi Direnci ve Sevk Performansının Gemi Ölçeğinde Seyir Testleriile Sayısal Doğrulaması(2020) Yilmaz, NazYıllardır gemi sevk performansının sayısal doğrulaması, genellikle model ölçeğindeki gemi deney sonuçları ile karşılaştırılarak yapılmaktadır. Gemi model deney havuzlarında gerçekleştirilen bu deneylerde gemi ölçeğini değiştirmek oldukça zor ve zahmetli iken, gelişen teknoloji ve artan hesaplama gücüyle nümerik analiz ve modellemeleri tam gemi ölçeğinde gerçekleştirmek daha makul hale gelmiştir. Bu durum aynı zamanda, ölçeklendirme sebebiyle ortaya çıkan ve akış dinamiklerinin tahminindeki belirsizlikleri ve model ölçeğinden gemi ölçeğine geçişteki ampirik hesaplamalardaki belirsizlikleri de ortadan kaldırmaktadır. Ne yazık ki, gemi ölçeğindeki sayısal sonuçları doğrulamak amacıyla, uygun deniz koşullarında ve yüksek kalitede verilerin ölçülebilmesi için gerçekleştirilen gemi seyir testleri sonuçlarına ulaşmak konusunda bazı zorluklar yaşanmaktadır. Bunun üstesinden gelmek için Lloyd Register (LR) bünyesindeki Gemi Performansı Grubu, bir kargo gemisi ile gerçekleştirilen gemi seyir testlerinin deneysel sonuçlarını, gemi ölçeğinde Hesaplamalı Akışkanlar Dinamiği (HAD) yöntemlerinin güvenilirliğini arttırmak ve nümerik modelleme araçlarının kabiliyetlerinin değerlendirilmesi amacıyla bir çalıştay vasıtasıyla paylaşmıştır. Bu çalışmada, LR çalıştayında sunulan tam gemi ölçeğindeki gemi direnci, açık su pervane performansı, gemi sevki, pervane performansı ve pervane kavitasyonu konularındaki sayısal doğrulama çalışmaları sunulmaktadır. Sayısal hesaplamalar, çalıştayın başında sonuçlar bilinmeksizin (kör bir şekilde) gerçekleştirilmiş olup, simülasyonlar esnasında ticari bir Reynolds-Averaged Navier Stokes (RANS) türbülans ve Volume of Fluid (VoF) modeli kullanılarak gerçekleştirilmiştir. Pervane kavitasyonunun hesaplanması için ise Schnerr-Sauer kavitasyon modeli kullanılmıştır. Gemi sevki analizlerinde pervane dönüşünün tanımlanabilmesi için kayan çözüm ağı (sliding mesh) yaklaşımı kullanılmıştır. Geminin kendi kendini sevk noktası, sabit pervane dönüş hızı (çalıştay tarafından sağlanan veriler arasındadır) ile gemi hızı değiştirilerek tespit edilmiştir. Nümerik olarak tahmin edilen pervane kavitasyon görselleri, gemi seyir deneyleri esnasında kaydedilen gerçek fotoğraflar ile karşılaştırılmıştır. HAD yöntemi kullanılarak analiz edilen tüm vakalar, deneysel sonuçlar ile karşılaştırılmış olup, gemi direnci, açık su pervane performansı, güç ve kavitasyon tahminleri açısından oldukça iyi sonuçlar elde edilmiştir.Öğe Hydrodynamic optimization of full-scale aeration tanks using field measurements and computational fluid dynamics modeling(Aip Publishing, 2025) Celik, Damla Yilmaz; Yilmaz, Naz; Sibil, Rahim; Aras, Egemen; Vaheddoost, BabakImproving energy efficiency and operational performance in wastewater treatment plants largely relies on precise hydrodynamic analysis. In this context, field-based studies are essential for understanding system behavior under real operational conditions. This study was conducted at a full-scale wastewater treatment plant, where flow dynamics in the aeration tank were evaluated through extensive field measurements and computational fluid dynamics modeling. Data were collected from 98 locations across 15 different depth levels using an Acoustic Doppler Current Profiler and a Hach FH950 velocity meter. The numerical model was initially validated with the help of experimental field data, enabling an accurate assessment of flow characteristics at varying depths. Results revealed that the low-velocity zones and non-uniform velocity distributions negatively affect system performance. It is also concluded that the inlet and outlet positions disturb the favorable circulation patterns and flow uniformity. Geometric optimization strategies were implemented to develop solutions, which led to a more uniform velocity distribution and improved hydraulic efficiency. By integrating detailed field measurements with numerical modeling, this study provides a comprehensive understanding of aeration tank hydrodynamics and offers practical design recommendations for improving overall system performance.Öğe Numerical investigations of aerodynamic performance for flettner rotors in the presence of full-scale ship-rotor interaction(Pergamon-Elsevier Science Ltd, 2026) Yilmaz, Naz; Bordogna, Giovanni; Aktas, BatuhanThis study presents numerical investigations of aerodynamic characteristics (lift and drag coefficients) for Flettner rotors in the presence of the interaction between the rotor and the full-scale merchant ship. For this purpose, several numerical investigations have been conducted for two different isolated rotors in model and fullscale conditions using Reynolds Averaged Navier-Stokes (RANS) based Computational Fluid Dynamics (CFD) approaches. The effects of different turbulence models, mesh types and sizes, and boundary conditions on the domain's bottom surface have been investigated for a reference rotor in isolation and model-scale conditions. After that, selected methods were implemented on a full-scale isolated rotor geometry. The results of the computations were compared with experimental and computational results from the open literature and showed good agreement. As a result of the validation studies in isolated conditions, a similar CFD approach was applied on a full-scale rotor, which is operating on a capsize bulk carrier (merchant ship) to investigate the interaction between the rotor and the ship. During these numerical calculations, different ship and wind speeds, rotation rates for rotor and Thom, and also different wind profiles such as Straight and Atmospheric Boundary Layer (ABL) were investigated for the Flettner rotors in interaction with the full-scale ship. In conclusion, not only the aerodynamic characteristics of the Flettner rotor but also the effects of this complex interaction between the rotor and ship were analysed and investigated computationally. Results show that rotor-ship interaction significantly affects aerodynamic performance at spin ratios above 3, with drag forces increasing and lift forces decreasing compared to isolated conditions. Moreover, ABL profiles consistently led to lower lift coefficients than uniform wind conditions, underlining the importance of realistic environmental modeling.Öğe Taguchi and CFD-based hydrodynamic performance investigations of diffuser-augmented hydrokinetic turbines(Pergamon-Elsevier Science Ltd, 2026) Kale, Fatih Mehmet; Yilmaz, Naz; Bademlioglu, Ali Husnu; Sokmen, Kemal Furkan; Shi, WeichaoIn recent years, interest in renewable energy technologies has been increasing as part of the effort to obtain clean energy. One of these technologies, Hydrokinetic Turbines (HKT), converts the kinetic energy of water flow into electricity. However, these turbines fail to reach the theoretically calculated power coefficient (CP). To overcome this issue, researchers are developing various diffuser designs to enhance efficiency. In this study, the effects of the parameters used in diffuser design (foil type, diffuser length, tip clearance, and angle of attack) on the CP were investigated using Taguchi analysis, and an optimum diffuser design was developed for the Horizontal Axis Hydrokinetic Turbine (HAHT) based on the obtained experimental results. For the validation study of HAHT and CP calculations of the Diffuser-Augmented Hydrokinetic Turbine (DAHT), the Computational Fluid Dynamics (CFD) method was employed. According to the results of the Taguchi analysis, it was determined that diffuser length is the most influential parameter on the CP. Additionally, it was found that the effect of tip clearance on CP is relatively limited compared to other parameters. For the optimum operating parameters, maximum CP value was calculated as 0.7006. Consequently, a 67 % increase in the CP of the existing HAHT was achieved.
