Rüzgâr türbini kanatlarındaki buzlanmanın türbin yüklerine etkisinin incelenmesi
Wind turbine load analysis of blade icing condition
Yazar: CEM ŞAHİN
Danışman: DOÇ. DR. ZEYNEP PARLAR
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Makine Mühendisliği Ana Bilim Dalı / Konstrüksiyon Bilim Dalı
Derece: Yüksek Lisans, 2024
Konu: Enerji = Energy ; Makine Mühendisliği = Mechanical Engineering

Özet:
Doğadaki enerjiyi işe yarar hale getirip kullanmak insanlık tarihi boyunca hep ilerlemenin en önemli unsuru olmuştur. Özellikle sanayi devrimi sonrası bu enerji farklı alanlarda kullanılarak medeniyetin hızla ilerlemesini sağlamıştır. Enerji talebi artarken üretilen enerjinin kaynağı da önem kazanmıştır. Günümüzde doğaya zarar vermeden sürdürülebilir enerji üretiminin yolları aranmaktadır. Yenilenebilir enerji kaynakları yarının enerji talebini karşılayacak şekilde kullanılmak istenmektedir. Rüzgâr enerjisi de bu konuda öncü alanlardan biridir.
Rüzgâr enerjisinin yüksek potansiyeli, çevreye minimum etkisi, ekonomik avantajları ve geniş bir uygulama bölgesi olması nedeniyle son zamanlarda sıkça çalışılmaktadır. Rüzgâr türbinlerinin zorlu iklim koşullarında da sorunsuz çalışması, enerji arzının sürekliliği için yüksek ehemmiyet taşımaktadır. Rüzgâr enerjisi üretiminde öncü ülkelerin genelde soğuk iklim kuşağında bulunması ve enerji talebinin bu ülkelerde kış aylarındaki artışı da göz önüne alındığında rüzgâr türbinlerinin sıfır santigrat derecenin altında uzun süre çalışması gerekmektedir. 
Düşük sıcaklıklarda kanatlarda birikebilecek buz parçalarının, hava sıcaklığının uzun süre düşük kalmasıyla kanatlarda ciddi buzlanmalara neden olması olağandır. Buzlanma kanat profilini ve kütlesini değiştirmekte ve türbindeki bazı yükleri arttırmaktadır. Türbinlerin tasarımı ve sertifikasyonu sırasında buzlanma yükleri de dahil edilmelidir.
Tezin içeriği buzlanma yüklerinin artışının nicel incelemesine odaklanmıştır. Bu inceleme yapılırken dünya çapında kabul edilen IEC standartları temel alınmıştır. Buzlanma durumunun oluşturduğu ekstrem yükler ve türbin ömrünü doğrudan etkileyen yorulma yükleri hem buzlanma olan hem de buzlanma olmayan durumda incelenmiş, yük değişimi temel nedenleriyle birlikte ortaya konulmuştur.
Çalışmada NREL'in 5MW'lık kara üzerinde kurulu açık model rüzgâr türbini kullanılmıştı. NREL'in açık kaynak aero-servo-elastik yazılımı olan OpenFAST programı kullanılmıştır. Simülasyonlar IEC'nin tasarım yük senaryolarını kapsayacak şekilde koşulmuştur. Standartlarda belirtilen rüzgâr şartları (II-B) alınmış ve buzlanma modellemesi yine IEC standartlarında belirtilen şekilde yapılmıştır. Ekstrem yükler tasarım yükü formatına, yorulma yükleri eşdeğer yük formatına dönüştürülüp incelenmiştir.
Sonuç olarak buzlanma sebepli rotor dengesizliği ve aerodinamik kanat profillerinin değişiminin; özellikle türbin kanat kenarı (edge) yönündeki momentlerin ve türbin kulelerindeki sağ-sol (side-to-side) yönündeki momentlerin artışına sebep olduğu gözlenmiştir. Bu artış hem ekstrem yüklerde hem de yorulma yüklerinde oldukça belirgindir. Soğuk iklim kuşağında bulunan türbinlerin bu yükler hesaba katılarak tasarlanması gerekliliği nicel olarak ortaya konmuştur.

Abstract:
Making use of the energy in nature has always been the most important element of progress throughout human history. Especially after the industrial revolution, this energy was used in different areas, enabling the rapid progress of civilization. As energy demand increases, the source of the produced energy has also gained importance. Nowadays, ways to produce sustainable energy without harming nature are sought. Renewable energy resources are intended to be used to meet tomorrow's energy demand. Wind energy is one of the leading fields in this regard.
Wind energy has been studied frequently recently due to its high potential, minimal impact on the environment, economic advantages and a wide application area. The smooth operation of wind turbines even in harsh climatic conditions has great importance for the continuity of energy supply. Considering that the leading countries in wind energy production are generally located in cold climate zones and the increase in energy demand in these countries during the winter months, wind turbines must operate below zero degrees Celsius for a long time.
It is normal for ice particles to accumulate on the wings at low temperatures, causing serious icing on the wings when the air temperature remains low for a long time. Icing changes the aerofoil profile and mass and increases some loads on the turbine. Icing loads should also be included during the design and certification of turbines.
The content of the thesis focuses on the quantitative examination of the increase in icing loads. The study employs the OpenFAST software to develop an aero-servo-elastic model capable of simulating the dynamic responses of wind turbines under different operational scenarios, including those with icing conditions. All conditions were based on IEC standards accepted worldwide. Extreme loads caused by icing and fatigue loads that directly affect turbine life have been examined in both icing and non-icing conditions, and the load change has been revealed together with its main reasons. Through this investigation, the study seeks to provide insights that could enhance the design and operational strategies of wind turbines, especially in cold climates where icing is a common and persistent issue. 
The literature review section provides an extensive overview of wind energy and wind turbines, detailing their historical evolution, various types, and key components. The phenomenon of icing is examined in depth, discussing its formation, types, and its impact on the aerodynamic performance of turbine blades. Historical data and case studies of turbine failures due to icing are also reviewed to provide a contextual background and underscore the importance of addressing this issue.
The methodology sections detail the development of the aero-servo-elastic model using OpenFAST, which is an advanced simulation tool designed to analyse the coupled aerodynamic, structural, and control dynamics of wind turbines. The model development process involves generating wind files that represent different atmospheric conditions, modelling the aerodynamic and elastic properties of the turbine, and integrating the control system.
NREL's 5MW land-based open model wind turbine was used in the study. OpenFAST program, NREL's open source aero-servo-elastic software, was used. Simulations were run to cover IEC design load scenarios. Wind conditions (II-B) specified in the standards were taken and icing modelling was done as specified in IEC standards. Extreme loads were converted to design load format and fatigue loads were converted to equivalent load format and examined.
In generating wind files, turbulent conditions are created to simulate realistic operating environments. Turbulent winds are generated using standard models such as the Normal Turbulence Model (NTM) and the Extreme Wind Model (EWM). The aerodynamic characteristics of the turbine blades are modelled to assess how icing affects lift, drag, and overall aerodynamic efficiency. 
The structural properties of the turbine, including the blades, rotor shaft, and tower, are modelled to understand how they respond to dynamic loads under icing conditions. The structural integrity and deformation of these components are analysed under different loading scenarios. The turbine's control system, which adjusts the blade pitch and rotational speed to optimize performance and protect the turbine from excessive loads, is incorporated into the model. This integration is crucial for simulating realistic operational responses to icing.
Simulations are conducted across various design load cases (DLCs) to evaluate the performance of the turbine under both normal and icing conditions. These DLCs cover a range of scenarios, including normal operation, idling, extreme wind speeds, and system faults. The loads on different turbine components, such as the rotor shaft, tower, and blades, are compared between scenarios with and without icing. The analysis focuses on extreme loads, fatigue loads, and the overall impact on turbine performance and reliability.
The study's detailed simulations using the OpenFAST software provide a clear picture of how icing influences the loads experienced by various turbine components. For instance, during normal operation without icing, the aerodynamic forces on the blades are balanced to optimize energy capture. However, the presence of ice disrupts this balance, leading to uneven loading and increased mechanical stress.
The simulation results reveal that icing significantly increases the loads on wind turbine components. Key findings from the study include increased aerodynamic drag forces on the blades, resulting in higher blade edge bending moments and stresses. This can accelerate fatigue damage and reduce the lifespan of the blades. The rotor shaft experiences slight changes at torsional and bending loads under icing conditions. Because of rotor imbalance, the dynamic response of the tower is also affected. Increased displacement at tower top and higher side-to side bending moments observed during simulations with icing.
The study also examines the economic implications of icing on wind turbines. Increased loads due to icing not only pose a risk of mechanical failure but also lead to higher maintenance costs and reduced energy production efficiency. By implementing effective mitigation strategies, the long-term operational costs of wind turbines can be reduced, enhancing their economic viability.
Furthermore, the research highlights the importance of site-specific analysis when designing and operating wind turbines in cold climates. Different regions experience varying levels of icing severity, and thus, tailored solutions are necessary to address the unique challenges presented by each location. This site-specific approach ensures that wind turbines are optimally designed and operated to withstand local environmental conditions.
Addressing these challenges requires a multi-faceted approach. One of the primary strategies discussed in the study is the integration of blade heating systems. These systems can be designed to activate when icing conditions are detected, preventing the accumulation of ice by maintaining the blade surface temperature above freezing. While this solution can be effective, it also introduces additional power consumption, which must be balanced against the overall energy output of the turbine.
Another approach involves operational adjustments. For example, reducing the rotational speed of the turbine during icing conditions can decrease the aerodynamic loads on the blades, mitigating the impact of ice accumulation. Similarly, altering the blade pitch to reduce the angle of attack can help to maintain more stable aerodynamic performance, even with ice on the blades.
The use of advanced materials and coatings is also explored as a means of reducing ice formation. Anti-icing coatings can be applied to the blade surfaces to prevent ice from adhering. These coatings typically work by creating a low-friction surface that ice cannot easily bond to.
The economic implications of these mitigation strategies are significant. While the initial investment in blade heating systems, advanced coatings, and other technologies may be substantial, the long-term benefits in terms of reduced maintenance costs and enhanced turbine reliability can justify these expenditures. 
In addition to technical and economic considerations, the study highlights the importance of regulatory and policy support for the adoption of anti-icing technologies. Governments and regulatory bodies can play a crucial role by providing incentives for the integration of these technologies, thereby accelerating their adoption and ensuring that wind energy remains a competitive and reliable source of renewable energy.
In conclusion, this research underscores the significant impact of icing on wind turbine performance and structural loads. The study contributes valuable insights into the effects of icing on wind turbine loads and offers a range of mitigation strategies to enhance the performance and reliability of wind turbines in cold climates. These findings are crucial for engineers, designers, and operators in the wind energy sector, providing them with the knowledge and tools needed to tackle the challenges posed by icing and to optimize the performance of wind turbines in diverse environmental conditions. The research emphasizes the importance of continuous innovation and adaptation in the wind energy industry to address emerging challenges and to ensure the efficient and sustainable generation of clean energy.