A State-of-the-Art Review of Wind Turbine Blades: Principles, Flow-Induced Vibrations, Failure, Maintenance, and Vibration Suppression Techniques

Abstract

The growing demand for renewable energy has underscored the importance of wind power, with wind turbines playing a pivotal role in sustainable electricity generation. However, wind turbine blades are exposed to various challenges, particularly flow-induced vibrations (FIVs), including vortex-induced vibrations, flutter, and galloping, which significantly impact the performance, efficiency, reliability, and lifespan of turbines. This review presents an in-depth analysis of wind turbine blade technology, covering the fundamental principles of operation, aerodynamic characteristics, material selection, and failure mechanisms. It examines the effects of these vibrations on blade integrity and turbine performance, highlighting the need for effective vibration suppression techniques. The paper also discusses current advancements in maintenance strategies, including active and passive vibration control methods, sensor networks, and drone-based inspections, aimed at improving turbine reliability and reducing operational costs. Furthermore, emerging technologies, such as artificial intelligence (AI)-driven prognostic assessments and novel materials for vibration damping, are explored as potential solutions to enhance turbine performance. The review emphasizes the importance of continued research in addressing the challenges posed by FIVs, particularly for offshore turbines operating in harsh environments.

1. Introduction

Rapid technological advancements are fueling growing energy demand, posing a significant challenge to meeting global needs sustainably [1,2,3]. Traditional energy sources (Figure 1a), such as fossil fuels and biomass, pose significant environmental risks and are incompatible with the greenhouse gas reduction goals set by the Kyoto Protocol [4,5]. In contrast, renewable energy sources (e.g., solar, wind, and biomass) provide a cleaner, more sustainable alternative, driving increased research and investment in their development and gaining considerable attention for their numerous benefits over conventional energy sources. Over the past five years, renewables have received greater budgetary support than coal and other conventional sources (Figure 1b). Wind energy has emerged as a focal point for researchers and the energy business due to its lower carbon dioxide emissions (Figure 1c) and abundant global availability [6,7,8].

The historical use of wind energy for various tasks dates back centuries. Windmills and watermills (Figure 2a,b) were employed in Egypt, Persia, Mesopotamia, and China as early as the seventh century. Examples include King Hammurabi’s vertical axis machines in Babylon and the Sistan Windmills (644 A.D.) in Persia [9]. This marked the beginning of the wind-driven machine industry, which has evolved into the third-largest source of energy production globally, following hydropower and solar. In ancient times, wind was used for grinding grain, sawing timber, pressing oil, shredding tobacco, and pumping water, as shown in Figure 2c [10,11].

The evolution of the wind industry can be divided into five major periods: traditional (before 1750), empirical (1750–1900), establishment (1900–1960), growth (1960–1980), and modern (1980–present) [12]. While wind energy was utilized for various purposes, electricity generation from wind turbines became prevalent in the late 19th century. Charles Brush, an American engineer, developed the first automatic 12 kW wind turbine in 1888, powering his home in Ohio for twenty years. In the 1920s, Marcellus Jacobs, another American, built small wind turbines with three-bladed rotors resembling modern designs, incorporating battery storage for home power systems in Minneapolis, MN, USA [9]. Poul La Cour, a Danish scientist, followed, constructed approximately one hundred 20–35 KW wind turbines with generators in Denmark [9,13,14]. Germans developed complex horizontal-axis wind turbines with bearings at the rotor hub. Professor Ulrich Hutter created wind turbines using airfoil sections, fiberglass, and plastic blades to reduce weight and improve efficiency in Stuttgart, Germany [15] (Figure 2d). By the early 1930s, Russians constructed larger-scale utility wind turbines up to 100 KW [16]. These advancements led to experimental wind plants in the USA, Germany, and Denmark from 1935 to 1970, demonstrating the viability of larger-scale wind turbines.

Wind turbine technology has evolved from smaller vertical-axis designs to the larger, more efficient horizontal-axis turbines that are now widely used around the globe. Many onshore and offshore regions are suitable for wind turbine installations, with some coastal cities in Europe, Asia, and America relying on wind energy as a major electricity source. The Global Wind Energy Council (GWEC) reported that 2023 was a record year for wind turbine installations, with a global addition of 117 GW of new capacity, nearly 50% more than the previous year [17]. This included 106 GW onshore and 10.8 GW offshore. At the UN Climate Change Conference (COP28), 200 countries agreed to triple renewables by 2030 to generate 11,000 GW, increasing installation capacity to 320 GW [17]. Given the critical role of wind turbines in sustainable energy production, ensuring their smooth and reliable operation is essential for the continued growth and success of the industry.

Consequently, considerable research has been dedicated to enhancing turbine efficiency and improving component safety. Rotor blades, gearboxes, generators, and towers are primary components of onshore and offshore wind turbines and are prone to failure [18,19,20]. Figure 3 shows the different components of onshore and offshore wind turbines and their failure percentage. Clearly, blades and generators account for the largest share of failures in wind turbine systems. Blades interacting with incoming wind convert wind kinetic energy into mechanical torque for electricity generation. However, they are subjected to harsh operating conditions, including extreme temperatures, intense solar radiation, and seismic activity, which can impact their performance and longevity [21,22,23]. Additionally, wind turbine blades endure extraordinary events, such as lightning strikes and bird collisions [24,25,26,27], while also bearing substantial inertial, gravitational, aerodynamic, and fatigue loads [28]. Furthermore, they are designed with multiple airfoil sections, extending from the root to the tip [29,30]. Their complex design makes their performance critical to the reliability of the entire generator system [31]. Blade failures can disrupt the balanced rotation, causing violent vibrations and the potential collapse of the entire turbine structure [32].

Recent wind turbine blade damage incidents have resulted in significant economic losses. In December 2024, a turbine blade failed at the Sneddon Law Wind Farm in Scotland. Other incidents in 2024 include a blade failure at the Dogger Bank offshore wind farm in the UK and a blade collapse at the Hoa Binh Wind Power Project No. 5 in Vietnam, resulting in an estimated loss of US$ 8.1 million. Similar incidents occurred in 2022 and 2023, such as the Ørsted Wind Farm Blade Failure in May 2023 and the Vestas Wind Turbine failure in Germany in June 2022. In autumn 2021, a storm damaged wind farms in Germany and France, including severe damage to the blades of an Enercon E-138 EP3 4.2 MW fan at the Nattheim Wind Farm (Figure 4a). In January 2018, a blade broke on a wind turbine in Liaoning, China (Figure 4b). Similarly, in other applications where similar blades are used, severe accidents and loss of life have occurred due to blade failure. For instance, the main rotor blade of an AH-1 Cobra helicopter in South Korea unexpectedly broke and detached (Figure 4c), while Southeast Atlantic Airlines Flight 529 was destroyed when damaged propeller blades led to a catastrophic failure (Figure 4d). This crash tragically resulted in the death of eight people, including seven passengers and the captain.

Megawatt-class wind turbines are now the mainstay of the wind power market [33], with blades moving towards larger diameters and lighter masses, particularly in deep-sea wind turbines, where blade lengths can reach 120 m [23,34]. For example, the GE Haliade-X, the world’s largest wind turbine, has a height of 260 m, a power capacity of 14 megawatts, a rotor diameter of 220 m, and a blade length of 107 m [35]. These large-diameter blades are susceptible to vibrations due to pendulum motions, wind-induced instability, and inertial forces [36]. When bending, heaving, and pitching motions are coupled, strong classical flutter can occur, which is rapid, destructive, and must be avoided in wind turbine design and operation [20,27,37,38]. Reducing wind turbine damage caused by vibration and improving wind energy utilization efficiency are, therefore, critical for the development of wind power generation. This paper provides a review of wind turbine blade technology, including principles of operation, aerodynamics, material selection, design, analysis of flow-induced vibrations (vortex-induced vibrations, flutter, and galloping), failure modes, maintenance, and vibration mitigation techniques.

2. Types of Wind Turbines

Wind turbines can be differentiated and named based on several criteria, including the orientation of their rotation axis (horizontal or vertical), the type of torque they produce (lift or drag), their location (onshore or offshore), and their rated power generation capacity (Figure 5). Based on the orientation of their rotation axis, wind turbines are classified as either horizontal-axis wind turbines (HAWTs) (Figure 6a,b) or vertical-axis wind turbines (VAWTs) (Figure 7a,b). Their performance, suitability, and efficiency are sensitive to locations. The most popular HAWT design has blades that revolve on a horizontal axis, just like a conventional windmill (Figure 6c). Similar to airplane wings [39], these aerodynamically designed blades generate lift and efficiently convert wind energy into rotational motion. High efficiency is achieved, particularly in regions with higher wind speeds and stable wind direction. However, their complex blade design requires precise engineering and optimal wind alignment, often necessitating yaw devices to adjust the rotor’s orientation. While their higher energy output under ideal conditions justifies their complexity, this also leads to increased production and maintenance costs. In contrast, the blades of VAWTs are typically simpler in design—either curved or straight—and are arranged in configurations such as helical or Darrieus-style [40] (Figure 7c). VAWTs rotating around a vertical axis are highly adaptable to turbulent or variable wind conditions. Their design allows them to capture wind from any direction. While VAWTs typically have lower efficiency due to slower rotational speeds and higher drag forces, their small size and unidirectional capabilities offer significant advantages in certain applications. Furthermore, VAWTs distribute stress more evenly, reducing blade fatigue and extending the lifespan of the turbine blades. Their simple mechanical design, along with ease of installation and maintenance, makes them an ideal choice for energy extraction in spaces with limited room or less consistent wind.

However, selecting the appropriate turbine for a specific location requires considering factors such as energy needs and environmental conditions. Both turbine types offer distinct advantages: HAWTs excel in stable wind conditions, offering higher efficiency and energy output, while VAWTs are more adaptable to dynamic and complex wind patterns, with the added benefit of easier maintenance. The choice of turbine is typically based on the operating site and the expected atmospheric variables. Given the larger-scale applications of HAWTs in both onshore and offshore environments, this paper focuses on the HAWTs blade, as more research is currently directed towards this type of wind turbine blade.

3. Principle of Wind Turbine Blade

The principle of wind turbine blades is grounded in the conversion of kinetic energy from the wind into mechanical energy through the process of aerodynamic lift and drag. The efficiency of this energy conversion depends on various factors, including the blade’s shape, size, material, and the wind conditions at the turbine’s location. Understanding the fundamental principles behind wind turbine blades is crucial for optimizing their design and performance in harnessing renewable wind energy.

3.1. Aerodynamics

Wind turbine blades rotate due to fundamental fluid mechanics principles, primarily the Bernoulli effect and Newton’s Third Law [45]. When wind strikes the blade at a pitch angle, it is deflected, generating a force that pushes the blade away from the deflected wind. To maximize energy extraction and aerodynamic efficiency, an optimal pitch angle is crucial [46]. Without an appropriate pitch, the blades would only experience drag, a backward force. Figure 8 illustrates the wind stream and the forces acting on the blade elements, including lift and drag, induced by the interaction between the blade and the incoming wind flow. Wind turbine blades are designed to engage with the wind at an angle, enabling effective deflection and rotation (Figure 8b) [47,48].

Blade design incorporates tapering, twisting, and multiple airfoil sections [50]. Figure 9a–d displays the various blade sections used from the root to the tip, while Figure 9e provides the schematics of the blade. The airfoil shape, with a curved upper surface and a relatively flatter lower surface, creates a pressure difference as air flows over it. The higher velocity over the curved upper surface results in lower pressure, while the lower velocity on the flat lower surface results in higher pressure (Figure 9f). This pressure differential generates lift, which drives the blade’s rotation [51,52,53].

Lift generation is influenced by blade shape, the angle of the blade relative to the incoming flow, and airspeed. To maximize energy conversion, blades are designed to maximize lift and minimize drag. The lift force acts perpendicular to the incoming flow, while the drag force acts parallel. The lift-to-drag ratio is a critical consideration in blade design to optimize energy extraction [54], with turbines ideally operating at the maximum ratio [50]. The angle of attack (α), the angle between the blade and the incoming flow, significantly impacts lift [55,56]. Increasing the angle of attack increases lift, but exceeding an optimal angle leads to stall, reducing lift [57,58,59]. Therefore, various methods are employed to determine the best angle of attack for a specific airfoil [60] to maximize power output [61,62]. Another key aerodynamic parameter is the tip speed ratio. The tip speed is calculated as

$$\mathrm{Tip}\hspace{0.17em}\mathrm{speed}\hspace{0.17em}=\hspace{0.17em}\hspace{0.17em}\omega \hspace{0.17em}\times \hspace{0.17em}r,$$

(1)

where radius r is the distance from the hub to the blade tip and ω is the angular velocity. The blade tip travels much faster than the blade root because the tip covers a larger circumference in the same amount of time; the root, being closer to the hub, has a smaller radius and thus a lower speed. The tip speed ratio (TSR) is calculated as the ratio between the tip speed and the wind speed.

$$\mathrm{Tip}\hspace{0.17em}\mathrm{Speed}\hspace{0.17em}\mathrm{Ratio}\hspace{0.17em}(TSR)\hspace{0.17em}=\hspace{0.17em}{\displaystyle \frac{\mathrm{Tip}\hspace{0.17em}\mathrm{speed}}{\mathrm{Wind}\hspace{0.17em}\mathrm{speed}}}\hspace{0.17em}=\hspace{0.17em}{\displaystyle \frac{\omega \hspace{0.17em}\times \hspace{0.17em}r\hspace{0.17em}}{U_{\infty }}}$$

(2)

Here, U_∞ is the freestream wind speed. A higher TSR (>1.0) indicates that the blade tip moves faster than the incoming wind, which can increase lift but may also lead to a corresponding increase in drag. Therefore, blade designs aim for an optimal tip speed ratio, generally recommended to be between six and eight, though the ideal value depends on various factors [63,64], including pitch control and blade loading. Thus, TSR is a crucial parameter in blade aerodynamics.

Numerous advanced aerodynamic strategies are employed to optimize blade design and performance in fluctuating wind environments. One of the foundational approaches is the Blade Element Momentum Theory (BEMT) [65,66], which combines blade element theory with momentum conservation principles. It offers a fast and computationally efficient means of estimating blade performance. However, BEMT is limited to steady, axisymmetric flows and cannot capture complex unsteady phenomena such as stall and flow separation, which are common in turbulent or yawed conditions.

A more detailed approach is computational fluid dynamics (CFD) [67], which provides high-fidelity insights into the flow behavior along blade sections. CFD can model unsteady flow dynamics, turbulence (e.g., LES and RANS), and three-dimensional effects, enabling precise design iterations. Despite its accuracy, CFD is computationally intensive and often impractical for real-time design evaluations or large parametric studies.

Other advanced methods include Active Flow Control (AFC) and multi-objective optimization techniques. AFC strategies, such as boundary layer suction/blowing and plasma actuators [68], actively manage flow separation and delay stall, allowing real-time adaptation to varying wind conditions. However, the AFC adds system complexity and energy demands. Multi-objective optimization [69], including genetic algorithms and response surface methods, is increasingly used to balance aerodynamic performance with structural constraints and noise reduction. While effective in navigating complex design spaces, these approaches depend heavily on high-quality surrogate models and extensive datasets.

3.2. Structural Consideration

Wind turbine blade design is a complex and critical process that balances structural integrity and geometric optimization to enhance performance, dependability, and lifespan prediction (Figure 9g). Designs incorporate various airfoils, typically from the NACA and SERL series, to ensure an ideal angle of attack across the blade span, with variations in chord length, twist angle, and thickness from root to tip [70,71]. Airfoil selection is crucial, guided by the need to optimize the lift-to-drag ratio, reduce sensitivity to surface roughness, and meet design objectives like high power coefficients and minimized chord length [71].

Longer blades are favored to enhance the kinetic energy conversion efficiency of wind turbines [72]. However, longer blades present additional challenges, including the need for complex and expensive composite materials to ensure sufficient strength and the need to withstand supplementary loading and aerodynamic forces due to the increased span [40,73]. Figure 10 presents a typical cross-sectional schematic diagram of a wind turbine blade, illustrating internal layers such as balsa wood, spar caps, and skin laminates. It also highlights how various segments of the blade bear flapwise and edgewise loads under compression and tension. The diagram further emphasizes the role of adhesive joints and material layers in distributing loads throughout the blade structure. The number of blades directly influences aerodynamic performance and balanced rotation, impacting turbine speed. The use of three blades facilitates smooth rotation, making it a common selection criterion [31].

Adjustable pitch control extends turbine lifespan by enabling blades to adapt to changing wind speeds, optimizing energy conversion while mitigating drag and fatigue effects [74,75]. Meticulous wind turbine design integrates practical considerations, such as weight optimization and fatigue resistance, with aerodynamic principles, like maximizing lift and minimizing drag, to ensure efficient energy conversion and structural integrity. When combined with advanced materials, these blade designs provide long-term stability and efficient energy extraction.

Figure 10. Schematic diagram of a wind turbine blade section; a cross-section of the Clipper C96 wind turbine blade [76].

Figure 10. Schematic diagram of a wind turbine blade section; a cross-section of the Clipper C96 wind turbine blade [76].

Recent advances in the structural determination of wind turbine blades involve swept and tapered geometries [77], which improve load distribution and reduce unstable aerodynamic forces, enhancing stability. They, nevertheless, introduce some additional manufacturing challenges. Aeroelastic tailoring, which aligns fibers in composite materials to enable passive twisting or bending under load, reduces vibrations without the need for active control systems. Topology optimization further contributes by minimizing weight while maintaining structural integrity through optimized internal material distribution, although its practical application remains limited due to fabrication constraints [78]. Finally, smart structural integration comprises embedding sensors, piezoelectrics, or shape memory materials, which enables real-time health monitoring and dynamic load reduction. However, long-term durability and cost remain significant hurdles.

3.3. Material

The selection of materials for wind turbine blades is influenced by several factors, including weight, durability, strength, low density, ease of processing, recyclability, and cost, to ensure long-term performance under varying load conditions and fatigue [79]. Over the years, various materials have been used for blade manufacturing, but the most common options today include fiberglass-reinforced polyester or epoxy resin, E-glass fiber, and carbon fiber composites (Table 1). Carbon fiber composites are preferred in high-performance applications due to their exceptional mechanical properties and lightweight nature [80]. However, their high cost limits their broader use. Modern materials are designed to offer superior strength-to-weight ratios, excellent corrosion resistance, and improved fatigue performance, making them ideal for meeting the structural and aerodynamic demands of large modern turbine blades. Materials like balsa wood or foam are often used in sandwich structures to increase stiffness while keeping the weight low.

To lighten blades and increase durability, advanced research focuses on the structural use of bamboo timber to significantly reduce manufacturing costs [81,82]. This could improve the economic viability of wind turbines, leading to lower electricity costs [83]. Significant challenges remain before bamboo wood can be considered a viable alternative on a larger scale, particularly regarding the lifespan of bamboo blades and their resistance to demanding environmental and operational conditions. Recent studies on nano-enhanced materials, such as carbon nanotube-reinforced resins, demonstrate improved durability and damage tolerance, although their scalability and cost-effectiveness remain under evaluation. Additionally, hybrid composites combining glass, carbon, or natural fibers are being investigated to optimize both cost and mechanical performance [84] (Table 2).

Material selection is also influenced by environmental factors, such as recyclability and resistance to ultraviolet (UV) degradation. Several tools are used to select appropriate materials for different wind and environmental conditions to enhance blade lifespan according to site requirements [85]. Furthermore, developments in biocomposites and hybrid materials are emerging as sustainable alternatives for optimized performance with minimized environmental impact.

Table 1. List of materials utilized for wind turbine blade manufacturing over the years [86,87,88].

Period	Types	Description	Advantages
Early years: 1970–1980	Wood	Laminated wood was used in early wind turbine blades, often in small-scale turbines.	Readily available and easy to shape.
1981–1990	Fiberglass	Fiberglass became the most commonly used material due to its lightweight and high strength. Composites are often made with epoxy or polyester resins.	High strength-to-weight ratio, corrosion, and resistance.
1991–2000	Wood—epoxy composites	The integration of wood fibers with epoxy represented a major improvement over traditional wood construction, enhancing both strength and durability.	Cost-effective with better mechanical properties.
2001–present	Carbon-fiber-reinforced plastics and glass-fiber-reinforced plastics	Carbon fiber composites, combined with resins, offer high performance and low weight. Glass fibers are also used in blade manufacturing due to their low cost and ease of production.	Good mechanical properties and low cost. Environmentally friendly and sustainable.
Recent Developments: 2010–present	Natural fiber composites	Natural fiber composites, such as those made from hemp, flax, and jute, are receiving increasing attention due to their moderate mechanical properties and sustainability benefits.	Environmentally friendly and sustainable.
Present and Emerging: 2020–present	Biocomposites (natural fibers + bio-based resins); thermoplastic composites; and bamboo composites	Biocomposites—made from natural fibers such as flax or bamboo combined with bio-based resins like PLA or plant oil epoxy—offer advantages in sustainability, recyclability, and weight reduction. While thermoplastics like polypropylene (PP) and polyamide (PA) are being explored for recyclable wind turbine blades, bamboo fibers are particularly valued for their resilience.	High recyclability and faster manufacturing times. Sustainable and low-cost with good mechanical performance.

Table 1. List of materials utilized for wind turbine blade manufacturing over the years [86,87,88].

Period	Types	Description	Advantages
Early years: 1970–1980	Wood	Laminated wood was used in early wind turbine blades, often in small-scale turbines.	Readily available and easy to shape.
1981–1990	Fiberglass	Fiberglass became the most commonly used material due to its lightweight and high strength. Composites are often made with epoxy or polyester resins.	High strength-to-weight ratio, corrosion, and resistance.
1991–2000	Wood—epoxy composites	The integration of wood fibers with epoxy represented a major improvement over traditional wood construction, enhancing both strength and durability.	Cost-effective with better mechanical properties.
2001–present	Carbon-fiber-reinforced plastics and glass-fiber-reinforced plastics	Carbon fiber composites, combined with resins, offer high performance and low weight. Glass fibers are also used in blade manufacturing due to their low cost and ease of production.	Good mechanical properties and low cost. Environmentally friendly and sustainable.
Recent Developments: 2010–present	Natural fiber composites	Natural fiber composites, such as those made from hemp, flax, and jute, are receiving increasing attention due to their moderate mechanical properties and sustainability benefits.	Environmentally friendly and sustainable.
Present and Emerging: 2020–present	Biocomposites (natural fibers + bio-based resins); thermoplastic composites; and bamboo composites	Biocomposites—made from natural fibers such as flax or bamboo combined with bio-based resins like PLA or plant oil epoxy—offer advantages in sustainability, recyclability, and weight reduction. While thermoplastics like polypropylene (PP) and polyamide (PA) are being explored for recyclable wind turbine blades, bamboo fibers are particularly valued for their resilience.	High recyclability and faster manufacturing times. Sustainable and low-cost with good mechanical performance.

Table 2. A comparison of key methodologies in the technology of the blade of a wind turbine.

Area	Methodology	Pros	Restrictions
Aerodynamics	Blade element momentum (BEM) rheory	Simple and effective for design improvement	Not very accurate in unstable or complicated flow conditions
	CFD simulations	Better reliability in aerodynamic estimations	High computational cost AND needs expertise
	Active flow control (AFC)	Expand proficiency by flow control	Difficult integration and energy requirements
	Multi-objective optimization	Optimizes multiple aerodynamics parameters	High dependence on modal precision
Structure	Tapered and swept blades	Decreases unstable loads and enhances fatigue life	Manufacturing complications
	Aeroelastic tailoring	Increases the load regulator via material alignment	Needs high accuracy in the design and material positioning
	Topology optimization	Effective material utilization and novel structural arrangements	Frequently produces unproducible shapes
	Smart structural integration	Active load adjustments by embedded sensors/actuators	Costly and dependability in fatigue is still under research
Materials	Hybrid composites	Moderate strength, resistance to fatigue, and low cost	Interfacial bonding and compatibility issues
	Nano-enhanced materials	Enhanced durability with sensing capability	Costly and expandability issues
	Glass-fiber-reinforced plastics	Economical, decent tensile strength, erosion resistance, and largely utilized in current wind turbine blades	Lesser stiffness and fatigue resistance compared to carbon fiber composites and susceptible to deprivation under long-term UV exposure
Manufacturing	Vacuum-assisted resin infusion (VARI)	Economical, good for big blades, and scalable	Takes a longer time to cure with risks of dry spots
	Resin transfer molding (RTM)	High-quality finishing and improved fiber volume regulation	Higher molding cost and prone to leakages
	Additive manufacturing	Quick prototyping and customizable geometry	Restricted to molds and non-structural parts currently

Table 2. A comparison of key methodologies in the technology of the blade of a wind turbine.

Area	Methodology	Pros	Restrictions
Aerodynamics	Blade element momentum (BEM) rheory	Simple and effective for design improvement	Not very accurate in unstable or complicated flow conditions
	CFD simulations	Better reliability in aerodynamic estimations	High computational cost AND needs expertise
	Active flow control (AFC)	Expand proficiency by flow control	Difficult integration and energy requirements
	Multi-objective optimization	Optimizes multiple aerodynamics parameters	High dependence on modal precision
Structure	Tapered and swept blades	Decreases unstable loads and enhances fatigue life	Manufacturing complications
	Aeroelastic tailoring	Increases the load regulator via material alignment	Needs high accuracy in the design and material positioning
	Topology optimization	Effective material utilization and novel structural arrangements	Frequently produces unproducible shapes
	Smart structural integration	Active load adjustments by embedded sensors/actuators	Costly and dependability in fatigue is still under research
Materials	Hybrid composites	Moderate strength, resistance to fatigue, and low cost	Interfacial bonding and compatibility issues
	Nano-enhanced materials	Enhanced durability with sensing capability	Costly and expandability issues
	Glass-fiber-reinforced plastics	Economical, decent tensile strength, erosion resistance, and largely utilized in current wind turbine blades	Lesser stiffness and fatigue resistance compared to carbon fiber composites and susceptible to deprivation under long-term UV exposure
Manufacturing	Vacuum-assisted resin infusion (VARI)	Economical, good for big blades, and scalable	Takes a longer time to cure with risks of dry spots
	Resin transfer molding (RTM)	High-quality finishing and improved fiber volume regulation	Higher molding cost and prone to leakages
	Additive manufacturing	Quick prototyping and customizable geometry	Restricted to molds and non-structural parts currently

3.4. Manufacturing Processes

The manufacturing of wind turbine blades is a complex process that combines advanced materials with precise fabrication techniques to ensure structural integrity, aerodynamic efficiency, and durability. Modern methods are tailored to produce longer, lighter, and stronger blades. Common production techniques include hand lay-up, vacuum-assisted resin infusion (VARI), and resin transfer molding (RTM) [89]. The hand lay-up method, though labor-intensive, remains popular for small-scale and prototype blades due to its flexibility with complex designs but may result in inconsistent fiber placement and resin content. Resin transfer molding (RTM) produces high-quality, complex blades with better fiber alignment and fewer voids, though it is sensitive to resin flow and mold quality. Vacuum-assisted resin infusion (VARI) [90] remains widely used due to its cost-effectiveness and scalability for large blades, although it may result in less uniform fiber distribution compared to RTM. Additive manufacturing (3D printing) [91] is an emerging method for producing molds and blade segments, enabling rapid prototyping and design flexibility; however, current limitations in printable materials and mechanical strength restrict its use to non-structural parts or small-scale experimental blades.

4. Flow-Induced Vibrations

4.1. Basic Principles and Types of Flow-Induced Vibrations

Flow-induced vibrations (FIVs) are the consequence of the interaction between fluid flow and structure [92,93,94,95,96]. The interaction generates unsteady aerodynamic forces through vortex shedding, turbulence, and wake interference, which in turn alter the structure’s motion, position, or stress distribution [97,98]. FIVs can have a particularly detrimental impact on the structural integrity, operational consistency, and fatigue life of applications, such as wind turbines. A common type of FIV is vortex-induced vibration (VIV), caused by alternate vortex shedding from a structure, where the vortex shedding frequency resonates with the structure’s natural frequency. Similarly, stall-induced vibrations (SIV) are an aeroelastic instability occurring when a large section of a wind turbine blade operates in moderate stall. A major difference between SIV and VIV is that SIV is indeed directly linked to changes in flow separation, specifically the dynamics of large areas of stalled flow on the blade, while VIV is associated with vortex shedding [99,100].

Moreover, some other common types of FIV include galloping and flutter, as shown in the first columns of Figure 11 [101,102,103,104,105,106]. While VIV results from vortex shedding, galloping is excited by movement-induced instability [107,108,109]. Flutter is generated when the bending, heaving, and pitching vibrations are coupled with each other. The VIV is prevalent in cylindrical structures like pipelines, wind turbine blades, and cables, whereas galloping is more common in square cylinders, bridge decks, and tall buildings [110,111,112,113,114,115]. Particularly, blades may undergo all three types of FIV, while cables may experience VIV and flutter (Figure 11).

The following explains the types of vibrations:

Vortex-induced vibrations: VIV occurs when fluid flow creates alternating vortices in a structure’s wake, generating forces that excite its natural vibration modes, usually happening at moderate Reynolds numbers [116]. In cylindrical structures, vortex shedding leads to fluctuating pressure forces, with oscillation frequency and vibration amplitude primarily governed by the shedding frequency, which depends on the structure’s geometry, reduced velocity, and mass damping ratios [117,118]. VIV intensifies when the structure’s natural frequency matches the vortex shedding frequency, causing a phenomenon known as “lock-in,” where vibration amplitude increases dramatically, leading to potential damage or failure [119,120]. The structure’s damping characteristics and its interaction with fluid dynamics also influence VIV. In wind turbines, if the blade’s natural frequency aligns with the vortex shedding frequency, it leads to significant increases in vibration amplitude, causing severe fatigue, material degradation, and even failure [121,122,123]. This amplifies vibrations, reducing efficiency and compromising blade safety.

Galloping vibrations: Galloping is an instability that occurs in slender bodies when aerodynamic forces induce sustained oscillations [124,125]. It features large-amplitude, low-frequency fluctuations generally for non-circular cross-sections, resulting from negative aerodynamic damping. For wind turbines, galloping can arise from asymmetrical flow conditions, with key constraints consisting of the profile of the blade segment and the angle of attack, causing unstable aerodynamic forces that continuously excite blade motion, often triggered by blade deformation and fluctuating wind directions or low wind speeds [126].

Flutter vibrations: The interaction between aerodynamic stresses and structural dynamics can lead to flutter, where self-induced oscillations amplify aerodynamic loads and blade movement. In wind turbines, as wind velocity increases, torsional and bending modes can couple, forming flutter, particularly in lightweight and flexible blades operating at high tip speeds. Flutter can cause destructive vibrations, leading to blade failure [127,128]. Factors such as blade geometry, material properties, blade mass distribution, and operating conditions influence flutter formation [129,130]. Researchers use numerical and experimental methods, including active and passive control techniques and airfoil optimization, to predict and mitigate flutter [131].

Stall- and wake-induced vibrations: Stall-induced vibrations are another key instability in wind turbines, occurring when the blade operates near or beyond its stall angle, causing unbalanced flow separation and low-frequency oscillating aerodynamic forces that induce structural vibrations [132,133]. These are often observed in thick airfoil sections. Along with these vibration mechanisms, some external factors can also play their role in FIVs, such as blade–wake interactions [134], turbulent wind conditions, and tower shadow effects [135,136].

To understand these vibrations, researchers employ linear stability analysis, nonlinear time-domain simulations, and wind tunnel experiments. Linear stability analysis is used to identify critical wind speeds by solving eigenvalue problems that couple aerodynamic forces with structural dynamics, particularly useful for predicting flutter. Nonlinear simulations—combining CFD and structural solvers [137] explore post-critical behaviors such as periodic oscillations and mode coupling. (VIV is commonly modeled using wake oscillators, like the modified Van der Pol model, to capture the interaction between unsteady wakes and structural response.) These models can predict lock-in regions, amplitude responses, and the effects of damping and mass ratios. High-fidelity CFD approaches, including Large Eddy Simulation and Detached Eddy Simulation, are employed to capture vortex shedding and fluid–structure interaction, although they are computationally intensive [138]. Galloping and stall-induced vibrations require quasi-steady or unsteady aerodynamic models coupled with structural solvers. Experimental techniques such as wind tunnel testing [139], strain gauge measurements, and Particle Image Velocimetry (PIV) are essential for validating theoretical and computational models, especially in nonlinear and high Reynolds number regimes. The measurements help identify key parameters—such as the mass–damping ratio, added stiffness, and stability derivatives—that define the vibration characteristics and stability.

4.2. Impact of Vibrations on Turbine Performance and Longevity

FIVs are the primary contributors to wind turbine blade failures, significantly impacting the aerodynamic performance, strength, and operational lifespan of wind turbine components, as shown in Figure 12a [140]. Moreover, components like drive trains, rotors, and structural elements are also susceptible to FIV and may fail due to wear, tear, or misalignments [141,142]. Excessive and unwanted vibrations from FIV increase aerodynamic stresses, altering the aerodynamic interaction of blades with incoming wind. This reduces power generation efficiency by disrupting the ideal angle of attack and causing premature flow separation [143]. Structural fatigue becomes a major concern due to repeated stress cycles from VIV, flutter, and stall- and wake-induced vibrations. These accelerate material deterioration, leading to the initiation and propagation of cracks in critical blade areas [113,144]. Fatigue damage is more likely in offshore wind turbines, where turbulence and wave currents exacerbate loading effects [145]. Due to FIV, the lifespans of blade/tower, bearing/gearbox, and offshore turbines are reduced by 20%, 27%, and 35%, respectively (Figure 12a).

Moreover, continuous vibrations contribute to increased maintenance costs and downtime, resulting in substantial economic losses (Figure 12b). This endangers the financial viability of wind energy projects on larger, commercial scales and hinders the prospects for new wind turbine installations [146]. Resonance effects, as seen in past turbine failures with inadequate damping, can sometimes cause catastrophic blade failures. This underscores the need for enhanced monitoring and maintenance. Indeed, maintenance or replacements can incur significant costs, as turbine shutdowns increase electricity production costs. Researchers have explored various methods to mitigate these vibrations, such as adjusting the pitch angle and employing passive and active dampers.

These interventions can reduce the impact of unwanted vibrations on turbines. Reducing these vibrations can significantly enhance the performance and lifespan of wind turbine blades [147]. In order to enhance the performance, life cycle, and smooth operation of wind turbine blades, a complete awareness of FIVs is required, specifically in turbulent wind conditions, like offshore wind environments [148].

5. Vibration Suppression Techniques

In the design and maintenance of wind turbine blades, failures caused by flow-induced vibrations are a key concern, as explained above. Exorbitant vibrations can cause fatigue, premature failures, and reduced efficiency. Researchers investigated and proposed multiple tactics to mitigate these vibrations and improve the effectiveness of wind turbine blades.

5.1. Active and Passive Vibration Control Methods

It is essential to lower the vibration amplitudes to operate turbines at their full potential, maximize the extracted power, and maintain the strength of wind turbine blades. The solution involves leveraging active and passive vibration mitigation technologies, as detailed in Figure 13 [146,149]. Passive control methods involve fixed modifications to the blade. These include trailing edge modifications, such as serrations and Gurney flaps, leading-edge modifications such as tubercled edges, and surface modifications like vortex generators, suction holes, and blowing holes. Biomimicry, including bionic wings, also falls under passive blade shape control. They are placed or merged on the surface of the structures (Figure 14) to absorb and dissipate vibrational energy [150]. These aerodynamic modifications passively alter the local flow field and decrease lift oscillations produced by turbulent eddies or vortex shedding. In wind turbines, trailing edge serrations are tested on larger blades to lessen aerodynamic noise and loading patterns [151,152]. Passive flaps, which are made of elastic material, bend under load to postpone the flow separation and decrease aerodynamic fluxes. Additionally, tuned mass dampers (TMDs) are another vital part of passive vibration controllers, which have a secondary mass-spring damper connected to the main structure. Usually, TMDs are employed near the blade root, where they absorb vibrational energy and significantly decrease tip divergence and fatigue loading. An experimental study [153] reported a 30% decrease in vibration amplitude in the turbulent wind conditions. Using Tuned Liquid Column Dampers (TLCD) is another method included in passive dampers, which utilizes the motion of the liquid within a U-shaped tube to produce countering inertial forces that reduce blade oscillations. Even though it was previously used only in towers, design modifications and advancements have recently offered TLCD additions into hollow sections of large offshore wind turbines, reducing vibrational amplitude up to 30% to 40% [154,155]. Collectively, these passive techniques are preferred due to their simplicity, robust performance, and low maintenance requirements in the operational lifespan of turbines, particularly in offshore wind farms where accessibility is a major concern and reliability is crucial. Besides mitigating vibrations, passive devices boost blade rigidity, fatigue strength, and operating efficiency [156].

Active controllers, on the other hand, use external energy or adaptive devices to change blade characteristics during operation, vigorously opposing oscillations in real-time by utilizing actuators, sensors, and sophisticated regulatory algorithms [157]. Flow control devices with active blowing and suction, smart materials with piezoelectric actuators, and morphing blades with shape adaptation are examples of active control (Figure 13). Individual blade pitch control (IBPC), active trailing edge flaps, and plasma actuators also enable real-time regulations. Active flap control can reduce the blade-root fatigue loads by 20–30%, while piezoelectric systems efficiently damp vibrations of high frequency [158]. Although allowing adaptability and precise vibration suppression, active control involves complexity, requires sustained power, and must survive in the harsh operational conditions.

Figure 14. (a,b) High-frequency micro-vortex generator schematic. (c) Solid vortex generator configuration mounted on the surface at 20% of the trailing edge [159].

Figure 14. (a,b) High-frequency micro-vortex generator schematic. (c) Solid vortex generator configuration mounted on the surface at 20% of the trailing edge [159].

As wind turbines increase in size and complexity, advancements in vibration suppression become critical for stable, uninterrupted operation, enhancing efficiency and overall performance, especially in harsh offshore environments. The choice between active and passive control, or a combination of both, depends on the specific requirements of the wind turbine and its operating environment. Passive damping devices address baseline oscillations, while active control systems manage complex vibrations. Combining both approaches is an area of research for improved suppression [160].

5.2. Design Modifications and Innovative Materials for Vibration Reduction

Cutting-edge design changes and innovative materials have played a significant role in suppressing FIVs of turbine blades. One effective strategy to reduce vibration amplitudes is blade geometry modifications, including the thickness and profile of blades. The blades with adjustable tips or optimized twist angles, or swept back configurations, significantly decrease VIV [128]. For example, swept blades have been used in commercial blade models like the GE Haliade-X and Siemens SWT series, showing improved load distribution and reduced vulnerability to VIV. Additionally, other design changes like trailing edge serrations and flow control elements such as vortex generators and Gurney flaps have been verified in tunnel experiments and also on the full-scale models, demonstrating decreases in load fluctuation and noise. These design modifications enhance aerodynamic performance and lower the risk of fatigue damage from cyclic loads [132]. Increasing the toughness and strength of blades helps further reduce vibrations and the strain transmitted to structural components. Strengthening the blade root and improving junctions between the hub and blade enhances system resilience against vibrations, distributing vibrational energy evenly to minimize stress concentrations that may lead to failure.

Structural damping elements, such as viscoelastic materials or damping composites, and the adoption of hybrid compounds like glass/carbon-fiber-reinforced polymers (GFRP/CFRP) efficiently dissipate vibrational energy and offer enhanced stiffness-to-weight ratios and progressive damping features [161]. For example, the LM Wind Power Blade 107.0 P included such compound material optimizations to accomplish aeroelastic performance under the unsteady wind environments. Experimental investigation (e.g., blade section weariness tests and full-scale testing) has demonstrated that carbon-strengthened spar caps may expand dynamic performance and lessen resonance intensifications. Furthermore, nanomaterial boosted compounds (e.g., CNT reinforced polymers) are under examination and have exhibited encouraging results in lab-scale testing, where modal damping is enhanced by 15–25% compared to the traditional compounds. Moreover, integrating advanced materials into improved physical and aerodynamic designs provides a comprehensive approach to minimizing vibrations in turbine blades. Additionally, various coatings improve vibration absorption and overall blade performance. Surfaces are often coated with damping or friction-reducing materials to minimize aerodynamic dispersion and delay resonance conditions [162]. Composite coatings embedded with fibers or particles can enhance blade stiffness and reduce vibrations [163]. Restorative coatings are also practical for mitigating minor surface deterioration caused by vibrations, automatically repairing small cracks or defects to extend operational life. By combining innovative materials with advanced coatings, wind turbine blades can achieve better performance, increased longevity, and reduced vibration even under harsh weather conditions [164]. As demand for renewable energy sources rises, the development and applications of these technologies are crucial for maintaining the long-term reliability and efficiency of wind turbines.

5.3. Recent Innovations and Research in Vibration Suppression

The suppression of unwanted vibrations in turbine blades has significantly benefited from recent advancements in vibration-damping techniques, enhancing both blade longevity and energy efficiency. One recent innovative approach to vibration suppression is the addition of inerter-based devices into structural systems. Inerters are mechanical components that generate force in response to the relative acceleration between their terminals [165]. When integrated into tuned mass damper–inerter (TMDI) systems, they significantly improve vibration suppression performance. Unlike traditional tuned mass dampers (TMDs), tuned mass damper–inerter (TMDI) systems offer improved efficiency over a wider frequency range and under varying load conditions. The inerter ability to transmit large inertial forces without requiring substantial physical mass makes it particularly well-suited for wind turbine applications, where weight constraints are critical. In addition to inerter-based devices, other advanced and emerging technologies have shown significant potential for reducing vibrations in wind turbines. For example, hybrid tuned mass dampers (HMTDs) [166] utilize magnetorheological fluids, while electromagnetic vibration dampers (EMVDs) employ electromagnetic actuation to reduce vibrations and recover residual energy. These technologies offer several advantages, particularly for offshore wind turbine installations. Some other techniques include the design of a two-dimensional nonlinear tuned mass damper inerter (2D-NTMDI) [167,168]. This system integrates a mass with springs, dashpots, and inerters aligned along the two axes to effectively reduce structural responses in multiple directions. This provides nonlinear forces to counteract vibrations and may increase fatigue life by more than 35% when applied to a 5 MW turbine blade, demonstrating its value in improving blade durability under dynamic loads [167,169]. Another attractive technique is to use a one-way cable pendulum damper to lessen vibrations on massive wind turbine blades. This damping device has demonstrated remarkable success in reducing edgewise vibrations, which are often the source of blade fatigue and structural damage. Because it diminishes these vibrations and improves the overall reliability of the blades while also increasing their working lifespan, the cable pendulum damper is a helpful instrument for modern wind energy systems [170]. Shunt-damping techniques have also shown promise in reducing edgewise vibrations, particularly in smaller blades. This technique offers a more adaptable and efficient solution to control vibration in smaller turbines than traditional tuned mass dampers [171]. Furthermore, finite element analysis (FEA) has emerged as a productive technique for learning more about blade vibration behavior. FEA helps designers identify basic stress areas and refine blade designs to reduce vibrations and enhance overall performance by simulating various working conditions.

6. Failure Mechanisms in Wind Turbine Blades

Numerous failure mechanisms harm wind turbine blade performance, safety, and life cycle. A thorough understanding of these failure mechanisms is essential for designing robust blades capable of withstanding harsh operating conditions, particularly in offshore and high-wind environments.

6.1. Types of Failures

In wind turbine blades, vibrations can expedite the failure, applying cyclic strains to the blade structure, gradually increasing the stress concentration in critical regions such as the blade root and leading edges (Figure 15a–c). These oscillations exacerbate the buildup of fatigue damage in these areas, where the material is already subjected to high aerodynamic forces and fluctuating stress. Repeated loading accelerates the development and propagation of microcracks in the composite material [123].

The following is an explanation of the types of failures:

Fatigue failure: Stress and fatigue of turbine blades gradually build up over time. Fatigue damage is one of the most common and important failure mechanisms in turbine blades (Figure 16). This kind of failure happens when load cycles are applied repeatedly, which causes microcracks to start and spread throughout the material [144,175]. Examples of failures, damage, and defects that occur on wind turbine blades are illustrated in Figure 17. The figure presents various impairments, including scrapping, pitting, paint peeling, and cracking, specifically in critical areas such as the leading and trailing edges, where aerodynamic forces frequently fluctuate. If these cracks are not detected early, they may eventually cause a catastrophic failure by weakening the blade’s structural integrity as it progressively extends. Materials like fiberglass and carbon composites, which are commonly used for wind turbine blades, are particularly vulnerable to fatigue because they are prone to delamination and fracture under cyclic stress. The breakage phase may be accelerated by the repetitive stress that results in this delamination, since it may weaken the adhesive bond between composite layers [176].

Crack failure: Cracking is another important failure type that frequently occurs after fatigue-induced degradation. The microcracks created by the fatigue damage get severe on every cycle and extend to a physical formation of cracks, which later on reach up to a dangerous level and could become the reason for the failure of components over time. Moreover, cracks can be further widened or spread due to several reasons, like collision damage, working fluctuations, and environmental degradation. Blades can be damaged due to these cracks, or even failure can happen if they are not identified and repaired promptly. Crack formation is common in high-stress areas such as the leading edge (Figure 16), but predicting the specific location is challenging due to various factors, such as the loading intensity, turbine design, and materials alignment [177].

Atmospheric destruction: Along with mechanical stresses, atmospheric destruction also affects turbines negatively and can be the reason for the buildup of cracks and blade failure. As shown in Figure 16, air moisture, fluctuations in temperature, external factors, and ultraviolet (UV) light exposure for a long time can also damage the material alloy [178,179], especially on the farthest surface. For instance, UV light leads to material erosion and can undermine mechanical properties by breaking the chemical connection in the material’s resin matrix. Consistent modifications in the temperature at different times of day and night can induce thermal strain that intensifies material corrosion, and absorbing moisture can lead to swelling and cause material separation [180]. All of these factors can shorten the life of turbine blades, intensifying the need for regular checkups or even replacements [179,181].

Delamination is another crucial mode of failure noticed in composite blades of the wind turbines [182]. It happens due to the consistent cyclic stresses or poor bonding in the layers. This inner separation diminishes the structural strength and can enhance fatigue damage in operative strains.

6.2. Failure Detection Method

To decrease failure risk and improve reliability during operation, wind turbine monitoring and prognostic maintenance methods employ advanced surveillance systems. One such method is called structural health monitoring (SHM), which utilizes different types of sensors such as noise emanation sensors, vibration detection sensors, and strain gauges (Figure 18). Real-time data of blade dynamics is gathered with the help of these sensors. Probable resonance conditions and blade fluctuations are predicted based on this data. Additionally, some new developments in SHM systems for turbine blades involve the inclusion of fiber Bragg grating (FBG) sensors [183]. These sensors can correctly trace strain, temperature surges, and instabilities over a long period with negligible loss in signal. Similarly, acoustic emission (AE) practices are progressively being utilized for the early recognition of crack initiation and formation in composite materials, offering advanced and active monitoring of the blades during operation.

Close monitoring of blade structural characteristics enables operators to take timely corrective actions, preventing blades from reaching dangerous or near-failure conditions. This capability extends the lifespan of turbine blades and other key wind turbine components (Figure 19a). This active method decreases interruption and the cost of maintenance, and also increases safety [184].

Nondestructive testing (NDT) techniques, such as thermography and ultrasonic testing (Figure 18), can detect internal cracks or delamination (Figure 19b) that are difficult to identify during routine inspections. To identify fluctuations in temperature on the exterior of turbine blades, thermography utilizes thermal or infrared imaging, which can specify the foundational structural flaws, such as material partitioning or cracks. High-frequency sound waves are used in ultrasonic testing to identify damage by analyzing returned signals. Moreover, phased array ultrasonic testing (PAUT) [185] has appeared as a prevailing improvement to traditional ultrasonic checkups, providing advanced resolution and more precise location of inner flaws, for instance, delamination or adhesion features, allowing for better assessment and reducing scanning time in large complex structures. This and other advanced monitoring techniques allow operators to evaluate the internal condition of blades nondestructively and predict future issues. Integrating these NDT methods into maintenance improves turbine reliability and safety by addressing hidden problems [186,187].

7. Preventive Maintenance and Early Damage Techniques

Wind turbines require continuous maintenance to operate efficiently and maximize energy production, given their exposure to extreme conditions and dynamic stresses. Preventive maintenance solves possible problems in the beginning, at the initial state, making sure the turbine’s reliability and smooth operation in its lifespan [188].

7.1. Regular Monitoring

Continuous inspection, enabled by condition monitoring (CM), is key to detecting early signs of deterioration in major wind turbine components (blades, gearbox, generator, and bearings). CM uses sensors to gather and analyze data, identifying electrical, mechanical, and structural failure symptoms for prompt action, ensuring continuous turbine operation, and minimizing downtime (Figure 20). Surface monitoring is also crucial for identifying erosion, especially on the leading edge of blades vulnerable to environmental factors [172,178]. Moisture, debris, icing, rain, hail, and insect strikes can increase skin drag and surface roughness, significantly impacting aerodynamic efficiency and potentially causing up to 50% of power generation losses [189]. Inspections also target cracks or delamination in composite materials, which develop over time due to environmental and loading stresses (Figure 15d). Moreover, modern wind farms are equipped with advanced real-time data collection and remote sensing technologies like Supervisory Control and Data Acquisition (SCADA). Such systems consistently trace variables like angular speed, vibration, and temperature, allowing prognostic insights into turbine proficiency and early notifications of possible failures.

7.2. Lubrication and Protective Coatings

An explanation of lubrication and protective coatings is as follows:

Lubrication: Regularly lubricating the mechanical parts (e.g., pitch control systems, gearboxes, and bearings) is another essential part of preventive maintenance [190]. Currently, centralized lubrication systems (CLS) with conditional control are getting more popular and are progressively used, providing optimum lubricant volumes according to working situations. This minimizes manual interference and expands the life of the components, particularly in unsteady wind loads. To retain the best possible blade performance, adequate lubrication lowers friction, stops wear, and guarantees the seamless operation of these systems.

Protective Coatings: Wind turbine manufacturers use protective coatings to shield blades from harsh weather, UV rays, and corrosive materials [191,192]. These coatings, such as polyurethane and epoxy, act as a barrier against environmental factors, enhancing blade lifespan by resisting erosion, moisture, freezing, and UV degradation. By preserving aerodynamic performance and reducing maintenance, these coatings contribute to reliable and economical energy production [193,194]. Some recent developments in protective coatings involve nano-enhanced hydrophobic coatings, which advance resistance to leading edge destruction and decrease ice accumulation, and are particularly efficient in offshore wind farms where access for repairs is restricted. Figure 21 illustrates a detailed design for damage repair of a seaward wind turbine blade operating in harsh conditions (from damage to repairment) [195]. Figure 21a,b shows blade deformation and spar cap damage, with blade cross-sections and profiles in Figure 21c,d. Patching methods are shown in Figure 21e,f, and the repair process on a real turbine blade is presented in Figure 21g,h.

In short, preventive maintenance prolongs a wind turbine’s life, lowers repair costs, and minimizes downtime by proactively addressing these problems. If not managed properly and promptly, the operation and maintenance cost in a 20-year life cycle can account for 25 to 30 percent of the overall energy cost or 75 to 90 percent of the installation cost [188].

7.3. Early Damage Detection

Advanced monitoring techniques, such as Structural Health Monitoring (SHM), significantly improve early detection of wind turbine blade weakening and play a vital role in preventive maintenance and reducing the risk of failures. SHM systems use sensors (strain gauges, piezoelectric devices, fiber optics, and accelerometers) to monitor parameters like temperature, vibrations, strains, and acoustic emissions [197,198]. This enables operators to identify irregularities (microcracks, delamination, and unusual vibrations) before they become critical, enhancing safety, reliability, and uptime while extending working life. Active vibration monitoring, using methods like operational deflection shapes (ODS), natural frequency analysis, and frequency response functions (FRF), identifies anomalies that can cause separation, breakage, or resonance, potentially leading to blade failure [199,200]. These systems, combined with machine learning and neural networks, enable early recognition of anomalies, allowing timely maintenance and preventing system failures [201]. Predictive maintenance methods further enhance this by estimating future failures, optimizing maintenance schedules, and minimizing unplanned downtime.

8. Inspections, Repair, and Developing Maintenance Technologies

8.1. Inspections and Repair Strategies

Regular inspections and immediate repair are necessary to identify and resolve any potential problems and maintain the maximum efficiency throughout its operational lifetime. A variety of techniques are used to keep an eye on the blade state, but the most popular ones are thermography, ultrasonography, and visual inspections (both aerial and ground-based) [175]. Visual inspections, whether conducted from the ground or in the air, offer an easy and affordable method of evaluating the blade’s external condition. A schematic diagram of unmanned aerial inspections can be seen in Figure 22e. Nevertheless, more sophisticated methods like thermography, which measures temperature changes on the blade’s surface, and ultrasonography, which may spot internal structural problems, are also crucial for finding hidden flaws. Sensor networks and drone-based checkups have appeared as important advancements for monitoring and in the maintenance of wind turbine blades, improving reliability and decreasing operational costs. Sensor networks consist of distributed arrays of sensors—such as temperature sensors, accelerometers, strain gauges, and fiber optic sensors—that are placed, mounted, or embedded on the surface or within the blade structure to continuously monitor vibrations, temperature, and structural health parameters. Such networks aid real-time condition monitoring and pre-failure fault detection by transferring data to central control units, enabling early maintenance and decreasing the percentage of unexpected failures. For instance, fiber Bragg grating (FBG) sensors offer high sensitivity and resilience to electromagnetic interference, making them suitable for long-term monitoring in tough conditions. In practical applications, sensor networks are successfully tested to identify crack initiation, delamination, and material degradation before these damages expand, enhancing blade operational life.

Drone-based inspections have been increasingly popular in recent years because of their safe and effective means of inspecting turbine blades at high altitudes. Different types of drones used in such inspections are depicted in Figure 22a–c [202]. Drones are equipped with high-resolution cameras, thermal imaging, and LiDAR sensors, enabling them to scan blade surfaces for damage caused by lightning strikes, icing, or other environmental factors. Drone inspections decrease the manual rope or crane-based checkups. Recent studies have shown that drone-based inspections can detect surface anomalies quite accurately compared to traditional methods. Technicians focus on identifying typical wear, surface defects, and cracks, particularly in high-stress areas such as the blade’s joints and leading edges, with the help of these modern and advanced drones. Also, by using this method, the integrity of the wind turbine blade could be routinely examined, ensuring long-term operation and reducing the likelihood of unscheduled malfunctions.

Figure 22. (a) Multirotor, (b) fixed-wing, and (c) single-rotor drones. (d) Robotic platforms for the inspection of offshore wind farms. (e) The schematic working principle of unmanned aerial drones [203].

Figure 22. (a) Multirotor, (b) fixed-wing, and (c) single-rotor drones. (d) Robotic platforms for the inspection of offshore wind farms. (e) The schematic working principle of unmanned aerial drones [203].

The maintenance strategy depends on the severity and type of crack. Minor issues (small chips or cracks) can be resolved with adhesive materials that restore strength with minimal disruption. Severe damage (extensive cracking or large tears impacting aerodynamic efficiency) may require partial or full blade replacement to maintain performance and safety. Post-maintenance, thorough inspection is crucial to ensure proper alignment, firmness, and stability, directly impacting aerodynamic performance. Researchers are exploring innovative restoration methods and materials to enhance the effectiveness and longevity of blade repairs, aiming for robust, long-term solutions that reduce maintenance costs and downtime.

8.2. Challenges and Advancements in Maintenance Solutions

Maintaining wind turbines is a challenging task due to several factors, including their large size, remote locations (especially in deep-sea wind farms several miles off the coast), and exposure to harsh weather conditions. One of the most difficult aspects of maintenance is detecting subsurface damage, which is often not visible during regular inspections. Such damage may remain undetected for extended periods, gradually undermining the aerodynamic performance of the turbines and potentially leading to severe issues, including failure. This can significantly increase repair costs and downtime. Additionally, the thorough inspections required to detect these issues demand specialized instruments and skilled technicians, which raises operational costs and reduces power generation efficiency. Wind farm owners are particularly concerned about turbine downtime, as it directly impacts energy production costs and the economic viability of the turbines.

To address these challenges, innovations in maintenance strategies are emerging. Advancements such as modern sensor networks, drone-based inspections [204] (Figure 22d), and AI-guided prognostic assessments are transforming turbine monitoring and maintenance [205]. Drones equipped with infrared cameras, for example, can detect irregularities more quickly than human observers and reach difficult-to-access areas. For real-time monitoring, technologies like the Internet of Things (IoT), which includes multiple sensors, are being used to identify early signs of potential failures. Furthermore, autonomous drones equipped with laser scanning technology have significantly sped up monitoring processes [204]. These developments enhance the overall efficiency and extend the lifespan of turbines. Additionally, advances in materials, such as regenerative composites and coatings that can repair microscopic surface defects, have reduced the need for manual inspections. When combined with comprehensive monitoring systems, these innovations aim to lower maintenance costs.

9. Conclusions

This review paper provides an extensive analysis of wind turbine blade technology, focusing on the principles of blade operation, aerodynamics, material selection, flow-induced vibrations (FIV), failure mechanisms, and the methods of vibration suppression and maintenance. As wind turbines become increasingly pivotal in the global energy landscape, ensuring their efficiency and reliability, particularly for offshore and onshore installations, remains crucial to their successful operation and long-term viability. The study highlights the significant challenges associated with maintaining wind turbines, such as the detrimental impact of FIVs, including vortex-induced vibrations (VIV), flutter, and galloping, on blade performance and turbine lifespan.

Recent advancements in understanding the mechanisms behind FIVs have led to the development of a wide array of vibration suppression approaches. Both passive and active methods, including aerodynamic modifications, mechanical damping, and control-based techniques, have shown promising results in enhancing turbine blade performance and minimizing vibration-induced failures. However, despite these advancements, several challenges remain in deep-sea wind farms, where extreme weather and turbulent wind conditions exacerbate the challenges posed by FIVs.

The future of wind turbine technology lies in the integration of material science, structural mechanics, and innovative vibration suppression methods. The use of functionally graded materials (FGMs) and tailored composite laminates enhances structural efficiency and reduces fatigue damage. When integrated with structural health monitoring (SHM) systems that leverage real-time data, adaptive responses to aerodynamic loads become possible. Advances in structural mechanics—such as aeroelastic tailoring and topology optimization—enable the design of blades with inherent vibration-damping properties. Additionally, smart materials like shape memory alloys and piezoelectric layers provide self-sensing and actuation capabilities for on-demand vibration control. Concurrently, these multidisciplinary innovations pave the way for stronger, lighter, and more efficient wind turbine systems capable of withstanding complex environmental conditions. Additionally, research into real-time monitoring and prognostic maintenance using machine learning and artificial intelligence is expected to significantly improve predictive maintenance, further reducing operational costs and downtime. Moreover, a more comprehensive understanding of FIVs and their mitigation in extreme environments is essential to harnessing the full potential of wind energy.

As wind turbines continue to evolve in size and complexity, particularly with offshore deployments, further experimental studies and the development of more efficient prediction models are necessary. Collaboration between academia, industry, and governments could be vital to advancing the development of optimized wind turbine blades capable of withstanding the challenging conditions of modern wind power generation. The continued focus on reducing vibration-related issues should be central to the sustainable growth of wind energy as a key renewable resource in the global energy mix.