Turbine Blades Research Articles

High cycle fatigue properties of Ti-48Al-2Cr-2Nb alloy additively manufactured via twin-wire directed energy deposition-arc

Recently, additive manufacturing for titanium aluminide has received sustained attention. Considering the extensive applications on low pressure turbine blades in aerospace field, dynamic mechanical properties of titanium aluminide, especially the fatigue properties, are of great importance. In present work, fatigue test at ambient temperature was conducted for the first time on twin-wire directed energy deposition-arc (TW-DED-arc) fabricated Ti-48Al-2Cr-2Nb alloy with equiaxed lamellar colonies. More detailed researches on fatigue fracture characteristics and deformation modes are also investigated. The experiment results indicate that TW-DED-arc fabricated Ti-48Al-2Cr-2Nb alloy exhibits flat S–N behavior with a good resistance to fatigue. Fatigue life fluctuates widely at same stress level, but such fluctuations gradually weaken as stress decreases. Furthermore, γ/α2 interface and lamellar colony boundary as well as special microstructures of as-fabricated Ti-48Al-2Cr-2Nb alloy are weak areas during fatigue process, which easily become crack nucleation sites. As stress level decreases, deformation mode of as-fabricated Ti-48Al-2Cr-2Nb alloy translates from twinning and dislocation slip to predominantly dislocation slip. In general, these findings provide an important reference for engineering applications of titanium aluminide.

Heat transfer evaluation of return-flow impingement cooling considering inclined sidewall and conical return hole

Impingement cooling techniques are extensively utilized on the turbine blade leading edge to mitigate thermal load. This study is an extend of an anti-crossflow return-flow impingement cooling scheme. In this study, the effects of inclined sidewalls and return holes are numerically studied with jet Reynolds number varying from 5,000 to 15,000. Three sidewall schemes (vertical, inward inclined, and outward inclined) and two return hole shapes (constant cross section and conical cross section) are investigated and compared. Numerical results show that by inclining the sidewalls, the interaction and scrape effects from return flow on the sidewalls are changed, causing heat transfer performance and pressure loss vary. To be specific, as the sidewalls are inclined inwards/outwards, the heat transfer is enhanced/weakened accordingly, making a maximum increase by 12.9% and maximum decrease by 14.3% compared to the origin design. The introduction of conical return holes contributes to improving upwards velocity of return flow and subsequently enhancing scraping effects on sidewalls. For case with vertical sidewalls, inward-inclined sidewalls, and outward-inclined sidewalls, the area-averaged Nusselt number is maximum increased by 47.2%, 61.9% and 25.7% with the application of conical return holes.

Simulation of unsteady ice accretion on horizontal axis wind turbine blade sections in turbulent wind shear condition

This study presents a comprehensive simulation approach to quantify power losses in horizontal axis wind turbines under environmental icing conditions. It investigates how wind shear and turbulence affect a 2.5 MW wind turbine's performance, particularly under ice accretion. Turbulence intensity, ranging from 1% to 20%, impacts the relative flow fluctuations and angle of attack on the blade sections, influencing the aerodynamic penalty ratio. The incoming wind speed and the flow angle at various blade sections were determined using the unsteady blade element momentum method, considering vortex induction effects and Prandtl and Glauert corrections. For ice accretion analysis, a fully unsteady simulation of computational grid motion due to ice accretion was performed, along with the solution of the multiphase flow of water dispersed particles in cold air, derived from the psychrometric chart. The findings highlight the significant impact of the incoming turbulent wind fluctuations on the dispersion of the ice shape formed at sections corresponding to their radial position on the blade according to the momentary angle of attack fluctuations. The formation of ice profiles along the blade has led to a subsequent degradation in the aerodynamic efficiency of the blade sections, which is directly proportional to the escalation in turbulence intensity. This phenomenon leads to a continual reduction in the power output of the wind turbine. This research provides valuable insights into the performance of wind turbines under icing conditions in real wind fluctuations.

Quantitative analysis of the impact of wrinkle defects on the strength of wind turbine blade main spars

Abstract Understanding the impact of wrinkle defects on the main spar of wind turbine blades is crucial for maintaining structural integrity and ensuring operational efficiency. This paper focuses on a quantitative analysis to determine how varying severities of wrinkles affect the structural strength of wind turbine blades. First, the study employed infrared nondestructive testing technology to inspect in-service wind turbine blades, identifying wrinkle characteristics. Based on these detected characteristics, finite element models were established to simulate the structural behavior. The Hashin failure criterion was employed to forecast the initiation of intralaminar damage, while a cohesive model with a bilinear traction-separation criterion was used to evaluate the interlaminar stress state and damage behavior of the laminates. Last, to achieve accurate simulation, a VUMAT subroutine was developed and executed in the ABAQUS software environment. The simulation results for ultimate tensile strength at different ratios of amplitude to wavelength were found to be within 10% of the experimental values. This level of accuracy underscores the reliability of the models used. The study revealed that as the ratio of amplitude to wavelength increases from 0.4 to 0.69, the ultimate tensile strength of the laminate structure decreases to one-fourth of its original value. This significant reduction highlights the severe impact that wrinkle defects can have on structural performance.

Leading Edge Erosion Classification in Offshore Wind Turbines Using Feature Extraction and Classical Machine Learning

Leading edge (LE) erosion is a type of damage that inhibits the aerodynamic performance of a wind turbine, resulting in high operation and maintenance (O&M) costs. This paper makes use of a small dataset consisting of 50 images of LE erosion and healthy blades for feature extraction and the training of four types of classifiers, namely, support vector machine (SVM), random forest, K-nearest neighbour (KNN), and multi-layer perceptron (MLP). Six feature extraction methods were used with these classifiers to train 24 models. The dataset has also been used to train a convolutional neural network (CNN) model developed using Keras. The purpose of this work is to determine whether classical machine learning (ML) classifiers trained with extracted features can produce higher-accuracy results, train faster, and classify faster than deep learning (DL) models for the application of LE damage detection of wind turbine blades. The oriented fast and rotated brief (ORB)-trained SVM achieved an accuracy of 90% ± 0.01, took 80.4 s to train, and achieved inference speeds of 63 frames per second (FPS), compared to the CNN model, which achieved an accuracy of 79.4% ± 2.07, took 4667.4 s to train, and achieved an inference speed of 1.3 FPS. These results suggest that classical ML models can be more accurate and efficient than DL models if the appropriate feature extraction method is used.

Vibration fatigue of film cooling hole structure of Ni-based single crystal turbine blade: Failure behavior and life prediction

The vibration fatigue failure behavior and fatigue life of the film cooling hole (FCH) structure of Ni-based single crystal superalloy were investigated at high temperature. The vibration fatigue test of the FCH specimens were carried out based on the paired staircase method. The cracks are mostly initiated in the stress concentration area at the edge of the FCH, and may also be initiated in non-stress concentrated areas with large defects. At high temperature, the crack initiation mechanism of the FCH specimens of Ni-based single crystal superalloy is oxidative cracking nucleation in stress concentration area, and the crack propagation mechanism is the competition mechanism of dislocation slip and dislocation climbing. Based on the Fatigue Indicator Parameter (FIP) of the critical plane method, a vibration fatigue life prediction model for FCH structures considering stress concentration and high temperature oxidation damage is proposed. The life prediction model proposed in this paper is applied to the vibration fatigue life prediction of FCH specimens. The deviation between the predicted results and the experimental results is within 2.5 times at 850℃, and the deviation is within 2 times at 980℃. Besides, the life prediction method proposed is compared with other two FIP life prediction methods, and the high accuracy and effectiveness of the proposed life prediction method are verified.

Intelligent temperature measuring thermal spray multilayer thermal barrier coatings based on embedded thin film thermocouples

Thermal barrier coatings (TBCs) have garnered significant attention as crucial protective components for turbine blades. However, the current use of TBCs is limited by their singular functionality and the inability to accurately obtain the temperature gradient distribution within the coatings. Addressing the aforementioned issues, this paper proposes an intelligent thermal barrier coating embedded with thin-film thermocouples. This method not only provides effective thermal protection but also facilitates the precise measurement of the internal temperature gradient within the coating. To mitigate the thermal mismatch in TBCs under high-temperature environments, which can compromise their lifespan, this study employs multi-objective optimization of structural parameters to design an optimal coating thickness. This strategy ensures both superior thermal protection and extended service life. The intelligent temperature-sensing TBCs were fabricated using atmospheric plasma spraying and magnetron sputtering, followed by comprehensive characterization. To validate the performance of the intelligent temperature-sensing TBCs, static tests were conducted in a muffle furnace. The results demonstrated that the sensors exhibit excellent repeatability and high-temperature durability. Furthermore, a test platform replicating the thermal shock conditions of an engine environment was developed. This platform confirmed that the intelligent temperature-sensing TBCs are capable of accurately measuring the internal temperature gradient within the coating under engine-like conditions, offering a novel methodology for engine monitoring and diagnostics.

The industrialization of additive manufacturing

AbstractOur world is constantly facing a wide variety of social challenges — currently, issues such as climate change, security, demographic change, and resource conservation are of significant importance and show an acute need for action. Among other things, disruptive technologies are needed to tackle such problems. Additive manufacturing (AM) is regarded as the ‘game changer/paradigm shift’ technology for the digital, automated production of the future — as the key enabler of ‘Production 2.0’. This sustainable and resilient technology enables new paths to innovative solutions across all industries through a high degree of individualization (mass customization) and great design freedom (‘manufacture for design’ instead of ‘design for manufacture‘). For example, internally cooled turbine blades for H2‐capable gas turbines, lightweight structures for more efficient aircraft or patient‐specific implants are only made possible by AM. In this way, AM makes an important contribution to solving the social challenges mentioned above now it is necessary to transfer this technology to board industrial use.

Wind turbine blade health state assessment based on fuzzy evaluation

Abstract Due to the health state of wind turbine blade being affected by many factors and the mechanism being unclear, a fuzzy evaluation method using SCADA information is proposed. Firstly, the index structure of blade health state assessment is determined by correlation analysis of SCADA data. Secondly, entropy weight is used to allocate weights to all levels of parameters, and then the index data degradation function is optimized by the 3σ criterion. Thirdly, the ridge distribution function is utilized to establish the membership function of the health indexs. Finally, a mathematical model is created for the fuzzy comprehensive assessment of the blade health status. The described techniques is employed to assess the blade health state in the Qingdao wind farm. The “healthy” and “dangerous” states of the blade can be distinguished. The assessment result aligns with reality, verifying that the method in this paper is applicable to the blade health state assessment of wind farms.

Dynamic model decomposition study on the influence of cutback surface length on the wake characteristics of turbine blades

Abstract The flow within a cascade of pressure-side cutback cooling blades with different cutback surface lengths is predicted using the unsteady numerical method. Dynamic Mode Decomposition (DMD) is used for flow field order reduction analysis. The relationship between varying cutback surface lengths and the wake dynamics is analyzed. The analysis shows that the shear layer behind the trailing edge and lip dominates the unsteady flow in the wake region. As the cutback surface length diminishes, an increase in the modal frequencies of both the lip shear layer and the wake shear layer is observed. As the cutback surface length is shortened, the shear layer behind the lip causes stronger oscillations in the shear layer behind the trailing edge, subsequently leading to an augmentation in the amplitude width of the wake mode across the transverse direction.

Performance analysis of air-cooled turbine based on source terms method

Abstract Investigating turbine blade cooling and blade tip clearance leakage is crucial for reducing turbine losses and enhancing overall engine performance. Therefore, this paper uses the E3 two-stage high-pressure turbine as a case and employs the source term method to model the film cooling configuration, validating its efficacy and examining the performance parameters and flow field characteristics of air-cooled turbines under varying blade tip clearances. The outcomes demonstrate that the source term approach accurately forecasts the comprehensive performance parameters of air-cooled turbines, with blade tip clearance height predominantly impacting turbine performance in high-velocity regions. For small blade tip clearance, air-cooled turbines exhibit diminished efficiency with a decreasing expansion ratio in high-velocity regions, but they demonstrate an inverse behavior in low-velocity regions. Conversely, under conditions of larger blade tip clearances, the cooling effectiveness of air-cooled turbines is more pronounced in regions characterized by low expansion ratios and low speeds.

Analyzing rain erosion using a Pulsating Jet Erosion Tester (PJET): Effect of droplet impact frequencies and dry intervals on incubation times

Accelerated laboratory testing is essential to understand the rain erosion behavior of coated samples applied to the leading edge surface of a wind turbine blade. This study investigates the impact of droplet impact frequencies and dry intervals on the incubation time for damage on polyurethane-coated samples using a Pulsating Jet Erosion Tester (PJET). A novel theoretical model for water slug volume is introduced, allowing for a more accurate comparison across different impact velocities and frequencies. The effect of dry intervals on coating performance is quantified, revealing that longer dry intervals and shorter pre-dry rain exposure can significantly increase the number of impacts a coating can withstand before damage. The study challenges the traditional continuous impingement testing by demonstrating that dry intervals can extend incubation time by a factor of three to five. Additionally, this paper proposes a recalibrated approach to PJET testing, which better mimics the cyclic nature of real-world rainfall, leading to improved predictive models for material degradation. The findings emphasize the importance of considering the visco-elastic behavior of coatings and the role of intermittent rain exposure in erosion testing, offering invaluable insights for designing future PJET test parameters.

Highly separated transitional shock-wave/boundary-layer interactions: A spatial modal study

At cruise altitudes, the Reynolds number may become sufficiently low to allow a laminar boundary layer to persist on the suction side of a transonic fan blade up to the shock-wave/boundary-layer interaction (SBLI). In such a transitional SBLI with sufficiently large shock-induced separation, a shock oscillation mechanism occurs, with the source at the upstream growth (until a critical length) and natural suppression (through shear layer instabilities) of the separation bubble. The oscillation cycle is characterized by a temporarily vanishing upstream laminar part of the separation bubble. The suppression of this laminar part is accompanied by downstream advection of turbulence and subsequent entrainment into the bulk separation bubble, affecting the reflected shock movement. In order to study the spatial behavior of the mechanism, particle image velocimetry of a highly separated transitional oblique SBLI at Mach 2.3 is conducted in the high speed aerodynamics laboratory of Delft University of Technology. Statistical quantities, including root mean square velocity fluctuations, phase averages, and spatial modes from proper orthogonal decomposition, are investigated. The entrainment strength varies depending on the phase of the oscillation, and the turbulent shear layer is not fully developed. The main growth and shrinking mode of the separation bubble were extracted, which affects the slip line region size and shock position. Secondary modes that affect the shear layer undulation and upstream effects were also extracted. The study provides quantitative analyses of an important shock oscillation type, with the focus on capturing the separation bubble size variation and upstream effects.

Evaluation of a substitute bird for engine fan blade impact tests considering the bird-slicing state

Bird ingestion is one of the major threats to aero engines. To evaluate airworthiness compliance in bird ingestion events, dynamic structural tests are the most straightforward and intuitive method. These tests can be conducted using either real birds or substitute birds, the latter offering enhanced repeatability and more convenient test management. In this study, an equivalent strategy is proposed aimed at developing a suitable substitute bird for impact tests on engine fan blades by evaluating the dynamic bird-slicing responses. Two gelatine recipes are adopted to manufacture the substitute birds and the impact responses are measured with a wedge-Hopkinson bar (WHB) system. It is found that the inertial force is the dominant factor in the impact load, and the gelatin resistance also has a certain influence. Generally, the impact responses of the gelatine birds show a constant distribution of the normalized peak impact force with good dispersion as velocity increases. The momentum transfer (MT) exhibits both a “velocity effect” and a “mass effect”, duplicating the responses observed in real bird tests. Besides, the temporal distribution of the force history for the gelatine birds closely matches that of the real birds. The results indicate that the equivalent strategy effectively evaluates the substitution, and the proposed gelatin recipe can be used for real bird alternatives in engine fan blade tests.

Twist and chord optimization using the linearization method on the taper blade of a micro-horizontal axis wind turbineTwist and chord optimization using the linearization method on the taper blade of a micro-horizontal axis wind turbine

The research aims to optimize the geometry of taper blade profiles for the Horizontal Axis Wind Turbine (HAWT) to improve aerodynamic performance and minimize fabrication complexity. The study used blade linearization as an optimization method for identifying a desirable twist (β) and chord (Cr). This approach enhances accuracy and boosts computational efficiency. It simplifies the optimization process by reducing complexity. In contrast, traditional nonlinear methods are slower and more resource-intensive due to complex aerodynamic interactions. The best β and Cr distributions were found by linearization with elements 1 and 10 of the blade length and positions 5%, 15%, 25%, 35%, 45%, 55%, 65%, 75%, 85, and 95% of the blade elements. The linearization results were used to determine the optimum performance of the HAWT design using simulation. The optimal blades for HAWT were fabricated and their performance evaluated under real wind conditions. The linearization of the 45% twist and chord of elements 1 and 10 provided the best blade shape. Optimized twist and chord yielded HAWT performance with the Cp of 45% to 47% at rotational speeds of 200–900 rpm and wind speeds of 2–10 m/s. Twist and chord optimization increased the Cp from 39.71% to 46.43% with a rotational speed of 550 rpm at a wind speed of 6 m/s, as well as the maximum mechanical power from 424.28 watts to 500.35 watts at a wind speed of 10 m/s. The result from real wind conditions showed that manufactured HWAT produced an average electrical power of 294.19 watts at a rotational speed of 590.66 rpm. These results demonstrate that the optimized design approach presents a close match and is still reasonable in comparison to practical conditions.

Savonius wind turbine blade selection based on computational fluid dynamics

The Savonius vertical axis wind turbine is widely used because of its simple design and efficiency at low wind speeds. The next development is the mini multi-blade Savonius helical wind turbine. At this miniature size, the performance of a mini multi-blade helical Savonius turbine due to variations in the number of blades and its impact on the energy produced has not been investigated in depth. Therefore, adjustments to the size and number of blades need to be made to optimize the performance of this turbine. The research aims to obtain the performance of the Savonius type S wind turbine with 3 blades and 4 blades using the CFD (Computational Fluid Dynamics) method. The main dimensions of the simulation model are the shaft diameter of 0.008 m, the outer diameter of 0.24 m, the height of 0.4 m, and the number of blades 3 and 4. The inner diameter of the 3-blade turbine is 0.21 m while the inner diameter of the 4-blade turbine is also 0.21 m. Both turbine models are subjected to wind speeds of 4 m/s, 5 m/s, and 6 m/s. Based on the simulation results, a turbine with 4 blades has more optimal performance compared to the 3-blade type. At a wind speed of 6 m/s, the 4-blade Savonius helical turbine produces a rotation of 498,215 rpm and a maximum power of 6,129 watts. Meanwhile, the Savonius turbine with 3 blades at a wind speed of 6 m/s produces a rotation of 545,655 rpm and a maximum power of 4,390 watts. This difference in performance shows the importance of adjusting the number of blades in wind turbine design to achieve optimal efficiency. This research provides useful insights for the further development of mini helical Savonius wind turbines in various wind conditions

Studying and analysis of deformation and stresses in horizontal-axis wind turbine using fluid-structure interaction method

Fluid-structure interaction (FSI) studies have become an important tool in the development of wind turbine blades as well as for analyzing and optimizing Horizontal Axis Wind Turbine (HAWT). The most essential elements for estimating the turbine blade strength to withstand extreme wind loads and aerodynamic performance are the blade deformation and the associated stresses. This study aims to compare the strength and analyze the deformation behavior of two models of HAWT blades. A three-dimensional model was created and loaded into a Finite Element (FE) model for analysis. The Computational Fluid Dynamics (CFD) investigation was coupled with the structural model using one-way FSI. In this article, the effect of the aerodynamics on the blade surface of a small HAWT has been studied numerically and experimentally. The airfoil used for the blade profile is S826 airfoil. To provide an appropriate displacement for static measurements, the blade in the experimental investigation is made of thermoplastic polyurethane material (TPU). It is noted that the current experimental findings verify the simulation results, and a comparison between the simulations and the experimental findings reveals a reasonable agreement. The numerical simulations are also implemented on a HAWT epoxy E-glass unidirectional (EEGUD) material. It can be concluded from this study that the blade deformation and stress on the blades are related to the wind speed. The deformation along the span length exhibits nonlinear variation that gradually increases from the blade root and reaches its maximum at the blade tip position. The tip deflection and equivalent stress were found to increase with an increase in wind speed. The dynamic analysis at different tip speed ratios shows the highest deformation at λ = 4, for wind speed of 20 m/s.

Improving fatigue life of a titanium alloy through coupled electromagnetic treatments

TC11 titanium alloy is widely used in the manufacture of key components such as blades of gas turbine and aero engine because of its high specific strength and good processing performance. In the case of gas turbine or aero engine, the fatigue performance of TC11 will directly determine the life of the turbine or engine, and the surface residual stress generated on the alloy during manufacturing often affects the fatigue life of the material. In this study, a new method of coupled electromagnetic treatment (CEMT) was applied to regulate the surface residual stress of the alloy after manufacturing, so as to improve the fatigue life of the TC11. The results show that after the CEMT, the residual compressive stress in the length direction and width direction increased by 63.7% and 56.0% respectively, the fatigue life of the TC11 is increased by 39.9%. The microstructure analysis shows that after CEMT, the width of fatigue striations is significantly reduced. This paper proposes that CEMT can be used as an effective method to adjust the residual stress of materials and improve the fatigue life of titanium alloys. The research is also relevant for improvement of the fatigue life of other alloy materials.

CFD simulation and experimental investigation of a Magnus wind turbine with an improved blade shape

With the advancement of technology and growing concern for environmental issues, the demand for energy derived from renewable sources is expected to increase. It is well established that traditional bladed wind turbines exhibit inefficiency in low wind speed conditions. To address this, Magnus wind turbines, featuring cylindrical blades, have been developed specifically for regions with predominantly low-speed winds. However, these turbines present a significant drawback, as they require electric drives to rotate the blades. This study aims to conduct a three-dimensional numerical and experimental investigation of the aerodynamics around a wind turbine with a geometrically complex blade design. The scientific contribution of this work lies in the introduction of a deflector to the cylindrical blades, intended to eliminate the need for an electric drive to initiate blade rotation. A laboratory prototype of a wind turbine with the proposed blade configuration was constructed, and numerical simulations were performed using Ansys Fluent, based on the Reynolds-averaged Navier—Stokes (RANS) equations. The results demonstrate that the turbine's power coefficient (Cp) is approximately 20 % higher than that of traditional Magnus wind turbines. These findings underscore the enhanced efficiency provided by the addition of a deflector to the cylindrical blades.

Simulation of Small-Scale Wind Turbine Performance with Taperless Blade

Utilizing wind turbines typically involves a large-scale project with extremely huge wind turbine sizes. Because of this, the use of wind turbines in Indonesia is not yet very common and widespread among the community. Basically, a wind turbine has blades; the number of blades on a wind turbine can affect the overall performance of the turbine. Large-scale wind turbine projects usually implement tapered blades, while small-scale projects use taperless blades. Therefore, in this research, a horizontal-axis wind turbine with taperless blades will be used as the object of study to find out the optimal number of taperless blades that can achieve the best performance of a small-scale wind turbine category. The method used in this research is to design a horizontal axis wind turbine equipped with taperless blades with varying numbers of blades, namely three blades, four blades, and five blades, and then simulate the turbine's performance with wind speeds of 3 m/s to 6 m/s. The present research found that the greater the number of turbine blades tends to produce greater power. This is proven by research results, where the highest power in a small-scale horizontal axis wind turbine produces a power of 20,30 Watts in a 5-blade turbine variation for the wind speed of 6 m/s.