Turbine Blade Surface Research Articles

Insights into the hot corrosion of CoCrFeNi high entropy alloy in molten Na2SO4 + 25 %K2SO4 at 900 °C

Hot corrosion is the accelerated oxidation of salt contaminants such as (Na,K)2SO4 deposited on the turbine blade surface. This paper provides an insight into the potential application of CoCrFeNi high entropy alloy (HEA) as a hot corrosion-resistant alloy working at high temperatures. The hot corrosion behavior of CoCrFeNi HEA was investigated through mass gain, EIS, SEM, EDS, and XRD. The results show that the mass gain of hot corrosion increased in the first 20 h and decreased after 30 h due to a large amount of oxide film peeling off. The EIS comprised three capacitive loops before 4 h, and two capacitive loops after 6 h. It indicates that discontinuous spinel oxide composed of multi-elements is rapidly formed on the surface of the alloy at the initial stage of hot corrosion, and a Cr-rich (Cr,Fe)2O3 layer is formed inside the alloy as time passes. The corrosion products for 10 h are mainly composed of porous (Fe,Cr,Co)3O4 spinel in the outer layer and Cr-rich (Cr,Fe)2O3 in the inner layer. As time approaches 100 h, the outer spinel layer peels off seriously. The primary corrosion product consists of (Fe,Cr,Co)3O4. The internal sulfide phenomenon occurs in the matrix.

Wind tunnel test of ice accretion on blade airfoil for wind turbine under offshore atmospheric condition

For wind turbines under offshore conditions, ice accretion occurs on the blade surface in winter because of the cold and humid environment, which leads to the performance degradation of the wind turbine. The characteristics of icing on the wind turbine blade surface under the in-cloud condition with salinity are explored. A blade segment with an airfoil of NACA0018 is selected. The tests of icing on the blade surface in different conditions of salinities, temperatures, and wind speeds are conducted in a return-flow icing wind tunnel. Two parameters are defined to evaluate icing characteristics. The distribution and amount of ice are analyzed quantitatively. Results show that salinity can restrain the amount of ice accretion. Oppositely, low temperatures and high wind speeds can increase the amount of ice. A self-developed device was manufactured to measure the adhesion strength of ice. The effects of salinity, temperature, and wind speed on adhesion strength are studied. Research indicates that adhesion strength decreases sharply first and then slowly with an increase in salinity. Even though low temperature and high wind speed both increase the adhesion strength, the growth rate decreases. The research provides a reference for anti- and de-icing technologies of offshore wind turbines.

Analyzing the aerodynamic characteristics of eroded wind turbine blades

The study investigates the influence of erosion over the leading edge of S809 series airfoil and its impact on the aerodynamic performance of wind turbine blades. The research work determines how erosion affects the performance of wind turbine blades at an angle of attack varying from 0° to 45° for the fixed Reynolds number of 2.1 x 105. To analyse the flow characteristics, the average pressure acting around the surface of the airfoil is scanned with the aid of 20 pressure taps. The time series pressure of 10,000 samples at each point has been collected. The roughness is introduced at the leading edge of the airfoil and measures 0.1% of the total chord at the top and bottom surface, respectively. Six different intensities of roughness are introduced and tested. The base airfoil, as well as roughed surface airfoil, is compared and the results are discussed. The aerodynamic parameters like lift, drag, and pressure coefficients are included. The estimated data suggests the erosion that occurs on the wind turbine blade surface alters the flow pattern and the aerodynamic properties of the wind turbine blades. Collectively, the experiment on analysing the eroded surface possibly taking place over the wind turbine blade surface affects the lift parameter with a considerable increment in drag. However, the roughness allows the airflow to remain fixed with the airfoil surface, favouring the concept of extending the stall.

Deep‐Learning-Based Uncertainty Analysis of Flat Plate Film Cooling With Application to Gas Turbine

Nowadays, gas turbines intake jet air at high temperatures to improve the power output as much as possible. However, the excessive temperature typically puts the blade in the face of unpredictable damage. Film cooling is one of the prevailing methods applied in engineering scenarios, with the advantages of a simple structure and high cooling efficiency. This study aims to assess the uncertain effect that the three major film cooling parameters exert on the global and fixed-cord-averaged film cooling effectiveness under low, medium, and high blowing ratios br. The three input parameters include coolant hole diameter d, coolant tube inclination angle θ, and density ratio dr. The training dataset is obtained by Computational Fluid Dynamics (CFD). Moreover, a seven-layer artificial neural network (ANN) algorithm is applied to explore the complex non-linear mapping between the input flat film cooling parameters and the output fixed-cord-averaged film cooling effectiveness on the external turbine blade surface. The sensitivity experiment conducted using Monte Carlo (MC) simulation shows that the d and θ are the two most sensitive parameters in the low-blowing-ratio cases. The θ comes to be the only leading factor of sensitivity in larger blowing ratio cases. As the blowing ratio rises, the uncertainty of the three parameters d, θ, and dr all decrease. The combined effect of the three parameters is also dissected and shows that it has a more significant influence on the general cooling effectiveness than any single effect. The d has the widest variation of uncertainty interval at three blowing ratios, while the θ has the largest uncertain influence on the general cooling effectiveness. With the aforementioned results, the cooling effectiveness of the gas turbine can be furthermore enhanced.

Durability and Degradation Mechanisms of Antifrosting Surfaces.

Rapid implementation of renewable energy technologies has exacerbated the potential for economic loss and safety concerns caused by ice and frost accretion, which occurs on the surfaces of wind turbine blades, photovoltaic panels, and residential and electric vehicle air-source heat pumps. The past decade has seen advances in surface chemistry and micro- and nanostructures that can promote passive antifrosting and enhance defrosting. However, the durability of these surfaces remains the major obstacle preventing real-life applications, with degradation mechanisms remaining poorly understood. Here, we conducted durability tests on antifrosting surfaces, including superhydrophobic, hydrophobic, superhydrophilic, and slippery liquid-infused surfaces. For superhydrophobic surfaces, we demonstrate durability with progressive degradation for up to 1000 cycles of atmospheric frosting-defrosting and month-long outdoor exposure tests. We show that progressive degradation, as reflected by increased condensate retention and reduced droplet shedding, results from molecular-level degradation of the low-surface-energy self-assembled monolayer (SAM). The degradation of the SAM leads to local high-surface-energy defects, which further deteriorate the surface by promoting accumulation of atmospheric particulate matter during cyclic condensation, frosting, and melt drying. Furthermore, cyclic frosting and defrost tests demonstrate the durability and degradation mechanisms of other surfaces to show, for example, the loss of water affinity of superhydrophilic surfaces after 22 days due to atmospheric volatile organic compound (VOC) adsorption and significant lubricant drainage for lubricant-infused surfaces after 100 cycles. Our work reveals the degradation mechanism of functional surfaces during exposure to long-term frost-defrost cycling and elucidates guidelines for the development of future surfaces for real-life antifrosting/icing applications.

Investigation of Hafnium Oxide Containing Zirconium in the Scaled Region on the Surface of As-Cast Nickel-Based Single Crystal Superalloy Turbine Blades

Surface scale is usually formed in the aerofoil part of as-cast nickel-based single crystal turbine blades by the strong interaction between the mould wall and the melt, and the subsequent oxidation of the fresh metallic surface of the casting. For better understanding of the scaling, the scaled region was investigated, and an interesting region containing hafnium oxides and a rhenium-rich particle was found. Generally, a continuous aluminium oxide layer was detected on the outer surface of the base material and covered the surface of an unscaled region. In contrast, there was no oxide on the surface of a scaled region, but it was replaced by several tiny particles remaining locally on the outer surface of the base material. SEM-EDX and TEM-EDX point analysis of these particles indicated not only the existence of high amounts of hafnium, but also several particles such as hafnium oxide, aluminium oxide, and even tiny metallic particles. Most of all, STEM-EDX point analysis clearly detected zirconium in the hafnium oxide. Furthermore, a rhenium-rich particle was also detected towards the outer surface of the base material, which suggested that the surface of the scaled region might be exposed to high enough temperatures to allow the diffusion of heavy alloying elements. Based on the observation, the formation mechanism of hafnium oxide containing zirconium and its meaning was discussed.

Portable motorized telescope system for wind turbine blades damage detection

AbstractWind turbines are among the fastest‐growing sources of energy production and the maintenance operations include regular inspection of their blades, causing considerable downtime and cost. In addition, the manual inspection process involves a great risk. To address this challenge, in this article a preventive maintenance system for wind turbines based on deep computational learning techniques is presented. This open‐source project aims to detect and classify possible surface damages on wind turbine blades to facilitate and improve the inspection of such infrastructures. The system consists of a stand‐alone Android application that makes use of convolutional neural networks for image processing, a portable telescope to take precise photographs of the turbine blades, and a motorized mount that allows the movement of the telescope. The application tries to carry out a complete sweep of the surface of the wind turbine blades in an autonomous way based on the predictions of neural network models and finally presents the defects found to the user. Thanks to this, maintenance time would be reduced and the risk of manual intervention would be avoided. Accuracies of around 97% for label predictions and 90% for bounding box coordinate predictions have been achieved on the validation dataset. The proposed low‐cost inspection system for detecting surface damages on blades has been experimentally validated in a real wind farm.

Effect of the composition of multicomponent powders on the mechanical and tribotechnical properties of coatings obtained by laser additive technologies

The paper presents the results of metallographic studies and tribotechnical tests of samples of medium-carbon steel 34KhNi3MoA and coatings obtained by laser surfacing of a powder multicomponent charge based on iron and cobalt in a ratio of 3:1 with additives of nano particles of tantalum carbide. The samples were processed with a circular defocused beam and with transverse beam oscillations normal to the scanning speed. Comparative tests for friction and wear were carried out in a pair with a hardened 40Kh steel counterplate. The load and sliding speed during the tests varied discretely. Turbine oil TP 22C was used as a lubricant. It is shown that the introduction of additives of nano-tantalum carbide into the charge reduces friction losses, increases the wear resistance of coatings compared to the charge without carbides and the base material. The wear resistance of coatings with an increase in the amount of the hardening phase increases compared to the original steel. It has been established that the technology of laser surfacing with multicomponent coatings with nano particles of tantalum carbide can be used to restore worn surfaces of shaft necks, turbine blades, thrust discs, shut-off valves and other parts operating at high temperatures and in corrosive environments.

EXPERIMENTAL INVESTIGATIONS FOR EFFECTIVENESS OF COMBINED IMPINGEMENT FILM COOLING

Protecting the gas turbine blades from high-temperature gases and increasing the specific work output is one of the most challenging tasks for most gas turbine design engineers. Combined impingement and film cooling can be used as a hybrid cooling technology to improve the film cooling performance over the gas turbine blade surfaces. In the present work, experimentations were performed on a flat plate with combined impingement film cooling for two thermally conductive materials (Perspex and stainless steel) at different blowing ratios and compared with the computational results. Thermo chronic liquid crystal sheets were used for measuring the temperature distribution. Effectiveness is the parameter that plays a vital role in determining thermal performance. Uniform effectiveness distribution was observed in stainless steel material because of its more thermal conductivity. Combined impingement film cooling showed higher effectiveness compared to film cooling. Uncertainty of ± 7% present in TLC data and experimental results agreed with the computational results.

Research on Anti-Icing Performance of Graphene Photothermal Superhydrophobic Surface for Wind Turbine Blades

In this study, graphene is used as a photothermal material, which is added to the SiO2 superhydrophobic solution treated with fluorine silane, and then sprayed on the copper plate surface to prepare a new type of photothermal superhydrophobic surface with contact angles up to 160.5° and 159.8°. Under the conditions of natural convection, the effects of photothermal superhydrophobic surfaces on droplet condensation, freezing, and frost growth are investigated in different environments. The results show that the photothermal superhydrophobic surface can not only delay the freezing of surface droplets, prolong the freezing time of droplets, and reduce the thickness of the frost layer, but also allow for the rapid removal of droplets under near-infrared (NIR) irradiation. If the droplet is irradiated by an infrared laser emitter while the cooling system is still turned on, the internal temperature of the droplet will always be higher than the crystallization temperature under the illumination intensity of 2 W/cm2, and the droplets will not freeze. With the extension of irradiation time, the droplet will evaporate, and the volume of the droplet will decrease. On the basis of summarizing and evaluating the study on the anti-icing performance of superhydrophobic surfaces and the properties of photothermal materials, a new research direction regarding the anti-icing of fan blade surfaces was established. This kind of surface combines the photothermal capabilities of light absorption materials with the micro- and nanostructure of the superhydrophobic surface to improve the anti-icing capability of wind turbine blade surfaces in difficult conditions.

Use of Green Fs Lasers to Generate a Superhydrophobic Behavior in the Surface of Wind Turbine Blades.

Ice generation on the surface of wind generator blades can affect the performance of the generator in several aspects. It can deteriorate sensor performance, reduce efficiency, and cause mechanical failures. One of the alternatives to minimize these effects is to include passive solutions based on the modification of the blade surfaces, and in particular to generate superhydrophobic behavior. Ultra-short laser systems enable improved micromachining of polymer surfaces by reducing the heat affected zone (HAZ) and improving the quality of the final surface topography. In this study, a green fs laser is used to micromachine different patterns on the surface of materials with the same structure that can be found in turbine blades. Convenient optimization of surface topography via fs laser micromachining enables the transformation of an initially hydrophilic surface into a superhydrophobic one. Thus, an initial surface finish with a contact angle ca. 69° is transformed via laser treatment into one with contact angle values above 170°. In addition, it is observed that the performance of the surface is maintained or even improved with time. These results open the possibility of using lasers to control turbine blade surface microstructure while avoiding the use of additional chemical coatings. This can be used as a complementary passive treatment to avoid ice formation in these large structures.

Using thermal spray coating method to produce system composites (Ni-Al2O3-B4C(

Thermal plasma spraying method was used for coating the pre-prepared surfaces of turbine blades. Nickel (Ni) was used as a base material with a fixed percentage of alumina (5%Al2O3), and (5,10,15,20,25%) of Boron carbide (B4C) as reinforcement material. Cermet powders were mixed for one hour, then the coating bases of steel type (316L) were prepared and roughened using sandblasting to increase the adhesion strength between the coated materials and the base. The bonding material represented by (Ni-22% Cr-10%Al-1%Y) was sprayed with a thickness of (150µm), and then the base and reinforcement material were sprayed with a thickness of (350-400 µm). Thus, the final thickness of the prepared samples was (550-500 µm). After that, the samples were sintered at 900°C for two hours. The hardness test was applied to the samples, indicating the best hardness after sintering at (25%) reinforcement ratio of 590Hv. As for porosity, its lowest value was obtained at 7%, while the best value of adhesion strength was obtained after sintering at (25%) of B4C. However, the results of the scanning electron microscope (SEM) showed the weakness and the presence of pores in the coating layers at the low percentage of reinforcement. While the mechanical and physical properties were improved with the increase in the percentage of reinforcement to reach the best at 25% of B4C.

A Survey on Non-Destructive Smart Inspection of Wind Turbine Blades Based on Industry 4.0 Strategy

Wind turbines are known to be the most efficient method of green energy production, and wind turbine blades (WTBs) are known as a key component of the wind turbine system, with a major influence on the efficiency of the entire system. Wind turbine blades have a quite manual production process of composite materials, which induces various types of defects in the blade. Blades are susceptible to the damage developed by complex and irregular loading or even catastrophic collapse and are expensive to maintain. Failure or damage to wind turbine blades not only decreases the lifespan, efficiency, and fault diagnosis capability but also increases safety hazards and maintenance costs. Hence, non-destructive testing (NDT) methods providing surface and subsurface information for the blade are indispensable in the maintenance of wind turbines. Damage detection is a critical part of the inspection methods for failure prevention, maintenance planning, and the sustainability of wind turbine operation. Industry 4.0 technologies provide a framework for deploying smart inspection, one of the key requirements for sustainable wind energy production. The wind energy industry is about to undergo a significant revolution due to the integration of the physical and virtual worlds driven by Industry 4.0. This paper aims to highlight the potential of Industry 4.0 to help exploit smart inspections for sustainable wind energy production. This study is also elaborated by damage categorization and a thorough review of the state-of-the-art non-destructive techniques for surface and sub-surface inspection of wind turbine blades.

Experimental flow control investigation over suction surface of turbine blade with local surface passive oscillation

Impact of the local flexible membrane (LFM) on aerodynamic phenomena including the formation of a laminar separation bubble (LSB) and transition to turbulence was experimentally investigated over the suction surface of a Clark-Y airfoil first time in literature. The experiments such as aerodynamic force measurement, smoke-wire flow visualization and hot-film tests were carried out at the free-stream velocity of U∞ = 3.2 m/s, U∞ = 6.4 m/s, U∞ = 9.6 m/s, U∞ = 12.8 m/s, and Reynolds number based upon on the chord length was Rec = 3.5 × 104, Rec = 7.0 × 104, Rec = 1.05 × 105 and Rec = 1.4 × 105, respectively. The experimental angle of attack was set at 0° = α ≤ 20°. In detailed intermittency analysis by the hot-film sensor over the uncontrolled airfoil, it was seen that the LSB and transition to turbulence formed close to the trailing edge at a lower angle of attack, and it moved towards the leading edge when increasing the angle of attack simultaneously. Employing LFM on the suction surface obviously affected the progress of these flow phenomena. In the results of smoke-wire flow visualization, either the size of the laminar separation bubble (LSB) was reduced or its presence was suppressed at lower incidences. The aerodynamic force measurement results also supported those behaviors. In particular, at lower incidences, the negative effects of LSB were mitigated, resulting in the presence of a more stable lift curve. Additionally, it was clearly observed that utilizing LFM ensured positive effects, especially at the pre- and the post-stall regions in terms of fewer fluctuations at the CL curve, meaning that less aerodynamic vibration and noise on wind/hydro turbine could be obtained.

Dynamic response of wind turbine blade surface material under water droplet high velocity impact

When a wind turbine blade exposure to some degree of rainfall, water droplets in the atmosphere impact the blade at high velocity will causes erosion damages of the leading edge. The damages have significant influence to the aerodynamic performance of the blade, and also the cost of power generation. In this paper, a high velocity impact dynamics model of water droplet impact on wind turbine blade is develops based on SPH-FEM coupling method, where SPH model is used to model the large deformation region of the fluid domain, and FEM method is used to model the small deformation region of the structure domain. Together with properties of gelcoat material on the blade surface, effects of varying impact velocities and angles on the impact response of the gelcoat material are analysed through numerical simulation. The results show that during a high velocity impact event of water droplet, the contact force history appears two peaks. Also contact forces and strains on the blade material decreases with decreasing droplet impact velocity and impact angle, the total contact duration of the droplet during the impact decreases with increasing droplet impact velocity and angle. The present study is expected to provide theoretical guidance for enhancing the erosive capacity of wind turbine blade gelcoat material.

Study on carbon particle deposition distribution of turbocharger turbine blade based on the gas-solid two-phase flow theory

The formation mechanism of non-uniform carbon deposition on the turbine blade under the gas-solid two-phase flow is analyzed, and the finite element model of turbine blade deposition is established. The carbon formation on turbine blade surfaces of turbochargers at different rotational speeds is investigated. The particle deposition test bench is designed and built. The distribution of turbine blade particle deposition is verified by the experiment of turbine blade particle deposition. The results show that the particles are mainly deposited on the pressure surface of the turbine blade, and the position of the carbon deposition varies with the change of the rotational speed.

Influence of Gas-to-Wall Temperature Ratio on the Leakage Flow and Cooling Performance of a Turbine Squealer Tip

In high-pressure turbines, there is a large difference in temperature between the mainstream and the turbine blade surface. Most of the turbine blade tip heat transfer studies were conducted under the assumption that the Over-Tip-Leakage (OTL) flow field is independent of the wall thermal condition. Recent numerical and experimental studies have revealed that the two-way coupling effect between aerodynamics and heat transfer should not be neglected. The heat transfer coefficient obtained by the conventional method is not able to match the realistic engine condition accurately. This study investigates the impact of the wall thermal boundary condition on the tip cooling performance of squealer turbine blades. The RANS CFD result was validated against experimental tip heat transfer data obtained from a high-speed test rig with the effect of high-speed relative casing motion. The aerothermal performance for both uncooled and cooled squealer tips was studied at two different gas-to-wall temperature ratios, 1.7 and 1.1; the reference temperature is 204 K. It was found that the location and strength of cavity vortices varied with different wall thermal boundary conditions, leading to different signatures in tip heat transfer and cooling performance. It is recommended that the experimental heat transfer data and film cooling effectiveness obtained at the near-adiabatic wall boundary condition should be corrected before their application to the tip cooling design process. It would be more reliable to match the wall-to-gas temperature ratio during the tip experimental study.

Research on Wind Turbine Blade Surface Damage Identification Based on Improved Convolution Neural Network

Wind turbine blades are easily affected by the working environment and often show damage features such as cracks and surface shedding. An improved convolution neural network, ED Net, is proposed to identify their damage features. An EAC block based on the improved asymmetric convolution is introduced which strengthens the feature extraction during convolution. A DPCI_SC block, which is improved based on the attention module, is embedded to enhance the ability to obtain spatial location information of the damage. GELU is used as the activation function. The loss function is smoothed and labeled during training. Finally, three sets of experiments were conducted. Experiment 1 confirmed the efficacy of the ED Net for identifying damaged wind turbine blades. Experiment 2 confirmed the efficacy of the relevant improvements proposed in this work. Experiment 3 compares the recognition of wind turbine blade damage by commonly used lightweight networks and shows that the ED Net model proposed has a better performance with an accuracy range of 99.12% to 99.23% and a recall of 99.23%

Strain self-sensing capability of a tidal turbine blade fabricated of PU-foam/glass fiber/epoxy composites using MWCNTs

A novel marine composite structure (experimental tidal turbine blade) made up of a polyurethane (PU) foam/glass fiber/epoxy resin composite with multiwall carbon nanotubes (MWCNTs) is proposed herein to self-sense its strain under a structural test scenario. To achieve this, MWCNTs were deposited onto glass fiber fabric by spray-coating technique in order to form an effective electrical percolation network onto the external skin surface of the tidal turbine blade which enables piezoresistive capability. After MWCNT deposition, the blade was manufactured by means of one-shot resin transfer molding (RTM) in a closed and heated metallic mold specially designed with a blade geometry of 67 cm length. The results confirm that the spray coating technique is a viable method to deposit MWCNTs onto glass fiber surface and form electrical networks into the blade at a relatively low MWCNT concentration. Finite element analysis (FEA) predicted a suitable structural blade design with a maximum failure index value of 0.9 attained in the blade shear web. The measured longitudinal strains of the tidal turbine blade were in good agreement with the numerical strain values predicted with FEA. Electromechanical tests carried out on a structural test rig designed and instrumented for tidal turbine blades showed that the electrical resistance change response of carbon nanotube (CNT) network integrated into the blade was capable of following the mechanical curve response up to the blade limit load, confirming its ability to self-sense its strain in real time.

Film Cooling Holes Performance on A Flat Plate

The present study aims to evaluate numerically the influence of film cooling holes configuration. Five models of holes configuration were studied to examine the effectiveness of a single film cooling hole (8 mm diameter). A cylindrical hole, square hole, rotated square, triangle hole and rotated triangle hole was employed to eject the coolant air with constant cross sectional area at 350 angle of injection. A 3-D finite-volume method was utilized to describe the turbulent flow over flat plate surface (as a model of a turbine blade surface). The mainstream domain (40d x10d x4d) had been represented in ANSYS FLUENT 16 with a standard turbulence model. So far, in term of effective cooling, the numerical results elucidate noticeable enhancement realized at BR=0.5 due to a reduction in plate surface temperature compared with BR =0.25 and 1 for cylindrical hole model. Moreover, the holes configuration performance demonstrate a better surface effectiveness about 1.6 % and 1.2 % for rotated triangle and square models respectively compared with the cylindrical holes model at BR=1. It was found that the numerical results had an excellent matching with related published results which show the solidity of ANSYS FLUENT code to predict the cooling efficiency with varying blowing ratio.