Leading Edge Erosion Research Articles

Effect of the water erosion on the non-equilibrium condensation in steam turbine cascade

In the final stage of steam turbines, droplets formed by non-equilibrium condensation continuously impact and erode the blades, leading to changes in surface roughness and leading edge erosion. This study investigates the effects of roughness changes and leading edge erosion, induced by water erosion, on non-equilibrium condensation in steam turbine cascades using numerical simulation methods. In a Moses-Stein nozzle, the mechanism of roughness influencing non-equilibrium condensation is analyzed. Subsequently, entropy generation theory is applied to assess the loss distribution caused by roughness variations in a Dykas cascade. Furthermore, flow field analysis and entropy generation theory are utilized to examine the loss distribution pattern resulting from leading edge erosion. Results show that increased roughness delays non-equilibrium condensation, reducing average outlet humidity (from 0.05351 to 0.04361 as roughness rises from 0 to 500 µm). The effect of roughness on thermodynamic entropy generation exhibits a non-linear relationship, balancing steam flow losses with mitigated phase-change-related losses at a roughness of 896 µm. Significant blade erosion (>3 mm) alters leading edge geometry, causing local flow separation and a substantial increase in airfoil losses.

Investigating the effect of BT direction on W source-to-core pathways during the SAS-VW campaign on DIII-D

Experiments using the V-shaped closed slot tungsten (W) coated SAS-VW divertor in DIII-D studied the effects of the BT direction on core contamination of eroded tungsten from a closed slot divertor configuration. Core W content is inferred using soft-X ray tomography (SXR) and vacuum ultraviolet spectroscopy (SPRED), while W divertor erosion is inferred from visible spectroscopy of W emission (400.9 nm) measured by in-slot filterscopes (filtered photo-multipliers). Post-mortem analysis from the campaign discovered tile misalignment leading to suspected pronounced leading-edge erosion in the unfavorable BT direction (ion B→×∇B→ drift away from divertor) likely not captured by diagnostics. However, empirical findings show up to ∼ 2-3x larger core contamination in the favorable BT direction even considering no additional W erosion from leading edges. A “source-to-core efficiency factor” is derived to estimate the effects of leading-edge erosion and compare W contamination for two pairs of H-mode discharges in opposite BT directions. While having differing absolute parameters, similar core impurity density gradients suggest comparable core impurity transport. These results show that favorable BT may have stronger source-to-core pathways for W impurities sourced from the outer divertor region. Possible explanations could include the effects of E→×B→ drifts on W transport in the scrape-off-layer (SOL) as well as previously determined fast SOL inner target directed flows in favorable BT.

Techno‐Economic Analysis of Additively‐Manufactured Wind Turbine Blade Tips That Enable Technology Integration

ABSTRACTThe Additively‐Manufactured, System‐Integrated Tip (AMSIT) project is leveraging the flexibility of 3D printing to integrate several technologies in a wind turbine blade tip, while reducing the levelized cost of electricity (LCOE) produced. The design integration is demonstrated for a 200‐kW–scale turbine with 13‐m blades, with the outer 15% of the blade replaced with a 3D‐printed design. Aerodynamic performance is enhanced without increasing swept area through inclusion of a winglet and surface texturing, both challenging for traditional manufacturing. Longevity and durability are improved through integrated lightning and leading edge erosion protection. Increased power, reduced repair frequency, and ease of repair through blade modularity all contribute to reduced LCOE. The analysis is also extended to modern MW‐scale designs to estimate the impact of the technology at scale, demonstrating the potential to reduce LCOE significantly for modern onshore turbines, with even higher potential savings offshore.

Influence of surface curvature on the impact force of water droplet

Although the global market for wind energy is growing rapidly, leading-edge erosion is a critical issue hindering the development of wind power. The impact force of a droplet colliding with flat surfaces has been investigated in previous studies. However, the impact force exerted on curved surfaces, such as that experienced by eroded wind turbine blades, is not well understood. This study discusses the relationship between the impact force generated on a solid surface by a water droplet and the radius of curvature of the impacting surface. The impact force by a droplet was measured using a force sensor mounted on semi-cylindrical caps with different radii of curvature. The measurement results showed that the impact force decreased as the radius of curvature decreased. A computational fluid dynamics model solving incompressible flows showed that, unlike the case of a curved surface, the initial momentum of the droplet was mostly transferred to the flat surface. This resulted in a high impulse for an impact with a flat surface. The falling droplet was blocked by the surface, and the lateral jet was accelerated sideward. This acceleration was moderate for curved surfaces. When colliding with a flat surface, a higher impact force was generated owing to the wider area of the excited surface pressure compared with that of the curved surface. Finally, the relationship between the peak of the impact force and the surface curvature was derived, suggesting that the force peak is inversely proportional to the curvature.

Aerodynamic effects of leading-edge erosion in wind farm flow modeling

Aerodynamic effects of leading-edge erosion in wind farm flow modeling

Analysis of performance improvement methods for offshore wind turbine blades affected by leading edge erosion

Leading edge erosion (LEE) poses greater challenges to the blade design of offshore wind turbines. This paper analyzes the influence of LEE on blade aerodynamic performance and wind turbine load based on high-power offshore wind turbines through the GH-Bladed computing platform. The study found that LEE severely weakens the blade aerodynamic performance, resulting in a lag in the wind turbine reaching its rated power. LEE expands the range of blade surface flow separation, leading to an increase in blade stall risk and a decrease in wind turbine load stability. The promotion of blade aerodynamic performance will cause an increase in blade force, which will strengthen the load level of both the blade and the wind turbine. The optimization of twist angle is an effective method to avoid the loss of power generation of wind turbines under LEE interference, but it is inevitable to cause a decrease in the load stability of wind turbines. Therefore, when the load safety margin of wind turbines is sufficient, adjusting the twist angle is an efficient technique to improve the blade aerodynamic performance and promote the stability of power output, which provides a novel solution for blade design of high-power offshore wind turbines.

Numerical Study on the Impact Pressure of Droplets on Wind Turbine Blades Using a Whirling Arm Rain Erosion Tester

The leading-edge erosion of a wind turbine blade was tested using a whirling arm rain erosion tester, whose rotation rate is considerably higher than that of a full-scale wind turbine owing to the scale effect. In this study, we assessed the impact pressure of droplets on a wet surface of wind turbine blades using numerical simulation of liquid droplet impact by solving the Navier–Stokes equations combined with the volume-of-fluid method. This was conducted in combination with an estimation of liquid film thickness on the rotating blade using an approximate solution of Navier–Stokes equations considering the centrifugal and Coriolis forces. Our study revealed that the impact pressure on the rain erosion tester exceeded that on the wind turbine blade, attributed to the thinner liquid film on the rain erosion tester than on the wind turbine blade caused by the influence of centrifugal and Coriolis forces. This indicates the importance of correcting the influence of liquid-film thickness in estimating the impact velocity of droplets on the wind turbine blade. Furthermore, we demonstrated the correction procedure when estimating the impact velocity of droplets on the wind turbine blade.

Generating Composite Material Maps from Numerical Simulation of Hailstone Impact

Over the lifetime of a wind turbine, the blades receive significant erosion to the leading edge caused by precipitation, leading to large losses in aerodynamic performance and therefore power output. It is therefore prudent to study the mechanics of the erosion process in order to predict and mitigate these losses. Whilst leading edge erosion due to raindrop impact has received much research attention in recent years, very little research has focussed the role of hailstone impact in erosion in wind turbine blades. This paper aims to use a computational simulation model to investigate and characterise the physics of the impact of a hailstone on a flat plate of composite glass fibre material typical of those used in the construction of wind turbine blades. This was achieved by modelling the ice projectile using a Single-Particle Hydrodynamic approach in the software package LS-DYNA. This simulation was used to determine how the impact response in the target plate was affected by various parameters of the impact scenario. Simulations were run using diameters of hailstone between 5 and 20 mm, impact speeds between 80 and 120 ms−1, and at angles of incidence between 90 and 0 degrees. The paper presents these observations in the form of “maps” of the material response at each angle of incidence. It was observed that whilst at low velocities, the material response varies linearly with diameter and velocity and at higher velocities, more complicated behaviour arises due to the interaction between the initial stress wave and the remainder of the impacting projectile.

Evaluation of wind turbine blades’ rain-induced leading edge erosion using rainfall measurements at offshore, coastal and onshore locations in the Netherlands

The impingement of rain drops on wind turbine blades determines leading edge erosion (LEE) which is a factor driving high maintenance costs. In order to better quantify rain-induced LEE, we carried out detailed rainfall measurements, by means of disdrometers, in conjunction with wind speed measurements. Measurements were performed at three different Dutch sites, encompassing an offshore, a coastal and an onshore location. Based on rainfall and wind speed measurements, and assuming a virtual 15 MW wind turbine, we estimated the blade’s LEE using a fatigue-based model. Developed by means of different published rotating arm erosion data, our fatigue model relates the measured rainfall characteristics to the LEE incubation period, here assumed as the leading edge protection (LEP) system’s end of life. Assuming a polyurethane LEP system, results indicate that the blades’ incubation period is around 3.9 years at the offshore location, 6.6 years at the coastal location and 8.3 years at the onshore location. These results are connected to the higher wind speeds during rainfalls, and higher occurrences of very intense rainy events which, according to the measurements, progressively occur at the onshore, coastal and offshore locations.

Assessing the impact of vortex generators on the dynamic stall behaviour of a thick airfoil

Modern slender wind turbine blades use thick inboard airfoils and thicker trailing edges prone to flow separation. The increasing size of these flexible blades amplifies the importance of considering unsteady aerodynamics during the design phase. Environmental conditions result in Leading Edge Erosion (LER), further complicating the sectional unsteady aerodynamic behaviour. Although vortex generators are a well-studied method for passive separation control under steady conditions, their influence on unsteady aerodynamics for clean and rough blade sections is an area that requires further exploration. While some numerical studies exist, reliable experimental data is lacking in the literature. This work presents experimental results on the dynamic stall behaviour of a DU97W300 airfoil, a typical thick root section. The investigation covers both clean and rough conditions, both with and without VGs, to create an understanding of how VGs impact dynamic stall. Moreover, various VG array configurations are used to study the parametric dependence of dynamic stall phenomena on the VG array parameters.

Erosion-safe operation using double deep Q-learning

Leading edge erosion on wind turbine blades can reduce aerodynamic efficiency and cause increased maintenance costs, potentially impacting the overall economic viability. Erosion-safe operation is the concept of reducing the blade tip speed during periods of heavy rain, thereby significantly reducing the erosion development and progression. This study explores the application of reinforcement learning, namely using a double deep Q-network, to implement erosion-safe operation. The proposed methodology involves learning a policy for tip speed control that maximizes revenue over a specific period of time. We demonstrate the concept based on 5 years of simulation of the DTU 10MW reference turbine and mesoscale weather simulation from Horns Rev. The trained model was found to increase the cumulative revenue by 1.6 % compared to not using erosion-safe operation. The model was able to effectively adapt to varying weather conditions and stochastic damage progression. Based on 10,000 random simulations, the trained model outperforms two baseline models in more than 98 % of the simulations.

Determination of annual energy production loss due to erosion on wind turbine blades

Increasing size of the modern wind turbines amplifies the issues of leading-edge erosion, especially on the outboard sections of the blades, impacting both their structural integrity and aerodynamic efficiency. Predicting and detection of the aerodynamic losses which occurs before a noticeable structural degradation on the blade can be crucial for operational predictive maintenance strategies to avoid significant loss production. This paper presents the results from the collaborative study between DTU and CENER in order to investigate the influence of leading-edge erosion on wind turbine aerodynamic performance. For this purpose, three distinct erosion scenarios are analyzed by means of computational fluid dynamics (CFD), both 2D and 3D, blade-element momentum theory (BEM) based solver (OpenFAST) and a Simplified Aerodynamic Loss Tool (SALT). The results from previous studies are used as an input for these tools, with outputs from each tool complementing and reinforcing one another. Furthermore, annual energy production (AEP) reductions due to leading-edge erosion across these tools are compared and validation of the SALT tool is presented. It is observed that the thrust and power losses from both CFD and OpenFAST exhibit comparable results and for a severe erosion case, spanning the last third of the blade, results in a 4.3 % reduction in the annual energy production.

An aerodynamic digital twin of real-world leading edge erosion: Acquisition, Generation and 3D CFD

Wind turbine blades face extremely challenging environmental conditions over their operating life-time, that can easily exceed 2 decades. Airborne particles (insects, sand, rain, hail, ice, sea spray etc.) strike the blade leading edge (LE) first and erode or attach to it, roughening its surface. Leading edge roughness (LER) can critically alter the aerodynamic performance of blades, as its aerodynamic impact is strongly coupled to its height with respect to the local boundary layer thickness, which is thinnest around the LE. The actual, detailed topographic manifestation of LER on in-service blades—needed to accurately assess its aerodynamic impact—is highly probabilistic, as it depends on the interaction of multiple stochastic parameters, like the environmental conditions, material composition and production process. Yet little high-resolution topographic LER data of this kind is currently available. This paper details how such data is collected from blades of different turbine manufacturers and processed consistently to build digital twins of the measured LER, that can be analysed aerodynamically using 3D CFD or wind tunnels. Here a special focus lies on how to reconstruct the LER topography and build the computational mesh such that the correct aerodynamic response is observed. For this purpose multiresolution signal decomposition is used to process the topographies and a special meshing procedure established.

Opensource machine learning metamodels for assessing blade performance impairment due to general leading edge degradation

Blades leading edge erosion can significantly reduce annual energy production of wind turbines. Accurate estimates of the resulting blade performance impairment are paramount to predict the resulting energy losses and enable cost-informed decisions on optimal maintenance and operational strategies, maximizing energy production and reducing maintenance costs. Computational Fluid Dynamics (CFD) is a robust approach for predicting the performance losses due to LEE. However, the impact of the damage on blade aerodynamics varies depending on damage pattern, extent and location. Therefore, direct CFD simulation of a sufficiently general set of damaged blades is computationally not viable in industrial applications, since the energy loss assessment needs to be performed for hundreds of turbines at many times of the wind farm operation. To address this issue, previous studies showed how CFD can be used to train machine learning metamodels of the perfomance of damaged blade sections, enabling the definition of multi-fidelity energy loss prediction systems. This study presents improved metamodels, using validated CFD to generate training datasets that cover a more general and wider range of erosion patterns, from low-amplitude roughness to severe grooves. In order to provide the industry with additional erosion geometry-linked tools for estimating energy yield losses, and foster further research and development in this area, the developed meta-models have been made available online with unrestricted access.

Quality assessment of the GPM IMERG product for lifetime prediction of turbine blades in complex terrain

Wind turbine blades may suffer leading edge erosion when rain hits the blades extremely fast, resulting in blade damage that will negatively impact power production. Since wind turbines are growing in size, this translates into higher tip speeds when the blades rotate and, therefore, are more prone to erosion. Wind turbines in mountainous terrain may also suffer erosion due to the high winds and precipitation rates. Therefore, it becomes important to estimate blade lifetimes in wind farm sites with terrain complexity. Blade lifetime prediction models utilize a time series of rainfall intensity, wind speeds, and a turbine-specific tip speed curve. In our study, we assess the quality of the Integrated Multi-satellitE Retrievals for GPM (IMERG) final product in a blade lifetime prediction model for a mountainous area during the period 2015-2020. We first compare the IMERG rainfall intensities against in situ observations at 28 stations in Navarra in Northern Spain. We find that the two datasets are closer to agreement when the rainfall intensities are aggregated in monthly rather than 30-minute temporal scales with correlation coefficients between 0.74 - 0.93. We calculate the average annual rainfall in the period, and we find that IMERG over(under)estimates precipitation in 15 (8) stations, in line with previous studies that have pinpointed the limitations of IMERG in complex terrain. We then input the 30-minute IMERG, in situ rainfall intensities, and the 30-minute New European Wind Atlas (NEWA) wind speeds, extracted at each station location and interpolated at 119 m height, into a blade lifetime model. Our results indicate blade lifetimes of 6-17 years in 13 stations, with the in situ data to provide, on average, longer estimates than the IMERG product. Despite the limitations, we conclude that the satellite-based precipitation from IMERG may become a useful dataset for the lifetime estimation of wind turbine blades in complex terrain, with calibration and adjustments of the IMERG data.

Prediction of rain erosion damage progression using disdrometer rain data: The importance of liquid water content

Wind turbine blade erosion poses a significant challenge to the durability and performance of wind turbines. Modeling of rain erosion damage, considering atmospheric conditions, improves our understanding of the progression of leading-edge erosion on wind turbine blades. In this study, we investigate the impact of varying raindrop characteristics on rain erosion damage development. We analyse 2.5 years of data from a disdrometer, which measures the size and velocity of falling rain droplets, at Risø campus. Various post-processing methods of the disdrometer data are used for estimating representative droplet diameters and fall velocities for each rain event. We compare measured droplet fall velocities with theoretical terminal velocities, revealing a necessity for revising theoretical approaches to raindrop fall velocity for erosion damage modeling. The measured rain rates and representative fall velocities are used to calculate the liquid water content in the air. We introduce a bin-wise summation method for estimating the liquid water content, circumventing the need for representative droplet assumptions. As this method provides the most accurate input for the damage model, we benchmark the other post-processing methods against it and employ it to evaluate bias estimates of associated damage predictions. The largest bias (22%) in accumulated damage is found with an arithmetic mean droplet diameter approach and the smallest bias (-2%) with the median volume estimation method for damage model input. Furthermore, we demonstrate that, for a given rainfall volume, smaller droplets contribute to larger accumulated damage compared to larger droplets.

Failsafe layer for wind turbine blades: Erosion protection of glass fiber composite through nanodiamond-treated flax composite top layer

Wind turbine blades are mainly made from E-glass fiber (GF) epoxy composites, because of their good ratio of strength to weight and costs. With the increase in blade length and tip speed, the problem of leading edge erosion is becoming more severe, reducing annual energy production and raising maintenance cost. It was recently shown that nanodiamond-treated flax fiber (FFND) composites have significantly less erosion than GF composites and could be an alternative for GF in the turbine blade aeroshells. However, FFND alone might not be suitable for manufacturing turbine blades at the large scale of modern wind turbines. Here, we show that a hybrid composite with a thin layer of only 1.5 mm of FFND on a GF base, can achieve the same superior results as bulk material FFND composite. In addition, we show and explain why aramid fibers, that are known for impact resistance, do not perform well as erosion protection. Our research shows the great potential of this technology to be implemented as a low-cost, lightweight skin layer on the leading edge. Acting as damage-tolerant failsafe layer, negligible ∼0.04% extra weight of the FFND could increase the blade’s base erosion resistance by a factor of 60±20 compared to plain GF, expanding the repair window, reducing costs, and enhancing reliability.

Sand-Laden Wind Erosion Pair Experimental Analysis of Aerodynamic Performance of the Wind Turbine Blades

In the Inner Mongolia region, sand and dust storms are prevalent throughout the year, with sand erosion having a particularly significant impact on the performance of wind turbine blades. To enhance the performance stability of wind turbines and reduce operation and maintenance costs, this study delves into the specific impact of sand-laden wind erosion on the aerodynamic performance of scaled-down wooden wind turbine blades. The experiment conducts vehicle-mounted tests on scaled models of 1.5 MW wind turbine blades that have been eroded by wind-sand flows from different zones, analyzing the changes in aerodynamic performance of wind turbines caused by the erosion. The results indicate that with an increase in the angle of installation, both the overall power output and the wind energy utilization coefficient of the wind turbines show a declining trend. The power outputs of both the partially eroded group and the fully eroded group are unable to reach the rated power level of 100 W. Compared to the uneroded group, the leading-edge eroded group demonstrated higher power output and wind energy utilization coefficients across most wind speed ranges. This finding verifies the possibility that the drag-reducing effect caused by pits from leading-edge erosion has a positive impact on the aerodynamic performance of the blades. It also provides a new research perspective and strong evidence for the study of erosion effects on wind turbine blades and the optimization of their aerodynamic performance.

Characterisation of Polyurethane-urea as Leading-Edge Erosion Resistant Materials of Wind Turbine Blades

Surrounded by oceans, building offshore wind turbines is a great strategy for archipelago countries, like Indonesia, to harvest renewable energy from wind. However, because of high rainfall rate, water droplet erosion on wind turbine blades is inevitably to be one of the most challenging problems. It causes decreasing produced energy and increasing cost of maintenance and repairment. A novel coating material which has better mechanical properties is therefore required. As a preliminary step, this work aims to characterise thermal and mechanical properties of soft and hard polyurethane-urea (PUU). In this work, the materials are soft PUU30 which has a hardness of 30 shore A, and hard PUU95 which has a hardness of 95 shore A. Thermal properties are characterised by Differential Scanning Calorimetry (DSC), while mechanical properties are investigated by tensile test at various strain rates. The results show that PUU95 has a higher strain rate dependence on modulus, tensile strength, and strain at break, which need to be considered for application regarding the range of wind speeds.

Impact of meteorological data factors and material characterization method on the predictions of leading edge erosion of wind turbine blades

Leading edge erosion of wind turbine blades is a major contributor to wind farm energy yield losses and maintenance costs. Presented is a multidisciplinary framework for predicting rain erosion lifetimes of wind turbine blades. Key aim is assessing the sensitivity of lifetime predictions to: modeling aspects (material erosion model, blade aerodynamics), input data and/or their preprocessing (joint frequency distribution of wind speed and droplet size based on synchronous site-specific measurements versus frequency distribution generated with partly site-agnostic modeling standards, wind speed records of nacelle anemometer or extrapolated at hub height from met masts), and environmental conditions (UV weathering). The analyses consider a Northwest England onshore site where a utility-scale turbine is operational, focus on a reference 5 MW turbine assumed operational at the site, and use a typical leading edge coating material. It is found that the largest variations in erosion lifetime predictions are due to material erosion model (based on rain erosion test data or fundamental material properties) and wind and rain model (measurement-based joint wind speed and droplet size distribution or standard-based modeled distribution). The use of joint wind and rain distribution also enables identifying wind/rain states with highest erosion potential, knowledge paramount to deploying erosion-safe turbine control.