Blade Erosion Research Articles

Experimental and numerical study of fogging cooling performance through a cylindrical duct for a micro gas turbine

Fogging cooling is one of the most effective methods for cooling gas turbine inlet air in hot areas. Most of the previous studies focused only on the influence of the fogging cooling effect on the gas turbine performance. Nevertheless, due to the limited space available for installing a system, the fogging system requires special attention, notably in micro gas turbines, to avoid the thermal stress and blade erosion risks at a compressor intake. Hence, in the current paper, the performance of the fogging cooling system for micro gas turbines has been investigated experimentally and numerically to enhance the cooling efficiency, temperature stability and accomplish complete droplets evaporation. An experimental setup has been designed and installed to study the fogging cooling effect through a cylindrical duct. Eulerian-Lagrangian CFD model was also adopted to simulate the trajectories of the injected droplets and to predict the evaporation cooling process through the spray duct. The CFD model was validated with the current experiments, and there is good agreement between the experimental data and simulation results with an average deviation of less than 6.4%. The droplets' size and injected mass flow were measured at different nozzles orifice diameters and injection pressures to select the appropriate spray nozzles at various test conditions. The fogging performance has been tested under various operating conditions, including nozzle arrangement and flow directions, to identify the crucial factors for obtaining fully saturated air and stable temperature from the spray duct. The results reveal that employing a single nozzle to achieve full saturation is ineffective. On the other hand, increasing the number of nozzles with the same input water flow rate improves droplets distribution across the duct and enhances the evaporation rate. It was found that the temperature drop can be reduced by 1.5 °C due to dividing the required water mass flow on four nozzles instead of one. Furthermore, it was observed that the cooling performance of the counter-current flow case could be improved by 3.4% compared to the co-flow one with a high uniform temperature profile through the duct. Finally, a counter-current spray design with four nozzles is proposed for micro gas turbines since it meets the design constraints best compared to other operating scenarios.

Study on sediment erosion of high head Francis turbine runner in Minjiang River basin

The Wenchuan earthquake greatly reduced the forest water conservation capacity along the banks of Minjiang River. With the intensified soil erosion and the rapid increasing sediment transport, the sediment erosion of hydraulic turbines running on the river has become more and more serious, especially of high head Francis turbines. In this study, the k-ε multiphase flow turbulence model was used to calculate the sediment-water flow of a high head Francis turbine with long and short blades in Minjiang River. The distribution pattern of sediment concentration (sediment volume fraction) on the blade surface shows that the sediment particles mainly gather on the outlet edge at 10% of the blade height on the suction surface of the long blade, while the sediment concentration on the surface of the short blade is small. The erosion of the 0Cr13Ni5Mo runner blade was tested by the flow around erosion method, and the erosion amount on the blade surface in the severe erosion area was obtained. Based on the test data of erosion and the numerical calculation results of sediment flow, a formula to calculate the sediment erosion rate of flow passage components with 0Cr13Ni5Mo material was given for turbines operating in Minjiang River. By using this formula, the sediment erosion of flow passage components in hydraulic turbines with 0Cr13Ni5Mo or similar materials operating in Minjiang River can be predicted.

The Springer Model for Lifetime Prediction of Wind Turbine Blade Leading Edge Protection Systems: A Review and Sensitivity Study.

The wind energy sector is growing rapidly. Wind turbines are increasing in size, leading to higher tip velocities. The leading edges of the blades interact with rain droplets, causing erosion damage over time. In order to mitigate the erosion, coating materials are required to protect the blades. To predict the fatigue lifetime of coated substrates, the Springer model is often used. The current work summarizes the research performed using this model in the wind energy sector and studies the sensitivity of the model to its input parameters. It is shown that the Springer model highly depends on the Poisson ratio, the strength values of the coating and the empirically fitted constant. The assumptions made in the Springer model are not physically representative, and we reasoned that more modern methods are required to accurately predict coating lifetimes. The proposed framework is split into three parts—(1) a contact pressure model, (2) a coating stress model and (3) a fatigue strength model—which overall is sufficient to capture the underlying physics during rain erosion of wind turbine blades. Possible improvements to each of the individual aspects of the framework are proposed.

Effect of drop‐size parameterization and rain amount on blade‐lifetime calculations considering leading‐edge erosion

AbstractLeading‐edge erosion (LEE) of wind turbine blades is caused by the impact of particles, for example, raindrops, and leads to a loss in the power production and high maintenance cost. Investigations have shown that a reduction in tip speed, so‐called erosion‐safe mode, increases the blade lifetime but the influence of different drop‐size parameterizations and rain amounts on the blade lifetime is unclear. This study compares blade lifetime calculations using two different drop‐size parameterizations, which both describe a characteristic drop size of a rain measurement. Furthermore, changes in blade lifetime in case rain amount is increased or decreased are investigated as well as the effect of different wind shear exponents. The blade‐lifetime calculations are based on a kinetic‐energy model and an accumulated rain model. The results show that a drop‐size parameterization based on rain rate leads to 44 times longer blade lifetime compared with a parameterization using in situ drop‐size measurements. This large difference is probably due to the underestimation of large drops of the first mentioned parameterization. A change in rain amount of about ±17 % results only in a marginal change in blade lifetime. For both cases and models, an extension of blade lifetime was calculated when reducing the tip speed during specific rain events. The change of wind shear exponents caused as well a considerable effect on the lifetime prediction. Overall, blade lifetime is primary depending on the chosen model, where the kinetic‐energy model is highly sensitive to the drop‐size parameterization.

Numerical simulation of the influence of mixed sand on erosion characteristics of centrifugal pump

PurposeThe purpose of the paper is to predict the erosion rate of the components of centrifugal pump under certain operating condition to identify the maximum erosion area and to discuss the factors affecting them. This helps to optimize design and estimate service life.Design/methodology/approachIn the paper, the Eulerian–Lagrangian approach method coupled with the erosion model to investigate the mixed sand characteristics on erosion characteristics of centrifugal pump flow-through wall. The hydraulic performance and wear characteristics experiment of the pump is used to verify the accuracy of the numerical simulation.FindingsThe blade erosion area mainly occurs near the blade inlet and the trailing edge of the pressure surface, the main erosion area of the impeller back shroud is near the outlet of the flow passage and the main erosion area of the volute is near the tongue and the I section. With the change of the average diameter and density of sand particles, the average erosion rate on different flow-through walls is positively correlated with the average mass concentration to a certain extent. However, for different sand shape factors, there is little correlation between the average erosion rate and the average mass concentration. In addition, compared with other erosion areas, the increase of average sand particle diameter and density has the greatest impact on the total erosion rate of blade pressure surface, while the shape of sand particles has a greater impact on the total erosion rate of each flow-through wall of centrifugal pump.Originality/valueIn this work, according to the characteristics of the mixed distribution of different sand diameters in the Yellow River Basin, the erosion characteristics of centrifugal pumps used in the Yellow River Basin are studied. The numerical calculation method for predicting the wall erosion of centrifugal pump is established and compared with the experimental results. The results can provide reference for optimizing design and increasing service life.

Performance Analysis of Eroded Compressor Stage

Erosion of compressor blades due to operation in dusty environments is a serious problem for the manufacturers and users of gas turbine engines, because of significant degradations in performance. This study has been devoted to estimating the change of performance parameters of an axial compressor stage due to erosive deterioration. The influence of erosion considered as consequences of a reduction of rotor blade airfoils, and an increase of tip clearance. The results of this study obtained using the CFD code “NUMECA Fine/Turbo”. This CFD code is a steady, quasi-three-dimensional Reynolds Averaged Navier-Stokes (RANS) solver. A Spalart-Allmaras turbulence model is used. The compressor stage parameters presented for three rotational speeds. Proposed a new approach to consider the changes of geometric parameters of blades due to erosion. Presented an analysis of the effect of erosion and its individual consequences on the pressure ratio, isentropic efficiency and stability margin of the stage. The obtained results verified using an existing experimental data.

Water-droplet erosion behavior of high-velocity oxygen-fuel-sprayed coatings for steam turbine blades

Abstract The water-droplet erosion of low-pressure steam turbine blades under wet steam environments can alter the vibration characteristics of the blade, and lead to its premature failure. Using high-velocity oxygen-fuel (HVOF) sprayed water-droplet erosion resistant coating is beneficial in preventing the erosion failure, while the erosion behavior of such coatings is still not revealed so far. Here, we examined the water-droplet erosion resistance of Cr3C2–25NiCr and WC–10Co–4Cr HVOF sprayed coatings using a pulsed water jet device with different impingement angles. Combined with microscopic characterization, indentation, and adhesion tests, we found that: (1) both of the coatings exhibited a similar three-stage erosion behavior, from the formation of discrete erosion surface cavities and continuous grooves to the broadening and deepening of the groove, (2) the erosion rate accelerates with the increasing impingement angle of the water jet; besides, the impingement angle had a nonlinear effect on the cumulative mass loss, and 30° sample exhibited the smallest mass loss per unit area (3) an improvement in the interfacial adhesion strength, fracture toughness, and hardness of the coating enhanced the water-droplet erosion resistance. These results provide guidance pertaining to the engineering application of water erosion protective coatings on steam turbine blades.

Study on water erosion and preventive measures of last stage blade of steam turbine

In the background of carbon peak and carbon neutralization, most thermal power plants are more involved in peak regulation and even in-depth peak regulation in order to absorb new energy such as wind power and Solar power. When the turbine is running under low load, the exhaust pressure decreases, which leads to the increase of exhaust humidity. More and more turbine blades have water erosion. The erosion of the last stage blades will worsen the dynamic performance of the turbine, increase the risk of the last stage blade fracture, and threaten the safe operation of the turbine. This paper studies the mechanism of the last stage blade erosion of steam turbine, and analyzes the main factors which influence the erosion with examples. Combined with the mechanism of water erosion, the relevant preventive measures are made for reference of power supply plant.

Impact Resistance and Properties of (Cr,Al,Si)N Coatings Deposited by Gas Flow Sputtering with Pulsed DC Supply

To increase the erosion and corrosion resistance of compressor blades, hard (Cr,Al,Si)N coatings are used. Physical vapor deposition (PVD) is a well‐known method for the deposition of nitride hard coatings. The application of pulse technique in power supply of conventional PVD technologies like magnetron sputtering shows a great potential for increasing the durability and lifetime of different tools and components. However, one disadvantage of conventional PVD is the line‐of‐sight characteristic. This is eliminated by means of the convection‐driven transport mechanism in high speed physical vapor deposition (HS‐PVD) technology, based on gas flow sputtering. Herein, the influence of gas flow sputtering with bipolar pulsed direct current (DC) power supply on coating properties and impact resistance of (Cr,Al,Si)N/substrate compound is investigated. Thereby, (Cr,Al,Si)N coatings are deposited onto X3CrNiMo13‐4 by HS‐PVD using continuous DC and bipolar pulsed DC supply. Nanoindentation analyses show an increase in indentation hardness using pulsed DC compared with continuous DC. Moreover, the lowest imprint depth and degree of cohesive and adhesive failures are observed in this case. These release a high potential for pulsed power supply in HS‐PVD, resulting in denser morphology, higher hardness and impact resistance compared with DC.

Effects of particle erosion on the submersible pump in an ultra-high voltage transformer

The submersible pump is the only power component of the ultra-high voltage (UHV) transformer which plays a key role in the cooling effect of the transformer. Metal particles produced by erosion and wear of submersible pump blades and walls can pose a serious threat to the transformer. Therefore, it is necessary to analyze the wear law of submersible pumps. In this study, the particle erosion of the submersible pump for solid–liquid flow is investigated numerically. Results show that the main erosion area occurs on the upper edge of the blades, and as the size and concentration of metal particles increase, the average erosion rate of each component also increases. The erosion patterns of blades and volute show asymmetry under the same conditions, the average erosion rate of each blade is related to its initial position, and the most severely eroded area of the volute occurs when the curvature angle of the volute is about 120°. When the particle size reaches 350 μm and the volume fraction is 0.4%, the average erosion rate of the blade reaches its peak. The outcome of this study can provide valuable reference data for the design of impurity monitoring of submersible pumps and proposing fault warning schemes.

Damage evolution behavior of TiN/Ti multilayer coatings under high-speed impact conditions

The erosion of compressor blades by solid particles brings huge safety hazards to aero engines. The application of erosion-resistant hard coating has become a good solution to protect titanium alloy blades. In this work, TiN monolayer and TiN/Ti multilayer coatings were prepared on Ti-6Al-4V alloy using a magnetic filtered cathode vacuum arc system (FCVA) and a metal vapor vacuum arc (MEVVA) ion implantation device. The mechanical properties of the coatings were evaluated by nanoindentation and scratch tests. The damage evolution behavior and mechanism of TiN monolayer and TiN/Ti multilayer coatings are studied by single-particle impact test and finite element simulation. The results show that the fracture toughness of TiN monolayer coating is lower than that of TiN/Ti multilayer coating; TiN/Ti multilayer coatings exhibit good erosion resistance. The main reason lies in that the Ti layer dissipates part of impact energy by plastic deformation and reduces the tensile stress. The interfaces in the multilayer coating inhibited the propagation of cracks.

Simulation Study on the Effect of Flue Gas on Flow Field and Rotor Stress in Gas Turbines

A flue gas turbine is the main energy recovery equipment in a heavy oil catalytic cracking unit. Blade erosion and fracture are the main reasons for gas turbine failure. In this study, the characteristics of the flow field and rotor stress in the gas turbine under different fume volumes are simulated and analyzed by simulation software (ANSYS). The influences of fume volume on the high-temperature fume flow field, temperature, velocity, catalyst particle movement rotor stress in the gas turbine, as well as the influence law of flue gas flow on temperature gradient, pressure gradient, velocity distribution, and the main position of blade erosion were studied. The stress distribution and maximum stress position of the impeller were also determined. It was found that the variation trends of the pressure gradient in the calculation domain of the gas turbine under different fume volumes are similar. The pressure on the working face of the rotor blade decreases gradually along the flow direction of the high-temperature fume. The highest pressure appears near the sharp corner with the large radius of the front edge of the rotor blade. The variation of the fume flow rate has little influence on the temperature field of the entire machine. The erosion wear of the rotor blade mainly occurs in the leading edge and tail. The maximum stress point of the blade is located at the large fillet of the first pair of tenon teeth. The maximum stress point of the disc is located at the large fillet of the third pair of tenon teeth. It is believed that these research results have reference help for analyzing the typical failure causes of flue gas turbine, optimizing the actual operating conditions and the reconstruction design of flue gas turbine.

Experimental and Numerical Study of Erosion Wear of Fan Blades in Microgrid

As one of the most important components of wind turbines, the fan blade is prone to erosion being exposed to multiphase flow environment, which affects the operation efficiency of wind turbines. In order to reduce the loss caused by the erosion of the fan blade, the erosion rate tests of the fan blade were carried out in this paper. The relevant function values of the simulation mathematical model were calculated from the test results, which were verified by a simplified two-dimensional case. Additionly, a numerical simulation of the three-dimensional full-size gas-solid two-phase flow around the fan blade was conducted, and then the variations of a single blade erosion rate with different wind speeds, sand sizes and impact angles were studied. The results showed that the sample erosion rate was increased with wind speeds and impact angles. The blade tip region was the most susceptible area to erosion, of which protection should be strengthened.

A probabilistic rainfall model to estimate the leading-edge lifetime of wind turbine blade coating system

Rain-induced leading-edge erosion of wind turbine blades is associated with high repair and maintenance costs. For efficient operation and maintenance, erosion models are required that provide estimates of blade coating lifetime at a real scale. In this study, a statistical rainfall model is established that describes probabilistic distributions of rain parameters that are critical for site-specific leading-edge erosion assessment. A new droplet size distribution (DSD) is determined based on two years’ onshore rainfall data of an inland site in the Netherlands and the obtained DSD is compared with those from the literature. Joint probability distribution functions of rain intensities and droplet sizes are also established for this site as well as for a coastal site in the Netherlands. Then, the application of the proposed model is presented for a 5 MW wind turbine, where the model is combined with wind statistics along with an analytical surface fatigue model that describes lab-scale coating degradation. The expected lifetime of the blade coating is found three to four times less for the wind turbine operating at the coastal site than for the inland site - primarily due to rainfall at higher wind speeds. Further, the robustness of the proposed model is found consistent with varying data periods used for the analyses.

Assessment of a Wind Turbine Blade Erosion Lifetime Prediction Model with Industrial Protection Materials and Testing Methods

Leading edge protection (LEP) coating systems are applied to protect turbine blade edges from rain erosion. The performance of a LEP system is assessed in an accelerated rain erosion test (RET) as a metric for industrial application, but these tests are expensive. Modelling methods are available to predict erosion, based on fundamental material properties, but there is a lack of validation. The Springer model (1976) is analysed in this work to assess it as a tool for using material fundamental properties to predict the time to failure in a rain erosion test. It has been applied, referenced and industry validated with important partial considerations. The method has been applied successfully for erosion damage by wear performance prediction when combined with prior material data from rain erosion test (RET), instead of obtaining it directly from fundamental properties measured separately as Springer proposed. The method also offers accurate predictions when coupled with modified numerical parameters obtained from experimental RET testing data. This research aims to understand the differences between the experimental data used by Springer and the current industry approach to rain erosion testing, and to determine how it may introduce inaccuracies into lifetime predictions of current LEP systems, since they are very different to those tested in the historic modelling validation. In this work, a review of the modelling is presented, allowing for the understanding of key issues of its computational implementation and the required experimental material characterisation. Modelling results are discussed for different original application issues and industry-related LEP configuration cases, offering the reader to interpret the limits of the performance prediction when considering the variation in material fundamental properties involved.

Cavitation Analysis of Kaplan-Series Propeller: Effect of Pitch Ratio and nProp using CFD

Cavitation is defined as a phenomenon or action of the traveling bubbles that pass through the hydrofoil in which the reduction of pressure below the liquid’s vapor pressure leads to the formation of small vapor bubbles (or cavities) caused by the dynamic pressure of the propeller blades. It caused some effects on the propeller of the ship i.e. it can greatly reduce a ship’s propelling efficiency, damaged propeller material or blade erosion, vibration, and disturbance noises. Cavitation can be minimized by proper attention regarding the design of the propellers and variation of propeller variables parameters. For that reason, this research conducts a cavitation analysis on the Kaplan-Series of the CPP by varying P/D b =0.4, P/D b =0.6, and P/D b =0.8; also the rotational speed of the propeller (nProp) i.e. 125 rpm, 175 rpm and, 225 rpm. The numerical analysis was made based on the Computational Fluid Dynamic Method (CFD) to calculate the pressure ratio (ΔP) and percentages of the cavitation area (R s ) due to a configuration of the propellers parameter. The simulation consists of the 3 steps; pre-processor, solver manager, and post-processor. The result shows that the value of the pressure ratio increased significantly at the higher P/D b and nProp. Also, the variation of P/D b and nProp has a significant effect on the development of R s (%) at the higher P/D b and nProp.

Cavitation and Induced Excitation Force of Ice-Class Propeller Blocked by Ice

The presence of broken ice in the flow field around a propeller causes severe blade erosion, shafting, and hull vibration. This study investigates the performance of the propeller of a ship sailing in the polar regions under the propeller–ice non-contact condition. To this end, we construct a test platform for the propeller-induced excitation force due to ice blockage in a large circulating water channel. The hydrodynamic load of the propeller, and the cavitation and propeller-induced fluctuating pressure, were measured and observed by varying the cavitation number and ice–propeller axial distance under atmospheric pressure and decompression conditions. The results show that the fluctuation range of the blade load increases with a decrease in cavitation number and ice–propeller axial distance. The decrease in the cavitation number leads to broadband characteristics in the frequency-domain curves of the propeller thrust coefficient and blade-bearing force. Under the combined effects of ice blockage and proximity, propeller suction, the circumfluence zone around the ice, and the Pirouette effect, propeller–hull vortex cavitation is generated between the ice and propeller. The decrease in cavitation number leads to a sharp increase in the amplitude of the high-order frequency of the propeller-induced fluctuating pressure.

Effect of sodium hydroxide solution concentration on liquid entrainment in a steam boiler

Liquid entrainment or carryover is a phenomenon that liquid droplets are carried out from a boiler or steam drum during steam generation. The droplets may convey some dissolved solids and cause damage to steam equipment such as scaling deposits in valves and steam piping and erosion of turbine blades. The appearance of dissolved solids in boiler water mainly comes from the internal water treatment process by dosing some chemical substances into the boiler in order to prevent corrosion and scale formation. Trisodium phosphate (Na3PO4) is one of chemical substances commonly added during boiler operation to control the pH of boiler water. However, it can cause the occurrence of sodium hydroxide (NaOH) solution which results in the increase of total dissolved solid (TDS) concentration in boiler water. Therefore, this study is aimed to develop a test section in order to investigate the parameters affected by liquid entrainment in the boiler. The experiment is performed in ambient conditions under an air-water system. Three variable factors are taken into consideration, including the concentration of NaOH solution, the height of the water level in the test tank, and the gas superficial velocity which represents the flow velocity of steam during steam generation. The results show that the increase of the gas superficial velocity and the water level height in the tank resulted in the enhancement of the entrainment rate. The increase of the water level height played an important role on the liquid entrainment. The increase of NaOH concentration directly impacted the existing film bubbles and the longer stability of foam bubbles at the water surface which resulted in a higher entrainment rate. Therefore, TDS control was one of the most important factors which could be incorporated with the appropriate height of the water level and the consistency rate of steam generation in order to minimize the liquid entrainment.

Influence of blade corrosion on aerodynamic characteristics of a gas turbine

Gas turbine blades, such as nozzle guide vanes and rotor blades, corrode over time and thus deteriorate, becoming thinner and shorter. In the present study, influences of blade corrosion on aerodynamic characteristics were examined numerically. The purposes of this study were to understand the influence of the blade deterioration on aerodynamic characteristics quantitatively under the same conditions with that in a power plant, and to clarify how to detect severe deterioration during gas turbine operation. Blade geometries before and after use were obtained from a real gas turbine using a 3-D scanner. Two parametric CFD simulations were carried out: one simulation was conducted with various turbine expansion ratios and a fixed turbine inlet temperature, and the other was conducted with various inlet temperatures and a fixed expansion ratio. According to the results of both simulations, a change in the throat area of the first-stage nozzle affected the aerodynamic characteristics significantly. The expansion ratio was found to be more useful. Numerical results obtained under actual operating conditions confirmed that the difference in the expansion ratio was about 3% between the new and old blades in the examined gas turbine.

Rain Erosion Load and Its Effect on Leading-Edge Lifetime and Potential of Erosion-Safe Mode at Wind Turbines in the North Sea and Baltic Sea

Leading-edge erosion at wind turbine blades cause a loss in profit for wind farm owners, in particular offshore. The characterization of the rain erosion environmental load at wind turbine blades is based on the long-term rain rate and wind speed observations at 10-minute resolutions at coastal stations around the North Sea, Baltic Sea, and inland. It is assumed that an IEA Wind 15 MW turbine is installed at each station. The leading-edge lifetime is found to increase from the South to the North along the German and Danish North Sea coastline from 1.4 to 2.8 years. In the Danish and German Baltic Sea, the lifetime in the West is shorter (~2 years) than further East (~3 to 4 years). It is recommended to use a time series of 10 years or longer because shorter time series most likely will cause an overestimation of the lifetime. The loss in profit due to leading-edge erosion can potentially be reduced by ~70% using the erosion-safe mode, i.e., reduce the tip speed during heavy rain events, to reduce blade erosion, aerodynamic loss, repair costs, and downtime during repair. The aerodynamic loss for the 18 stations is on average 0.46% of the annual energy production.