Gas Turbine Blades Research Articles

Enhancement of Digital Radiographic Images for Gas Turbine Blades Based on Simple Scattering Model

Enhancement of Digital Radiographic Images for Gas Turbine Blades Based on Simple Scattering Model

Heat transfer enhancement in array of impinging jets by a row of pin-fins on dead fluid zone

BackgroundImpinging jet is one of the most effective practice techniques used in many industrial applications and thermal treatments which is one of its main applications in gas turbine blades. Therefore, in the past decades, many studies investigated the effects of impinging jets on the flow and thermal characteristics. In the present work, a row of pins has been employed to enhance the heat transfer rate by disturbing the dead fluid zone between the impinging jets. MethodsA row of impinging jets with 10 mm diameter has been considered for cooling a heated flat surface. The pin fins with 2.0 mm diameter and 1.0 mm height were exactly placed between the jets. A silicon heater supplied the uniform heat flux of 2500 W/m2 on the target surface. The temperature of the target plate was exactly measured by an IR(infrared) camera. The effects of pin-fins in the middle distance of the jets on velocity distribution and thermal field have been carried out for two jets Reynolds numbers of 10,000 and15000 and two jet-to-surface spacing (H/D = 1.0, 2.0). Significant findingsThe present experimental and numerical results confirm that the dead fluid zone between jets can efficiently disappear by applying a row of pins at the middle distance of the jets. Results showed that at H/D = 1.0, by the presence of a row of pins in the dead fluid zone, the averaged Nusselt number on the dead fluid zone increases from 29.47 to 37.95 to 44.43 and 43.73 for Reynolds numbers of 10,000 and 15,000 respectively.

A real options model for remanufacturing facility installation decisions

In this paper, we consider a company that can satisfy customers’ demands for a product using two alternative sourcing strategies: (1) purchasing new products from outside sources (such as an international partner) or (2) collecting cores (used products) and remanufacturing them. As the purchase price from outside sources is subject to noticeable volatility (e.g., exchange rate volatility, raw material price volatility, etc.), we assume it is characterized by a geometric Brownian motion (gBm) with positive drift and volatility. Assuming the quality of the new and the remanufactured products are similar, and the customer’s demand is within the capacity of the remanufacturing facility, we show how a company utilizing the first alternative sourcing can optimally switch to the second alternative sourcing. We consider the profit maximization criterion and utilize the theory of real options to determine the optimal threshold of the outside purchasing price and the corresponding expected time to install the remanufacturing facility. We present a comprehensive numerical example of installing a Laser-Directed Energy Deposition (L-DED) system for remanufacturing gas turbine blades to demonstrate the model’s key features. We also perform analytical and numerical sensitivity analysis to examine how the purchasing price uncertainty and other factors influence the aforementioned threshold. Managerial insights and policy implications are also provided.

Method of Suppressing Solidification Cracking by Laser Surface Melting and Epitaxial Growth Behavior for Directionally Solidified 247LC Superalloy

In this study, the relationship between solidification cracking and epitaxial growth behavior with the high-speed laser surface melting of a directionally solidified 247LC superalloys was fundamentally and metallurgically investigated, to develop a successful welding procedure for the next generation of gas turbine blades. Under typical laser surface melting conditions (scan speed: 50 mm/s, heat input: 40 J/mm), severe solidification cracking phenomena occurs. The key metallurgical factors of solidification cracking have been identified as solidification segregation-assisted pipeline diffusion behavior at the solidification grain boundary, and in the randomly formed polycrystalline melting zone microstructure. In addition, under extremely low heat input and high-speed laser beam scan conditions (scan speed: 1000 mm/s, heat input: 2 J/mm), an effective surface melting zone can be obtained within a single directionally solidified grain under a relatively high-energy beam density (65 J/mm2) using the characteristics of single-mode fiber lasers. Results reveal that the laser melting zone successfully shows a 99.9% epitaxial growth achievement ratio. Because of the superior epitaxial growth ratio within the laser surface melting zone, and the rapid solidification phenomena, formation of a solidification grain boundary and solidification segregation-assisted pipeline diffusion behavior can be suppressed. Finally, a solidification crack-free laser melting zone can thus be achieved.

Numerical analysis on the impact of axial grooves on vortex cooling behavior in gas turbine blade's leading edge

In this article, a novel design for the vortex chamber with the axial grooves used for cooling the turbine blades leading edge is presented. The vortex chamber has nine tangential inlets that make a vortex in the chamber and an axial groove located along with the chamber. In addition to enhance the flow turbulence, these grooves cause an increasing heat transfer by cutting the thermal boundary layer and reformation. For this purpose, a 3D model based on Reynolds-averaged Navier–Stokes (RANS) equation was simulated in Ansys Fluent software. After comparing different turbulent models and experimental data, results showed Reynolds stress model (RSM) mode presents the best accuracy. Grooves with different sizes, positions, and numbers are used to investigate the vortex structure and the heat transfer mechanism. This study revealed that a chamber with grooves has a higher heat transfer in comparison with chambers without grooves. The best performance is achieved in a chamber with three grooves, where the average Nusselt number is increased by more than 4%. In this method, pressure difference between the inlet and outlet in the chamber with and without grooves are not very significant, and the highest friction factor happened in the case with three grooves.

Bayesian optimization with active learning of design constraints using an entropy-based approach

The design of alloys for use in gas turbine engine blades is a complex task that involves balancing multiple objectives and constraints. Candidate alloys must be ductile at room temperature and retain their yield strength at high temperatures, as well as possess low density, high thermal conductivity, narrow solidification range, high solidus temperature, and a small linear thermal expansion coefficient. Traditional Integrated Computational Materials Engineering (ICME) methods are not sufficient for exploring combinatorially-vast alloy design spaces, optimizing for multiple objectives, nor ensuring that multiple constraints are met. In this work, we propose an approach for solving a constrained multi-objective materials design problem over a large composition space, specifically focusing on the Mo-Nb-Ti-V-W system as a representative Multi-Principal Element Alloy (MPEA) for potential use in next-generation gas turbine blades. Our approach is able to learn and adapt to unknown constraints in the design space, making decisions about the best course of action at each stage of the process. As a result, we identify 21 Pareto-optimal alloys that satisfy all constraints. Our proposed framework is significantly more efficient and faster than a brute force approach.

Skin Cooling of Turbine Airfoils by Single-Wall Effusion—Part II: Computational Fluid Dynamics Validation and Preliminary Design Optimization on a Micro-Turbine Vane

Abstract A reduced-order model (ROM) is developed to capture conjugate aero-thermal physics of effusion cooling in an entire micro-turbine vane/blade. The model considers a single-wall effusion scheme with internal boundary layer flow between the shell and an inner core. Coolant is supplied inside the leading edge and spread to both suction and pressure sides. The compound effect of multiple effusion rows is used to calculate spanwise-averaged cooling effectiveness. Metal temperature is modeled both in streamwise and shell thickness directions. The development of the model and a number of numerical/experimental validation cases are presented in detail in Part I. Part II of the work is geared toward the application of this method to skin cooling of a turbine airfoil by single-wall effusion. The reduced-order model, with all its subroutines functioning together, is validated against a higher fidelity 3D Reynolds-averaged Navier–Stokes (RANS) computational fluid dynamics (CFD) solution. It is shown that the model can predict the main features of the combined internal and effusion cooling in gas-turbine blades at a computational cost which is 105 times lower than RANS (∼1 month with 700M elements and 24 modern Xeon Cores) on a whole turbine vane/blade. Due to this great advantage in speed, a design optimization is then accomplished toward minimizing coolant flow rate while keeping thermal gradients and temperature of the solid within acceptable levels. Implementing this scheme on a typical micro-gas-turbine vane, optimal distributions of the effusion-hole pitch and diameter are found within a given set of constraints. This preliminary design tool potentially enables wider and more efficient usage of effusion cooling in turbine vanes/blades.

Deformation Prediction Theory of Thermal Barrier Coatings near Cooling Holes under Thermal Cycling.

Thermal barrier coating (TBC) systems are widely adopted in gas turbine blades to improve the thermal efficiency of gas turbine engines. However, TBC failure will happen due to the thermal stress between the different layers of the TBC systems. The traditional two-layer theoretical model only considers TGO (thermally grown oxide) and a substrate in the inner cooling hole with the surface uncoated, which results in poor prediction of the deformations of the TBC systems. It should be mentioned that the effect of TBC is very important because the thickness of TBC is much larger than the TGO thickness. In this study, a new three-layer theoretical model was derived, which is composed of the cylindrical TGO and TBC mounted in the substrate with a circular hole, and the stress and strain of TGO near the cooling hole under the condition of the thermal cycles were calculated. The high temperature characteristics of TGO and the substrate including the high temperature strength and growth ratio were from the experiments. The results show that the strain of the developed three-layer model is irrelevant with increasing number of cycles, which indicates that TBC in the cooling hole significantly inhibits the deformation of TGO near the cooling hole. Therefore, aimed at confirming the feasibility of the three-layer theoretical model, the finite element analysis with coating in the cooling hole and on the surface was carried out with a three-layer axisymmetric model, which proves that the 3-layer theoretical model can predict the deformation trend near the cooling hole.

Optimization Model of the Shell Capsules Geometry for a System for Diagnosing Damage to Gas Turbine Blades in Non-stationary

Scientific research is devoted to the problem of diagnosing damage in the blades of gas turbine engines in non-stationary conditions. The paper proposes a model for a more accurate calculation of the parameters of the crack detection system using a system of capsules, inside of which, under the influence of pressure, there is a substance exhibiting ionizing properties. In the study, the relations for determining the uneven pressure due to the action of centrifugal tensile forces during the rotation of the turbine blade are obtained. The relations for calculating the minimum required diameter of the capsule to ensure the rupture of the capsule when cracks are opened for the effective operation of the crack detection system are obtained. Calculations of the pressure inside the capsule and the geometry of the capsule at different speeds of rotation of the turbine blade are carried out. An estimate of the error in calculating the pressure inside the capsule is given in the case of not taking into account the action of centrifugal forces. The obtained dependences will significantly optimize the system for detecting damage to turbine blades, and increase the efficiency and safety of the operation of gas turbine engines.

Numerical Investigation of Pressure Loss in a Rectangular Channel with a Sharp 180-Degree Turn: Influence of Design Variables and Geometric Shapes

Gas turbine blade cooling typically uses a cooling air passage with a sharp 180° turn in the midchord area of the airfoil. Its geometric shape and dimensions are strictly constrained within the airfoil to ensure both aerodynamic and cooling performance. These characteristics imply the importance of understanding the relationships between the geometric dimensions and the cooling channel performance. In this study, we validated a numerical method using the commercial software, Ansys Fluent 2021 R2, by predicting a total pressure loss coefficient with less than 6% deviation from the experimental results of Metzger et al. for four different Reynolds numbers. Through parameter studies, the divider tip-to-wall clearance was found to be the most significant parameter influencing the pressure loss. Parameter correlations and predictive models between the design variables and the pressure loss were derived by regression analysis using the R language; the regression model predicted the pressure loss to within 2.29% of the numerical method. As the geometries changed, the response surface and the adjoint solver improved the pressure loss by approximately 20.87% and 25.96%, respectively, at the representative Reynolds number of 24,230; this showed that the adjoint solver was a relatively simple and effective method with minimal geometric changes.

Gas turbine blade fracturing fault diagnosis based on broadband casing vibration

Blade fault is a catastrophic failure of gas turbines. In order to improve the reliability of blade during operation, condition monitoring is one of the effective methods. However, there always exist two problems with blade monitoring: 1) challenges in warning of the occurrence of blade failure in advance and 2) difficulties finding the location after blade failure. In this article, we solve these problems by excavating the characteristics of blade-related signals in broadband casing vibration with advanced signal processing methods and machine learning technology. First, a novel method--Sparse Harmonic Product Spectrum (SHPS)--is proposed to accurately calculate blade passing frequency from gas turbine broadband casing vibration. The SPHS relies on Fourier transform, and its calculation utilizes the physical relationship between fundamental frequency and blade passing frequencies. Combining Vold-Kalman filter with adaptive parameter optimization process (AVKF), the blade-related vibration can be separated from casing vibration even in strong noise. Analysis of simulated casing vibration signal is used to verify the effectiveness and superiority of proposed method. Based on blade-related vibration, we build a gas turbine blade condition model in an unsupervised learning manner. The model can excavate potential blade failures earlier and more accurately than conventional threshold methods. Then, three coefficients are constructed according to the blade-related vibration characteristics to identify the blade fault location in multi-stage system. Moreover, the effectiveness of the proposed blade diagnosis framework is verified using actual industrial gas turbine blade fracturing failure data.

Crystal plasticity analysis of fatigue-creep behavior at cooling holes in single crystal Nickel based gas turbine blade components

We build a crystal plasticity finite element framework to investigate slip localisation and fatigue-creep behaviour at the cooling holes of single crystal Nickel (Ni) based components under cyclic thermomechanical loading. The total slip rate is decomposed into a thermally activated dislocation glide rate which dominates at moderate/low temperatures (T) and/or high stresses, and a climb rate which dominates at high temperatures and increases as inelastic strain accumulates. This formulation captures the monotonic and long-term creep response of Ni alloys in the wide range 20 <T < 1100 °C and indicates that room temperature plasticity during unloading increases the high temperature creep rate during loading (creep dwell), eventually increasing the total slip accumulation per cycle; the effect depends on the way the inelastic strain accumulates upon successive slip reversals. Elastic material anisotropy is shown to modify drastically the stress concentration around holes such that slip tends to localise at locations where the max principal stress, tangent to the hole surface, aligns with stiff crystallographic directions. This highlights the importance of plastic and creep anisotropy and creates new avenues for optimising hole shape to minimise slip activity. Our study brings to light key material-component relationships that concern the wider material science, high temperature and fatigue communities.

Effect of Dimples/Protrusion Concavity on Heat Transfer Performance of Rotating Channel

The continuing increase in gas turbine inlet temperature requires additional heat transfer at the trailing edge. Therefore, a large amount of research has been carried out to find a highly efficient cooling process for gas turbine blades. Pin-fins have been widely used in the trailing edge of gas turbines to enhance heat transfer performance. Pin-fins also strengthen the structure between the inlet and outlet faces of the gas turbine. According to previous research, the flow structure and heat transfer characteristics are influenced by many parameters of the pin-fin array, especially the pin-fin shape, height, diameter as well as layout. In this study, instead of changing the structure of the pin-fin array, the work focused on the design of protrusion/dimple points on the leading and trailing edges. Numerical simulations using the SST (Shear Stress Transport) turbulence model were performed to investigate the effect of dimple/protrusion concavity on flow structure and heat transfer characteristics in a rotating channel with pin-fin array. The pin-fins are arranged staggered to each other. The results show that when changing the dimple/protrusion concavity on the leading and trailing edges combined with the rotation speed, the heat transfer efficiency changes positively.

A comparison of oscillating sweeping jet and steady normal jet in cooling gas turbine leading edge: Numerical analysis

Impinging jets have emerged as a prominent cooling technology in the gas turbine industry. With the addition of fluidic oscillators as heat removal devices, steady-state impinging jets can be converted to sweeping impinging jets, presenting an opportunity to improve the heat transfer performance of current impinging jets by covering a larger cooling surface area on the leading edge of a gas turbine blade. Sweeping jets are self-oscillating devices that operate based on the Coanda effect, making them self-sustaining. In this study, the flow and heat transfer performance of an array of seven steady and sweeping impinging jets were investigated using the unsteady Reynolds-averaged Navier-Stokes turbulent SST k-ω model. The sweeping jet impingement improved the heat removal performance by cooling a larger surface area of the leading edge with a constant heat flux and by improving the overall time-averaged cooling effectiveness. Compared with the steady jet case, the sweeping jet case shows an improvement in heat transfer of 12.2%. Further, the use of fluidic oscillators (sweeping jets) produced a more uniform mass flow rate distribution from all jets compared with a simple jet.

Vibration fatigue behavior and life prediction of directionally solidified superalloy based on the phase transformation theory

Directionally solidified nickel base superalloy DZ125L is the main material that has been widely used to manufacture aviation gas turbine blades and hot-end structural parts. Aeroengine is under vibration load for a long time in the service process, which makes vibration fatigue become one of the main failure modes of aero-engine structures. In this study, vibration fatigue behavior and excitation frequency response curves of DZ125L alloy under different stress levels were investigated through vibration fatigue tests. The fatigue crack initiation and growth mechanism of DZ125L alloy under vibration load is studied based on the results of the vibration fatigue test and finite element simulation. A vibration fatigue life prediction model based on the phase transformation theory is developed. Each parameter has clear physical significance in the model. The comparison between the model prediction results and the test results shows that the theoretical prediction results have reasonable accuracy.

Numerical investigation of forward, lateral, and backward injection of the coolant fluid in various flow characteristics to find the optimum film cooling effectiveness

Film cooling is a major thermal protection method to protect the hot components in aero-engines like modern gas turbine blades. In this article, to find the optimum film cooling effectiveness, a numerical study was conducted in various forward, lateral, and backward injection angles (cross-flow injection angle φ = 0 ° , 45 ° , 90 ° , 135 ° , 180 ° ) and flow characteristics. For validation, the predicted results are compared with available experimental data and are shown to be in good agreement. It is found that by increasing the density ratio (DR), the film cooling effectiveness of the holes with φ = 0 ° and φ = 90 ° increases, while the film cooling effectiveness with φ = 45 ° , 135 ° , and 180 ° have a slight reduction. In addition, by increasing the injection angle from φ = 0 ° to φ = 180 ° , the film cooling effectiveness increases and has a maximum of φ = 90 ° . One of the most important results is optimum effectiveness, with φ = 90 ° (lateral injection) and velocity ratio (VR) = 0.5, DR = 1.79, and Tu = 2%.

Effect of Cr/Ti/Al Elements on High Temperature Oxidation Behavior of a Ni-Based Superalloy with Thermal Exposure

High-temperature oxidation of a Ni-based superalloy was analyzed with samples taken from gas turbine blades, where the samples were heat-treated and thermally exposed. The effect of Cr/Ti/Al elements in the alloy on high temperature oxidation was investigated using an optical microscope, SEM/EDS, and TEM. A high-Cr/high-Ti oxide layer was formed on the blade surface under the heat-treated state considered to be the initial stage of high-temperature oxidation. In addition, a PFZ (γ’ precipitate free zone) accompanied by Cr carbide of Cr23C6 and high Cr-Co phase as a kind of TCP precipitation was formed under the surface layer. Pits of several µm depth containing high-Al content oxide was observed at the boundary between the oxide layer and PFZ. However, high temperature oxidation formed on the thermally exposed blade surface consisted of the following steps: ① Ti-oxide formation in the center of the oxide layer, ② Cr-oxide formation surrounding the inner oxide layer, and ③ Al-oxide formation in the pits directly under the Cr oxide layer. It is estimated that the Cr content of Ni-based superalloys improves the oxidation resistance of the alloy by forming dense oxide layer, but produced the σ or µ phase of TCP precipitation with the high-Cr component resulting in material brittleness.

A multiaxial probabilistic fatigue life prediction method for nickel‐based single crystal turbine blade considering mean stress correction

AbstractGas turbine blades normally operate under high‐temperatures, extreme pressure, and high‐speed conditions, which leads to complex failure mechanisms and difficulties in fatigue life assessment. Moreover, due to the randomness of manufacturing errors, working loads, and material properties, the low cycle fatigue (LCF) life normally presents unavoidable stochastic behavior. Therefore, accurate and efficient fatigue life prediction is critical for the design of gas turbine blades. Accordingly, this paper analyzes the effects of mean stress, anisotropy, and uncertainties on the LCF life of nickel‐based single‐crystal turbine blades. The modified Hill yield criterion is employed to deal with the anisotropic damage characteristics of nickel‐based single‐crystal superalloy (NSCS) under a multiaxial stress state. Meanwhile, the effects of the temperature and crystal orientation are introduced into the walker mean stress correction term. A multiaxial LCF life prediction model is developed based on the energy criterion‐based fatigue life estimation method. Moreover, multi‐source uncertainties originating from rotation speeds, material properties, and temperature are analyzed and quantified. Comparison between the predicted and tested life indicates that the proposed method produces good accuracy and robustness, which can provide a reference for the reliability design of NSCS turbine blades.

Strategy of Suppressing the Solidification Cracking Susceptibility of 247LC Superalloy Weld Metals using Commercial Ni-Based Fillers

The solidification cracking susceptibility of 247LC superalloy dissimilar welds with ERNiCrCoMo-1, ERNiCrMo3, and ERNiFeCr-2 commercial fillers was quantitatively evaluated using Varestraint testing for the sound weld geometries of gas turbine blades. We confirmed that the solidification brittle temperature range (BTR) of the 247LC/ ERNiCrMo-3 dissimilar weld was 217 K, which was measured using a thermo-vision camera during the Varestraint testing, and the BTR increased to 260, and 485 K with the ERNiCrCoMo-1 and ERNiFeCr-2 fillers, respectively, Based on theoretical calculations of the weld solidification path (i.e., using Scheil’s model; performed via the software Thermo-Calc) for each dissimilar weld, the variation in the BTR can be considered to be highly dependent on the solid-liquid coexistence temperature range of the dissimilar welds, and it is also correlated with the low-temperature formation of topologically closed packed phases during the terminal stage. Based on the experimental and theoretical results, the commercial Ni-based filler ERNiCrMo-3 is expected to be an effective welding material for 247LC dissimilar welding and the successful manufacturing of high-soundness blades.

Creation of a Life Prediction Model for Combined High-Cycle Fatigue and Creep

Abstract While industrial gas turbine blades are commonly designed to resist creep and high-cycle fatigue (HCF) failure, the combination of these two loading conditions is seldom considered. The effect of creep damage elicited prior or concurrent to HCF loading is not well established and can significantly reduce the HCF lifetime of these critical components. A comprehensive life prediction model capable of capturing these superimposed effects is needed to ensure current reliability standards are maintained when designing aggressively loaded, next-generation industrial gas turbine blades. The consequence of combined HCF and creep loading to the lifetime a Ni-base superalloy is characterized and modeled in this study. Composition and calibration of the model are carried out using data from HCF tests conducted on virgin and pre-crept specimens at 750 °C and 850 °C. The experimental data encompass a wide range of stress ratios and pre-creep strains to mimic to the expansive set of potential turbine blade loading conditions. The proposed microstructurally informed model is based on existing principles and relies on test data and information gathered from a comprehensive failure analysis of the tested samples.