Gas Turbine Blades Research Articles

CFD Analysis of Gas Turbine Blade Cooling with Staggered Holes

The role of turbine inlet temperature plays a pivotal role in determining overall turbine performance. As the temperature at the turbine inlet increases, it leads to an enhancement in the turbine's average efficiency. Gas turbines operate under extremely elevated temperatures, reaching levels of 1200°C to 1500°C. This extreme heat poses the risk of turbine blade melting and potential failure. Consequently, the need arises for a sophisticated cooling mechanism for the turbine blades. Optimally increasing the inlet temperature of the turbine blades can certainly elevate the turbine's overall efficiency. However, it's important to recognize that this increase in temperature directly impacts the durability of the turbine blades. To address this challenge, various innovative cooling technologies have been devised, including the implementation of distinct blade cooling hole configurations. These methodologies aim to ameliorate blade temperatures and consequently enhance turbine performance.Turbine blades are engineered using superalloys, renowned for their ability to withstand high thermal stress. Advanced software tools are harnessed to assess their performance under extreme temperatures. Computational Fluid Dynamics (CFD) software is commonly employed for analyzing turbine blades. A prevailing approach for blade temperature reduction entails employing diverse cooling systems, often utilizing air as a cooling agent. This directed airflow over the blades significantly curtails their temperatures. In this context, blade design featuring staggered hole layouts is applied, and both STATIC and CFD simulations, grounded in defined boundary conditions, are executed, yielding commensurate outcomes. Comparative analysis demonstrates that staggered hole configurations provide superior temperature distribution uniformity across blade surfaces, effectively reducing peak temperatures in contrast to blade configurations devoid of cooling holes..

Performance Evaluation of Damaged Blades Using Numerical Simulation and Machine Learning

The formulation of maintenance strategies for gas turbines requires an accurate and rapid assessment of damaged blade performance. Variety and uncertainty in the three-dimensional geometric deformation of gas turbine vanes and blades increase the difficulty of degradation analysis. In this paper, the effects on the aerodynamic performance of partial damage to turbine nozzle guide vanes are investigated experimentally and numerically. A methodology for constructing a deformation–degradation model for high-pressure gas turbine vanes/blades is proposed based on machine learning. A database consisting of 670 numerical simulation results with various deformation patterns is constructed for the vane cascade. A mapping is constructed between the matrices defining geometric deformations and the total pressure loss coefficient of the cascades based on a convolutional neural network model. The accuracy of this deformation–degradation model is verified against experimental results. We find that deformation on the suction side of the blade has the most significant influence on aerodynamic performance. The deformation–degradation model constructed for a specific cascade provides a rapid evaluation of aerodynamic performance based on rough geometrical measurements without additional experiments or numerical simulations, providing a potential tool in the precise repair of gas turbines.

A Short Introduction of Blade Cooling Mechanisms in Old Gas Turbines with the Aim of Proper Distribution of Temperature Profile

Presently, old gas turbines are used in the industry of some developing countries without high tech, which face many problems in the field of thermal efficiency and output power. Typically, turbines operate in the temperature range of 1200 to 1500 degrees Celsius. Many studies have been done to increase the efficiency of such systems. The results show that this increase in temperature at the inlet of the gas turbine has negative consequences, such as increasing the thermal load of the turbine blades and thus reducing the lifetime of the blades. On the other hand, a damaged blade can cause serious damage to other blades as well as the main shaft and other parts in various ways and sometimes lead to complete failure of the turbine. Therefore, it is reasonable to consider cost reduction considerations, including maintenance. Hence, due to the limitation of thermal stresses for the continuous operation of gas turbine blades, the distribution of heat transferred to them must be controlled. In this regard, the presence of blade cooling mechanisms is necessary for its safe operation, because the operating temperature of the gas turbine is much higher than the allowable temperature of the blades. In addition to cooling the blades, cooling the shell and inlet nozzle of gas turbines is also extremely important. But since the blades are exposed to high-level stress and tension for a long time, their cooling is more important and sensitive. For this reason, in the present article, the authors tried to provide a short introduction to the efficient mechanisms in cooling the blades related to the old systems, whose effect is noticeable on increasing the lifetime of the blades.

Turbulent Flow Heat Transfer and Thermal Stress Improvement of Gas Turbine Blade Trailing Edge Cooling with Diamond-Type TPMS Structure

Additive manufacturing allows the fabrication of relatively complex cooling structures, such as triply periodic minimal surface (TPMS), which offers high heat transfer per unit volume. This study shows the turbulent flow heat transfer and thermal stress of the Diamond-TPMS topology in the gas turbine blade trailing edge channel. The thermal-fluid-solid analysis of the Diamond-TPMS structure, made of directionally solidified GTD111, at the nearly realistic gas turbine condition is executed, and the results are compared with the conventional pin fin array at the Reynolds number of 30,000. Compared to the baseline pin fin structure, the Diamond-TPMS model distributes flow characteristics more uniformly throughout the channel. The overall heat transfer enhancement, friction factor ratio, and thermal performance are increased by 145.3%, 200.9%, and 32.5%, respectively. The temperature, displacement, and thermal stress in the Diamond-TPMS model are also distributed more evenly. The average temperature on the external surface in the Diamond-TPMS model is lower than the baseline pin fin array by 19.9%. The Diamond-TPMS network in the wedge-shaped cooling channel helps reduce the volume displacement due to the material thermal expansion by 29.3%. Moreover, the volume-averaged von Mises stress in the Diamond-TPMS structure is decreased by 28.8%.

Method of scanning thin surfaces in repairing gas turbine blades

Improving the efficiency of weld overlay repair of gas turbine blades by developing and implementing a method of scanning complex curved surfaces of gas turbine blades directly on the machine is the aim of this work. The paper proposes an approach to scanning a blade with a computer vision system mounted near the nozzle on the same machine that is used for direct metal deposition. The computer vision system consists of a triangulation laser sensor and a camera. The proposed algorithm is adaptive to the mechanical condition of the equipment used for scanning and metal deposition. The scans obtained from the machine vision system have precision better than 0.05mm in 67.56% of cases, and precision better than 0.1mm in 95.75% of cases. That accuracy, with a laser spot of 0.5 to 1.0mm, is sufficient for further use of the scans in repairing gas turbine blades. The proposed approach makes it possible to speed up the preparation of technological programs for direct metal deposition by 10 times compared to the manual scanning method.

Synchronous Vibration Parameter Recognition of Constant-Speed Blades Based on Blade Tip Clearance Measurement

A new method for the synchronous vibration parameter identification of constant-speed rotating blades based on blade tip clearance (BTC) measurement and blade tip timing (BTT) is introduced. A BTC sensor is used to measure the BTC when the blade tip passes through each sensor. The BTT method is used to determine whether the blade tip arrives in advance or lags. The geometric model between the BTC and the blade tip vibration displacement (BTVD) is established, and the BTVD of the blade tip passing through each sensor is obtained. Then, the nonlinear least squares method is used to determine the synchronous vibration parameters of the constant-speed rotating blade. The results show that with an increase in amplitude, the higher the accuracy of the vibration parameter identification proposed in this paper; with a decrease in the random error of the BTC measurement, the higher the accuracy of the vibration parameter identification proposed in this paper; with a decrease in the random error in the measurement of the blade disk dimensions, the higher the accuracy of the vibration parameter identification proposed in this paper. In addition, the smaller the ratio of the blade length to the blade disk radius, the higher the accuracy of the vibration parameter identification method introduced in this paper. Because the structure of the gas turbine compressor and turbine blade disk has a small blade disk ratio, the method proposed in this paper is suitable for the simultaneous vibration parameter identification of gas turbine compressor blades and turbine blades.

A hybrid modeling method of fatigue crack growth for gas turbine blades under combined high and low cycle fatigue loadings

Fatigue crack is one of the major faults of the gas turbine blades. Previous modeling studies on fatigue crack growth of blades mainly focus on a single numerical or analytical approach considering different sizes of cracks under various fatigue loadings. However, the actual crack propagation process is time-varying. The iteration and update of the model are necessary to evaluate the fatigue life of blades precisely. This paper proposes a hybrid modeling method to study blade crack growth under combined high and low cycle fatigue (CCF) loadings. The method emphasizes the combination and interaction between the finite element (FE) numerical simulation and the analytical calculation based on the fracture mechanics model. The current crack propagation length of the blade FE model is calculated from the crack growth rate obtained by the stress intensity factor (SIF) range according to Paris law. Then, a new SIF range is resolved from the FE model with the updated crack length. The proposed method is verified by the first-stage compressor blade from an in-service gas turbine. Results show that the crack growth is faster using the proposed hybrid modeling method than the traditional method. The update of the SIF range under CCF loadings cannot be ignored when predicting the fatigue life of the blade. Also, a sensitivity analysis is carried out. Suggestions are given on how to set the crack extension length at each stage during modeling, especially when the blade approaches failure.

Optimization of turbine blade trailing edge cooling using self-organized geometries and multi-objective approaches

Gas turbines are widely utilized as essential power machinery across diverse energy-related industries. Efficient and durable cooling of gas turbine blades is crucial for the performance and life of gas turbine. However, achieving effective cooling for turbine blade trailing edges remained challenging due to the narrow, thin and structurally limited spaces. To address the aforementioned challenge, this study proposed a generative design method by employing self-organization equations to parameterize the topology of wedge-shaped channels within the trailing edge region as a substitute for the conventional pin-fin structures. Additionally, a multi-objective Bayesian approach was utilized to optimize the topological parameters, with comprehensive emphases on improving five design objectives. A comparative analysis of the performance was conducted between self-organized structures and pin-fin structures. Notably, the selected self-organized structure achieved an impressive 43 % increase in the total Nusselt number and a substantial 37 % reduction in local Nusselt number variance under the same pressure loss. The results demonstrated that self-organized structures exhibited superior heat transfer performance with lower pressure drop and improved uniformity. The performance improvement could be attributed to the strategic generation of solids by the proposed generative design algorithm, distributing the flow more reasonable.

Cyclic and Isothermal Oxidation Behavior of a Directionally Solidified Ni-Al-Ti-Co-Cr Superalloy

Nickel based superalloys are widely used in such applications as gas turbine blades due to their excellent mechanical properties at elevated temperatures. Oxidation is one of the life limiting factors at such temperatures since it accelerates failure mechanisms, e.g. fatigue and creep. In this project, oxidation behavior of Ni-3Al-4.8Ti-9.5Co-14Cr (wt.%) superalloy was investigated under various testing conditions. The alloy was investment-cast with preferential crystal growth direction [100]. Isothermal oxidation tests were carried out at 800°C for 150h. Cyclic oxidation tests were then conducted between 100-800°C for 150 one-hour cycles. An additional one-hour cycle was tested to replicate real-life working condition of the alloy, which consisted of heating the samples up to 800°C followed by slow cooling to 400°C. During the testing, samples were periodically taken from the furnace and weighted with an accuracy of 10-4 g to calculate the weight gain and to analyze the microstructure of formed oxide. Scanning electron microscopy (SEM) combined with energy-dispersive spectroscopy (EDS) and X-ray diffraction were used to study the microstructure of oxidation products. The results reveal that the highest amount of weight gain is obtained in isothermal testing, while the lowest in cyclic. Diffusion of Ti and Ni to the free surface results in the early-stage formation of needle-shaped oxide phases followed by severe oxidation of Cr and Al. The layer of chromium oxide is continuous while aluminum oxide is blocky at the deepest position from the free surface. Cracks form at the interface of carbide particles and gamma phase near the free surface of cyclic oxidation samples due to concentration gradient of Ni and Al. Precipitate-free zone are observed near the free surface of all the samples at the end of the tests, but internal oxidation does not occur significantly in all the samples. It is found that temperature fluctuation increases oxide spallation, which causes crack formation. At the same time, in isothermal testing, dense, crack-free layer of oxide form on the surface of superalloy.

Detection mechanism of delamination in thermal barrier coatings of turbine blade using a Rayleigh wave EMAT

Nondestructive testing (NDT) for damage in thermal barrier coatings (TBCs) is significant for the safety guarantee of gas turbine blades. As a new NDT technology, electromagnetic acoustic transducer (EMAT) is widely applied for NDT of conductive structural components due to its advantages of coupling-free and high adaptability. In this paper, numerical simulations are conducted to study the wave propagation and interaction with delamination defects in TBCs inspected with a Rayleigh wave EMAT of the Lorentz force mechanism. Based on the numerical results, the wave structure in TBC, wave conversion at delamination defect, time domain EMAT signals, and its B-scan images are evaluated and the feasibility of Rayleigh wave EMAT to inspect delamination in TBCs was theoretically clarified.

Aerothermodynamic features of a Coriolis-applied smooth U channel for gas turbine blade

Rising temperature of gas turbine inlet brings great challenge for blade temperature tolerance, thus high effective cooling structure for turbine blade is vital. In this paper, aerothermodynamic features including heat transfer and pressure drop of a Coriolis-applied rotating smooth U channel are studied in detail. Both experiment and numerical methods are utilized in the study. A rotating cooling structure experiment rig system has been established and validated. The experiments were conducted in the rotating cooling structure experiment rig. Besides, RANS was chosen in the simulation. In the experiment and numerical studies, Reynolds number is constant at 16000 and Rotation number ranges from 0 to 0.024. The results indicate that Coriolis force plays a dominant and positive role on heat transfer ability on trailing wall, and that bend outlet impingement effect is the primary factor compared to Coriolis force for the Nusselt number of smooth leading surface. Besides, Coriolis force at bend region probably suppresses the formation of K–H vortices, thus boosts the flow stability, reduce pressure loss of channel and weakens second heat transfer peak of impingement at the bend outlet. What's more, the total performance of the Coriolis-applied smooth U channel at Ro of 0.006 and 0.024 are 2.18 % and 8.51 % higher than the channel at Ro of 0, which means that rotation is good for the Coriolis-applied smooth U channel and that the channel has superior performance and is encouraging in future rotating blade cooling application.

Computational and Experimental Study on Failure Mechanism of a GTD-111 First-Stage Blade of an Industrial Gas Turbine

This paper investigates the root cause of a recurring failure observed in the first-stage blades of an industrial gas turbine. The failure involves the loss of the trailing edge tip of the blades. The study employs a combination of metallographic analysis and computational simulations utilizing the finite element method and computational fluid dynamics. The metallographic analysis reveals significant degradation in the GTD-111 nickel-based superalloy within the region where the failure occurs. This degradation is characterized by the coarsening and coalescence of the gamma prime phase, which can be attributed to localized overheating. Additionally, the computational study enables the calculation of the trajectory, pressure, and temperature profiles of the hot gases, as well as the distribution of temperatures within the blade. These findings demonstrate that the cooling airflow is influenced by the hot gas flow, particularly in the vicinity of the fault location, owing to the orientation of the cooling ducts, which results in overheating in this area. Ultimately, the temperatures derived from the microstructural analysis using the Ostwald-ripening theory align remarkably well with the results obtained from the simulation, validating the accuracy of the computational model. By combining metallographic analysis and computational simulations, this study provides crucial insights into the failure mechanism of the first-stage blades.

Study of wear and tensile behavior of 3D printed CM 247 super alloy

CM247, a nickel-based superalloy derived from MAR M247 initially designed for gas turbine blades, continues to play a pivotal role in enhancing efficiency for aerospace and gas turbine vane blade applications. There are lot materials and other alloys are used to increase the efficiency for aerospace and gas turbine vane blade applications. In modern days manufacturing of super alloys are increased. Ni based super alloys and Co based super alloys are introduced to increase the strength of the alloys. Like this, a lot of unknown superalloys are being manufactured and used for aviation and industrial purposes. Most of the unknown super alloys are used in aerospace industries like CM 247. CM247 will be used to increase or improve the mechanical properties of the material. This is a characteristic of normal superalloy. To increase efficiency to the maximum, additive manufacturing, or 3D printing, is used. The methodology is manufacturing the material 3D printing process, the normal super alloy is replaced by 3D printed super alloys to attain maximum strength. It is highly corrosion- and wear resistant. It is brittle by nature since it is 3D printed. Despite inherent brittleness due to the 3D printing process, these alloys exhibit remarkable corrosion and wear resistance. Their application, particularly in scenarios demanding high strength and durability, remains viable with judicious post-processing. The tensile for the material have been studied as CM 247 obtained maximum peak load. Same as wear behaviour of 3D printed CM 247 has been studied and dry wear has been conducted by various conditions.

The Application of Fluidic Sealing in Shrouded Gas Turbine Blades

Abstract This paper presents a study conducted on a new gas turbine designed to limit leakage in the labyrinth seal. The slots in the fin are used to generate a bypass flow, which obstructs the flow in the gap above the fin. The method was tested numerically and experimentally beforehand using a simplified model without rotation or blade passages. In this paper, the validation of the method using a model of a turbine stage is shown. Reynolds-averaged Navier–Stokes simulations using two turbulence models—Spalart–Allmaras (SA) and k-ω EARSM—were conducted. Comparisons of leakage flow and stage efficiency for reference and fluidic sealing configurations are presented. Fluidic sealing configuration is effective and reduces the leakage flow by 13–18.5% (depending on the turbulence model). The analysis of the flow structure in the seal region revealed that the use of fluidic sealing resulted in significant circumferential flow anisotropy.

Investigation of Gas Turbine Blade Materials for Efficient Energy System

The present study aims to determine the best and most economical material for a gas turbine blade, which operates under high-temperature conditions and experiences high static structural and thermal loads. To achieve this objective, three different types of material alloys, namely Titanium alloy Ti6AL4V, Magnesium alloy AZ80, and Aluminum alloy 7075-T6, were selected for comparison. A turbine blade model was designed using Solid Works software, and structural and thermal analyses were performed using ANYAS 15.0 under steady-state conditions. The structural analysis aimed to determine the stress, strain, and deformation results on turbine blades by applying high pressure, while the thermal analysis aimed to determine the temperature distribution influences and heat flux generation by applying high temperatures. Based on the results obtained from both analyses of the three different materials, Titanium alloy Ti6AL4V is the best and most economical material. This material showed low stress, strain, and little deformation and the best material properties at high temperatures when compared to Magnesium alloy AZ80 and Aluminum alloy 7075-T6.

Film cooling instability analyses for trailing edge cutback with a novel linear sand-dune inspired lip under mainstream pulsation

Inspired by natural linear sand-dune (LSD), the present work proposed a cutback cooling configuration with novel lip design applied in trailing edges of gas turbine blade. By time-resolved experiments and large eddy simulations, transient flow and film coverage performances of the novel configuration are investigated, and the effect of inevitable mainstream pulsation is included. Through the analyses of unsteady flow characteristics, the LSD lip design can help hinder the propagation of mainstream pulsation, and generates a series of separation wakes to destroy the highly-unsteady shedding vortices, which leads to a high film effectiveness and low level of cooling instability. Quantitatively, by the novel design, time-averaged film effectiveness can be locally increased at least 26% and the unsteadiness level can be maximally reduced by 86% compared to the baseline elliptic lip design. The analyses on probability distribution of transient film effectiveness also conform an obvious advantage of LSD design, from the perspective of statistics. Additional aerodynamic loss induced by the LSD lip is always less than 7% in both steady and pulsed conditions, which remains low and is worthy considering the significant improvement in cooling performance.

Effects of laser shock peening on Inconel 738LC to improve mechanical and fatigue characteristics

The effectiveness of laser shock peening at both room and elevated temperatures was examined for Inconel 738 low-carbon, a material widely used for gas turbine blades. Laser shock peening was performed with a Nd:YAG laser (wavelength = 532 nm, pulse duration = 8 ns, repetition rate = 10 Hz, top-hat profile) using aluminum foil (100 μm thick) as the protective coating at a laser intensity of 10 GW/cm2 and pass number of 10. As a result of laser shock peening, the surface hardness increased by 38%, and the compressive residual stress increased by approximately eleven times compared with that of the unpeened samples. A low cycle fatigue test was performed at room temperature and elevated temperature (850 °C) under strain control. At room temperature, the fatigue life of laser shock-peened samples increased by approximately 2.4 times that of the unpeened samples. At the high temperature of 850 °C, the fatigue life of the laser shock peened samples was overall similar to that of the unpeened samples, either slightly higher or lower depending on the applied total stress level. The results showed that laser shock peening is beneficial for enhancing fatigue strength at low temperatures, but its effectiveness largely disappears at a temperature as high as 850 °C, possibly owing to severe thermal relaxation.

Study on continuous adjoint-based optimization method for internal cooling structures in turbine blades with conjugate heat transfer

A continuous adjoint-based shape optimization system is presented in this paper for conjugate heat transfer (CHT) problems and is applied to the optimization for internal cooling structures of gas turbine blades. With the consideration for the variation of heat conduction equation in the solid regions, the adjoint equations and adjoint boundary conditions in different regions are derived. The adjoint energy correction equation is also derived successfully based on the SIMPLE algorithm, and the adjoint CHT solver is implemented by imposing the values of adjoint energy at the interfaces. Two cases of full 3D optimization for the C3X hollow blade and cooling channel with pin fins are conducted by using the optimization system. In both cases, their flow and heat transfer characteristics are optimized and analyzed in detail. This study demonstrates the potential advantages and basic capabilities of the continuous adjoint method in dealing with CHT optimization problems.

Research on a Method for Online Damage Evaluation of Turbine Blades in a Gas Turbine Based on Operating Conditions

Performing online damage evaluation of blades subjected to complex cyclic loads based on the operating state of a gas turbine enables real-time reflection of a blade’s damage condition. This, in turn, facilitates the achievement of predictive maintenance objectives, enhancing the economic and operational stability of gas turbine operations. This study establishes a hybrid model for online damage evaluation of gas turbine blades based on their operational state. The model comprises a gas turbine performance model based on thermodynamic simulation, a component load calculation model based on a surrogate model, an updated cycle counting method based on four-point rainflow, and an improved damage mechanism evaluation model. In the new model, the use of a surrogate model for the estimation of blade loading information based on gas turbine operating parameters replaces the conventional physical modeling methods. This substitution enhances the accuracy of blade loading calculations while ensuring real-time performance. Additionally, the new model introduces an updated cycle counting method based on four-point rainflow and an improved damage mechanism evaluation model. In the temperature counting part, a characteristic stress that represents the stress information during the cyclic process is proposed. This inclusion allows for the consideration of the impact of stress fluctuations on creep damage, thereby enhancing the accuracy of the fatigue damage assessment. In the stress counting part, the model incorporates time information associated with each cycle. This concept is subsequently applied in determining the identified cyclic strain information, thereby improving the accuracy of the fatigue damage evaluation. Finally, this study applies the new model to an online damage evaluation of a turbine stationary blade using actual operating data from a micro gas turbine. The results obtained from the new model are compared with the EOH recommended by the OEM, validating the accuracy and applicability of the new model.

Optimization of heat transfer and friction characteristics of a rotating U-channel with a combination of variable size connecting bridges

Gas turbine blades typically feature a U-shaped or multi-flow snake channel in their mid-chord region, both incorporating a 180° turn. However, the addition of fins and dimple or protrusion turbulent flow structures can result in excessive pressure losses within the flow channel. This study aims to reduce pressure loss and improve flow uniformity by inserting one to three connecting bridges of varying sizes in the gap between the two channels. The suitability of various connecting bridges with different angles and sizes is assessed in both stationary and rotating states through simulations. Subsequently, the cooling efficiency and reduction in resistance performance of different-sized connecting bridge combinations are evaluated. A layout scheme for optimal connecting bridge placement within the U-shaped channel is proposed. Results indicate that the incorporation of a single minimum-size connecting bridge leads to an average 22.6 % decrease in overall flow resistance within the U-shaped channel, and simultaneously yields a 3.5 % increase in the overall thermal performance. When using the recommended connecting bridge angle and layout combinations, the incorporation of connecting bridges leads to an average 46 % and 49.7 % reduction in overall flow resistance within the U-shaped channel in order to counterbalance pressure losses generated by turbulent structures. This effect consequently results in a 6.5 % and 6.6 % increase of the overall thermal performance. This study offers new insights and data-backed evidence that can potentially facilitate the design of high-efficiency and low-resistance cooling methods in the mid-chord region of high-temperature turbine blades.