High Pressure Turbine Blade Research Articles

3D printing ceramic cores for investment casting of turbine blades, using LCD screen printers: The mixture design and characterisation

The primary objective of this study is to demonstrate the possibility of developing silica, alumina, and zircon-based photocurable ceramic suspensions that can be used for visible light photopolymerization (> 450 nm) and to optimise the binder formulations for the purpose of LCD-based ceramic 3D printing applications. Reference ceramic components for this work are ceramic cores employed in the investment casting of high-pressure turbine blades and vanes. Arguably, one of the most critical steps in photoinduced ceramic 3D printing is developing suitable ceramic suspensions, having high ceramic loading, low viscosity, and short curing times. Ceramic suspensions with four different novel binder formulations and commercial ceramic powders used in core manufacturing (SiO2, Al2O3 and ZrSiO4) were investigated to achieve the best trade-off between: (1) their curing performance (cure depth and curing speed), (2) rheological properties of the binder mixtures at the solid loadings of 60 vol.% for SiO2, 55 vol.% for ZrSiO4, and 45 vol.% for Al2O3; and (3) the green body mechanical properties of the mixtures after printing. The effect of ceramic particles on the selected binders was examined individually, and the correlation between cure depth (Cd), volumetric loading, and curing speed are evaluated. The results show all binders designed in this study provide an adequate cure depth, even at high ceramic loadings. When the curing behaviour of all unloaded binder mixtures from the previous study [1] compared with the 10 vol.% SiO2 loaded mixtures, the cure depth of all formulated binder mixtures increased 50–55 % and the curing thickness of 60 vol.% SiO2 loaded suspensions were still slightly higher than their unloaded counterparts. The rheology outcomes indicate that lower viscosity binders always result in lower viscosity of the ceramic loaded inks, even without taking the effect of dispersants into account. Besides, the addition of N-Vinyl-2-Pyrrolidone (NVP) monofunctional monomer to the binder mixtures significantly reduces the viscosity and changes the normally linear relationship of the mix viscosity and its silica loading content. Among the binder formulations loaded with 60 vol.% of SiO2, the formulation providing the lowest viscosity and highest mechanical property consists of 5 wt.% of NVP, 45 wt.% of HDDA and 50 wt.% of Photocentric 34 resin. Although this binder mixture showed the highest green flexural strength when loaded by 55 vol.% ZrSiO4, all other mixtures loaded with zircon flour also demonstrated a near-fluid behaviour, below 200 s−1. In Al2O3 loaded mixtures, the HDDA di-functional binder formulations present lowest viscosity and the di- and multifunctional monomer blends (HDDA-Photocentric27) showed the highest mechanical properties when used in a 50/50 ratio. This work summarises the best binder choices for silica, alumina and zircon based ceramic suspensions used in core printing for investment casting applications through LCD screen printing.

Investigation of the requirements for the selection of materials for high pressure Turbine blades of conventional turbojet engines

The material selection method is critically evaluated to enable high pressure (HP) turbine blades to deal with in-service damaging phenomena such as creep, low cycle fatigue and high cycle fatigue, oxidation and corrosion. The material selection method is analyzed in order to improve the service life of the aero engine. To increase the turbine inlet temperature, HP turbine blades need improved creep and fatigue resistance. more quality. By the typical working condition of HP turbine blade, using CES Edu Pack (CES) material selection software was used to select suitable materials for HP turbine blade material. Nickel based alloys are selected for HP turbine blades, such as Nickel-Cr-Co-Mo superalloy.

In-service aircraft engines turbine blades life prediction based on multi-modal operation and maintenance data

The in-service life of turbine blades directly affects the on-wing lifetime and operating cost of aircraft engines. It would be essential to accurately evaluate the remaining useful life of turbine blades for safe engine operation and reasonable maintenance decision-making. In this paper, a machine learning-based mechanism with multiple information fusion is proposed to predict the remaining useful life of high-pressure turbine blades. The developed method takes account of the in-service operating factors such as the high-pressure rotor speed and exhaust gas temperature, as well as the engine operating environments and performance degradation. The effectiveness of this method is demonstrated on simulated test cases generated by an integrated blade creep-life assessment model, which comprises engine performance, blade stress, thermal, and creep life estimation models. The results show that the proposed method provides a prospective result for in-service life evaluation of turbine blades and is of significance to evaluating the engine on-wing lifetime and making a reasonable maintenance plan.

Co content dependence on the microstructure characteristic and creep performance at elevated temperature in Ru-containing single crystal superalloys

The composition design and optimization of Ru-containing fourth generation single crystal superalloys, which are currently considered as the most advanced and practical materials for manufacturing high-pressure turbine blades of aero-engines, have been in increasing and urgent demands. In this work, significant adjustments to the pivotal alloying element Co were made and the synthetic effect of Co on the microstructure as well as high-temperature creep property in Ru-containing alloys were systematically evaluated. The results illustrated that the size of γ′ phase was inversely proportional to the Co content but the volume fraction of γ′ precipitates stayed the same in different alloys. The TCP phases were more likely to precipitate in alloys with lower or extremely high Co addition during long-term aging, while the morphology of these particles transformed from long needle-like to short rod-like or blocky as Co content increased. It was noted that the element diffusion as well as the resultant coarsening and rafting of γ/γ′ structures were favorably facilitated by the increasing Co addition. The alloy with 12 wt% Co exhibited the longest stress rupture life at 1140 °C/137 MPa, regardless of the moderate precipitation of blocky TCP particles during creep. Moreover, the TCP phases in different alloys were analyzed to be typical μ phase but the specific element distributions varied with Co addition. Moreover, plenty of 2nd γ′ precipitates were observed after creep rupture, while their nucleation and precipitation could be affected by the Co addition in alloys. Ultimately, the comprehensive Co-effect was discussed and the optimum Co content was determined, in order to provide further guidance in the design and development of Ru-containing single crystal superalloys.

Aerothermal Effect of Cavity Welding Beads on a Transonic Squealer Tip

Abstract High-pressure turbine blade tips are critical for gas turbine performance and are sensitive to small geometric variations. For this reason, it is increasingly important for experiments and simulations to consider real geometry features. One commonly absent detail is the presence of welding beads on the cavity of the blade tip, which are an inherent by-product of the blade manufacturing process. This paper therefore investigates how such welds affect the Nusselt number, film cooling effectiveness and aerodynamic performance. Measurements are performed on a linear cascade of high-pressure turbine blades at engine realistic Mach and Reynolds numbers. Two cooled blade tip geometries were tested: a baseline squealer geometry without welding beads, and a case with representative welding beads added to the tip cavity. Combinations of two tip gaps and several coolant mass flow rates were analyzed. Pressure sensitive paint was used to measure the adiabatic film cooling effectiveness on the tip, which is supplemented by heat transfer coefficient measurements obtained via infrared thermography. Drawing from all of this data, it is shown that the weld beads have a generally detrimental impact on thermal performance, but with local variations. Aerodynamic loss measured downstream of the cascade is shown to be largely insensitive to the weld beads.

Thermally Sprayed Nickel-Based Repair Coatings for High-Pressure Turbine Blades: Controlling Void Formation during a Combined Brazing and Aluminizing Process

Turbine blades must withstand severe loading conditions and damage can occur during operation due to heat, pressure, foreign objects and hot gas corrosion, despite the protective coatings applied onto the turbine blades. Instead of replacing the damaged components, maintenance, repair and overhaul are key to extend the total service life. Besides welding, the repair of turbine blades by brazing is an established repair process in the industry and involves many individual steps that often require a high degree of manual work. In the present study, a hybrid joining and coating technology was developed to shorten the state-of-the-art process chain for repairing turbine blades. With this approach, a repair coating, which consists of a filler metal, a hot gas corrosion protective layer and an aluminum top layer, is applied by atmospheric plasma spraying. The coated turbine blade then undergoes a heat-treatment so that a brazing and aluminizing process is carried out simultaneously. Due to diffusion and segregation processes, pores can occur in the heat-treated coating. In the present study, a full factorial design of experiment was performed to reduce the pores in the coating. The microstructure of the repair coating was investigated by optical- and scanning electron microscopy (SEM), and the impact of the process parameters on the resulting microstructure is discussed.

PHANTOM COOLING EFFECTS ON ROTOR BLADE SURFACE HEAT FLUX IN A TRANSONIC FULL SCALE 1+1/2 STAGE ROTATING TURBINE

Abstract An experimental and numerical investigation of phantom cooling effects on cooled and uncooled rotating high pressure turbine blades in a full scale 1+1/2 stage turbine test is carried out. Objectives set to capture, separate, and quantify the effects of upstream vane film-cooling and leakage flows on the downstream rotor blade surface heat flux. Multiple series of tests were carried out in the Air Force Research Laboratory, Turbine Research Facility, at Wright-Patterson Air Force Base, Ohio. A non-proprietary research turbine test article is uniquely instrumented with high frequency double-sided thin film heat flux gauges custom made at AFRL. High bandwidth, time resolved surface heat flux is measured on multiple film-cooled and non-film-cooled HPT rotor blades downstream of both film-cooled and non-film-cooled vane sectors. Upstream wake passing and heat flux is characterized on both rotor pressure and suction side surfaces, along with quantifying rotor phantom cooling effects from non-uniform 1st stage vane film cooling and leakage flows. Fast response heat flux measurements quantify how rotor phantom cooling impacts the blade pressure side greatest; increasing along the pressure side towards the trailing edge. It is discovered upstream vane film-cooling alone can account for 50% of the rotor blade cooling effect, and even outweigh the rotor blade film cooling effect far from the blade showerhead holes. Added unsteady numerical simulation demonstrates how variations in inlet total temperature and incidence angle can also contribute to circumferentially non-uniform rotor heat flux.

Effect of the withdrawal rate on the microstructure and thermal durability of a third-generation single crystal superalloy

Single crystal Ni-based superalloys are the typical structural materials for high-pressure turbine blades, and their microstructure is critical in determining their mechanical properties. The withdrawal rate is a key parameter affecting the microstructure during the single crystal growth process. In the present work the effect of the withdrawal rate on the microstructure of a third-generation single crystal superalloy containing 6.8 ​wt% Re has been investigated, and the creep resistance of the alloy determined. The results showed that increased withdrawal rate refined the dendritic structure, reduced dendritic arm spacing, promoted the growth of secondary tertiary dendrites and decreased solidification segregation with a reduced size of γ′ phase. The porosity density of the as-cast alloy first decreased and then increased with the withdrawal rate, while the minimum porosity densityoccurred when the alloy was under the solidification condition of withdrawal rate of 4.5 ​mm/min. The maximum creep rupture life of 326.4 ​h of the heat-treated alloys under the test condition of 1100 ​°C/140 ​MPa also appeared at the alloys under the withdrawal rates of 4.5 ​mm/min. It is believed that the minimum porosity density and reduced size of the γ′ phase may be the main reasons for the enhanced creep rupture life of the alloys with withdrawal rates of 4.5 ​mm/min. This investigation provides theoretical support and a practical basis for the development of third-generation single crystal superalloys.

The Effect of Heat Transfer on Turbine Performance

Abstract For over 50 years, high-pressure gas turbine blades have been cooled using air bled from the compressor. This cooling results in very high rates of heat transfer, both within the fluid and within the blade. The heat transfer often occurs across large differences in temperature and thus is highly irreversible. It is therefore surprising that little is understood about the effect of this heat transfer on turbine performance. This paper solves this problem by applying a new method known as mechanical work potential, or euergy, analysis. The key consequence of the analysis is that the value placed on all heat, relative to work, becomes set by the Joule (Brayton) cycle efficiency. This means that when heat is transferred locally within a flow, or when viscous reheat occurs, the value of this heat should be set by the Joule cycle efficiency. This paper demonstrates how the new method can be implemented both in the preliminary design systems and in the analysis of conjugate CFD solutions of complex engine representative components. The new method provides the cooling designer with a new way of raising turbine efficiency, a form of recuperation locally in the flow. This method offers the exciting potential to design cooling systems that, when added to a blade profile, actually reduces profile loss by up to 7.3%.

Application of Scale Adaptive Simulation Model to Studying Cooling Characteristics of a High Pressure Turbine Blade Cutback Trailing Edge With Different Cooling Configurations

Abstract Effective cooling structure design in the trailing edge (TE) of a high pressure turbine (HPT) blade is essential to increase turbine efficiency and maintain structural integrity. To obtain efficient cooling structures and understand clearly cooling mechanism, this paper adopted numerical simulation methods to investigate fluid flow and cooling characteristics in detail downstream of an HPT blade TE cutback region. The effects of typical TE configurations on cutback cooling performance are investigated including three types of internal turbulators (cylindrical pin fins and elliptic pin fins arranged in streamwise and spanwise orientations), the cutback with/without land extensions and three kinds of ejection lip profiles (one straight lip shape marked as “A” and two rounded lip shapes marked as “B” and “C,” respectively). The scale adaptive simulation (SAS) is implemented to study the complex unsteady mixing process downstream of the cutback under operating condition of blowing ratio M = 0.65. The results from the shear stress transport (SST) k–ω model are compared as well. SAS is capable to reproduce the periodical vortex shedding phenomena and resolve the vortices coherent structures. Compared with the experimental data, SAS provides more accurate predictions in terms of laterally averaged adiabatic cooling effectiveness ηaw and discharge coefficient Cd than the SST k–ω model. At the rear part of the cutback surface, large deterioration in ηaw is predicted by SAS for all configurations, but ηaw is considerably overpredicted by the SST k–ω model except for the case of elliptic pin fins with spanwise orientation. The elliptic pin fins with streamwise orientation significantly improve ηaw at the rear part of the cutback surface over the baseline model with cylindrical pin fins and slightly increase Cd. However, the elliptic pin fins with spanwise orientation drastically reduce the ηaw and Cd. Downstream of the cutback, the coherent structures are strongly disturbed and become chaotic compared with the TE with cylindrical and streamwise oriented elliptic pin fins. The application of land extensions only causes an evident change to the coherent structure immediate downstream of the lip and slightly improves ηaw and reduces Cd over the baseline model at the rear part of the cutback surface. Rounded lip shapes B and C also show an obvious increase in ηaw at the rear part of the cutback surface but only a minor increase in Cd compared with the straight lip shape A. The rounded lip helps the coolant diffuse into the TE cutback and reduce the intensity of mixing. Due to larger rounding radius of shape B, the cooling effectiveness predicted by shape B is slightly better than shape C.

Probing the failure mechanisms and microstructure evolution of a high-pressure turbine blade coated with AlSiY

A long-term test run followed by room-temperature fatigue test was performed for the first-stage high-pressure turbine blades of an aero-engine. The investigation showed the appearance of cracks at the trailing edge of the blade coated with AlSiY. The failure mechanism was investigated by macroscopic observation, fracture analysis, metallographic analysis, hardness testing and structural evolution analysis by electron backscatter diffraction (EBSD), kernel average misorientation (KAM) and strain analysis. The results showed that thermal fatigue cracks initiated and propagated on the trailing edge during the test run and cracks further propagated during the fatigue test. Brittle and hard phases including M23C6 carbides, μ phase and γ'(Ni3Al) phase precipitated in the inter diffusion zone with a high dislocation density and maximum hardness and strain, resulting in thermal fatigue cracks initiation during frequent start-stop of the aero-engine test run. The cracks propagated outward along the β-NiAl grain boundaries with interconnected γ'(Ni3Al) phases in coating, and propagated inward along the lathlike precipitates including M23C6 carbides, M6C carbides and μ phase in the secondary reaction zone to the grain boundaries of the substrate. Chainlike M6C carbides locally precipitated on the substrate grain boundary, causing grain boundary embrittlement and further promoting cracks propagation.

Investigation of a Rotor Blade With Tip Cooling Subject to a Nonuniform Temperature Profile

Abstract One of the challenges in the design of a high-pressure turbine blade is that a considerable amount of cooling is required so that the blade can survive high temperature levels during engine operation. Another challenge is that the addition of cooling should not adversely affect blade aerodynamic performance. The typical flat tips used in designs have evolved into squealer form that implements rims on the tip, which has been reported in several studies to achieve better heat transfer characteristics as well as to decrease pressure losses at the tip. This paper demonstrates a numerical study focusing on a squealer turbine blade tip that is operating in a turbine environment matching the typical design ratios of pressure, temperature, and coolant blowing. The blades rotate at a realistic rpm and are subjected to a turbine rotor inlet temperature profile that has a nonuniform shape. For comparison, a uniform profile is also considered as it is typically used in computational studies for simplicity. The effect of tip cooling is investigated by implementing seven holes on the tip near the blade pressure side. Results confirm that the temperature profile nonuniformity and the addition of cooling are the drivers for loss generation, and they further increase losses when combined. Temperature profile migration is not pronounced with a uniform profile but shows distinct features with a nonuniform profile for which hot gas migration toward the blade pressure side is observed. The blade tip also receives higher coolant coverage when subject to the nonuniform profile.

Formation of High-Temperature Minerals From an Evaporite-Rich Dust in Gas Turbine Engine Ingestion Tests

Abstract The ingestion of multi-mineral dusts by gas turbine engines during routine operations is a significant problem for engine manufacturers because of the damage caused to engine components and their protective thermal barrier coatings. A complete understanding of the reactions forming these deposits is limited by a lack of knowledge of compositions of ingested dusts and unknown engine conditions. Testbed engines can be dosed with dusts of known composition under controlled operating conditions, but past engine tests have used standardized test dusts that do not resemble the composition of the background dust in the operating regions. New evaporite-rich test dust was developed and used in a full engine ingestion test, designed to simulate operation in regions with evaporite-rich geology, such as Doha or Dubai. Analysis of the engine deposits showed that mineral fractionation was present in the cooler, upstream sections of the engine. In the hotter, downstream sections, deposits contained new, high-temperature phases formed by the reaction of minerals in the test dust. The mineral assemblages in these deposits are similar to those found from previous analyses of service returns. Segregation of anhydrite from other high-temperature phases in a deposited sample taken from a high-pressure turbine blade suggests a relationship between temperature and sulfur content. This study highlights the potential for manipulating deposit chemistry to mitigate the damage caused in the downstream sections of gas turbine engines. The results of this study also suggest that the concentration of ingested dust in the inlet air may not be a significant contributing factor to deposit chemistry.

Application of Spectral Method for Vibration-Induced High-Cycle Fatigue Evaluation of an High-Pressure Turbine Blade

Abstract A method of fluid–structure interaction coupling is implemented for a forced-response, vibration-induced fatigue life estimation of a high-pressure turbine blade. Two simulations approaches; a two-way (fully coupled) and one-way (uncoupled) methods are implemented to investigate the influence of fluid–solid coupling on a turbine blade structural response. The fatigue analysis is performed using the frequency domain spectral moments estimated from the response power spectral density (PSD) of the two simulation cases. The method is demonstrated in relation to the time-domain method of the rainflow cycle counting method with mean stress correction. Correspondingly, the mean stress and multi-axiality effects are also accounted for in the frequency domain spectral approach. In this case, a multiplication coefficient is derived based on the Morrow equation, while the case of multi-axiality is based on a criterion which reduces the triaxial stress state to an equivalent uniaxial stress using the critical plane assumption. The analyses show that while the vibration-induced stress histories of both simulation approaches are stationary, they violate the assumption of normality of the frequency domain approaches. The stress history profile of both processes can be described as platykurtic with the distributions having less mass near its mean and in the tail region, as compared to a Gaussian distribution with an equal standard deviation. The fully coupled method is right leaning with positive skewness while the uncoupled approach is left leaning with negative skewness. The directional orientation of the principal axes was also analyzed based on the Euler angle estimation. Although noticeable differences were found in the peak distribution of the normal stresses for both methods, the predicted Euler angle orientations were consistent in both cases, depicting a similar orientation of the critical plane during a crack initiation and propagation process. Finally, the fatigue life estimation was shown to be conservative in the fully coupled solution approach.

Закономірності формування структури приповерхневого рекристалізованого шару в процесі відновлювальної термічної обробки нікелевих жароміцних сплавів

In modern nickel nickel-based high-temperature strength alloys of the ZhS32 type with a directional and single-crystal structure on surfaces that were previously subjected to mechanical treatment, with the subsequent isothermal exposure in the vicinity of the homogenization temperature lasting more than 15 minutes a subsurface recrystallized layer up to 40-65 μm deep is formed such us a chain of grains. The formation of this layer is a side effect that restrained the industrial application of vacuum heat treatment to restore local operational degradation ("raft"-structure) on the overheated inlet edges of non-bandage shelved gas-cooled high-pressure turbine blades of some modern aircraft turbine engines. Given the technical complexity of reliable removal of this recrystallized layer from the tract surface of thin-walled gas-cooled blades, it is important to develop technological measures to translate grain boundaries in unremoved residues of recrystallized near-surface layer into a safer structural state. The regularities of recrystallized layer formation in the process of 3-stage reductive vacuum treatment has been investigated by the methods of raster electron microscopy and X-ray structural (EDX) microanalysis at magnification up to × 2000 on fragments of TVT blades with ZhS26-VI alloy (directional structure) and ZhS32-VI alloy (monocrystalline structure). It has been established that the recrystallized layer formed in the process of aging 1.25-1.5 hours at the temperature of alloy homogenization, is a chain of grain with a tightly packed γ׳-phase with layers at their boundaries, which consist of the non-reinforcing γ׳-phase up to 1-3 μm wide with the carbide phases presence. It has been shown that the rational choice of the temperature of high-temperature aging is an effective technological control of the grain boundaries structural state in a near-surface recrystallized layer of the considered high-temperature strength alloys. Assigning a temperature of 1050°C for isothermal exposure after homogenization heat treatment for ZhS26 and ZhS32 alloys allows to reduce the grain boundaries width in the recrystallized layer to 1-2 μm, keep them intermittent and avoid systematic release of carbide particles at the grain boundaries. On the basis of established in the Paton welding institute of regularities of formation and control of the structure of the near-surface recrystallized layer developed technological recommendations for optimizing the vacuum heat treatment modes to restore the structure of non-bandage shelved gas-cooled high-pressure turbine blades with type ZhS32 high-temperature strength alloys. This technology has passed experimental and practical testing during the next maintenance cycle of flight operation on one of the modern turbojet double-circuit gas turbine engines with afterburner combustion chamber. Keywords: nickel nickel-based high-temperature strength alloys, vacuum heat treatment, restoration of alloys structure, subsurface recrystallized layer, raster electron microscopy.

Design of Stress Constrained SiC/SiC Ceramic Matrix Composite Turbine Blades

Abstract The structural and aerodynamic performance of a low aspect ratio SiC/SiC ceramic matrix composite (CMC) high pressure turbine (HPT) blade was determined. The application was a NASA notional single aisle aircraft engine to be available in the N + 3, beyond 2030, time frame. The notional rpm was maintained, and to satisfy stress constraints, the annulus area was constrained. This led to a low span blade. For a given clearance, low span blade is likely to have improved efficiency when shrouded. The efficiency improvement due to shrouding was found to strongly depend on the axial gap between the shroud and casing. Axial gap, unlike clearance or reaction, is not a common parameter used to correlate the efficiency improvement due to shrouding. The zero clearance stage efficiency of the low aspect ratio turbine was 0.920. Structural analyses showed that the rotor blade could be shrouded without excessive stresses. The goal was to have blade stresses less than 100 MPa (14.5 ksi) for the unshrouded blade. Under some not very restrictive circumstances, such as blade stacking, a one-dimensional radial stress equation accurately predicted area averaged Von Mises stress at the blade hub. With appropriate stacking, radial and Von Mises stresses were similar.

High pressure turbine blade internal cooling in a realistic rib roughened two-pass channel

Simplified rectangular or square channels are commonly adopted for studying turbine blade internal cooling characteristics under constant temperature or constant heat flux boundary conditions, but the effects caused by those simplifications have not been considered in detail. This paper used a numerical method to study blade internal cooling in a realistic rib roughened two-pass channel of a Pratt & Whitney Energy Efficient Engine high-pressure turbine blade under turbine design conditions. The purposes are two-fold: 1) to investigate the effects of the types of wall boundary condition on blade internal heat transfer, including coupled wall, constant temperature wall, and constant heat flux wall; 2) to present the internal heat transfer and pressure losses in the channel with two types of rib roughened walls, i.e., Model A with 60-degree inclined ribs and Model B with 60-degree V-shaped ribs. Both stationary and two rotating conditions with rotation number Ro= 0.1 and 0.2 are considered. The turbulence model is Shear Stress Transport k-ω model. The results revealed that: 1) The types of wall boundary conditions have large effects on blade internal cooling performance. At the stationary condition, the maximum difference in local normalized Nusselt number (Nu/Nu0) on the trailing surface can be as large as 44.4% between the coupled wall and constant temperature at the inlet pass, and 50% between the coupled wall and constant heat flux at the outlet pass. Under blade rotations, the large difference in Nu/Nu0 remains on the trailing surface, while on the leading surface only minor difference exists. 2) At the stationary condition, the maximum difference in Nu/Nu0 between the trailing surface and leading surface for Model A 51.3%, and Model B 40.7%. 3) At the stationary condition, in the inlet pass, the results of Mode A and B are close to the simplified channels. In the outlet pass, a relatively large discrepancy exists between the two ribbed models and their corresponding simplified channel results. 4) Blade rotation results in a large increase in Nu/Nu0 on the trailing surface in the inlet pass and bend regions of the three models. The maximum change in Nu/Nu0 reaches over 100% for each model, which is significantly higher than that of the simplified channels. 5) The friction factor of the two ribbed models decreases with the rotation number. The difference in pressure drop and friction factor between the two ribbed models also decreases with the rotation number.

Assessment of the Degraded High-Pressure Blades in a Land-Based Gas Turbine

The purpose of this paper is to evaluate high-pressure turbine blades after a long-term thermal exposure in a land-based gas turbine. Emphasis is placed upon structure and composition of the various layers evolving, on the one hand, due to hot oxidation/corrosion attacks and, on the other hand, because of interdiffusion phenomena between the substrates and their protective coatings. This work therefore discusses the influence of γ′-Ni3 (Al, Ti) precipitates coarsening, needle σ-phase nucleation, and M23C6-Carbides formation on the hardness properties of blades. In addition, this assessment attempts to evaluate the influence of γ′-Ni3 (Al, Ti) orientation changes and crystallites size growth on the intrinsic degradation of GTD-111 and IN738LC substrates.

Thermomechanical model for solidification and cooling simulation of Ni-based superalloy components

One of the challenges encountered in the industrialization of new single-crystal superalloys parts (like high-pressure turbine blades and vanes for aircraft engines) is to limit the mechanical stresses during the solidification and cooling of the metal. In order to accurately predict the viscoplastic flow as well as the thermo-mechanical behaviour of Ni-based superalloy during its cooling, in this study a thermodynamically-consistent thermo-elasto-viscoplastic model was developed. This model takes into account the solid-liquid transition occurring in the material during the cooling phase. This is done by introducing a compressible-type viscoplastic yield function based on appropriate equivalent stress depending on volume fraction of the solid phase formed by the propagation of dendrites inside the liquid phase of the material. This model was implemented in Abaqus/Standard© F.E. code and applied to the identification of material parameters of Ni-based superalloy using isothermal tensile-relaxation tests driven for different strain rates and temperatures. First, anisothermal tensile-compression test was simulated on a single integration point. A comparison of the experimental and numerical stress-strain response partially validate the model. Second, a benchmark test involving casting of a rectangular Ni-based superalloy bar in a sand mold was simulated and analyzed.

A Novel Multi-Stage Impingement Cooling Scheme—Part I: Concept Study

Abstract The impingement cooling for a modern gas turbine component, either a combustor liner or a high-pressure turbine blade, is often not as efficient as required due to strong cross-flow effect and coolant maldistribution. This paper reports a novel multi-stage impingement cooling scheme to effectively use the coolant and minimize the cross-flow effect. The design concept and general working mechanism are introduced in this Part I paper. The extra design flexibilities and optimization strategies are reported in Part II. Numerical simulations on conjugate heat transfer (CHT) were carried out to assess the flow structure and thermal performance between a typical single-stage cooling design and a three-stage cooling design at typical operating conditions. It has been observed that the novel multi-stage cooling design can reinitiate impingement jets at each stage, which greatly reduces the cross-flow impact and local thermal gradient. The staging of cooling air for the target surface also offers better utilization of the cooling capacity. Even by using 50% of the coolant designed for the single-stage impingement cooling, the multi-stage case can still sufficiently cool the target surface. The additional pressure loss penalty introduced in multi-stage design needs further efforts on design optimization.