Gas Turbine Blades Research Articles

Thermal Aging Effect on In-Plane and Cross-Plane Thermal Diffusivities of Plasma-Sprayed Thermal Barrier Coating

Thermal barrier coatings (TBCs) are used to shield from heat and wear of components which are used at high temperature situation, for example, the blades of gas turbines. There is a pressing need to evaluate the thermal conductivity of TBCs in the thermal design of advanced gas turbines with high energy efficiency. In the case of gas turbines, these TBCs consist of a ceramic-based top-coat (TC) and a bond-coat (BC) on a superalloy substrate. TBCs are commonly prepared by plasma spraying process. The TC is expected to play the role of a thermal shield. Thus, thermal conductivity of thickness direction of TBC has been investigated. However, plasma-sprayed TCs were known that they have anisotropic microstructure. We have been investigating in-plane and cross-plane thermal diffusivities of plasma-sprayed Yttria-stabilized zirconia (YSZ) TCs at 300 K in detail in a previous study. From the results of thermal diffusivity measurements for four kinds of TCs, it was found that plasma-sprayed TCs had significantly anisotropic thermal diffusivity depending on their microstructures. In this study, we measured in-plane and cross-plane thermal diffusivities of typical two plasma-sprayed TCs from 300 K to 1200 K in vacuum. And we also measured in-plane and cross-plane thermal diffusivities of annealed TC with different aging time. It was found that anisotropy estimated from in-plane and cross-plane thermal diffusivities did not change from 300 K to 1200 K. There was a tendency that thermal diffusivity value and anisotropy slightly increased by thermal aging effects.

Data‐Driven “Cross‐Component” Design and Optimization of γ′‐Strengthened Co‐Based Superalloys

The design of complex multicomponent superalloys has always been challenging due to the interaction of multiple elements and stringent requirements for various properties. Herein, an integrated approach to designing the high‐component (>7) γ′‐strengthened Co‐based superalloys with well‐balanced properties is developed by combining the diffusion multiples and machine‐learning models. A “cross‐component” prediction is achieved by the machine‐learning models, where two types of novenary superalloys are screened out for aeroengine and industrial gas turbine blades, respectively, based on the experimental database mainly consisting of six to seven elements. The method is verified to be effective or slightly more favorable than the Calculation of Phase Diagram (CALPHAD) in predicting the γ′ solvus temperature (Tγ′) and phase constituent of the high‐component alloys when reasonable data of low‐component alloys are just provided. Furthermore, the oxidation resistance and hardness of polycrystal superalloys as well as the compressive strength of single‐crystal superalloys are tested. Finally, some factors affecting the accuracy of “cross‐component” prediction are discussed. Expanding the compositional range and supplementing the critical interaction data of multiple elements in the database are beneficial for improving the accuracy of the “cross‐component” prediction.

Investigation of the stress-strain state of a turbine blade twisted according to the potential vortex law by the finite element method

Increase of power and complication of turbomachinery design is accompanied by stricter requirements to their reliability. Increasing the service life of turbomachinery is also one of the main tasks of quality improvement. Since the blade is a highly loaded element of any turbomachine, high operational requirements are imposed on it, expressed in reliability and durability of this element. A large number of factors affect the performance of the blade, one of which is its twist. The purpose of the current study is to determine the effect of twist of a gas turbine blade twisted according to the potential vortex law.The results of research of twist law influence on stress-strain state of the blade of the last stage of axial gas turbine, twisted according to the potential vortex laware presented. For this purpose, using the internal packages Ansys, CFX and Static Structural, we performed an interdisciplinary conjugate analysis of the solutions of the computational gas dynamics and static strength problems. During the analysis of the static strength problem we considered the tensile stresses arising in the field of centrifugal forces, bending stress (in different planes — from the pressure difference between inlet and outlet and from the pressure difference on the concave and convex surfaces of the blade), torsional stress, as well as thermal stress.Evaluation of the obtained results in conjunction with the analysis of previously derived analytical dependencies allowed to establish the influence of blade twist on the stress-strain state. The factor of torsion stresses and deformations should be taken into account when designing twisted blades and their subsequent gas-dynamic and strength estimation.

Review of the State of the Art for Radial Rotating Heat Pipe Technology Potentially Applicable to Gas Turbine Cooling

Improvements in the efficiency of gas turbine engines over the decades have led to increasing turbine inlet temperatures. This, in turn, has resulted in the need to cool the turbine blades themselves to avoid damage to them. While air-cooling and film-cooling methods have been adopted as the primary methods of gas turbine blade cooling, the heat pipe cooling method shows greater potential in terms of temperature uniformity, maximum allowable gas temperature, reliability, and durability. This paper reviews the state-of-the-art research activities on the radial rotating heat pipes (RRHP) potentially applicable to gas turbine cooling. The emergence of the heat-pipe-cooled turbine blade concept, designs, and variants will be described at the beginning. Then the paper will review the literature addressing the heat transfer performance of RRHPs, and the effects on them of rotational forces, working fluid properties, and geometry, as well as operational limits they may be subject to. Additionally, the effects of secondary flow and numerical simulation of RRHPs will be reviewed and discussed. It can be concluded that fundamental studies are still needed for the understanding of the RRHP, as well as the improvement of numerical models.

Structural degradation and elemental variations in an ex-service first-stage gas turbine blade

Structural degradation and elemental variations in an ex-service first-stage gas turbine blade

EFFECT OF STAND-OFF DISTANCE ON ABRASIVE WATER JET PIERCING OF CERAMIC-COATED SUPERALLOY

The drilling of film cooling holes on gas turbine blades made out of ceramic-coated superalloy improves the efficiency of the gas turbine and prolongs the life of the turbine blade. The purpose of this study was to investigate the effects of different stand-off distances (SODs) on abrasive water jet (AWJ)-pierced holes, in which the machining time, entry and exit hole diameters, overcut, hole taper, and surface morphology were studied. In this study, the water jet pressure (WJP) of 275[Formula: see text]MPa, piercing angle of [Formula: see text], dwell time of 0.2[Formula: see text]s, and abrasive flow rates (AFRs) of 350[Formula: see text]g/min and 400[Formula: see text]g/min were considered for the AWJ piercing operations. The entry and exit hole diameters and overcut linearly increased with an increase of SOD with different abrasive flow rates. And hole taper was observed at the coating and substrate sections in which it decreased with an increase of SOD up to 2[Formula: see text]mm, and a further increase of SOD increased the hole taper. Besides, the drilled holes were found to have an absence of delamination, cracks, and thermal defects. It was also noted that there is a transformation from a brittle to a ductile mode of erosion that may occur in the high-erosion kinetic energy impact region in the YSZ material section. Based on the experimental results, it is confirmed that SOD of 2[Formula: see text]mm became an influencing factor in AWJ for piercing quality holes in the YSZ-coated superalloy.

Thermodynamic sensitivity analysis of SOFC integrated with blade cooled gas turbine hybrid cycle

In the area of clean energy production along with higher efficiency, integrated combine power system, specifically gas turbine (GT) cycle with solid oxide fuel (SOFC) system, is gaining the attention of researchers. Thermodynamic modeling for the SOFC-GT hybrid cycle has been presented in this paper. For the proposed hybrid cycle, a high-temperature SOFC has successfully integrated with the recuperated-blade cooled gas turbine cycle. The gas turbine outlet waste heat has perfectly utilized the recuperator to power the fuel cell system. However, to maintain the temperature of the gas turbine blade within the permissible limit, air–film blade cooling scheme has been used. The SOFC-GT hybrid cycle has been operated under steady-state conditions, and a developed MATLAB program has been used to solve the governing equations for the components of the hybrid cycle. The impact of main operating parameters such as the temperature intake turbine (TIT), compression ratio (rpc), fuel utilization ratio (UF), and recirculation ratio are examined. From the obtained result, it can be revealed that the integration of the SOFC has seen significant improves overall hybrid cycle efficiency. The performance of fuel cell (SOFC) increases notably as the level of recuperation increases. To check the influence of main operating parameters, a sensitivity analysis has been performed for the hybrid cycle, and the maximum efficiency of 73% has been achieved. Moreover, to extend this research, an exclusive performance map has been plotted for power plant designers.

Film cooling improvement analysis in gas turbine blades by swirling coolant flow using a numerical study and an RBF artificial neural network

BackgroundA numerical simulation is carried out to assess the film cooling improvement of the gas turbine blades using proposed hole shapes. The manipulation of the hole shapes is only conducted on the suction and pressure side. The study follows having converging round-to-slot holes and making the coolant flow to be swirled by considering the screwed holes’ wall or inserting a twisted tape, with different rotation angles or the tape's widths, in the film-cooling holes. MethodsUsing the numerical simulation results, total and individual coolant mass flow rates, bulk-averaged blowing ratio, energy loss, and averaged adiabatic coolant effectiveness are computed. A post-processing method is used for calculating the parameters. The numerical results are also fed to an artificial neural network to evaluate its ability to predict. Significant findingsConsidering an overall comprehensive evaluation, the swirling patterns can be beneficial, as they lead to 11% higher adiabatic cooling effectiveness and 4% lower energy loss, compared to the traditional cylindrical holes. Further, inserting twisted tape in the holes requires a 33% lower coolant mass flow rate compared to cylindrical holes. RBF neural network shows a powerful tool to predict mass flow rates.

Flow and Heat Transfer Characteristics of the Turbine Blade Variable Cross-Section Internal Cooling Channel with Turning Vane

The gas turbine blades are scoured by high temperature gas sustainedly and long-term in harsh environment. It is of great significance to explore effective cooling methods to lower the turbine blade temperature so as to ensure safe and stable operation of the gas turbine. However, there are few studies on the cooling channel considering the turning vane, variable cross-section characteristics, and rotation effect. In this paper, five kinds of serpentine cooling channel models with variable cross-section properties and different thickness guide vanes are constructed. The effects of different thickness guide vanes on the overall performance of the channel under stationary and rotating conditions are discussed and compared by numerical method. The result shows that when stationary (Re = 10,000–50,000), the turning vane with suitable thickness can increase the Nu/Nu0 by 56.5%. The f/f0 is decreased by 14.2%, and the comprehensive thermal performance is increased by 4.5%. When rotating (Re = 10,000, Ro = 0–0.5), the turning vane with suitable thickness can increase the Nuup/Nu0 and Nuall/Nu0 by 33.0% and 4.0%, respectively. The comprehensive performance of the variable cross-section serpentine channel can be greatly improved by arranging the turning vane structure with appropriate thickness.

Camera-based high precision position detection for hybrid additive manufacturing with laser powder bed fusion

Additive manufacturing (AM) in general and laser powder bed fusion (PBF-LB/M) in particular are becoming increasingly important in the field of production technologies. Especially the high achievable accuracies and the great freedom in design make PBF-LB/M interesting for the manufacturing and repair of gas turbine blades. Part repair involves building AM-geometries onto an existing component. To minimise the offset between component and AM-geometry, a precise knowledge of the position of the component in the PBF-LB/M machine is mandatory. However, components cannot be inserted into the PBF-LB/M machine with repeatable accuracy, so the actual position will differ for each part. For an offset-free build-up, the actual position of the component in the PBF-LB/M machine has to be determined. In this paper, a camera-based position detection system is developed considering PBF-LB/M constraints and system requirements. This includes finding an optimal camera position considering the spatial limitations of the PBF-LB/M machine and analysing the resulting process coordinate systems. In addition, a workflow is developed to align different coordinate systems and simultaneously correct the perspective distortion in the acquired camera images. Thus, position characteristics can be determined from images by image moments. For this purpose, different image segmentation algorithms are compared. The precision of the system developed is evaluated in tests with 2D objects. A precision of up to 30μm in translational direction and an angular precision of 0.021∘ is achieved. Finally, a 3D demonstrator was built using this proposed hybrid strategy. The offset between base component and AM-geometry is determined by 3D scanning and is 69μm.

Investigation into femtosecond based laser ablation and morphology of micro-hole in titanium alloy

Creating good surface quality micro holes for cooling gas turbine blades made of titanium alloy is still challenging for manufacturers of aerospace engine components. Therefore, the goal of this work is to comprehend how an ultra-short pulse laser interacts with titanium alloy and to explore the effect of laser fluence, pulse overlap and pulse repetition rate on hole diameter, depth, heat affected zone and recast layer. The threshold for femtosecond laser ablation is determined for different laser fluence, pulse repetition rates, and hole sizes. By using a 3D profilometer and field emission scanning electron microscopy, the ablated micro hole features are determined. Regardless of laser fluence or hole size, better micro hole shape is seen at a threshold repetition rate of 10 kHz. Better hole geometry is obtained at fluence of 0.44 J/cm2, 10 kHz repetition rate and 85% of pulse overlap. At higher pulse overlap, micro-cracks, heat-affected zones, and recast layers are more prominent, which is related to higher heat accumulation since titanium alloy has a low thermal conductivity.

Mode (I, II, III) Stress Intensity Factors of Composite-Coated Gas Turbine Blade Using Semi-Elliptical Crack

Mode (I, II, III) Stress Intensity Factors of Composite-Coated Gas Turbine Blade Using Semi-Elliptical Crack

Computational flow and heat transfer study on impingement cooling in a turbine blade leading edge using an innovative convergent nozzles

The present paper discusses a detailed numerical study performed to investigate flow and heat transfer characteristics of impingement cooling of the leading edge of a HP gas turbine blade model. An array of innovative converging shape nozzles are used as jets which strike the surface to be cooled. A comprehensive study is presented investigating various parameters which effect impingement cooling. These parameters include varying Mach number of the flow as 0.2 to 0.8, converging ratio of the nozzle varied as 2 to 8 at two different minor diameters of 0.25–0.5 mm of the jet, pitch distance is changed from 3 to 5 mm, and inter-jet distance changed from 3 mm to 6 mm. Each parameter is independently scrutinized keeping other parameters constant. The results indicate the formation of primary stagnation region where Nusselt number augmentation is maximum compared to secondary stagnation region. Cross-flow effect plays a significant role in reducing peak values in the Nusselt number in the downstream region. Enhancement in peak Nusselt number value is greater for high values of Mach number of the flow, lower jet-to-target distances and the higher converging ratio at a lower value of jet diameter. Average Nusselt number is found to be higher for lower values of pitch distance.

Modeling and experimental study on deformation prediction of thin-walled turbine blades during investment casting process

Due to variable cross-sections and a thin-walled structure, gas turbine blades have stringent dimensional, and geometrical tolerance requirements. Single-crystal hollow blades are manufactured using the following investment casting processes: ceramic core preparation, wax injection, ceramic coating, wax removal, metal casting, and finishing. The main causes of the final casting deformation are wax pattern deformation, core deflection, and metal solidification warpage. This paper proposes a numerical simulation method to predict the deformation of the wax pattern, core deflection, and the directional solidification (DS) process of large single-crystal blades. Additionally, it investigates the displacement field and the influence of casting process parameters on dimensional accuracy. Three groups of DS process parameters were selected for experiments, and the deformation prediction was in agreement with the experimental results. The selected blade section deformation is the smallest when the pouring temperature is 1530°C and the withdrawal rate is 5 mm/min. The proposed finite element model is efficient to predict the deformation in all the investment casting processes, providing geometric guidance for the control of the dimensional accuracy of the turbine blade.

A Novel Yield Criterion for Nickel-Based Superalloys

Abstract With the significant evolution of modern gas turbine engines, selection of high-temperature resistant alloys in the hot section is known to be the fundamental solution to enhance the capabilities of these engines. In general, the high-temperature components are mainly comprised of polycrystalline, directionally solidified, and single crystal superalloys. Single crystal (SX) superalloys were developed in the 1980s to achieve high fatigue resistance and substantial creep rupture strength by eliminating grain boundaries. Directional solidification methods enabled the solidification arrangement of the materials to be comprised of columnar grains which are aligned parallel to the 〈001〉 direction. These casting types have been frequently used with nickel-based superalloys (NBSAs) to develop modern gas turbine blades. In this work, the yield behavior of generic SX and directionally solidified (DS) NBSAs is studied. By observing various SX and DS alloys, it was concluded with need for a novel criterion that can present anisotropic and tensile/compressive asymmetric yield surfaces. This novel criterion is comprised of the criterion proposed by Hill for anisotropic materials and the method developed by Drucker and Prager for alloys that have different tensile and compressive yield strengths. Additional terms to Hill's criterion are introduced to capture the coupling effect of normal stress and shear stress when the applied loads are not in the direction of principal axes of the material coordinate system for single crystal alloys. The parameters for the criterion are obtained from simple uniaxial tension and compression experiments. Results are compared with various well-established yield criterions. Additionally, the novel criterion is utilized to capture the effective stress and strain of multi-axial loading of turbine blades under nonisothermal conditions

Cooling and Flow Characteristics of Multi-Channel Wall Jet Structure With Film Holes at Blade Leading Edge

Abstract Efficient cooling is imperative for gas turbine blades that suffer from hot gas erosion. Cooling and flow characteristics of multi-channel wall jet structure combined with film holes for blade leading edge are numerically investigated through the Reynolds-averaged Navier–Stokes method in this paper. Several geometrical schemes with different rows and diameters of film holes were conducted, and the influences of the cooling air mass flow ratio of the first coolant supply cavity were also considered, which presented the detailed flow and cooling characteristics of wall jet and film composite cooling on conjugate heat transfer. The results implied that film extraction improves the overall cooling effectiveness compared with pure wall jet cooling. And the mainstream intrusion happens in some film holes at the bottom of blades, especially on the pressure side. The film-hole diameter can raise the mass flow ratio and enhance external thermal protection produced by cooling air, and it also affects the uniformity of film flow and the temperature gradient of some regions for turbine blades. Furthermore, the cooling performance and pressure loss are significantly influenced by the coolant mass flowrate of the first cooling air supply cavity. This study will offer a consultation for the design of film-hole structures for multi-channel wall jet cooling.

An experimental and numerical study on the liquid cooling of a gas turbine blade

In this paper, two kinds of internal liquid kerosene and one film cooling channels are designed for a static blade of turbine engine. The cooling efficiency is studied through numerical and experimental approaches. Two internal liquid cooling channels include a regular-sized(di = 4 mm) and a micro-channel(di = 0.8 mm). Regular sized cooling structure is three U-shaped channels. Higher heat transfer coefficient is observed in the area near the inner wall before the elbow and near the outer wall after the elbow. The regular sized channel cannot be designed approaching the leading edge of the blade due to the larger channel diameter. It will lead to poor cooling efficiency at the leading edge. The micro channel cooling structure can be mounted closer to the leading edge because of its smaller diameter. It covers a wide area and can be evenly arranged on the pressure and suction surfaces of the blade. For the film cooling structure, it shows that the film cooling method can effectively reduce the leading edge temperature when the blowing ratio is greater than 1.3. The optimal blowing ratio for this blade is about 2.5. Experiments are carried out under high temperature conditions (1000 K). Experiment results show that the micro channel cooling structure can reduce the blade temperature by more than 230 K, and the error between simulation and experiment is less than ± 10 %.

Aerothermal performance analysis and knowledge discovery of film holes on the squealer tip of a gas turbine blade

This paper aims to explore the effects of the size/location of film holes on gas turbine rotor tips and improve tip aerothermal performance by establishing a knowledge discovery platform. The study is conducted on the squealer tip of the GE_E3 rotor. Firstly, the effects of the size/location parameters of the single film hole at the different regions on the tip are investigated. Under the same working conditions, detailed flow structure and cooling analysis reveal the size/location parameters of a single hole have an effect on local film cooling effectiveness but little effect on aerodynamic loss, especially for the leading edge hole. Then, a knowledge discovery platform is established, which includes optimization design, aerothermal analysis, and data mining. On the squealer tips, by optimizing the size and location parameters of all film holes, the average film cooling effectiveness is increased from 1.301% to 6.132% while the total pressure recovery coefficient almost remains at 91.395%. Further, the analysis of variance (ANOVA) method uncovers that the size/location of the holes on the leading edge have the most important effect on the film cooling performance, and hole diameter exerts a more significant effect than the location. These results indicate that the cooling performance of tips can be improved by expanding the diameter of the film hole and moving forward the holes to the leading edge.

Electrochemical Machining Process Using Different Electrolytes for Improved Process Efficiency

Electrochemical machining (ECM) was developed as a result of the manufacturing and production industry's need to cut extremely hard alloys without leaving a troublesome layer. Manufacturing industries involved in gas turbine blades and aerospace need intricate geometries that would be difficult to make using standard methods. Because of high tool wear (TW) and metal removal rate (MRR), traditional machining processes such as milling and other conventional machining are inefficient for extracting metal from hard materials. This study outlines, a comprehensive analysis of the ECM processes using different electrolytes for better process efficiency.

EXPERIMENTAL INVESTIGATIONS FOR EFFECTIVENESS OF COMBINED IMPINGEMENT FILM COOLING

Protecting the gas turbine blades from high-temperature gases and increasing the specific work output is one of the most challenging tasks for most gas turbine design engineers. Combined impingement and film cooling can be used as a hybrid cooling technology to improve the film cooling performance over the gas turbine blade surfaces. In the present work, experimentations were performed on a flat plate with combined impingement film cooling for two thermally conductive materials (Perspex and stainless steel) at different blowing ratios and compared with the computational results. Thermo chronic liquid crystal sheets were used for measuring the temperature distribution. Effectiveness is the parameter that plays a vital role in determining thermal performance. Uniform effectiveness distribution was observed in stainless steel material because of its more thermal conductivity. Combined impingement film cooling showed higher effectiveness compared to film cooling. Uncertainty of ± 7% present in TLC data and experimental results agreed with the computational results.