bluuebunny/crossref_metadata_2025 huggingface dataset:
Validation of the Numerical Simulation of Rotor/Stator Interactions in Aircraft Engine Low-Pressure Compressors
Authors: Favretti Isabelle , Roux Louis , Batailly Alain
Published: August 2024

This contribution focuses on the validation of a numerical strategy developed jointly by Safran and Polytechnique Montréal for the simulation and the analysis of blade-tip/casing contact interactions in low-pressure compressor stages. A large experimental campaign provided data (including strain measurements on the blade and abradable coating wear profiles) for several contact configurations involving four distinct blades and one type of abradable coating. The numerical strategy is here improved by introducing a new cut-off criterion to ensure the physical relevance of the presented results, specifically by keeping the maximum stress within the blade below the material’s yield stress. Similarly to previous publications involving a single contact configuration, the numerical model is first calibrated for one of the four blades of interest. It is seen that the results using the numerical model — critical speed, relative wear depth between leading edge and trailing edge, maximum stress levels within the blade — are in good agreement with the experimental observations. Using the same calibration, numerical simulations are then blindly run for the three other blades. The results demonstrate that numerically predicted key quantities align well with experimental data. Additionally, the numerical model provides an accurate relative assessment of a blade’s sensitivity to contact in agreement with experimental observations. This paper thus presents the first blind validation of a numerical strategy dedicated to blade-tip/casing contact interactions. Simultaneously, it also demonstrates that this model may be considered for the early discrimination of blade profiles depending on their sensitivity to contact.
Development and Validation of a Numerical Multiphysics Algorithm for Wall Condensation Heat Transfer for Steam Turbines Starting Phases
Authors: Rafanelli Isacco , Andreini Antonio , Facchini Bruno , Diurno Tommaso , Tomasello Stella Grazia , Girezzi Gabriele
Published: August 2024

Due to the rising interest in using renewable energy for environmental impact reduction, steam turbines are facing with a radical change in design practices and operability. In particular, the unpredictable and variable production of renewable plants drives to frequent shutdowns and fast start-ups of steam turbines, which have a huge impact on structural integrity. During start-up phases, the high temperature steam could face with a below-saturation wall temperature causing condensation and then high temperature gradients on solid components.

Hence, the proper thermal gradient evolution and condensing mass prediction are quite relevant in steam turbine design. Nowadays, numerical Conjugate Heat Transfer (CHT) analysis is a good industrial practice to quantify the thermal distribution in turbomachinery components. On the other hand, the usual bottleneck of these analyses is the fluid timestep and the required temporal discretization that is one or two order of magnitude smaller than the solid one: therefore a fully coupled unsteady is still unaffordable in terms of computational costs.

In this context, this work presents a low dimensional multiphysics approach which models the condensation phenomenon through correlations and the solid heat transfer through discrete 1D transient heat equation. Furthermore, a 3D CHT by employing the eulerian wall film multiphase approach is presented and compared with the developed algorithm.

Finally, the numerical results obtained are compared with field data on a real unit where the inlet section, as usual, is subjected to the described condensation phenomenon.
Scale Cooling -- A Novel Fractal Cooling Structure for Turbine Vanes
Authors: Chi Zhongran , Wang Longfei
Published: August 2024

Additive manufacturing technology provides the possibility of more efficient turbine cooling structures. In this work, a novel structure for turbine air-cooled vane based on fractal structure, named Scale Cooling Structure, was proposed. Fractal channel arrays are arranged on the leading edge, pressure side, and suction side of the novel vane. The design of the fractal channel units takes into account the internal cooling effect, film cooling effect, manufacturing accessibility of the channels, and adaptability to non-uniform thermal loads. The initiated cooling structure allows for the use of larger wall thickness to improve strength.

A parameterized design and automated mesh generation technique based on in-house code was developed for the vanes installed with Scale Cooling Structure. And typical turbine vanes with impingement-film cooling structure and Scale Cooling Structure were evaluated by both IR measurement and conjugate heat transfer CFD analysis. Experimental studies have shown that the local overall cooling effectiveness at the leading edge of the Scale Cooling Structure vane is obviously improved compared to the prototype design with impingement-film structure. The consistency between the IR measurements and the CHT CFD results is favorable.

It is found that the improvement in cooling performance of Scale Cooling Structure is mainly due to the improvement of film cooling. Its internal cooling relies on enhanced heat transfer at the branching positions of fractal channels. The Scale Cooling Structure is more sensitive to insufficient coolant supply pressure. It is suggested that the entire pressure difference between the cooling air and the mainstream shall be utilized by the Scale Cooling Structure, which can provide sufficient backflow margin while enhancing internal cooling.
Experimental Investigation of Randomly Oriented Wire Mesh Damper Performance
Authors: Pietrowski Seth P. , Villanueva Bryce , Kauffman Jeffrey L.
Published: August 2024

Wire mesh dampers can provide excellent damping for extreme environments and structures that repeatedly experience large vibrations. As a subset of friction damping, the fundamental technology has been explored through extensive material and empirical testing. Compared to more traditional friction dampers, however, the performance of wire mesh dampers remains relatively unexplored, both empirically and analytically. Limited studies address meshes aligned in very specific, repeating arrangements; this paper seeks to characterize performance for randomly oriented wire meshes. This paper explores the damping behavior across the parameter space of several mesh dampers, varying mesh parameters like wire diameter, mesh density, and compression force. Specific properties include the mesh effective stiffness and damping performance, measured across several compression set curves. Experiments show that a mesh compressed against a plate structure adds significant damping to the structure, and higher compression levels increase both the added damping and added stiffness effects of the mesh. Randomly oriented wire meshes provide a potential avenue for further study and implementation in extreme environments.
Direct and Refined Characterization of Rebound for Irregularly Shaped, High-Speed Particles Incident on Aerospace Grade Titanium
Authors: Weindorf Brandon J. , Ehlers Alix , Lowe Todd , Ng Wing , Caddick Mark , Loebig Jim , Morrison Matthew
Published: August 2024

The observed stochasticity in rebounding trajectories for particle-surface interactions in turbomachinery is often attributed to irregularities in particle shape. However, at higher speeds, plastic deformation of the surface can significantly influence the rebounding particle trajectory. This work explores the interaction between particle shape and surface plastic deformation at high speeds and the effect that it has on the observed spread in rebounding trajectories. Two parameters often used to characterize particle-surface interactions in turbomachinery are the coefficient of restitution (COR) and rebounding angle. A fully time-resolved two-dimensional Particle Tracking Velocimetry (2DPTV) system is employed on a high-speed free jet rig to study particle-surface interactions for 150 μm – 250 μm crushed quartz incident on Grade 4 (Commercial) Titanium. Particle speeds range between 50 m/s and 130 m/s and nominal incidence angles of 30° and 90° are studied. In this work, a novel approach that couples the study of both the particle and particle-surface interactions is discussed. In addition to a full description of the experimental procedure, a source of random uncertainly stemming from particle shape coupled with rotation and inter-pixel effects is presented for both velocity and rebounding angle measurements. Moreover, the sensitivity of particle rebounding trajectories to particle shape is explored. A model from the literature is modified to include the effects that particle shape has on the normal coefficient of restitution. The sensitivity study of particle shape is then expanded to total COR and rebounding angle. It is shown that increases in plastic deformation decrease the sensitivity of the COR (both total and normal) to particle shape, reducing the spread of COR values. In contrast, the spread in rebounding angles is dominated by particle shape irregularities and incidence angle with little dependence on plastic deformation.
Numerical Investigation of Windage Heating in High-Pressure Compressor Shrouded Stator Cavities
Authors: Damgacioglu Altay , Cottier Francois , Gümmer Volker
Published: August 2024

Literature provides valuable insights into the thermodynamic behavior of labyrinth seals, but modelling is still incomplete. In this study, a 3D CFD model of a shrouded stator passage was constructed. Various model variations such as increased wall roughness, fixed temperature boundary conditions and walls with fixed heat flux values have been applied to the model to accurately simulate the heat pickup in the labyrinth seal. The heat pickup in the cavity was then quantitatively analyzed and compared with experimental values and with various methods in the literature. Finally, a coupled CFD-FEM method was used as an additional validation mechanism. The study showed that the flow behavior in the experiments was accurately simulated in terms of core swirl ratios, pressure ratios and total temperature rise. The total temperature rise, on the other hand, can be successfully partitioned between conductive heat transfer and windage heating. Future studies may be required to validate the confidence of this study, especially for a range of engines and test rigs. Additionally, future investigations could focus on enhancing the accuracy of predicting the total temperature increase in inner air seals and exploring the effect of honeycomb structures on flow behavior.
Model-Based Inference of Flame Transfer Matrices From Acoustic Measurements in an Aero-Engine Test Rig
Authors: Eder Alexander J. , Merk Moritz , Hollweck Thomas , Fischer André , Lahiri Claus , Silva Camilo F. , Polifke Wolfgang
Published: August 2024

Flame dynamics in the form of aflame transfer matrix (FTM) is not directly measurable in a test rig, but must be deduced from transfer matrix measurements of the combustion system. The burner-flame transfer matrix (BFTM) approach for estimating the FTM is based on local pressure signals from two microphone arrays located upstream and downstream of the combustor. It combines acoustic transfer matrix measurements in non-reacting and reacting conditions, where the latter implicitly includes the flame dynamics. A simple matrix operation then yields the FTM. However, this approach assumes that there is loss-free wave propagation at a constant speed of sound with no change in cross-sectional area between the microphone locations and the burner/flame. The present work demonstrates the limitations of these assumptions when applied to a test rig with complex features, such as effusion cooling, bypass annulus, and downstream end contraction. To remedy the shortcomings of the BFTM approach, this work proposes a novel method to infer the FTM for complex combustors by combining reactive transfer matrix measurements of the entire combustor with an accurate low-order thermoacoustic network model (LOM) of the test rig. This generalized method reduces to the BFTM approach as a special case.

In this work, the Rolls-Royce Scaled Acoustic Rig for Low Emission Technology (SCARLET) operated under realistic engine conditions (Tin ≈ 825 K, pin ≈ 25 bar, kerosene) is used to analyze the capabilities of the proposed model-based inference method and the limitations of the BFTM approach. In a first step, a LOM based on the geometry and operating point of SCARLET is formulated using a generic FTM. This generic model is used to visualize the limitations of the BFTM approach in terms of various physical and geometrical parameters. Finally, experimental measurement data is used to deduce the FTM of SCARLET using the proposed approach.
Numerical and Experimental Investigation of Steady Flow Distortion in Drooped Turbofan Intakes
Authors: Zhang Yuhan , Dong Xu , Li Zhenyu , Sun Dakun , Sun Xiaofeng
Published: August 2024

In some civil aero engines, steady flow distortion in turbofan intakes is often caused by the non-axisymmetric geometry, mostly droop and scarf, and the trend of shortening the nacelle exacerbates this distortion. Much analysis of previous research has established models for numerically predicting the propagation of modes through the region of steady flow distortion, but experimental measurements of the internal flow field in the intake remain challenging. The main objective of this paper is to demonstrate the feasibility of experimentally investigating the steady flow distortion in drooped turbofan intakes, providing a framework for a deeper understanding of the flow mechanisms in these intakes. Firstly, based on two types of geometrical shape, droop and scarf, three different geometries of intakes are designed, and the steady flow distortions they generate are compared using computational fluid dynamics (CFD). Secondly, the generation mechanism of steady-state distortion will be briefly discussed. Finally, this study designs fan experiments under static inlet conditions. The experiments are conducted on an aspirated fan test rig, and total pressure and static pressure measurements are recorded with a 5-hole Aero-Probe. The research results indicate that the fan experiment is successful in capturing this steady flow distortion. Both droop and scarf type intakes cause minor steady flow distortion at the outlet of the intake, which rapidly decays in the duct.
A Speed Control Method for Hydrogen-Fueled Turbojet Using Improved Internal Model Control
Authors: Pan Mengni , He Ai , Chen Zhixiong , Liu Yuan , Hu Zhongzhi
Published: August 2024

Hydrogen is expected to be widely used in aviation, but accurately measuring its flow rate remains challenging due to its compressibility, potentially compromising engine performance. Prolonged operation of aero-engines in high-temperature environments can alter the health parameters of the engine’s gas path, potentially leading to performance degradation or even damage. Maintaining good dynamic quality of aero-engine speed is crucial despite uncertainties in hydrogen measurement and engine degradation. This paper proposes an internal model control algorithm and designs a robust speed controller that considers these uncertainties. Simulation results demonstrate that, unlike traditional PI methods where the relationship between robustness and design parameters is unclear, the proposed speed controller exhibits strong robustness. Even in the presence of uncertainties in metering and engine degradation, it effectively maintains speed control robustness.
A Modal Analysis of Spray Structures From a Transversely Injected Liquid Jet in Subsonic and Supersonic Crossflows
Authors: McKelvy Aubrey J. , Braun James , Paniagua Guillermo , Choquet Etienne , Andre Thierry , Falempin Francois
Published: August 2024

Flow instabilities in high-Reynolds flows are difficult to characterize because the increasingly chaotic interactions of fluid particles allow for larger variety and superpositions of flow patterns. These are especially underexplored in transversely injected liquid jets, which are a popular mixing strategy for high-Reynolds gaseous flows. This study utilizes proper orthogonal decomposition (POD) to identify periodic flow patterns in experimental spray images. A liquid ethanol jet is injected into both a linear subsonic (Mach 0.25 to Mach 0.7) and an expanding Mach 2 gaseous crossflow with plain-orifice injectors of 0.5, 1, and 2 mm diameter. The subsonic test section is rectangular with a 50 cm length and a 23 × 17 cm cross section; a contoured insert is installed in this rectangular test section to generate the supersonic flow path with a 2.54 × 23 cm throat area. Across both regimes, crossflow mass flows vary from 0.5 to 12 kg/s with injectant momentum flux ratios between 0.3 and 180. Reynolds numbers scaled by the injector diameter varied between 4,000 and 52,000. A high-speed camera is used with backlit, shadowgraph, and schlieren imaging systems to collect transmittance contours of the spray at 50 kHz. Unique ‘dagger’ and ‘hump’ shaped spray features are identified and correlated with the shear breakup regime of turbulent and semi-turbulent liquid jets and the catastrophic breakup regime. The same features are identified as ‘advection modes’ with the POD along with a ‘breathing mode’ corresponding to a low frequency oscillation of the mean penetration, and the mode images provide an accurate representation of the phase-averaged size and shape of these periodic spray structures. A characteristic length is used to normalize the peak POD frequencies and produces a mapping that places the three breakup regimes in specific groupings of Weber number and momentum flux ratio.
Exploiting a Transformer Architecture for Simultaneous Development of Transition and Turbulence Models for Turbine Flow Predictions
Authors: Fang Yuan , Reissmann Maximilian , Pacciani Roberto , Zhao Yaomin , Ooi Andrew S. H. , Marconcini Michele , Akolekar Harshal D. , Sandberg Richard D.
Published: August 2024

Previous studies have shown the potential of using a multiobjective CFD (computational fluid dynamics)-driven machine-learning approach to train both transition and turbulence models in RANS (Reynolds averaged Navier-Stokes) calculations for improved turbine flow predictions (Akolekar et al., GT2022-81091; Fang et al., GT2023-102902). However, conducting CFD-driven training incurs a high computational cost as thousands of RANS calculations are required if the starting guesses are taken from an initial population of randomly generated models. This paper, for the first time, adopts a transformer technique, belonging to the class of natural language processing models, in gene expression programming (GEP), to expedite the training process for transition and turbulence models. The efficacy of utilizing the transformer is investigated for two scenarios. In one, we introduce previously trained models to randomly generated ones in the initial population of candidate models, facilitating the generation of models with a higher likelihood of achieving lower cost function values from the outset. In the other scenario, assuming that no suitable information is available from pre-training, a dynamic approach is employed at certain training iterations, where models exhibiting significant errors are excluded and replaced by those trained on the fly by the transformer and demonstrating smaller errors. Additionally, we incorporate mathematical operators such as minimum, maximum, and exponential functions, along with a technique called a rolling window, to avoid nested functions in the trained models. This enhances the flexibility in constructing trained models while still allowing us to delve into the underlying physics and provide recommendations for developing physical models. Finally, we also introduce two additional physical features that serve as training inputs for the turbulence model that contribute to smaller errors. With these enhancements to the previous GEP framework, model training is accelerated considerably and the models found show improved performance for both training and previously unseen testing cases.
Reduction of the Emission Footprint of Gas Turbines in Future Energy System Scenarios Through Optimized Hydrogen Admixture Strategies
Authors: Goßrau Christian , Petersen Nils Hendrik , Wirsum Manfred
Published: August 2024

Within the energy sector, the mitigation of climate change necessitates a paradigm change towards the replacement of conventional with sustainable power generation technologies. Due to the inherent volatility of renewable power generation technologies, dispatchable components, such as gas turbines (GT) will have to be used increasingly for residual load balancing. In addition, GTs are expected to operate fewer hours per year, more flexibly, and at lower capacities. However, fuel utilization in GT is inherently linked to emissions. As a potentially CO2-free energy carrier, hydrogen is a promising fuel for GTs and manufacturers are working on suitable combustor technologies. However, the availability of large quantities of CO2-free H2 remains unclear in the near future. Other pollutants such as NOx and emissions due to incomplete combustion are formed differently in part-load. Therefore, optimizing natural gas substitution based on available H2 quantities and load profiles can improve the overall emission footprint beyond just reducing CO2 emissions.

In this study, a physical-based gas turbine performance model and an emission calculation tool are used to derive an optimized H2 admixture strategy for different load profiles. Characteristic load demand scenarios are derived from actual load profiles of gas power plants and the emission footprints are comprehensively evaluated by different environmental impact categories. In general, the emission footprint is increased significantly and moderately for capacity reduction and flexibility increase of GT operation. The availability of H2 in the near future is derived from forecasts for Germany, and the corresponding quantities are allocated to the partial loads according to the optimized strategy. In most scenarios, the addition of H2 is associated with a reduction in emissions compared to conventional fossil fuel operation. The greatest leverage of H2 admixture in reducing the environmental footprint is found when applied from the lowest load up, thus assisting in the start-up and shut-down process.
Preventing Tilting Pad Fluttering by Using Elastic Pad Fixation
Authors: Schüler Eckhard , Faulhaber Stephan
Published: August 2024

Tilting pad fluttering is a well-known phenomenon in journal and thrust bearings. It can occur on unloaded pads where the buildup of hydrodynamic pressure is not or not sufficiently achieved, which can be attributed to several causes. In severe forms of pad fluttering there is repetitive contact between the pad and the shaft. This can lead to bearing damages and, in the case of journal bearings, trigger subsynchronous rotor vibration with high amplitudes. There are various approaches to solving the problem, some of which relate to the elimination of existing pad fluttering. Proactive approaches are also described in the literature, but these are often associated with restrictions or certain disadvantages, meaning that these measures are not always applied in practice. To investigate a new approach, tilting pad fluttering was first caused and measured during experimental investigations on a conventional bearing. The bearing was then modified with the design solution “elastic pad fixation” which reliably prevented tilting pad fluttering without impairing the general properties and performance of the bearing.
Prediction of Soot in an RQL Burner Using a Semi-Detailed JetA-1 Chemistry
Authors: Lameloise Etienne , Cuenot Bénédicte , Riber Eleonore , Perrier Aurélien , Cabot Gilles , Grisch Frédéric
Published: August 2024

The present work proposes a methodology to include accurate kinetics for soot modeling taking into account real fuel complexity in Large Eddy Simulation (LES) of aeronautical engines at a reasonable computational cost. The methodology is based on the construction of an analytically reduced kinetic mechanism describing both combustion and gaseous soot precursors growth with sufficient accuracy on selected target properties. This is achieved in several steps, starting from the selection of the detailed kinetic model for combustion and soot precursors growth, followed by the determination of a fuel surrogate model describing the complex real fuel blend. Finally the selected kinetic model is analytically reduced with the code ARCANE while controlling the error on flame properties and soot prediction for the considered fuel surrogate. To perform all evaluation and reduction tests on canonical sooting flames, a Discrete Sectional Model (DSM) for soot has been implemented in Cantera. The resulting code (Cantera-soot) is now available for the fast calculation of soot production in laminar flames for any fuel. The obtained reduced kinetic scheme is finally validated in a Rich-Quench-Lean (RQL) burner of the literature in terms of soot prediction capabilities by comparison of LES coupled to the Lagrangian Soot Tracking model (LST) with measurements. Results show a significant improvement of the soot level prediction when using the reduced more realistic kinetics, which also allows a more detailed analysis of the soot emission mechanisms. This demonstrates the gain in accuracy obtained with improved reduced kinetics, and validates the methodology to build such schemes.
Optimization of a Battery Electric Hybrid Propulsion System for a Short Range Aircraft
Authors: Schroeter Jonas , Armbrüster Fabian , Schaber Reinhold , Gümmer Volker
Published: August 2024

In this paper, a serial electric hybrid propulsion system with a technology level of an entry into service in 2035 is designed and evaluated in a multidisciplinary way. The propulsion system is targeted for a 70-passenger regional aircraft with an typical mission of 400nm. The boundary conditions are set in the LuFo VI project TELEM.

In a novel approach the complete propulsion system consisting of propulsors, electric motors, electrical system, generator, batteries, gas turbine and nacelles is modelled. With this approach the propulsion system can be optimized regarding a given figure of merit and tailored to the specific boundary conditions in a multi-design point approach for all relevant operating points. Design rules for an electro-hybrid propulsion system were developed, which can consider any degree of hybridization in any operating point. In addition to the thermodynamic and aerodynamic design, weights, nacelle geometry, drag, thermal management, emissions and operating costs can be assessed, resulting in an integrated propulsion system design. Individual dependencies between the disciplines, such as the dependence of the nacelle drag on the performance of the thermal management are taken into consideration during the multi-design point sizing of the components. This allows the evaluation of the multidisciplinary figure of merit “block energy”.
Effect of Water Injection on Turbofan Engine Compressor Operation and Aerodynamics
Authors: Zawadzki Natan , Szymański Artur , Igie Uyioghosa
Published: August 2024

Water injection (WI) can potentially remedy aircraft-related nitrogen oxide (NOx) pollution around airports and substantially extend the hot section’s life. No high-fidelity study exists examining the effects of deploying compressor water injection (CWI) on turbofans — an engine type dominating the civil aviation market. The available analytical work is bound to several limitations, such as uniform droplet size distribution, simplified droplet transport and no phase coupling. Effects of local changes in the gas composition, interaction of turbulence with dispersed phase and the underlying loss production mechanism of wet compressions are neglected and thus remain unquantified.

The present work investigated the effect of WI on key performance and aerodynamic parameters in a fully integrated compressor of a generic turbofan engine using Computational Fluid Dynamics (CFD) analysis. The compressor layout comprised a fan stage and two core stages called booster. Water was injected behind the fan rotor at the inlet to the booster. Take-off operation was simulated at dry conditions and a range of wet scenarios with 1% and 2% water-to-air mass injection rates and varying droplet diameters from 10 to 20 microns.

Effects on the stage-by-stage compressor performance are discussed in detail, including water distribution, mass flow, temperature, pressure ratio, and efficiency. Particular attention was paid to the aerodynamic effects, which are impossible to obtain based on analytical results. Furthermore, the detailed droplet evolution inside the compressor was scrutinised, including particle residence time, change in size and distribution due to evaporation and interaction with compressor flow and components. The outcomes showed that water injection can result in favourable conditions for compressor operation. Furthermore, a reduction in compressor delivery temperature of up to 40 degrees Kelvin was predicted if finely atomised water was injected.
Analytical Leakage Model Development for Labyrinth Seals With Honeycomb Structure: Validation and Design of Experiments
Authors: Ertuğral Gürkan , Öksüz Özhan
Published: August 2024

Honeycomb structures are commonly used for many years in land and air turbomachinery applications to enhance the sealing effectiveness of labyrinth seals. Leakage control is the primary asset for honeycomb seals and directly impacts system-level efficiency; thus, estimating the correct leakage flow rate is crucial for the gas turbine engine performance. Leakage predictions are reliable for smooth land configurations using empirical correlations from available literature, however, accurate predictions are considerably challenging in the presence of honeycomb structures.

This paper aims to develop a robust analytical model to estimate accurate leakage mass flow rate by identifying the parameters influencing the flow discharge behavior of honeycomb seals. Reynolds-Averaged Navier-Stokes (RANS) based numerical simulations were performed to investigate flow phenomenon inside the labyrinth seals and honeycomb structures. Experimental test results of Stocker and Collins are the basis of numerical simulations for validation and design of experiments studies. Design of experiments studies were conducted to derive flow coefficients by changing operating conditions and geometric parameters of honeycomb and labyrinth seals. In the available literature, there are limited efforts taken to investigate the flow dynamic behavior of alternative and deteriorated honeycomb structures. For this reason, deteriorated honeycomb structures were investigated for radial displacement, rub groove events, and alternative liner geometries (slanted, square, triangle, circle) were examined and discussed in addition to the conventional honeycomb structures.

The proposed analytical model shows good agreement with the test results and has an extensive application range with reliable leakage prediction accuracy for straight-through labyrinth seals with honeycomb structures. The current model serves as a guideline for secondary air system design engineers and helps in the progress of honeycomb seal design in addition to analytical leakage models.
Review of the Impact of Hydrogen-Containing Fuels on Gas Turbine Hot-Section Materials
Authors: O’Connor Jacqueline , Noble David R. , Bridges Alexander , Shingledecker John , Scheibel John , Gagliano Michael
Published: August 2024

In an effort to achieve worldwide decarbonization goals, a range of low-carbon fuels is being proposed for use in power-generation gas turbines. Two promising fuels are hydrogen and ammonia, which do not produce any CO2 upon combustion. While the use cases of these fuels differ, each has the potential to reduce the carbon intensity of power generation as compared to the current use of natural gas and fuel oil. Many studies have considered the impact that these fuels will have on combustion stability and emissions, as well as other practical considerations like balance of plant. However, potential challenges for the material systems in these engines, particularly high-temperature metal alloys and coatings, have not been sufficiently considered in preparation for the introduction of these fuels. The goal of this paper is to provide a review of the potential material issues associated with implementation of these hydrogen-containing fuels, with a focus on materials in the hot section of existing power-generation gas turbines. To date, relatively little research has considered these material issues at realistic gas turbine conditions, resulting in a need for new research. This paper provides a review of the literature, first-order analyses of the magnitude of potential issues, and avenues for research to facilitate the safe and reliable introduction of these fuels in power-generation gas turbines.
Investigation of Hot Streak Migrations in a Triple Dual-Stage Swirler Combustor Coupled With Turbine Vanes Under Different Contraction Ratios
Authors: Lyu Jiacheng , Hu Keqi , Zhu Zhixin , Wang Gaofeng
Published: August 2024

With the rapid development of modern gas turbines and aeronautical engines, temperature at the combustor outlet is consistently increasing, leading to an intensified interaction between combustor and turbine. Meanwhile, the turbulence, residual swirl, and presence of hot streak at the combustor outlet exert a considerable influence on the downstream turbine, notably affecting blade aerodynamics and heat transfer dynamics.

Nowadays, significant research efforts have been focused on the coupled system of combustor and turbine, aiming to elucidate the flow dynamics and migration patterns of hot streak under complex interactions. This study presents a setup comprising a three-sector combustor and six turbine guide vanes (TGVs) equipped with advanced lean-burn dual-stage swirlers. Temperature distribution at the combustor outlet in the coupled system is measured through a high-temperature dual-axis displacement system. Numerical simulations are conducted to reveal the initiation and progression of hot streak within the combustor, operating within the coupled system. Moreover, the study investigates the impact of various contraction ratios on the mixing characteristics of gas and coolant within the combustor, as well as the migration process of hot streak in turbine guide vanes in the coupled system.

Overall, numerical results indicate that the influence zone of the TGVs on the pressure within the combustor can reach the position of the dilution holes, significantly affecting both the depth and mixing characteristics of the jet from the dilution holes. As the contraction ratio increases, there is an observed increase in the outlet temperature distribution factor (OTDF) within the combustor, which is attributed to reduced mixing effects. Conversely, at the TGVs’ outlet, an increased flow velocity and improved mixing effects in the TGVs’ flow channel contribute to a more uniform temperature field. Furthermore, the clocking position of TGVs in this study is found to impede the mixing of coolant in various flow channels. This highlights the significance of establishing a correlation between TGVs’ clocking position and the inlet hot streak.
Effect of Thermal Barrier Coating Simulation Method on Cooling Characteristics of Turbine Vanes
Authors: Du Zequn , You Ruquan , Li Haiwang , Huang Yi
Published: August 2024

Thermal barrier coating (TBC) is widely used in turbine vanes relying on the good thermal resistance, corrosion resistance. It is of great significance to accurately simulate the flow and heat transfer characteristics of coated vanes. However, there is no uniform standard for the simulation method of TBC. In this paper, the numerical study of vanes with a single-layer coating was conducted. The effect of the simulation methods (real model, called Method-1, and virtual thin-wall, called Method-2) on the flow and heat transfer characteristics was investigated under different TBC properties and turbulence intensity (Tu). The results showed the mass flow of film cooling on the suction surface of real TBC vanes was reduced by 25.5 %, when the TBC thickness was 0.3 mm. The TBC temperature differences between the two simulation methods on the overall and section surfaces were 5.4 K and 25.4 K. The TBC temperature was more sensitive to coating simulation methods. Modifying the property, the change of TBC temperature was the smallest at the leading edge, about 6.5 K. While the change of metal temperature was the largest there, about 37 K. The larger the thermal conductivity, the larger the metal temperature difference and the smaller the TBC temperature difference, which were caused by simulation methods. The sensitivity of temperature to Tu was relatively low for Method-1. As Tu increased, the absolute value of temperature difference on the section between simulation methods decreased first and then increased, and it decreased gradually on the overall surface. Finally, a simplified simulation method (Method-3) was proposed, in which the metal surface was thickened outwards with the virtual thermal conduction resistance added at the interfaces. And the accuracy of this method on the heat transfer characteristics of vanes with a double-layer coating was verified. For all turbulence intensity, the differences of coolant mass flow and temperature between Method-1 and Method-3 were less than 0.15 % and 2 K, respectively.
Assessment of Additive Manufactured Micro-Channel Characteristics: Impact of Hydraulic Diameter Evaluation
Authors: Bacci Tommaso , Picchi Alessio , Castelli Niccolò , Facchini Bruno , Morante Francesco , Innocenti Luca
Published: August 2024

Among internal cooling techniques for gas turbines components, skin cooling is recognized as one of the most promising, especially thanks to the spread of additive manufacturing techniques. In this regard, several studies have tried to characterize heat transfer and pressure loss performance of additive manufactured micro-channels, as well as the impact of AM characteristic parameters, mainly in the form of building angle, and resulting surface roughness and channel shape. The open literature offers several correlations in terms of friction and heat transfer coefficient using a representative hydraulic diameter. Despite that, little attention is given on the importance of such characteristic length definition which may lead to under/over estimation of the cooling rates when correlations are used in the design.

In this work, coupons featuring circular micro-channels with diameters of 0.5 and 1 mm and different building angles have been tested, to retrieve pressure losses and an average heat transfer coefficient through a lumped approach. The coupons were additive manufactured using the Laser Powder Bed Fusion (L-PBF) technique. Exploiting the experimental survey, the impact of the considered hydraulic diameter was investigated, by comparing different approaches based on a direct measurement. An additional and new approach, aimed at the identification of an “effective” diameter, based on fluid-dynamic considerations, was also considered.

The data correlation and the comparison with available correlations from different authors showed the newly proposed approach to provide superior scaling capabilities and, in turn, allowing for the development of more accurate prediction methods.
Investigation on the Interaction of Tip Leakage Flow/ Shock Wave/ Boundary Layer in a Transonic Compressor Stage
Authors: Ma Jianci , Li Jiabin , Ji Lucheng
Published: August 2024

The performance of transonic compressor blades is significantly influenced by the interaction among blade tip leakage flow, shockwaves, and boundary layers at their tips. In this study, a numerical investigation was conducted on a transonic compressor stage with and without shrouded rotor blades. Key factors affecting rotor tip performance were identified, including tip leakage flow/shock wave interaction and shock wave/boundary layer interaction. Observations also indicated that tip leakage flow played a mitigating role in reducing flow separation. Based on these findings, a design approach involving part-shrouded rotor blades was proposed. The optimal shrouded region of the rotor extends from the leading edge to slightly upstream the location of shock wave under near stall condition. Controlling the location of the tip leakage flow mitigates the interaction between tip leakage flow and shock waves, as well as the flow separation resulting from shock wave/boundary layer interactions, thus improving the stage performance. In NASA Stage 35, 20%–30% shrouded rotors can achieve both efficiency and stall margin improvements compared to the prototype. The 20% shrouded rotors exhibit an improvement in stall margin by 1.24% without any efficiency loss.
Calculation of the Overspeed at Emergency Shutdown of a Transonic Test Turbine Facility Using a Web-Based Thermodynamic Simulation Tool
Authors: Sanz Wolfgang , Perz Erhard , Göttlich Emil
Published: August 2024

The Institute of Thermal Turbomachinery and Machine Dynamics at Graz University of Technology operates a Transonic Test Turbine Facility of 3 MW power. The test turbine is a two-spool two-stage turbine. The high-pressure high-speed stage is connected to a brake compressor via a coupling, whereas the second low-pressure low-speed stage is connected to a water brake.

In the case of a coupling failure or a break-off of the water brake, an emergency shutdown is triggered in order to avoid excessive overspeed of the turbine stages, leading to blade dismantling or even disk bursting. For a previous one-stage setup, the shutdown procedure was developed and adjusted with the help of a dynamic thermodynamic simulation of the test rig which allowed to calculate the occurring maximum speeds. With this approach, the safe operation of the test rig shall be guaranteed.

This work presents a simulation model for the existing two-spool two-stage test rig. With a dynamic simulation, the overspeeds of the high-speed and low-speed shafts are calculated for the cases of coupling failure and water brake break-off as well as for the case of both shafts running freely. In this way, it is checked that the maximum speeds of the shafts in the case of an emergency stay within the allowable limits.

However, a break-off of the water brake in July 2022 led to higher overspeeds as predicted. The following investigations detected an error in the control system, which could have harmed the low-pressure turbine.

For the modeling and simulation, the newly developed web-based version of a thermodynamic simulation tool, IPSE GO, was used because it allows easy access to the simulation by all partners via a web browser.
Experimental and Numerical Investigation on Heat Transfer and Flow Characteristics of Array Jet Impingement Cooling With Film Extraction at the Turbine Shroud
Authors: Li Guodong , Guo Tao , Zeng Fei , Liu Cunliang , Li Jiayu , Li Changwei , Liu Shanjie
Published: August 2024

Jet impingement cooling is applied as an effective forced convection cooling method in regions with high thermal loads. This paper investigates the application of an array jet impingement with film holes extraction system on the turbine shroud. The cooling air is first accelerated through jet holes and impinging on the internal wall. Subsequently, the spent air is discharged in perpendicular directions through film holes. The distribution of wall Nusselt number is spatially resolved through liquid crystal thermography (LCT), and the flow structure of the impinging jets is obtained by 3D steady-state numerical simulation to further analyze the mechanism of jet-enhanced heat transfer. The effect of jet Reynolds number based on the jet hole diameter, jet-to-target spacing, and jet-to-jet spacing in the X and Y direction are investigated with a parameter range of 9100 ⩽ Re ⩽ 19800, 6.0 ⩽ H/D ⩽ 12.5, 4.0 ⩽ A/D ⩽ 7.5, 9.0 ⩽ C/D ⩽ 17.0. The results show that the wall heat transfer is mainly affected by the impinging jets, wall jets, the interaction between adjacent wall jets, and film hole extraction. The jet Reynolds number does not affect the flow structure and wall heat transfer distribution. The increased momentum decay of the jet flow due to the increase in jet-to-target spacing causes the wall heat transfer to decrease monotonically. The variation of jet-to-jet spacing in the Y direction has little effect on the area-averaged Nusselt number of the target wall, but it will shift the stagnation region. While the heat transfer at the sidewall is more sensitive to the jet-to-jet spacing in the Y direction. With the decreasing of the jet-to-jet spacing in the X direction, the area occupied by the stagnation gradually increases, thus, the area-averaged Nusselt number is significantly enhanced. In addition, other heat transfer regions are also significantly enhanced due to the increased amount of cooling air.
Efficient Energy Harvesting and Storage in Small-Scale Solar-Biomass-Micro Gas Turbine Systems
Authors: Simeoni Patrizia , Arnulfi Gianmario L. , Della Putta Andrea
Published: August 2024

In this paper, a small-scale plant operating in stand-alone mode, powered by a micro gas turbine and a solar system, is proposed and analyzed. The main consideration in this perspective is environmental sustainability, which drives the use of renewable energy sources such as solar energy and biomass. In this research, the proposed system comprises solar panels, a micro gas turbine and a battery. The gas turbine is fed by syngas generated by a gasifier, on its turn supplied by biomass. The biomass used consists of waste from food production, such as olive pits. The gas turbine, battery, gasifier and gas tank, together with their auxiliary devices, were modelled following the methodologies described in the technical literature and an in-house simulation code is suitably written. It includes a control system to manage the allocation of demand among solar energy, the gas turbine, and the battery. The aim is to keep the gas turbine away from low-efficiency conditions, while also taking into account the state of charge of the battery to avoid values that are either too low or too high. Initial results suggest a promising potential, with a preliminary analysis indicating a possible fuel (biomass) saving up to 15%. Potential improvements are currently under investigation.