bluuebunny/crossref_metadata_2025 huggingface dataset:
A High-Temperature, High-Speed, Oil-Free Syngas Compressor for Small-Scale Combined Heat and Power
Authors: He Victoria , Van Herle Jan , Schiffmann Jürg
Published: August 2024

For low-emission, small-scale combined heat and power generation, integrating a biomass gasifier with a downstream solid oxide fuel cell system is very promising due to their similar operating conditions in terms of temperatures and pressures. This match avoids intermediate high-temperature heat exchangers and improves system efficiency. However, to couple both systems, a high-temperature and oil-free compressor is required to compress and push the low-density, high-temperature bio-syngas from the gasifier to the solid oxide fuel cell stack. The design and development of this high-temperature, high-speed, and gas-bearing supported compressor is presented in this work. An iterative process involving preliminary design, meanline analysis using commercial tools and in-house models is used for the design, which is then numerically analyzed using computational fluid dynamics. The goal is to achieve a design with a wide operating range and high robustness that withstands extreme working conditions. The 727 W machine is designed to run up to 210 krpm to compress 18.23kgh−1 of syngas at 350°C and 0.81bar. The centrifugal compressor has a tip diameter of 38 mm and consists of 9 backswept main and splitter blades. The impeller is made of Ti6Al4V and coated to prevent hydrogen embrittlement from the hot and highly reactive bio-syngas. The results obtained from the established models suggest a good concordance with the results from numerical analyses, despite the high temperatures and small scale of this design.
The Impact of Pad Elasticity on Frequency-Dependent Linear Dynamic Coefficients of Tilting-Pad Journal Bearings
Authors: Vetter Daniel , Zemella Philipp , Hagemann Thomas , Schwarze Hubert
Published: August 2024

The frequency-dependent dynamic coefficients of tilting-pad bearings are significantly influenced by the pad pivot elasticity. In addition to the elasticity of the pivot, there is also the flexibility of the structure that predominantly leads to a bending of the pad. For the calculation of the dynamic coefficients, it is common to describe the structural stiffness by a support stiffness in series with the lubricant film. For this purpose, the stiffness according to Hertz’s theory is widely used. This approach only allows the rigid body motion of the pad in the theoretical model. However, the elasticity of the pad leads to a film thickness characteristic, which cannot be represented with a pure rigid-body motion. Additionally, the structural elasticity already includes the stiffness of the contact between the pad and the support and, therefore, the elasticity according to Hertz cannot simply be added. This paper investigates the influence of dynamic pad deformation on dynamic bearing coefficients considering the contact boundary conditions, and examines whether it can be replaced by a suitable support stiffness. A 3D finite element model provides the eigenmodes for calculating the dynamic coefficients by perturbed Reynolds equations within a thermo-elasto-hydrodynamic (TEHD) bearing analysis. The model is validated with measurement data.
A Reduced Order Methodology for Optimizing Turbine Expanders Working With Rotating Detonation Combustors
Authors: Varatharajulu Purgunan Gokkul Raj , Asli Majid , Klopsch Roman , Meister Josh , Stathopoulos Panagiotis
Published: August 2024

Redesigning a gas turbine cycle with creative concepts is one of the most critical possibilities for achieving a significant increase in efficiency. Pressure Gain Combustion (PGC) can be used in place of conventional deflagration combustion since PGC contributes to a considerable gain in thermal efficiency while also emitting low NOx levels. One of the major challenges of PGC is the turbine integration to the outlet of the combustor due to the unsteady turbine inflow conditions. This unsteady exhaust flow causes turbomachinery components to operate under fluctuating off-design conditions which in turn, reduces their performance. In this work, the turbine integration to the Rotating Detonation Combustor (RDC) and an optimization methodology for the turbine are discussed. Due to the highly fluctuating unsteady flow of RDC, three-dimensional CFD simulation of turbine becomes very expensive, specifically if it is considered as the objective function evaluator in an optimization process. Thus, an alternative approach of using one-dimensional unsteady Euler model for the turbine is adopted. A two-stage axial turbine is optimized considering unsteady flow features of a hydrogen-air RDC to minimize the entropy generation. When compared to the baseline design, the optimized turbine shows a nearly 2.6% reduction in entropy generation.
Creep-Fatigue Life Assessment Technique for Steam Turbine Rotors: An Efficient Continuum Damage Mechanics Based Approach
Authors: Sen Suvadeep , Almstedt Henning
Published: August 2024

Incorporation of renewable energy, in the era of energy transition, lead to enhanced creep-fatigue life consumption of conventional power plant components, e.g., steam turbine rotors. The present requirements are difficult to address with the conventional uncoupled life assessment methods due to their inherent conservatism. The use of damage coupled unified constitutive models for the analysis of steam turbine rotors in the past decade has shown promising results. High computational efforts is a major drawback of these models. The methods available for reduction in computation time are based on fixed start-up conditions repeating cyclically, however, flex operation result in arbitrary or non-fixed cycle types. In this paper, novel techniques of mapping the data generated from temperature measurements to derive inelastic strain history for arbitrary cycle types is proposed. Unlike the conventional uncoupled techniques utilizing stress/strain ranges, the derived strain history enables a path dependent progressive creep-fatigue damage prediction employing unified constitutive models. The derived strain history is used together with the concept of Representative Input Cycle using a non-iterative Asymptotic Numerical Method for highly efficient damage computation. Various transient loadings on a steam turbine rotor are studied using a unified constitutive model based on Chaboche’s kinematic hardening including the damage parameter, Chaboche-Rousselier’s isotropic hardening model including the damage parameter, Norton’s viscoplastic flow model, Lemaitre’s damage potential function and Kachanov-Rabotnov’s creep damage law. First, a conventional full finite element method is used and then the proposed method is employed to study the evolution of damage and compared.
Design of a Relational Database for Turbine Center Frames With Application for Geometry Optimization
Authors: Staggl Marian , Sanz Wolfgang , Sterner Thomas
Published: August 2024

The flow path between high- and low-pressure turbines (TCF) is a key component of modern aero engines; the radial offset between the two stages and the small axial length result in a strong curvature and complex flow behavior. A solid database is an important foundation for design and further investigations, especially when applying modern artificial intelligence (AI) methods.

Due to a long research history, the Institute for Thermal Turbomachinery and Machine Dynamics (ITTM) at Graz University of Technology owns an extensive TCF data collection. In order to reuse these data samples, a database application has been developed, providing the functionalities to normalize and store the data uniformly. The TCF data samples are mapped into a common parametric space during import, making them comparable and accessible to AI applications. Furthermore, statistical evaluation tools and an automated CFD export are available.

In the second part of the paper, the database is used for an exemplary geometry optimization task. The approach is to train a surrogate model with data from the database and then use the model for optimization. The results agree with the findings of other authors, and the surrogate model’s predictions coincide well with CFD results.
Numerical Study of Low Engine Order Excitations due to Manufacturing Variability Part 2: An Efficient Approach for Stochastic Studies
Authors: Gallardo Juan Manuel , Pérez Escobar Óscar
Published: August 2024

In turbomachinery rows, the geometric variability between the airfoils induces non-uniformity in the flow, which directly translates into Low Engine Order (LEO) excitation and vibration in the adjacent rows. Direct simulations of this phenomenon involve full-row CFD analyses, where the exact geometry of each individual blade needs to be properly reproduced. The related computational cost of such simulations is very significant. Since the geometric variability due to the manufacturing scatter is stochastic, valuable information could be derived from Monte Carlo analyses involving randomly generated geometries; nevertheless, this approach would be very resource-intensive. In this paper, we propose a simplified method to determine the flow perturbation generated by this geometric variability. The method is based on studying the underlying properties of the geometric scatter using PCA techniques, obtaining a compact description of the variability of the airfoils. The flow perturbation due to a reduced number of reference cases is obtained through direct, large scale simulations. By assuming linearity in the flow perturbations, the solution for a general case of geometric distortion may be obtained very efficiently from these reference cases, which makes Monte Carlo studies to analyze stochastic geometric distortion easily affordable. The capabilities of the method are demonstrated in a test case considering the real geometry scatter from an aircraft turbine. According to the results, the average LEO response due to the random geometry scatter involves significant vibration levels, comparable (in terms of alternating stress) to the response due to the blade-passing excitation.
Equivalence Ratio Driven Flame Response of an Industrial Premixed Burner: Experiments and Modeling
Authors: John Tony , Magina Nicholas , Han Fei , Kaufmann Jan , Vogel Manuel , Sattelmayer Thomas
Published: August 2024

This paper presents an analysis of the unsteady heat release rate response of premixed flames to equivalence ratio perturbations for an industrial premixed swirl-based burner. During this investigation, perfectly and technically premixed flames were acoustically forced via fuel/air mixture flow and air flow modulations respectively, at the same operating conditions. From the resulting flame transfer functions (FTFs), measured using the multi-microphone method, the equivalence ratio driven FTF was isolated and extracted by removing the velocity driven component, i.e. the measured FTF from the perfectly premixed flame, from the technically premixed FTF with two novel extraction techniques. The results are compared with FTFs obtained directly in a previous experimental campaign [1] where the fuel flow was acoustically forced, the resulting equivalence ratio fluctuations measured via an IR absorption technique, and the heat release rate response to the forcing was quantified using chemiluminescence measurements. The results from both measurement approaches agreed well highlighting the validity of the techniques. Further, to understand the governing features of the equivalence ratio driven FTF, a physics-based analytical model following the G-equation approach was developed. The contributions from flame surface area, flame speed, and heat of reaction oscillations were modeled to describe the heat release rate dynamics. A limited number of physical parameters in the analytical model were anchored on one test condition, optimized and restricted to values which were all physically reasonable, and were subsequently used for model predictions at other operating conditions. The FTF model predictions compared well with experimental data across a range of different operating conditions. Finally, the relative contributions from flame surface area, flame speed, and heat of reaction oscillations on the features of the FTFs were identified and explored.
Fusion Energy and Future Fusion Power Plants
Authors: Acres Jack , Clements Chris
Published: August 2024

Fusion energy offers clean, reliable power for future generations and is undeniably part of a fully sustainable energy mix. Fusion combines two light atomic nuclei to form a single heavier one while releasing massive amounts of energy. To fuse atoms requires extremely high temperatures and pressures, in a plasma, to overcome the nuclei’s mutual electrical repulsion — achieving these conditions on earth, which is typically achieved in stars, has a host of challenges.

Within a magnetic confinement device (tokamak), plasma is heated using ohmic and a mixture of neutral beam and/or radio-frequency heating to exceed 80 million Kelvin (K) where fusion happens. Strong magnets are needed to shape and control the plasma. Generating and sustaining the extreme temperatures and magnetic conditions, requires significant amounts of energy — which is difficult to manage at scale.

The technical challenge of efficiently and effectively extracting power from a fusion machine and integrating these multiple energy sources into a thermodynamic cycle is significant. This requirement is further compounded by the operational timeframes of typical tokamaks.

These challenges and the scales of the next generation of fusion tokamaks will require significant thermal electrical power transfer and conversion technologies, as well as electrical infrastructure equipment. This paper illustrates these challenges by evaluating possible fusion power plant efficiencies and how this is significantly influenced by the thermodynamic efficiency of the power conversion technology.

Experimental research has been in progress for nearly 70 years, but we are now at a tipping point with active private and public funded fusion power plants programs seeking to exploit fusion energy. UKAEA’s Spherical Tokamak for Energy Production (STEP) project and Tokamak Energy’s Spherical Tokamak Fusion Pilot Plant (ST-X FPP) are examples of such programs.
The Role of Materials in Enabling Gas Turbine Technologies
Authors: Shifler David A.
Published: August 2024

Materials used in high-temperature structures have design constraints in additional to those materials used at or near room temperature. Three important constraints are time-dependent inelastic strain (creep), thermal stability of microstructure, and high-temperature oxidation and/or corrosion. The U.S. Navy employs gas turbine engines for aero-propulsion and for propulsion and auxiliary power for select surface ships. For modern aircraft gas turbines, combustion gas temperatures up to 2100°C and alloy temperatures as high as 1150°C is possible. This is well above the melting point of most alloys, so film cooling of the combustion chamber is necessary. Materials (nickel-base superalloys, ceramic matrix composites (CMCs), refractory alloys, overlay, diffusion, and thermal barrier- and environmental barrier coatings) in commercial, marine and aero gas turbine engines must be able to withstand a variety of aggressive, harsh operating conditions. Current gas turbine engines employ the Brayton cycle where overall turbine efficiencies increase as the engine temperatures increase.

Predicting corrosion of metals, alloys, or coated alloys is often difficult because of the variable operational demands placed on Predicting corrosion of metals, alloys, or coated alloys is often difficult because of the variable operational demands placed on a given power system, and the variable composition of the corrosive environment. Prediction is further complicated because materials often degrade in a high-temperature environment by more than a single corrosion mechanism.

Research is underway to use other cycles such as the Atkinson or Humphrey Cycles that hold the promise of improved efficiency when applied to gas turbine type machinery. A rotating detonation engine (RDE) is an engine is an engine using a form of pressure gain combustion, where one or more detonations continuously travel around an annular channel. In detonative combustion, the flame front expands at supersonic speed. It is theoretically more efficient than conventional deflagrative combustion by as much as 25%. That would translate to major fuel savings. During the combustion very high temperatures (3000–4000K) and pressure (1–100 bar) levels are attained through the combustor. Although RDE research is continuing to establish combustion stability and reduce noise, materials will need to be developed or applied to promote long term performance. These materials will need to endure temperature spacial inhomogenieties and fluctuations, pressure cycling, and harsh environmental operational conditions.
Experimental Investigation of the Film Cooling Effectiveness Deviation Using Pressure Sensitive Paint Measurement for Different Hole Structures
Authors: Lou Yuzhu , Tao Zhi , Li Haiwang , Zhou Zhiyu , Zhang Jinghan , Xie Gang
Published: August 2024

Film cooling is a crucial cooling method to ensure the operation of turbine blades under high-temperature conditions. Turbine blades operate under high-speed and complex flow conditions. In the classic method of measuring adiabatic film cooling effectiveness using Pressure Sensitive Paint, the substitution of the pressure field of the air-case with that of the foreign gas-case has introduced measurement deviation, when the density of two jets is different. The use of a specific ternary oxygen mixture during the test processes enables the correction of the deviation. The shaped holes widely used in turbine blade alter the mainstream-jet mixing process. To obtain the deviation distribution generated during the PSP measurement of shaped holes, measurements were conducted on a flat plate operating at a mainstream Mach number of 0.5 using both the traditional method based on Test3-Air and the corrected method based on Test3-OM for five types of film holes, including a circular hole, a hole with a 45-degree compound angle, double jet ejection, a fan-shaped hole, and a laid-back fan-shaped hole The results reveal that various hole structures broadly exhibit measurement deviation, which generally increases with an increase in the blowing ratio. The deviation originates from the difference in momentum between jets of different densities under the same blowing ratio, leading to distinct flow patterns. Significant negative deviation is observed near the holes under high blowing ratios, while pronounced positive deviation occurs downstream. The distributions of deviation are varied for different structures. The compound angle leads to increased and asymmetrical deviation. For the same pressure deviation, the effectiveness deviation is larger where the film cooling effectiveness is lower. Due to the higher effectiveness downstream of the double jet ejection deviation, the range of the deviation is limited near the hole. The fan-shaped hole and the laid-back fan-shaped hole prevent coolant jet lift-off from the wall, reducing measurement deviation. However, under high blowing ratio conditions, the measurement deviation remains significant and should not be neglected.
A Low Mach Preconditioned Harmonic Balance Solver for Cavity Flutter Computations
Authors: Sivel Pierre , Frey Christian , Kersken Hans-Peter , Kügeler Edmund
Published: August 2024

Labyrinth seal flutter is a critical phenomenon in turbomachinery, as it can lead to severe structural vibrations and potential component damage. Accurate prediction and mitigation of flutter are paramount to ensuring the reliability and performance of modern turbomachinery systems. This paper explores the numerical computation of a labyrinth seal flutter test case using a low Mach preconditioned harmonic balance (HB) solver and investigates how this approach can improve the accuracy and response time of flutter computations.

HB solvers have gained prominence in turbomachinery computations for their ability to efficiently capture unsteady flow phenomena and significantly reduce computational time compared to time-domain analyses. In labyrinth seals, however, the flow is often characterized by low Mach numbers, and preconditioning for these conditions has been shown to significantly improve convergence and accuracy. The goal of this paper is to demonstrate how to implement low Mach preconditioning in a HB solver in the frequency domain.

We employ iterative preconditioning to alleviate the stiffness associated with density-based solvers under low Mach conditions and analyze the effect of the preconditioning parameters on the convergence rate. Furthermore, we address inaccuracies linked to the classical Roe solver in low Mach scenarios by adapting it to the low Mach preconditioned governing equations. Through the combined utilization of iterative preconditioning and a preconditioned Roe solver, this study aims to improve convergence rates and the overall quality of flutter predictions.

We demonstrate the method with an academic labyrinth seal test case originally presented by Corral et al. [1]. While previous investigations have primarily relied on linearized frequency domain solvers and reduce-order models, in this research a preconditioned HB solver is applied to this test case.
Assessment of Rotordynamic Characteristics for the Fully-Partitioned Pocket Damper Seal in a 150MW Steam Turbine
Authors: Zhao Weijun , Sun Wei , Li Zepei , Zhang Zihan , Li Zhigang
Published: August 2024

Pocket damper seal, Hole-pattern/Honeycomb damper seals have been commonly used for many years as damper seals in multiple-stage centrifugal compressor, introducing additional damping to improve the shaft rotordynamic stability. However, there are few literatures focusing on the application assessment of damper seals in high-pressure steam turbines.

This paper presents a comprehensive assessment and comparison on the rotordynamic characteristics of a fully-partitioned pocket damper seal and a staggered labyrinth seal used as the balance piston seal in a 150MW 3000rpm multistage single casing steam turbine. The staggered labyrinth seal is an original seal scheme where the steam turbine experienced strong subsynchronous rotordynamic instability, preventing full load operation of the machine. The fully-partitioned pocket damper seal was designed (the same sealing clearance, inner diameter and axial length) to increase the rotor net damping and eliminate the subsynchronous vibration. The straight swirl brake device also was implemented at seal entrance as a solution scheme to reduce the swirl velocity and enhance the seal net damping capability at high inlet preswirl condition (inlet preswirl ratio is 0.5). Numerical results of seal rotordynamic force coefficients, cavity pressure and swirl velocity developments were presented and discussed, using a proposed transient CFD-based perturbation method based on the multiple-frequency elliptical-orbit rotor whirling model. Results show that the present fully-partitioned pocket damper seal with inlet swirl brake is a good balance piston seal scheme for the present steam turbine, as a replacement scheme of the original staggered labyrinth seal, to increase the rotor net damping and eliminate the subsynchronous vibration.
Adaptation of the Low Dissipation Low Dispersion Scheme for Reactive Multi Component Flows on Unstructured Grids Using Density-Based Solvers
Authors: Lipkowicz Jonathan Timo , Goevert Simon , Janus Bertram
Published: August 2024

The Low Dissipation Low Dispersion (LD2) second order accurate scheme has been proven successful for scale-resolving simulations via finite volume Computational Fluid Dynamics (CFD) solvers. The improved stability attributes stem from a novel combination of a skew-symmetric split form for convective terms in the governing equations and matrix-valued artificial dissipation fluxes. However, additional challenges arise in simulating reactive multi-component flows due to the presence of steep gradients in the flame zone and spatially varying gas properties. In this study, we substitute the previously used skew-symmetric scheme with the recently proposed Kinetic Energy and Entropy Preserving (KEEP) scheme, which employs quadratic and cubic split forms of convective terms, thereby further augmenting stability. Given the non-smoothness of fluid interfaces in simulations of reactive flow, the use of upwind fluxes becomes imperative for the convection of reactive scalars in order to limit total variation (TV). This choice also implies upwind fluxes for internal energy, as it depends on the local scalar composition. All remaining convective terms are treated with central discretizations from the original KEEP scheme, utilizing the spatial reconstruction of the LD2 scheme to minimize dispersive errors. It is shown by numerical assessments that this treatment effectively minimizes spurious pressure oscillations that otherwise appear in both single and multi-component flows. The absolute flux Jacobian for the calculation of dissipation fluxes is efficiently computed by expanding Turkel’s approach for thermally perfect gas mixtures. The partial pressure derivatives with respect to conservative variables, inherent in the absolute flux Jacobian, are approximated when using the Flamelet Generated Manifolds (FGM) combustion model. The proposed scheme is evaluated through scale resolving simulations of the Cambridge burner flame SWB1 on a fully unstructured grid using the density-based solver TRACE, employing both Finite Rate Chemistry (FRC) and FGM combustion models. Comparative analysis is conducted against results obtained using the all-speed scheme SLAU2. The findings demonstrate the superior performance of the proposed scheme in handling turbulent reactive multi-component flows.
Numerical Investigation of Different Forming Approaches for the Manufacturing of Titanium Bipolar Plates for the Aviation Industry
Authors: Sommer Jan , Meerkamp Max , Müller Martina , Horstkotte Rainer , Gierlings Sascha , Herrig Tim , Bergs Thomas
Published: August 2024

The challenges of climate change have led to an increased commitment from both industry and government to environmentally friendly technologies. In the aviation industry, goals of CO2 and NOx reduction were implemented in the Flightpath 2050. One way to reach this goal is by using alternative propulsion systems, such as fuel cells. The ecologic feasibility of the hydrogen fuel cell depends heavily on its performance which in turn is largely determined by the power to weight ratio as well as the volumetric flows of reactants conveyed within the cell. In this context, a key component for the performance is the bipolar plate (BPP), as its channel geometry defines the volumetric flows of reactants. To reduce the mass of the bipolar plate, lightweight materials such as titanium are used. This on the other hand leads to challenges in the forming of BPP regarding its quality and safety due to its material properties.

In this paper, three different manufacturing methods are investigated numerically regarding their feasibility for the use in bipolar plate manufacturing for the aviation industry. To evaluate the suitability of the regarded manufacturing processes, the results are compared in terms of shape accuracy, material thinning as well as stress states. The three-dimensional simulations showed that hydroforming leads to the highest material thinning compared to rubber pad forming and embossing. The shape accuracy was the highest for rubber pad forming, while the stress states varied just marginal.
Optimization of a CO2-Free Offshore Power Plant Using Supercritical CO2
Authors: Pedersen Kjartan , Pilarczyk Marcin , Quinkertz Rainer , Glos Stefan , Kuhn Martin
Published: August 2024

Oil and gas companies face a diverse range of challenges in optimizing their value streams. Some aim to extract maximum value from gas fields with high CO2 content, while others seek to decarbonize their electricity consumption, enhance production via boosting, or provide balancing power to offshore wind farms.

In response to all these needs, an innovative CO2 free offshore power plant burning gas with pure oxygen is presented. The solution called ZEUS (Zero Emission Unmanned power Station) is planned to be located offshore, close to the production wells. One novelty is oxy-fuel combustion at high pressure, which will be obtained naturally from the nearby wells. The high pressure ensures that when cooled, the exhaust is liquified instantly and can be re-injected directly into suitable underground formations in the vicinity. This gives short-traveled gas, short-traveled CO2, no emission to environment, and only requires an export power cable running to shore or to offshore installations.

The paper presents the optimization of the indirect power cycle for ZEUS concept, comparing water-steam and sCO2 as working fluids. The analyses cover various power cycle layouts and heat exchanger designs. The comparison includes efficiency, equipment footprint and cost. The results show that supercritical CO2 cycle fits well to the offshore power plant designs such as ZEUS concept.
Low Data Prognostic Model for Rolling Element Bearing Remaining Useful Life
Authors: Gheller Edoardo , Natarajan Sivachakaravarthy , Pazhoor Abyjith , Chatterton Steven , Vania Andrea , Pennacchi Paolo
Published: August 2024

Rolling element bearings play a pivotal role in rotating machines and are key components of small gas turbine engines. Due to the limited lifespan of these components, they are critical under the maintenance point of view. Various techniques, relying on different algorithms, exist for damage identification. However, the prognostics and residual useful life (RUL) estimation for rolling element bearings present a more challenging task mainly due to the complexity of these components and of their damaging mechanisms. To characterize the bearing failure, extensive and costly testing of several bearings until failure is required. In this paper, a data-driven prognostic model is trained using data obtained from a single run-to-failure test. The bearing is already damaged at the beginning of the test. The bearing acceleration data is processed, and kurtosis is the selected feature to describe the damage evolution of the bearing. The Dynamic Mode Decomposition (DMD) algorithm is employed as surrogate model. To further enhance model accuracy, a time delay or Hankel matrix is used to facilitate state-space modeling and the identification of dynamic behavior within the time series. Subsequently, a particle filter is developed with the trained surrogate models to estimate the RUL of the bearing. The developed model is tested on run-to-failure data from the Center for Intelligent Maintenance Systems (IMS) of the University of Cincinnati. Remarkably, a relatively small volume of data is sufficient to obtain accurate predictions, especially close to the bearing end-of-life, for different bearing geometries and operating conditions.
Durability Test of Advanced TBC’s
Authors: van Esch Hans , Pietersen Stijn , Scheibel John , Barth Olaf
Published: August 2024

To accelerate development and demonstration of hydrogen as fuel for gas turbines, durability testing of conventional and advanced thermal barrier coatings (TBC) applied on hot section gas turbine components. Note: Hydrogen creates a harsher environment for the TBC (erosion, delamination, heat transfer or other).

Eight (8) coating and repair facilities provided twelve (12) different conventional (6%–8% yttria stabilized) and advanced (rare earth element stabilized) TBC applications. Three (3) Frame 7F .03 Stage 1 Buckets (S1B) for each application were coated together with samples and tabs. After the first article inspection (FAI) review, the S1B were inspected and verified quality recorded. The S1B were installed in the Dominion Chesterfield Frame 7F .03 which utilizes a MNQC (steam injection) combustion system with operation beginning in November of 2022. [Reference [4]

These buckets are planned to be removed in 2026 with semiannual borescope inspections being performed until that time. This paper describes the inspections performed on the S1B prior to installation and the phase change and thermal conductivity test performed before and after thermal exposure of these twelve (12) coatings systems test coupons.

The objective of this program is to test the durability of conventional and advanced TBC on Frame 7F .03 Stage 1 Buckets (S1B) under severe circumstances (Steam injected and high heat transfer) comparable to low carbon operational conditions (hydrogen fuel) and determine which coating system can best withstand this environment while also reducing base material temperature during operation.
Experimental and Numerical Study of a Premixed Two Stage Ammonia Combustor at High Pressure
Authors: Esquivias Brandon , McDonell Vincent , Abdul Sater Hassan , Tschirren Stefan , Piffaretti Stefano , Toqan Majed
Published: August 2024

Ammonia combustion at high pressure, in a microturbine combustor configuration, represents a promising avenue for utilization of ammonia as an alternative fuel source. Ammonia is increasingly regarded as a carbon-neutral fuel with potential applications in power generation. Nevertheless, burning ammonia can produce high NOx emissions, which decreases its potential as a clean energy source. Numerical studies show that, by increasing the pressure in the combustor, NOx emission levels can be reduced compared to levels at atmospheric pressure. However, there are few experimental studies that have studied the role of pressure and those that exist show discrepancies regarding the equivalence ratio at which minimum NOx emission levels can be attained. The present study examines the combustion of ammonia in a high-pressure combustion test rig and thus adds to the body of knowledge regarding how pressure and equivalence ratio impact NOx emissions. The combustor configuration utilizes a first stage combustion chamber into which ammonia fuel and air are injected into using a proprietary injection arrangement. This design demonstrates reduced NOx emissions from ammonia combustion, especially at elevated pressures. The research conducted shows that NOx levels below 50 ppm can be achieved under realistic engine conditions. Furthermore, the species concentrations measured at the end of the combustion zone agree with the values predicted by numerical simulations. It is also observed that simulation results are affected by choice of reaction mechanism and the comparison with experimental results affirm further work is needed on the kinetics of ammonia combustion.
Thermodynamic Performance Assessment of a Combined Micro Humid Air Turbine and Organic Rankine Cycle System for Maritime Application
Authors: MosayebNezhad Mohsen , Gjoni Eglantin
Published: August 2024

For centuries, maritime transport has remained among the most vital means of connecting the world. The shipping industry is currently under great pressure to reduce its environmental impact. One method of reducing carbon emissions are highly efficient power generation systems. Interest in ensuring reliable power, and controlling energy costs, has led to advanced power generation technologies on land. Large ships are considered as an ideal entry point to the offshore market for these technologies. This study proposes a novel power generation system for installation in seagoing vessels either as the main prime mover or as an auxiliary power unit system. The proposed plant includes a 1 MW micro humid air turbine system fed by liquefied natural gas (LNG) combined with organic Rankine cycle (ORC) system for recovering waste exhaust heat from the turbine and converting it to useful power. The findings of this study show that the proposed plant for marine vessels can achieve an electrical efficiency of 54.95 % where both liquefied natural gas and required make-up water for inlet air humidification are available. It was also found that integration of the ORC system leads to 5 % increase in the net electrical efficiency of the baseline humid air turbine system.
Transient Behavior of Boundary Layer Flows in a Prototype Rotor-Stator Cavity During an Instantaneous Spinning-Up Process
Authors: Xie Lei , Du Qiang , Liu Guang , Lian Zengyan , Xie Yaguang
Published: August 2024

The transient dynamics of boundary layer flows in a prototype rotor-stator cavity during spinning-up process is investigated using Large Eddy Simulation (LES). Various stages of temporal evolution are discerned by examining the torque coefficient on both the stator and rotor plates. The rotor boundary layer temporal evolution can be divided into three stages, involving an instantaneous spinning-up process, a subsequent torque coefficient decrease influenced by viscous forces, and the final stabilization. Simultaneously, the stator boundary layer undergoes a continuous velocity increases driven by initial cavity recirculation and axial momentum transfer before reaching final stabilized stage. Vortical structures induced by type I crossflow instability play a pivotal role in the transient evolution of the studied system. In the rotor boundary layer, these structures form rapidly, undergo elongation and stretching in the second stage, facilitating axial momentum transfer. However, in the final stage, these vortical structures vanish, coinciding with the laminar nature of the rotor boundary layer. In contrast, the stator boundary layer exhibits a different behavior. Vortical structures in this layer gradually emerge and persist until the flow reaches its final stabilization, in accordance with the turbulent nature of the stator boundary layer. This comprehensive investigation enhances the understanding of the intricate dynamics within rotor-stator cavities.
Shockwave Structures Optimization and Flow Mechanisms in Axial Supersonic Through-Flow Fan Cascades
Authors: Xu Huitong , Li Jiabin , Fei Teng , Ji Lucheng
Published: August 2024

The improvement of the compression system by the axial supersonic through-flow fan (STFF) can promote the development of an aircraft to the higher standard of performance, such as high stealth, high maneuverability and supersonic cruise. This paper constructs the STFF cascade optimization design method by using optimization algorithm NSGA-II to minimize the loss of cascades with constraint flow turning capacity, based on ANN models predicting the loss coefficient and outflow direction. By analyzing the geometric modeling, aerodynamic performance, and shockwave structure of the optimal STFF cascades, it is suggested that reducing the maximum thickness, shifting the position of the maximum thickness forward, and loading backward can eliminate the seperation bubble to reduce the passage losses. While around the solidity at 3 and the stagger angle at 24°, there is a low-loss region in which the STFF cascades operate under axial inlet Mach number of 2.0 with a 27-degree turning angle. The intersection of shock waves in the same direction in STFF passage should be avoided when the flow field is constructed, and the reflected shockwaves of the suction surface should merge with the fishtail shockwave on the same TE as far as possible without aggravating the wake vortex.
Fuel Thermal Management and Injector Part Design for LPBF Manufacturing
Authors: Becker Ralf , Kasperovich Galina , Tiessen Peter , Haubrich Jan , Behrendt Thomas , Janus Bertram
Published: August 2024

Additive Manufacturing (AM) methods such as Laser Powder Bed Fusion (LPBF) are particularly attractive methods for manufacturing aero-engine burners as they allow for a complex design with well-tailored features at reasonable production costs. Unfavorable is still the lower precision in terms of geometrical accuracy and surface roughness compared to classical machining, especially if surfaces are oriented in unfavorable orientation to the working platform. With regard to coke formation and the possibility of fuel line blockage due to too small cross-sectional areas these drawbacks raise the question how fuel lines may be manufactured by AM methods and how AM affects the propensity of coke formation.

In this experimental study the geometrical accuracy of LPBF manufactured parts built in small inclination angles to the working bed with “standard parameters” and a well-adapted parameters is examined. For further improvement two shape adjustment strategies — oval and droplet-like — are proposed and validated. Regarding the risk of coke formation deposition rates on LBPF manufactured parts as-built and post-processed with chemical etching are evaluated.

It is shown that an optimized set of machining parameters increases the geometrical precision substantially and the adjustment of the shape helps to meet the desired cross-sectional areas. Due to the increased roughness of LPBF manufactured parts the evaluated coke deposition rates exceed the rates measured on classical machined parts by an order of magnitude. As presented chemical etching the parts is an effective measure against coke deposition since the deposition rates descend to less than the half.
Film Cooling and Thermal Performances of a Blade Tip Winglet Operated in an Annular Test Rig and a Test Gas Turbine Power Plant
Authors: Naik Shailendra , Henze Marc , Wilhelm Manuel , Schiffer Heinz-Peter
Published: August 2024

This paper investigates the film cooling performances and thermal behavior of a blade tip winglet, which was initially investigated in a 1.5 stage experimental axial turbine facility and subsequently also tested in a gas turbine power plant. The adiabatic film cooling effectiveness was measured in the rotating 1.5 stage axial turbine facility, whereas in the gas turbine power plant the tip winglet had active internal cooling coupled to the airfoil and winglet film cooling system.

For both test facilities, the tip winglet consisted of several fan shaped diffuser cooling holes, which were distributed in various regions of the tip winglet and airfoil. The pressure-sensitive paint method was employed to measure the film cooling effectiveness in the 1.5 stage test rig, which was conducted for two tip clearances and a range of blowing ratios. The tip winglet in the gas turbine test power plant was operated for a long duration and under various gas turbine steady-state and transient operating conditions. The blade and tip metal temperatures were measured with embedded thermocrystal sensors and thermocouples for a wide range of operating conditions.

Measured local film cooling distributions from the 1.5 stage experimental turbine indicated that it was strongly dependent on the coolant blowing ratios but relatively insensitive to the tip clearances and coolant to hot gas density ratio. The measurements also indicated that there was a reasonably good coverage of film cooling in large areas of the winglet cavity floor and pressure and suction side tip rims. Metal temperature measurements at various locations of the tip winglet from the gas turbine power plant tests, also indicated that the measured values were within the expected ranges of the predicted metal temperatures.
Machine Learning Regression of Under-Expanded Hydrogen Jets
Authors: Cerbarano Davide , Tieghi Lorenzo , Delibra Giovanni , Minotti Stefano , Corsini Alessandro
Published: August 2024

The introduction of hydrogen-methane blends as fuel in gas turbines rises concerns on the capability of state-of-art ventilation systems to dilute possible fuel leaks in the enclosures. Traditional numerical methods to perform leak analysis are limited by the number of factors involved, i.e. location and direction of the leak, cross-section area, gas pressure in the pipelines, gas composition, and location of external objects. Hence, this arise the need for novel and fast tools capable for the accurate prediction of fuel dispersion in leak scenarios. To this extent, we propose a novel machine learning approach to model gas leaks. The model is trained on a dataset of numerical simulations accounting for several hydrogen/methane concentrations in the fuel, different storage to ambient pressure ratios at the leak section, and a set of cross-flow ventilation velocities. The architecture of the machine learning model is based on graph neural networks, to solve a node-level regression task predicting fuel concentration in space for different high pressure leak scenarios. The model shows a significant speed-up in predicting fuel dispersion with respect to conventional methodology (0.1 s vs 3.5 h) but the GPU memory requirements proved to be a problem when dealing with 3D domains.
Nature of Transonic Compressor Flow: Importance of 3D Athroat/Ainlet Part I: Subsonic Mach Numbers
Authors: Lefas Demetrios
Published: August 2024

A key problem in transonic compressor and fan design is that although a 3D description of the flow is necessary to correctly capture the shock, accounting for it during the sectional detailed design is difficult because the key driving design parameters are unknown. In this paper, it is shown that for inlet relative Mach numbers between 0.85 to 1.30, the pressure rise across the shock is primarily a function of the 3D streamtube area at the throat At over the inlet area A1. This key finding is based on three key transonic flow features, discussed in detail within this paper, being present together across a wide range of more than 3000 representative transonic compressor and fan designs published online: (https://whittle.digital/). Only the subsonic regime approaching a Mach number of unity is analysed in this paper, whilst the supersonic regime is analysed separately in Part II.

Moreover, it is shown that the effect of changes in the blade geometry, or the 3D streamtube height, on the transonic flow field is one of the same and can be explained simply by keeping track of the associated changes in At/A1. Surprisingly, the pre-shock Mach number at a given At/A1 is shown to be insensitive to the details of the blade surface geometry. Only geometric design choices made in the preliminary design phase, such as the maximum thickness and the inlet relative flow angles, are shown to have a second-order effect. These findings suggest, that the purpose of the sectional detailed design phase should be solely to make the desired changes in the real spanwise 3D At/A1.

The final part of the paper concerns itself with the level of fidelity necessary when calculating the spanwise 3D At/A1, for it to positively influence design; especially while approaching a Mach number of unity when small changes in At/A1 become increasingly important. A key conclusion is that not resolving the subtle changes in the 3D radial flow within the blade passage at the appropriate level of fidelity, especially at the early through/low multistage compressor design stage, could potentially mislead the transonic design process. As a result, this paper advocates the use of 3D CFD, even at this early design stage, for the rapid exploration of future compressor designs.