bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Low Mach Preconditioned Harmonic Balance Solver for Cavity Flutter Computations
Authors: Sivel Pierre , Frey Christian , Kersken Hans-Peter , Kügeler Edmund 
Published: August 2024

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.