bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mass Mistuning Reduced Order Models for Bladed Disks With Shroud Friction Joints
Authors: Saletti Giacomo , Pourkiaee Mehrdad , Zucca Stefano 
Published: August 2024

Abstract
This paper introduces a new reduced order model (ROM) for nonlinear forced response analysis of mistuned bladed disks with localized contact nonlinearities. The developed technique is based on a Component Mode Synthesis (CMS) approach and introduces small frequency mistuning into the final ROM as deviations in the mass matrix. Critical to the development of CMS-based ROMs for mistuned systems, is the construction of a reduction basis that remains invariant to mistuning parameters, ensuring the ROM’s suitability for statistical analyses.
Traditionally, CMS-based reduction techniques for small mistuned systems fall into two major groups:
1. System-level approaches: in which mistuned system modeshapes are represented as a linear combination of tuned modes, typically overlooking mistuning impact on static constraint modes.
2. Component-level approaches: in which mistuning is confined to individual components (or superelements), preserving the independence of the reduction basis from mistuning patterns, typically overlooking mistuning impact on interface degrees-of-freedom (DOFs).
The proposed technique combines the strengths of both methods. It adopts a system-level approach, utilizing modeshapes of the fully stuck system within the reduction basis. Furthermore, it eliminates common assumptions on static constraint modes by incorporating mistuning effects directly into the mass matrix. As a result, the constraint modes employed in the reduction basis are precise and remain unaffected by mistuning, ensuring their invariance.
A comprehensive comparison between ROMs constructed using the new approach and the full model demonstrates the method strengths through modal and forced response analyses. The proposed approach presents a promising solution for accurate and efficient nonlinear dynamic analysis of mistuned bladed disk systems with shroud friction contacts.
Step-by-Step Evaluation of the Fuel Switch From Kerosene to Hydrogen on the Thermodynamic Cycle in Gas Turbine Engines
Authors: Görtz Alexander , Schneider Björn 
Published: August 2024

Abstract
Hydrogen combustion engines are one of the few possible ways forward to drastically reduce climate impact of aviation. While there is many information about the engine performance of hydrogen combustion engines it is not clear to which extend each property of the fuel switch effects the engines thermodynamic cycle and component behavior. The basic architecture is identical for both fuels but it is not known to which extend already existing and fully designed components can be used for the new application. In this work the basic differences between both fuels are presented using a thermodynamic model of simplified turbojet. The archived knowledge is applied to a reference turbo-fan for an application similar to an Airbus A320 while burning hydrogen.
Different effects occurring during the fuel switch, e.g. higher water loading after combustion and lower fuel mass flow, will be looked at separately. A retrofitted engine towards hydrogen combustion will use 1.5% less energy for the same thrust while operating at 60 K lower temperatures. The working line in the compressors will also switch towards higher mass flow rates despite the higher working fluid quality after combustion. Additionally, a new designed turbofan is presented on preliminary level for a constant fan diameter, to address the effects of different thrust requirements and has a 3.6% lower specific energy consumption.
Effects of a 3D-Printed Atomizer Component on Fuel-Spray and Flame Characteristics of a Jet-Stabilized Compact Gas Turbine Combustor Fed With Liquid Fuels
Authors: Kim Haisol , Pareja Jhon , Lammel Oliver 
Published: August 2024

Abstract
In this work, the effects of replacing an atomizer component of a confined jet-stabilized gas turbine combustor with a 3D-printed part have been studied. The part is called airblast, and it serves as a wall that collects and flows liquid droplets for a secondary atomization. Therefore, the liquid-surface interaction on the rough surface of the 3D-printed part was of interest.
The combustor was operated under various conditions with either a conventionally machined airblast or the 3D-printed airblast. Flames with two liquid fuels were studied for fuel flexibility, and the position of a primary fuel injection was varied to study the influence of the liquid-surface interaction length. Load flexibility was investigated with air jet velocity settings, and flame equivalence ratios of ϕ = 0.8 and 1.0 were tested.
Shadowgraphy-based particle tracking analyses presented a reduced atomization performance with the 3D-printed airblast, showing large droplet size distributions. However, no significant change in the combustor performance was observed from OH* chemiluminescence images and emission data, which confirms the versatility of the combustor and assures the compatibility of 3D-printed components with the combustor of this study.
Analysis of the Flow-Field Distortions Induced by Pneumatic Pressure Probes in Test Bench Experiments on Centrifugal Compressors: Are We Testing Right?
Authors: Baroni Alberto , Romani Luca , Balduzzi Francesco , Toni Lorenzo , Grimaldi Angelo , Belardini Elisabetta , Biliotti Davide , Bianchini Alessandro , Ferrara Giovanni 
Published: August 2024

Abstract
Experimental testing at the test rig still plays a key role in the development of new centrifugal compressor designs for industrial applications. Although a wide set of different probes is used as per common practice, the overall impact of the probes’ dimensions on the stage performance and rangeability is often assumed to be negligible. In this study, we aimed at quantifying the intrusiveness effects of pneumatic pressure probes on the flow-field inside a vaned diffuser using a model stage of an industrial centrifugal compressor, for which different experimental setups were tested at the University of Florence test rig. Performance and rangeability were initially assessed using a conventional set of pneumatic probes inserted in the flow path. Then, comparative analyses were realized through dedicated tests by either removing all probes at the diffuser inlet or introducing only a single pressure probe in the upstream section and varying its angular position in the measuring section. Experiments revealed an impact of upstream probes much higher than expected, with a decrease in efficiency and a substantial reduction of stall margin. Moving from this experimental evidence, accurate 3D CFD simulations of the entire stage were carried out including the actual geometry of the probes for two probes configurations and three operating points. Simulations highlighted the effect probes’ wakes on downstream vanes and the induced blockage effect, which both appear in line with experimental evidence. As a handout, a recommendation on the optimal probe positioning is suggested.
Numerical Investigation of Effusion Cooling Air Influence on the CO Emissions for a Single-Sector Aero-Engine Model Combustor
Authors: Recio Balmaseda Sandra , Karpowski Tim Jeremy Patrick , Nicolai Hendrik , Koob Philipp , Greifenstein Max , Dreizler Andreas , Hasse Christian 
Published: August 2024

Abstract
Stricter aviation emissions regulations have led to the desire for lean-premixed-vaporized combustors over rich-quench-lean burners. While this operation mode is beneficial for reducing NOx and particulate emissions, the interaction of the flame and hot exhaust gases with the cooling flow results in increased CO emissions. Predicting CO in computational fluid dynamics (CFD) simulations remains challenging. To assess current model performance under practically relevant conditions, Large-Eddy Simulation (LES) of a lab-scale effusion cooling test rig is performed. Flamelet-based manifolds, in combination with the Artificial Thickened Flame (ATF) approach, are utilized to model the Turbulence-Chemistry Interaction (TCI) in the test-rig with detailed chemical kinetics at reduced computational costs. Heat losses are considered via exhaust gas recirculation (EGR). Local transport effects in CO emissions are included through an additional transport equation. Additionally, a Conjugate Heat Transfer (CHT) simulation is performed for good estimations of the thermal boundary conditions. Extensive validation of this comprehensive model is conducted using the available experimental dataset for the studied configuration. Subsequently, model sensitivities for predicting CO are assessed, including the progress variable definition and the formulation of the CO source term in the corresponding transport equation. To investigate the flame thickening influence in the calculated CO, an ATF-postprocessing correction is further developed. Integrating multiple sophisticated pollutant submodels and evaluating their sensitivity offers insights for future investigations into modeling CO emissions in aero-engines and stationary gas turbines.
Development of a Reactor Network Model for a Practical Gas Turbine Combustor
Authors: Gubbi Srujan , Sun Wenting , Choi Nakjeong , Park Seik , Park Jungkeuk , Lee Sanghyup , Harper Jim , Steele Robert , Noble David 
Published: August 2024

Abstract
With a major drive for carbon-neutral energy sources, the viability of alternative fuels such as hydrogen and ammonia are being actively investigated. One idea currently being explored is to retrofit existing natural gas power generation technologies for use with these alternative fuels. Computational models that can replicate the behavior of these types of systems can be useful in optimizing operating conditions for this type of retrofit as well as providing guidance for updated designs. In this work, a reactor network model is developed for a practical gas turbine combustion system to simulate emissions data observed in detailed laboratory experiments with highly reduced computation time. Such work can enhance both the analytical models as well as assist in validating measurements in experiments. The design methodology of such a reactor network model for a gas turbine combustor is explored, as well as the effect of key parameters in simulations on the results. This includes the complexity of the model and the sensitivity of the results to any added details in modeling. Results show that possible air leakage and radiative effects can lead to discrepancy between simulation and measured values for turbine inlet temperature. NOx values and its ability to explain differences in simulation and experiments is discussed. The implemented chemical reactor network also shows areas for improvement such as more accurate geometric calculations and implementation of “recycling” to simulate recirculating gas. The sensitivity of the results to different chemical kinetics mechanisms is also shown, indicating room for possible improvements to chemical kinetics. The conversion of NO to NO2 and the usefulness of simulating this effect is also discussed.
Simultaneous Design Optimization of Binary CO2-Mixture-Based Power Cycles for Concentrated Solar Power Applications
Authors: Mutlu Balkan , Patchigolla Kumar , Thanganadar Dhinesh 
Published: August 2024

Abstract
This paper introduces a novel approach for optimizing binary CO2-mixture-based both condensing and non-condensing power cycles for high-temperature CSP applications, featuring a simple recuperative layout. It synchronously optimizes cycle design parameters, dopant selection, and working fluid composition. Scenarios investigated include two maximum cycle temperatures: 550°C for conventional solar power towers and 700°C for advanced systems, across three design dry bulb temperatures: 30°C, 35°C, and 40°C. Investigated dopants include SO2, C6F6, TiCl4, a non-organic dopant (NOD), and C2H3N. The multi-objective optimization focuses on thermal efficiency and specific work, while the suggested methodology allows for the expansion of the dopant list, to include any interesting dopant as long as their thermophysical properties are captured in 3D look-up tables using accurate Equation of State (EoS) and binary interaction parameters (BIP). Results show that including specific work as an optimization objective enhances cost effectiveness by minimizing power block costs, and helps to select optimized designs while retaining high efficiencies. Additionally, considering ΔT as an objective could further reduce potential thermal energy storage (TES) costs, increasing the cost competitiveness of CO2-mixture-based cycles to increase their chances in market entry.
Leakage Loss Reduction by Shroud Cavity Shape Improvement in Reaction Turbine
Authors: Sato Masahiro , Ndong Kazunobu , Taniguchi Hiroaki 
Published: August 2024

Abstract
In a steam turbine blade row, leakage flows through the radial clearance between the shroud at the tip of the blade and the sealing fins resulting in a reduction in efficiency, known as leakage loss.
During turbine operation, radial clearances are affected by various factors such as thermal deformation resulting in elongation difference between the rotor and casing, deflection due to the rotor’s weight, and changes in the state of the bearing oil film.
The design strategy commonly adopted to reduce the amount of leakage flow includes: reducing seal fin tip clearance, increasing the number of seal fins, etc...
All these countermeasures are implemented while satisfying the clearance under operating conditions.
Besides the leakage flow, another source of losses to be reduced is the difference in circumferential velocity component between the main flow leaving the moving blade passage, and the flow coming out of the shroud cavity of these same blades.
The focus in recent years has been on reducing this flow discrepancy, also called mixing loss. It should however be noted that the situation is different for reaction and impulse turbines. Generally, as the shroud cavity circumferential velocity after a stationary blade passage is slower than that after a nozzle passage, reducing the problematic velocity component coming out of the shroud cavity in a reaction turbine will not be as effective as it would be for an impulse turbine.
A final point to consider is manufacturability. Structures installed to correct the shroud cavity outflow in the axial direction often require non-axis-symmetrical geometries, hardly machined by just the use of a vertical lathe.
Considering the background above, the research presented in this paper focused on investigating the shroud cavity shape suitable for leakage flow reduction.
An improved shroud cavity shape was developed and the mechanism used by this new design to reduce leakage flow by using the generated counter vortex is discussed.
Topological Shape and Performance Optimisation of Microchannel Diffusion-Bonded Heat Exchangers Used in sCO2 Brayton Cycle
Authors: Vishwakarma Shubham Kumar , Srivastava Adhip , Kumar Pramod , Dutta Pradip , Somanath Nagendra 
Published: August 2024

Abstract
In recent years, Micro-Channel Heat Exchangers (MCHEs) have received significant interest in the context of energy systems and devices for supercritical carbon dioxide (sCO2) compact power blocks. The unprecedented ability of MCHEs to sustain extremities of both temperature and pressure makes them an ideal choice as recuperators/gas-cooler in a sCO2 Brayton cycle. The proposed approach uses a cylindrical-shaped heat exchanger with circular/non-circular channel holes that are topologically optimised. The channels are laser drilled into thin discs instead of electrochemically etched. The length is achieved by stacking and joining prepared discs with diffusion bonding. The MCHEs propose channels with different cross-sectional shapes and configurations defined in a cylindrical geometry as a novel alternative for conventional heat exchangers. The analysis focuses on enhancing heat transfer by arriving at suitable optimised forms and numbers of hot and cold channels based on the specified operating, manufacturing, and design constraints.
The numerical analysis uses a three-dimensional computational fluid dynamics (CFD) model, which accommodates the nonaxisymmetric behavior that arises in a global meshing system. The Navier Stokes (N-S) and energy equations are solved in cylindrical coordinates. The steady-state energy and momentum transport equations are discretised in a Finite Volume (FV) framework utilising a collocated grid. The approach provides flexibility to vary radial distribution of channels and the number of holes based on specified operating, manufacturing, and design constraints. The full-scale CFD model, which is an accurate method for performing property evolution studies, is computationally expensive. Hence, a parallel computing approach is adopted for a real, efficient, and versatile numerical model for evaluating the analyses and then performing optimization.
Enhancement in heat exchanger performance is achieved using an Elite Genetic Algorithm (EGA), resulting in an optimised heat exchanger geometry. The geometric parameters used to guide the EGA in generating multiple improved heat exchanger geometries, allow for design trade-offs along the Pareto front between heat exchanger efficiency and geometric location of channels. The current approach offers a promising method for optimising heat exchanger performance, resulting in nonintuitive designs that were previously unattainable. The process is demonstrated with an optimized design. The results predicted are validated using a commercial CFD solver. Test cases have shown a close agreement in temperature and velocity distributions.
The Unsteady Shock-Boundary Layer Interaction in a Compressor Cascade – Part 1: Measurements With Time-Resolved PIV
Authors: Klinner Joachim , Munoz Lopez Edwin J. , Hergt Alexander , Willert Chris 
Published: August 2024

Abstract
In the first part of this 3-paper-series time-resolved PIV is performed in the transonic cascade to elucidate the shock-boundary layer interaction process and to provide comparative data for numerical studies and analysis in part 2 and 3. The application of modern high-speed camera technology combined with a dual-pulse high-speed laser system enabled TR-PIV in the cascade for image areas covering ∼ 30% of the chord and ∼ 6% of the blade pitch, at fs = 20 kHz or 0.18tc for the acquisition of multiple time sequences with duration of ∼ 2000 tc. The sampling rate is sufficient to capture fluctuations of the separating region and accompanying movements of the shock system. To enable correlations of density variations of the shock system and velocity data, shadowgraphs are acquired synchronously with TR-PIV recordings at the same sampling rate. The TR-PIV and shadowgraph measurement setups, the image processing and the resulting spatial resolutions are described in this part. A analysis of power spectral densities along near-wall rows in PIV data reveals the chord-wise spatial distribution of specific peaks and bands, which are also visible in the shock buffet spectrum. A SPOD of TR-PIV data is conducted to enable inspection of spatio-temporal modes of velocity fluctuations at specific broad peaks and tones in the buffet frequency range. Results indicate, that upstream of the main shock oblique shock waves occur at higher order harmonics of the fundamental buffet frequency and at specific high-frequency tones. To locate possible sources of distinct tones at the entrance of the center passage, a SPOD of high-speed schlieren recordings is performed, capturing the shock systems in three passages. The results show that with these high-frequency tones opposing vibrations of bow and lip shocks occur for neighboring blades.
Development of a Virtual Chemistry Reaction Mechanism for H2/CH4 Turbulent Combustion Modelling
Authors: Castellani Simone , Andreini Antonio , Meloni Roberto 
Published: August 2024

Abstract
The identification of the combustion model is always guided by the compromise between accuracy and computational cost. While species transport models offer accuracy, their computational cost requirement can become prohibitive, especially when dealing with higher-order hydrocarbon fuels. To mitigate this, the virtual mechanism definition aims to optimise the predictivity minimizing the amount of information to be transported. Thereby the virtual mechanism leverages fictitious species and a few step reactions whose parameters calibration is performed with a genetic algorithm. This work outlines the procedure for the derivation of a virtual reaction mechanism for the study of lean H2/CH4 fuel mixtures with 60% of H2 content (by vol.). These conditions require an adequate characterization of the virtual species differential diffusion oriented to reconstruct the flame sensitivity towards the aerodynamic stretch. After the mechanism derivation, its predictivity has been validated on a swirl-stabilized perfectly premixed turbulent test case. The artificially thickened flame model has been adopted to allow the flame front discretization on an LES grid and to model the turbulence chemistry interaction. The numerical results show a very good agreement with the experimental optical measurements confirming the effectiveness of this approach for predicting the H2/CH4 blend.
Uncertainty Quantification Analysis on the Cooling Flow Rate of the Cooled Turbine in a Novel H2/O2 Cycle
Authors: Ma Bangyan , Shi Lei , Zhu Xiaocheng , Du Zhaohui 
Published: August 2024

Abstract
Using renewable energy, such as wind and solar, is one of the important ways to reduce carbon emissions. However, wind and solar energy have significant instability and uncontrollability. Hydrogen is a clean energy source and has great potential for development. In the future, hydrogen-fueled cycle will play an important role and is one of the main ways to achieve carbon neutrality. However, components in the cycle are affected by uncertainties. Therefore, the stochastic analysis is paramount in the design stage. In this work, a PCE method is employed to evaluate the variabilities in the coolant consumption and the isentropic efficiency of cooled turbines employed in a novel hydrogen-fueled cycle, considering the influence of the uncertainties in Stanton number empirical relationships and manufacturing errors. Sobol indices are utilized to denote the contribution of each input and to find the key parameter. The results showed that heat transfer at outer blade wall is the key factor which contributes about 85% to the total uncertainty in coolant consumption and isentropic efficiency. It was also discovered that the uncertainties in the coolant consumption and isentropic efficiency are higher for lower pressure cooled turbines.