bluuebunny/crossref_metadata_2025 huggingface dataset:
Image-Based Flashback Detection in a Hydrogen-Fired Gas Turbine Using a Convolutional Autoencoder
Authors: Porath Paul , Yadav Vikas , Panek Lukasz , Ghani Abdulla
Published: August 2024

Flame flashback is a major concern in hydrogen-fired gas turbines. In order to determine the flashback propensity of a hydrogen burner, several burner design tests at different operating points and fuel blends are performed at the test facility of Siemens Energy. A camera monitors the flame in the combustion chamber and the occurrence of flame flashback events in the image recordings becomes clearly visible. This anomalous behaviour clearly deviates from normal hydrogen operation. We develop a data-driven approach to detect flame flashback events based on the camera images at 100% hydrogen operation, where all images feature identical characteristics since the pure hydrogen flame is not visible for the camera. Simultaneously, the highest susceptibility to flashback is attained in this regime. We use both facts as well as the good suitability of image data to train a Convolutional Autoencoder (CAE) model to detect anomalies. Here, anomalies correspond to flashback events. Flashback is captured by the CAE using the reconstruction error associated with a dynamic threshold as a measure of anomaly. This newly developed dynamic threshold overcomes the difficulties in the generalization capability of the CAE. Regardless of the test campaign, burner design and camera settings, it reliably recognizes flashback events. Along with the CAE, the compressed representation, namely the latent space of the CAE, detects the position of flame flashback events. Our methodology is able to detect flame flashback using only flame images and provides a reliable tool even when unseen data are used.
Targeting Full-Hydrogen Operation on Industrial-Scale Gas Turbines: Impact of Unconventional Fuels on Turbine Module Performance and Aeromechanics
Authors: Bandini Alberto , Bettini Claudio , Peruzzi Lorenzo , Carretta Mauro , Canelli Claudio , Marconcini Michele , Pinelli Lorenzo , Arnone Andrea
Published: August 2024

With the trend to full decarbonization, a full hydrogen economy development is a key industrial objective. Gas turbines, currently one of the cleanest fossil fuel-based power generation solutions, provide reliable and on-demand power. The introduction of hydrogen into the fuel mix of existing gas turbines represents a solution with great potential to provide low-carbon or even carbon-free energy. High-hydrogen content fuels, however, challenge the efficient operation of the gas turbine expander, as crucial aspects such as increased flow rate, different gas properties and temperature operating range may affect performance and structural integrity. To evaluate the impact of this conversion, a numerical investigation of five cases with increasing percentages of hydrogen in the fuel was carried out for an industrial four stages gas turbine module. The variation of turbine inlet temperature distribution from combustion chamber was considered, to assess the impact of the unconventional fuel on the well-known aeromechanical behavior of the last stage blades. Variations in capacity, efficiency, power and potential limits due to aeroelasticity were evaluated, identifying the most relevant differences with respect to the full methane case. All these analyses confirm the possibility to employ high-hydrogen fuel operation in a current gas turbine without the need of a further redesign, while maintaining acceptable performance levels.
Air Cycle Machine Modeling Applied to Aeronautical Air Conditioning Unit
Authors: Merzvinskas Marcelo , Bringhenti Cleverson , Takachi Tomita Jesuino , Jefferds Dos Santos Silva Franco , Vitor Tozi Luiz , Lopes Salgado Mayara
Published: August 2024

The air conditioning system of executive, commercial, or military aircraft heavily relies on air cycle machines due to the availability of engine bleed air and their lightness and reliability compared to vapor cycle systems. The type of application, weight, refrigeration capacity, financial aspects, size, performance, and other specific design requirements drive the selection of suitable equipment for a particular aircraft. The motivation of this paper has been based on summarize the main concepts of the aeronautical environmental control system, as well as the mathematical aspects underlying the modeling of a simple/bootstrap air cycle unit in a software. The main aim is to develop software that can generate high level requirements that would be refined during the development phase of an aeronautical air conditioning system. It will be greatly benefit for engineers and students in the design of aeronautical air conditioning systems to better understand and to meet the design requirements. The results demonstrate the influence of the water-sprayer and chilled-recirculation system on air cycle performance and cabin inlet temperature, respectively. They also show changes in certain parameters of interest such as a function of altitude, power consumed by the secondary compressor, and air cycle machine fan. The computational model has proven to be a useful tool for performing parametric studies and evaluating critical points in designing and selecting an air conditioning unit based on a simple/bootstrap air cycle with humid air (any quantity of moist) as the working fluid.
Generative Model Based Parameterization for More Efficient Aerodynamic Optimization of Non-Axisymmetric Endwall
Authors: Li Cunxi , Song Liming , Guo Zhendong , Yang Zhao , Li Jun , Feng Zhenping
Published: August 2024

The Non-axisymmetric Endwall Contouring (NEC) technique has been proven effective in reducing the secondary losses of turbine cascades. However, the parameterization of NEC, especially for spline-based techniques, would face a tradeoff between issues such as the dimensionality of the design space, sample variability, and the proportion of abnormal shapes. To address the above issue and achieve a moreefficient NEC optimization, a generative model based parameterization method is proposed. Specifically, to build a comprehensive design space that contains sufficient variability of NEC shapes, the samples of a set of conventional classical NEC parameterization methods are collected, which are combined by representing them with scatter coordinates in a uniform format. Then, to reduce the number of variables to the minimum extent, the Variational Autoencoder (VAE) is used to learn the intrinsic dimensions of the parameterized NEC design space. To ensure the smoothness of the contours and avoid abnormal shapes, a layer of NURBS is incorporated into the neural network architecture of VAE. This proposed model was used for the NEC parameterization of a high-pressure turbine stage testcase with 9 variables. Additionally, the proposed VAE was used for aerodynamic optimization of the non-axisymmetric endwalls, compared to other NEC parameterization approaches. The results demonstrate that the generative model based parameterization method can optimize aerodynamic performance more effectively while maintaining a lower limit on the number of performance evaluations. The effectiveness of our proposed generative model based parameterization method is well demonstrated.
Evaluation of Current and Future Aviation Fuels at High-Pressure RQL-Type Combustor Conditions
Authors: Griebel Peter , Hampp Fabian , Lückerath Rainer , Lammel Oliver , Grein Tobias , Sallinen Reetu , Vilja Jesse , Sandberg Kati
Published: August 2024

De-carbonizing the aviation sector is one of the biggest challenges in order to minimize climate change effects associated with the emission of carbon dioxide. Sustainable aviation fuels (SAF) will play a major role in this context especially for long-distance flights where hydrogen or all-electric propulsion systems do not present a feasible alternative. In addition, aromatic-free aviation fuels offer a promising solution to lower soot emissions of aeroengines. Today, experience of SAF combustion under aeroengine-typical operation conditions is limited.

In this paper five fuels samples, Jet A-1 as reference fuel, 2 blends and two neat synthesized paraffinic kerosenes from hydro-processed esters and fatty acids (HEFA-SPK) supplied by Neste were tested to characterize the combustion behaviour of drop-in / near drop-in fuels. These experiments were performed for the first time in an optically accessible high-pressure rich-quench-lean (RQL)-type combustor at typical aeroengine conditions. Optical diagnostics (OH* chemiluminescence, Mie scattering) as well as exhaust gas and particle sampling measurements were performed to delineate the fuel effects on spray, flame and emission characteristics. Measurements were performed at pressures up to 10 bar, air preheating temperatures up to 773 K and at primary zone equivalence ratios up to 1.66.

The results showed that the liquid fuel distribution and fuel placement were sensitive to the fuel properties. By contrast, no pronounced influence of the fuel properties on flame position and shape were observed. As a consequence, NOx and CO emissions of the tested fuels differed only moderately. However, particulate matter measurements at the fuel richest operating condition showed a clear ranking of the five fuels with the lowest particle emissions evident for the two neat HEFA-SPK samples. Moreover, the particle volume concentration at the fuel richest condition followed the expected trend with fuel H-content.
Investigation of NO-Formation in Humid, Ammonia-Doped Combustion
Authors: Dybe Simeon , Helbig Hannah , Yasir Muhammad , Güthe Felix , Alemela Reddy , Bartlett Michael , Paschereit Christian Oliver , Bohon Myles D.
Published: August 2024

Decarbonizing the energy sector promotes the utilization of renewable fuel sources like Syngas from biomass. Syngas typically comprises small quantities of fuel-bound nitrogen (FBN) like ammonia which is associated with high NO-emissions when combusted in a customary gas turbine system.

In atmospheric combustion experiments conducted at TU Berlin, small quantities of ammonia were added to both natural gas and a surrogate Syngas representing Syngas derived from biomass. This results in an ammonia-to-NO conversion rate of around over 70%, which decreases with increasing ammonia concentration. A difference in conversion rate between surrogate Syngas and natural gas is particularly noticeable at lower ammonia concentrations, which diminishes as concentration increases.

The experimental combustion process is validated with a Chemical Reactor Network (CRN) using Cantera, which captures the emission behaviour observed in the experiment well. The chemical reactor representing the flame is additionally modeled as a 1D-flame in Cantera, providing the input for an in-depth investigation of the flame kinetics with a sub-mechanism accounting and reaction tracing algorithm (SMART) to investigate the NO-formation. NO is primarily generated within the flame zone predominantly through the fuel pathway, although production is diminished by the DeNOx pathway.

Finally, NO-formation is investigated for varying combustor diameter. NO-emissions decrease with increasing diameter of the combustion chamber. SMART analysis shows that with increasing the combustor’s diameter, the increase in NO depletion via the DeNOx pathway surpasses that of production via the Fuel NO pathway. Consequently, this results in a slight reduction in the overall NO output, which could arise from increased heat loss with increased diameter.
Interplay Between Unburned Emissions and NOx Emissions From a Dual Swirl Hydrogen Air Injector
Authors: Magnes Hervé , Vilespy Martin , Selle Laurent , Poinsot Thierry , Schuller Thierry
Published: August 2024

OH planar laser induced fluorescence and particle image velocimetry are employed to analyze the structure of hydrogen/air flames stabilized by a dual swirl injection system under globally lean and atmospheric conditions with preheat air temperature varied from ambient up to 673 K. The flames exhibit two distinct reaction branches. The first, located in the central recirculation zone, is a diffusion-controlled reaction layer characterized by a relatively large thickness associated with low strain rates. The second branch, stabilized in the shear layer of the swirling jet, is strongly influenced by large coherent structures. Depending on operating conditions, this front may adopt either the form of a fully diffusive strained reaction layer anchored to the hydrogen injector lip or a lifted diffusion front with a leading-edge flame evolving into a partially premixed flame at high air injection velocities. Flue gas analysis indicates NOx emission levels, typically below 10 ppm at 15% O2, for sufficiently large air injection velocities. Air preheating barely increases NOx emissions at lean operating conditions. The injector operational range is constrained only by the ultra-lean blowout limit reached for global equivalence ratios below 0.02. Furthermore, it demonstrates remarkable resilience to large and rapid drop in fuel flowrate. However, combustion efficiency drops close to the lean blowout limit due to intermittent fragmentation of the flame wings that progresses further upstream as the equivalence ratio drops. It is demonstrated that this fragmentation results from the combined drop in temperature of the central recirculation zone and the flame wings subjected to high shear stress. It is also shown that combustion efficiency at ultra lean conditions rapidly increases as the air preheat temperature increases.
Variable Cycle Engine Concepts and Component Technologies - An Overview
Authors: Zenkner Sebastian , Carvalho Francisco , Brakmann Robin G. , Goinis Georgios
Published: August 2024

The variable cycle engine (VCE) is of interest for military and supersonic civil platforms due to its improved operational flexibility. However, the increase in design and control degrees of freedom results in a more complex engine architecture. Numerous different VCE concepts have been proposed and studied in literature. This paper provides an overview of VCE concepts and technology. A historical outline moof important activities, investigated concepts and technical advancements is given and the main objectives and use cases of the technology are described. In addition, specific challenges and technical solutions for variable compressors and turbines are discussed in detail. Important VCE concepts are qualitatively evaluated and their advantages and disadvantages for specific applications highlighted.
Numerical Investigation on the Geometrical Scaling of Hydrogen Micromix Injectors
Authors: Sun Xiaoxiao , Morsy Mohamed , Wijesinghe Charith , Singh Gaurav , Sethi Vishal , Rimmer John , Young Kenneth
Published: August 2024

For future hydrogen-fuelled aircraft, the hydrogen needs to be stored in liquid phase. Converting liquid hydrogen into a gaseous state for combustion requires transitioning from extremely low temperatures (∼20.25K) to high temperatures (at least above 300K) to avoid compromising aero-engine thermal efficiency. Within the scope of the HYEST project, a hydrogen pre-conditioning system to provide the heat input is being designed and tested. The system comprises a pre-heater which provides the heat input for a downstream heat exchanger. The main requirements of the pre-heater include but are not limited to, uniform combustor outlet temperature and velocity distributions, low pressure loss, acceptable NOx emissions, stable operation for all engine power settings and minimum size and weight. Due to its unique configuration of repeating injector arrays, a hydrogen micromix combustor is a promising candidate to fulfil these requirements.

For a hydrogen micromix combustor, NOx production is very sensitive to flame-flame interactions and hot gas recirculation as well as the hydrogen jet diameter. Smaller hydrogen jet diameters will yield lower NOx emissions and will achieve a uniform outlet temperature distribution within a shorter distance downstream of the injector plate. However, to reduce manufacturing and maintenance complexity, a feasibility study on scaling up the hydrogen injection diameter of hydrogen micromix injectors was conducted using numerical CFD simulations on a pair of injectors. The resulting flames were evaluated and compared in terms of flame structure, total pressure loss, NOx emissions and outlet temperature uniformity.

It was concluded that for the pre-heater design a hydrogen injector diameter of 0.6mm fulfils all the requirements. A 0.6mm design reduces the number of injectors by 3/4 compared to a 0.3mm injector design without producing significantly more NOx. Additionally, it reduces the minimum distance to achieve a uniform radial temperature distribution by 50% compared to a 1.0mm injector design.

Although this study is specifically related to the preheater fuel conditioning system, the lessons learned are equally applicable to the design of hydrogen micromix combustion systems for both aero and stationary gas turbines.
Coupled Design of Multi-Component Distortion-Generating Devices for Aircraft Engine Ground Tests – Part II: Experimental Characterization in a Closed-Loop, High Speed Test Rig
Authors: Boufidi Elissavet , Madasseri Payyappalli Manas , Grondin Julissa , Leborgne Michaël , Baert Lieven , Gouttière Alexandre , Dieu Donavan , Wunsch Dirk , Spriet Tony , Talbotec Jérôme , Fontaneto Fabrizio
Published: August 2024

Next generation aircraft engine configurations, featuring a higher level of engine-airframe integration, are subjected to increased flow distortion levels at the fan inlet. The presence of such non-uniformities should be considered as early as possible in the design cycle, as it can have an impact on the engine performance, operability and vibration. Since testing under realistic distorted inlet flow is crucial in order to evaluate such effects, there is a clear need for devices able to generate complex distortion patterns. Part I of this two-part paper presents a numerical methodology enabling to design distortion generating devices capable of reproducing complex steady combined total pressure and swirl angle distortion patterns. The methodology has been applied to generate four different sets of distortion screens: one honeycomb total pressure screen, one swirl vane assembly, and two devices consisting of a coupling of the two components. The second part of the paper focuses on the experimental characterization of the distortion screens in the VKI R4 high speed test rig. The closed-loop facility has undergone major design modifications in order to implement the new distortion devices test section and reproduce engine-like flow conditions. The measurements have been carried out by means of stereo-PIV and multi-hole aerodynamic pressure probes. The cross-comparison between the two techniques allows to discuss the limitations of each technique. Finally, the comparison between the experimental results and the simulated patterns is presented and discussed.
Thermal Performance Characterization of Dry Gas Seals in a sCO2 Compressor
Authors: Bidkar Rahul A. , Kumar Uttara , Zhang Xiaohua , Molino Nora , Neveu Joshua , Klaerner John , Johnson Jeremy , Moore J. Jeffrey
Published: August 2024

Commercially available dry gas seals (DGS) are the seal-of-choice for shaft-end sealing locations in compressors used in the oil and gas industry, and supercritical carbon dioxide (sCO2) power cycles. Typically, a DGS operates with a very thin gas/supercritical fluid film (typically 2 to 7 microns thin). DGS reliability is tied to how well this ultra-thin film is sustained under varying pressure, thermal, and speed conditions. Recent sCO2 turbomachinery development efforts have experienced a couple of catastrophic DGS failures at the compressor shaft-end locations. A suspected root cause of these DGS failures is thermal deformations caused by the excessive windage heating expected with the supercritical CO2 working fluid when the compressor operates at high pressures and high rotational speeds. In this paper, the thermal behavior of a DGS operating in a typical sCO2 compressor is investigated. Specifically, test data are presented for a specially instrumented, commercially available DGS operating in the GE-SwRI sCO2 compressor. The test data include temperatures measured on the seal stationary ring and DGS housing locations using several embedded metal thermocouples to monitor the thermal behavior of the DGS during typical sCO2 compressor missions. This paper describes how an existing GE-SwRI sCO2 compressor housing was modified to accommodate and route temperature sensors to the instrumented DGS. Test data shows higher than expected temperatures (about 180 to 190 °C) in the cavities surrounding the DGS, which provides useful insights to turbomachinery designers for designing seal cavities. The main reason for these high temperatures is the low sCO2 flow purging the seal cavity. Furthermore, the measured temperatures are compared with the predictions of a steady-state thermal model of the GE-SwRI sCO2 compressor. The thermal model uses a 1D flow advection network (accounting for cavity swirl, windage and heat transfer coefficients for sCO2 flow, air flow and bearing oil flow) exchanging heat with the surrounding structure, along with heat transfer through the structure. The thermal model uses CFD-based flows to account for the sCO2 flow past the DGS. The predictions of the thermal model match reasonably well with the measured temperature data, thereby providing validation to the modeling assumptions. The high structural temperatures in the regions around the DGS that are predicted by the model as well as measured during the tests point to the importance of devising cooling strategies for reliable operation of the DGS.
Modal Identification of Rotating Blades by Tip Timing and Strain Gauge Measurements in Operating Condition
Authors: Guida Roberto , Carassale Luigi , Marrè-Brunenghi Michela
Published: August 2024

The modal identification of rotor blades in operating conditions is difficult for several reasons including the unavoidable transient effects that arise when resonances are crossed relatively fast. Algorithms to deal with this problem are available for the case of time-resolved signals (e.g. strain gauges), while for blade tip timing (BTT) data, the experience is much more limited, in particular as far as engines in operating conditions are concerned. This paper aims to contribute to the development and validation of system identification techniques applicable in transient conditions using BTT data. To this end, one method based on the fitting of the transient response and one method based on the fitting of the synchronous response are formalized, applied and compared to analyze the behavior of an operating engine in which both BTT and strain gauge measurements are available.
The Hybrid Pathway to Flexible Power Turbines: Part D, Automated Construction of Mesh Derived Thermal Network Models for Fast Full-Machine Thermal Analysis
Authors: Baker Mark , Rosic Budimir
Published: August 2024

The global drive towards renewable energy is imposing challenging operating requirements on power turbines. Flexible load-leveling applications must accept more frequent and demanding start-stop cycles. Full transient analyses are too computationally expensive for real-time simulation across all operating regimes so monitoring relies on sparse physical measurements. Alone, these sparse data lack the fidelity for real-time prediction of a complex thermal field. A new hybrid methodology is proposed, coupling data across a range of fidelities to bridge the limitations in the individual analyses. Combining several fidelity methods in parallel: low-order models, corrected by real-time physical measurements, are calibrated with high-fidelity simulations. The multi-faceted hybrid approach enables the real-time speed of low-order analysis at high resolution. This paper series develops the critical enabling features of the hybrid method. Fast 3D thermal simulation is fundamental to the methodology. Low-order network models enable the real-time thermal calculation of regions inaccessible to monitoring and facilitate clearance and stress simulation necessary for flexible turbine operation. A novel automated construction method is presented, allowing complex full turbine thermal networks to be built with ease. Developed in Tensorflow, the thermal networks directly support GPU acceleration and neural network integration for seamless data transfer within the hybrid system. Capturing flow and material physics from high fidelity data, the hybrid network method demonstrates comparable accuracy at greatly reduced computational cost. The method is validated using real-machine data capturing a period of flexible transient operation.
Flame Interaction and Stabilization Mechanisms in a Dual Premix Swirl Combustor With a Pilot Bluff Body
Authors: Li Linye , Tian Xiaojing , Yin Shengming , Zhang Haodong , Yang Yifan , Wang Guoqing , Feng Zhenzhen , Xu Liangliang , Xia Xi , Qi Fei
Published: August 2024

The utilization of centrally-staged lean-premixed swirl combustion is prevalent due to its capacity for stable flame maintenance and reduced emissions. The configuration of the pilot and main flames, whether they are stratified or merged, significantly influences flame behavior and combustion dynamics. This study explores the underlying mechanisms of merged and stratified flames in a newly designed dual-swirl model combustor. Utilizing a 10 kHz PIV/OH* synchronized measurement and a 20 kHz CH2O PLIF method, we delineate the flame and flow structures under varying Air Split Ratios (ASR) and Stratification Ratios (SR). The results indicate that ASR alters the heat release intensity by modifying the flame’s radial dimensions, whereas SR determines the spatial separation between the pilot and main flames. The merged flame displays a single-layer M-shaped structure, with the inner flame front perturbed by vigorous vortex shedding. In contrast, the stratified flame exhibits a dual-layer structure with an M-shaped pilot flame and a V-shaped main flame, where a precessing vortex core (PVC) emerges whose frequency correlates positively with the equivalence ratio of the pilot flame. The formation of these two modes is attributed to the stabilization of the outer branch of the pilot flame, governed by the interplay between flame propagation and flow convection of the pilot stage.
Experimental Investigation on Laser Ignition and Flame Stabilization in an Oxygen/Methane CO2-Diluted Combustor at Elevated Pressures
Authors: Di Sabatino Francesco , Partridge Kendyl , Connolly Brian , White Steve
Published: August 2024

Direct-fired oxy-fuel supercritical carbon dioxide (sCO2) combustors present a novel approach for near-total carbon capture. However, maintaining a stable flame under extreme pressure and temperatures, characteristic of these combustors, poses significant challenges. Re-ignition failure could necessitate depressurization to atmospheric levels, leading to substantial time and energy losses. This study experimentally investigates laser ignition and flame stabilization in a simplified oxygen/methane-fired, CO2-diluted combustor across various thermodynamic conditions. The test rig comprised a seven-hole showerhead nozzle installed in a pressure vessel, producing a jet flame at pressures up to 5 bar. Non-reactive laser-induced plasma kernel generation experiments were also performed to assess the effect of pressure on kernel dimensions up to 25 bar. The optical access of the combustor enabled plasma kernel generation and laser ignition by focusing a 532-nm laser beam, produced by a 10 Hz Nd:YAG laser, approximately 5 mm from the nozzle tip. The optical access also allowed the collection of images of the flame’s CH* chemiluminescence to assess flame stabilization and plasma kernel dimensions. The results indicate that pressure and CO2 dilution have a considerable impact on flame stabilization. Furthermore, the diameter of the plasma kernel was observed to decrease with increasing pressure, highlighting the importance of laser ignition testing at elevated pressures.
Investigation of an Ammonia-Fuelled SOFC-mGT Hybrid System: Performances Analysis and Comparison With Natural Gas-Based System
Authors: Anfosso Chiara , Crosa Silvia , Iester Federico , Bellotti Daria , Magistri Loredana
Published: August 2024

Among power generation systems, Hybrid Systems (HS) are very attractive due to the opportunity to reach higher power outputs and efficiencies by coupling different technologies. Among Solid Oxide Fuel Cell plants, one of the most studied innovative HS is the SOFC-Micro-Gas Turbine (mGT) integrated system: in the pressurized configuration, the Fuel Cell (FC) is in the place of the mGT combustion chamber, and an afterburner is used to complete the fuel combustion upstream the expander. Several system configurations, designs, and control system challenges have been studied in the last decades, and prototypes have been already developed around the world with satisfactory results in terms of system efficiency. However, these systems have been deeply studied feeding the FC with Natural Gas (NG) and Biogas, not completely allowing to reach zero carbon emissions. The growing global demand for carbon-free energy production is increasing, highlighting the importance of alternative fuels in the power generation sector: among them, thanks to its chemical and physical properties, ammonia is gaining more and more interest. In the present work, the authors want to investigate an innovative Ammonia-to-Power (A2P) system based on a SOFC-mGT HS, focusing on the main thermodynamic parameters, the system’s features, and critical aspects, from a technical and environmental point of view. To perform this analysis, a MATLAB/Simulink model has been developed, starting from a fully validated model of the HS fueled by NG and considering the FC operating with an anodic ejector recirculation. In the new plant configuration, the SOFC pre-reformer has been substituted by an ammonia cracker, permitting to investigate the effects of the anode gas recirculation and properly design the whole system. In particular, the operating parameters, such as anodic recirculation factor, fuel utilization, performance, gas turbine size, and features are presented and discussed. Finally, a comparison between hybrid systems and mGT fed by methane, biogas, and ammonia is carried out.
Transient Thermo-Structural Analysis of a Throttle Valve Operated With sCO2
Authors: Bianchini Cosimo , Bertini Davide , Sandrin Simone , Mariotti Vanessa , Maceli Nicola , Arcangeli Lorenzo
Published: August 2024

This paper presents thermo-structural analyzes performed on a throttle valve operated with CO2 at supercritical conditions. In more detail, the study started with the thermal characterization of the steady-state behavior under different load conditions. During this phase, a numerical methodology for the evaluation of thermal maps was defined based on a loosely coupled Conjugate Heat Transfer approach that exploits a flow network and a 3D finite element thermal solver. A decoupled CFD analysis helped defining the thermal loads on the sealing system around the stem. The following step was dedicated to the analysis of a typical start-up ramp. The start-up sequence was built by linearly increasing the sCO2 flow from zero to the design value and then holding it constant until the metal temperature reaches the steady state. The performed thermo-structural analysis allowed the calculation of the relative displacements between the stem and the valve casing along the entire transient process.
Non-Synchronous Vibration and Related Tip Clearance Flow Characteristic in a Low-Speed Axial Fan
Authors: Zhang He , Zhang Ming , Dong Xu , Sun Dakun , Sun Xiaofeng
Published: August 2024

An experimental study investigating non-synchronous vibration due to rotating instability was conducted on a singlestage axial fan. The experiment monitored high-amplitude vibrations that could lead to high-cycle fatigue of the blades, and a wire mesh casing treatment was successfully employed to suppress the vibration. Two blade materials, metal and nylon, were used in the experiment under two different tip clearance conditions. Under the small tip clearance condition, no vibration causing high-cycle fatigue was observed, and there was no indication of rotating instability flow. For the case of enlarged tip clearance with nylon blades, as throttling proceeded, the azimuthal mode decreased. When the frequency in the rotating frame of reference closely matched the blade vibration frequency, it induced high-amplitude non-synchronous vibration. In response to this phenomenon, the paper conducts a mechanism analysis on the mode and frequency of the rotating source. Under the same enlarged tip clearance configuration, a wire mesh casing treatment was tested. While expanding the stability margin, it successfully suppressed the high-amplitude vibration phenomenon occurring in the near-stall area.
Real Gas Effects on Autoignition Delay and Laminar Flame Speed Predictions for Direct-Fire sCO2 Combustion
Authors: Kinney Cory , Velez Carlos , Martin Scott , Forte Annalisa , Nassini Pier Carlo , Zucca Alessandro , Vasu Subith S.
Published: August 2024

Supercritical carbon dioxide (sCO2) power cycles are promising for improving the carbon footprint of natural gas based electricity generation through sequestration while also offering efficiency and size advantages; however, the cycle conditions pose challenges to in-situ experimental measurements needed for validating models due to extremely high working pressures (around 300 bar). There is still significant uncertainty in the best practices for modeling real gas effects at these conditions and the implications for optimal burner designs and configurations.

In this study, the impact of real gas models on chemical kinetic mechanism predictions for autoignition delay times, laminar flame speeds, and counterflow diffusion flames is assessed for conditions relevant to direct-fire sCO2 cycles. It is demonstrated that real gas effects result in a 15–20% decrease in ignition delay times at these conditions for the mechanisms studied. Additionally, laminar flame speed simulations were performed in Cantera to investigate the real gas effects and transport modeling with relevance to predicting flashback and blowout limits in combustors. Switching from an ideal gas equation of state to real gas only resulted in a 5–10% increase in flame speed predictions; however, flame speeds increased by a more significant 20–30% when a high-pressure transport model was implemented. The importance of equation of state consideration in chemical kinetic mechanism design is then discussed. The authors conclude that variations in density and transport properties are most important for simulation accuracy.
Blade Designs for Improved Multi-Phase Performance in sCO2 Compressors; Part II - Optical Diagnostics in sCO2 and Experimental Evaluation With Particle Image Velocimetry
Authors: Fernandez Erik , Gabriel-Ohanu Emmanuel , Vesely Ladislav , Kapat Jayanta , Hosangadi Ashvin , Cooper Paul
Published: August 2024

This paper presents the second part of a study in which the leading-edge and suction surface of a compressor blade was modified to delay onset of phase change for sCO2 compressors operating near the critical point. Using a first-of-its-kind apparatus for the measurement of sCO2 flow fields, Particle Image Velocimetry (PIV) is used for local flow field measurements of two compressor blade geometries: the modified “biased-wedge,” and a conventional constant thickness blade. Utilizing the developed hardware, the feasibility of a simple, laser-based diagnostic for qualitatively measuring liquid phase regions, is also presented. The design of the optical diagnostics rig, a discussion of numerous challenges, and necessary considerations involved in performing optical-based measurements like PIV, in sCO2, are discussed. Velocity field measurements for the modified compressor profile show a much lower suction peak compared to a conventional blade. These results validate numerical results at the tested conditions, where the suction side profile of the biased wedge works to minimize the local pressure gradient.
Characterization of the Swirl Velocity Field and Atomization Processes of a Lean Burn Gas Turbine Fuel Injector
Authors: Sahu Vivek , Jamod Preetam , K. P. Shanmugadas
Published: August 2024

The present work investigates the swirl velocity field and atomization processes of a lean burn gas turbine swirl injector. The injector includes a complex configuration of a pilot mixer and a main mixer with a mass flow split ratio of 31:69. The pilot and main mixer include a set of counter-rotating axial and radial swirlers of different swirl numbers. Incoming airflow from the pilot’s axial and radial swirler is separated by a prefilmer venturi. Jet in swirl cross-flow scheme is employed for injecting fuel into both pilot and main mixer. Particle image velocimetry (PIV) techniques are employed to investigate the air swirl flow field and atomization processes at the exit of the injector. Axial plane and transverse plane particle image velocimetry (PIV) experiments are conducted to obtain the three-component velocity of the gas phase at selected planes. Experiments are carried out at various air-to-liquid ratios ranging from 7.30 to 30.45, keeping the liquid flow rate constant, with three injector configurations: pilot, main, and pilot plus main mixer. Individual recirculating flow structures are observed in the case of both pilot and main mixer, and they merge to form a central toroidal recirculation zone in the case of the full injector assembly. The air momentum dominates the overall spray topology and droplet dispersion at higher air-to-liquid ratio conditions for all three configurations. Spray PIV measurements highlighted significant radial drifting of pilot spray droplets under the influence of main mixer swirl streams. Overall, swirl sense is controlled by the main mixer, and significant slip velocities are observed at the shear layer regions.
Parametric Study on the Duct Intake Reflection Coefficients for Fan Flutter Analyses
Authors: Perez Jose Miguel , Corral Roque
Published: August 2024

The coupling between the acoustic reflections of the intake and the fan vibration characterizes the fan flutter of aero-engines. Close to the intake cut-on/cut-off condition, the reflection of the intake is most significant and key to the appearance of the so-called flutter bite.

Rienstra’s model has been thoroughly used in this work to compute the amplitude and phase of the reflected acoustic wave in a zero-thickness intake. The methodology is based on the Wiener-Hopf technique, whereby close expressions involving the complex integration of several kernels are given. Because of its complexity, its usage has been hindered since Rienstra provided just a few results as examples.

Moreover, the existing results in the literature are intended for noise analyses, and the phase information of the reflected waves, which is critical for aeroelastic applications but irrelevant for most acoustic analyses, needs to be included.

This work presents a thorough data set of the modulus and phase of reflection coefficients for a zero-thickness intake, including variations of the inlet Mach number, inner-to-outer radius ratio, and circumferential wavenumber as a function of the dimensionless frequency. In addition, a simple-to-compute model is presented to help the characterization of the modulus and phase of the dominant waves scattered in the intake of aero-engines, easing the assessment of the flutter-bite occurrence.
Dynamic Characterization of a Low Drag Power Loss Tilting Pad Journal Bearing
Authors: Bradley Roarke , Delgado Adolfo , San Andrés Luis
Published: August 2024

High performance turbomachinery relies on tilting pad journal bearings (TPJB) for high-speed operation while maintaining acceptable stability margins. However, TPJBs can produce large drag power losses that increase with machine size and surface speed. In a conventional configuration, the unloaded pads will drag on the surface of the shaft while, presumably, having a minimum impact on the bearing dynamic performance. The effects of removing unloaded pads from a TPJB has been studied before but research has yet to describe the force coefficients of this bearing type. The present work aims to evaluate the effect on dynamic forced performance and power loss of a 4-pad TPJB configured as load on pad (LOP) and having the unloaded pad, opposite to the loaded pad, replaced by a fixed insert with a large clearance. The replacement insert has a significantly larger clearance (∼14.4 × nominal clearance), effectively making this a 3-pad bearing. The original 4-pad bearing was previously tested, hence allowing for an accurate comparison before and after the pad exchange. The experiments include operation at both 6 and 12 krpm (shaft surface speeds of 32 m/s and 64 m/s, respectively) with unit loads equaling 345 kPa, 862 kPa and 1379 kPa. The bearing is supplied with ISO VG 46 oil (inlet T = 50 °C) and flow equaling 50%, 100%, and 150% of a nominal flow set for the original 4-pad bearing. For the nominal flow and a unit load of 345 kPa, the modified bearing shows a substantial decrease in power loss, ∼38% at 6 krpm and ∼10% at 12 krpm. At the largest flow rate, however, the drag power loss reduction is less apparent, just ∼2% at 12 krpm. The 3-pad bearing shows signs of lubricant starvation due to the large volume created by replacing the unloaded pad with the large clearance fixed pad. Incipient sub-synchronous vibrations (SSV) appeared at 100% nominal flow, at both 6 and 12 krpm and a unit load of 1379 kPa. SSV hash is a common occurrence in bearings supplied with a low flow rate and low loads. During tests with the lowest flowrate, the modified bearing produced very small stiffness (∼75% reduction) and damping (∼57% reduction) coefficients along the unloaded direction, most likely due to lubricant starvation.
Improved Compressor Performance Prediction Using a Vortex-Reactive Turbulence-Model Extension
Authors: Mimic Dajan , Mahlstedt Janek , Herbst Florian
Published: August 2024

The accurate modelling of secondary-flow dynamics is a key aspect of reliable performance predictions for turbomachinery. This is due to the effect of secondary flow on the aerofoil boundary layers, as well as the overall energy budget.

In this paper, we assess the predictive performance of a vortex-reactive turbulence-model extension using integral performance data of a multi-stage compressor test rig. The model extension provides a more accurate prediction of multi-stage compressor characteristics, especially if cavities and squealer tips are considered. This is achieved by mitigating an underprediction of near-choke mass-flow rates, and of the total-pressure ratio and isentropic efficiency near stall. The analysis shows that this is achieved by affecting the formation and propagation of secondary flow.
Wake-Separation Bubble Interaction Over an Experimentally Simulated Axial Compressor Blade Under Low Reynolds Number Flow
Authors: Irps Thomas , Kanjirakkad Vasudevan
Published: August 2024

For the most part, the flow over an axial compressor blade is subjected to adverse pressure gradients. Under low Reynolds number conditions, the flow could separate off the blade surface especially on the suction side, where it first accelerates to a peak velocity and then decelerates to a higher-pressure condition at the blade exit. The ‘separation bubble’ thus formed could, in many cases, trigger flow transition from laminar to turbulent conditions on reattachment further downstream of the point of separation. Since blade profile losses depend on the transition location, the modification of the separation bubble due to any upstream generated disturbances is of great interest. In this paper the interaction between incoming wakes, that are generated periodically, and the separation bubble that exists on the blade surface is investigated. Results are presented from wind tunnel experiments conducted over a flat plate that is imposed with a surface pressure profile similar to that over a highly loaded compressor blade. The periodic wakes are introduced using an upstream bar passing mechanism that produces representative unsteady parameters. The spatial and temporal development of the flow along the mid-span region is described with the help of particle image velocimetry-based flow mapping at a relatively low Reynolds number of 210,000. Several interesting observations were made, but the most important one is the existence of a slow-moving thickened boundary layer feature that convects immediately behind the wake. While the calmed region that forms behind this feature can suppress the bubble, the thickened boundary layer itself is seen to have high unsteadiness and it contributes to a large momentum deficit.
Non-Synchronous Vibration: Characterisation of the Aerodynamic Disturbance and its Dependency on Local Tip Clearance
Authors: Tharreau Pierre , Hardy-Falch Magnus , Stapelfeldt Sina , Brandstetter Christoph
Published: August 2024

Non-synchronous vibrations (NSV) occurring near the stall boundary pose a major challenge to the design of safe and efficient compressors and fans. NSV occurs when aerodynamic disturbances which develop close to the aerodynamic stability limit couple with blade vibration. Despite its importance and a recent rise in research efforts, the exact nature of the aerodynamic disturbance is unknown and there are no robust modelling and prediction methods available. A characteristic parameter crucial to the successful prediction of NSV is the circumferential propagation velocity of the aerodynamic disturbance, which determines whether lock-in with a structural vibration mode is possible. This paper uses detailed aeroelastic measurements and coupled time-accurate simulations on the open-test-case composite fan ECL5, which was experimentally tested at Ecole Centrale de Lyon in project CATANA, to characterize the aerodynamic disturbance and determine the mechanisms responsible for its circumferential propagation. As part of this, the influence of blade-to-blade variations in tip clearance size is investigated.

The disturbance is identified as a vortical structure which originates in the tip clearance flow close to the leading edge and is convected across the passage to the trailing blade where it triggers the release of a new vortical structure. The tip clearance plays a crucial role in setting the convection speed across the passage and also influences the transfer mechanism across the blade. Overall, a larger tip clearance is found to increase the speed and strength of the disturbance in the subsequent passage. The implications of tip clearance variations for vibration are modelled and the results confirmed in the experimental analysis. It is shown that blade-to-blade variations in the tip clearance act as a form of aerodynamic mistuning, leading to vibrations in multiple nodal diameters.
Numerical Analysis and Design of New Exhaust Section Downstream of Constant Volume Combustor
Authors: Gallis Panagiotis , Misul Daniela Anna , Boust Bastien , Bellenoue Marc , Salvadori Simone
Published: August 2024

Pressure Gain Combustors (PGC) exploit either their iso-choric or detonative combustion increasing the theoretical thermal efficiency of a Gas Turbine cycle. On this basis, a Constant-Volume Combustor (CVC) is developed operating with rotary valves while the chamber is fed with mixture of air and liquid iso-octane. The present work describes the numerical design of a new exhaust section after the CVC. First, the design parametrization of the transition duct and the resulting Design of Experiments (DOE) of 81 samples are introduced. Every case is numerically tested and the election of the best sample is based on the pressure losses and the oscillations characterization. In the last part, the LS89-VKI vane is added at the aft part of the best transition duct and the ensemble exhaust system is analysed with the help of transient CFD analysis. Every component is evaluated in terms of pressure losses and oscillations, while the operation of the vane is investigated in details. The results of the stator’s performance are discussed and compared with steady experimental data. During a CVC period, the cycle average outlet flow angle remains close to the outlet metal angle denoting promising results for the future numerical analysis of the subsequent rotor.