bluuebunny/crossref_metadata_2025 huggingface dataset:
Rare finding of mucorales sporangia and chlamydospores in tissue
Authors: Kojima Misa , Kimura Masatomo , Kuwahara Kazuhiko , Tamaki Hisatomo , Yasumatsu Ryuji , Sadamoto Sota , Shinohara Takayuki , Amemiya Kazuki , Miyazaki Yoshitsugu , Ito Akihiko
Published: August 2024

Most elements of filamentous fungi seen in human tissue by pathologists are hyphae, and encountering other elements may interfere with diagnosis. Sporangia and chlamydospores are such elements that have been described in only a few case reports. We present an autopsy case with the extremely rare coexistence of Mucorales sporangia and chlamydospores in the lung. These fungal elements must be recognized and identified accurately because they can easily be mistaken for other fungi, microorganisms, or degenerated tissue structures.
Barriers and facilitators to early initiation of palliative care as perceived by nurses working on pneumology and nephrology, a descriptive qualitative study
Authors: Paque Kristel , Baudry Lars , Van Fraeyenhove Frank , Heyrman Bert
Published: August 2024

Aims and Objectives

Initiation of palliative care early in the disease trajectory is beneficial for patients with a life‐limiting disease. However, palliative care is still introduced rather late or not at all. Therefore, this study aims to explore barriers and facilitators to early initiation of palliative care as perceived by nurses working on pneumology and nephrology.

Methods

A descriptive interview‐based study was conducted from a critical realist perspective until data sufficiency was reached. Fifteen nurses presented and discussed a patient for whom palliative care was initiated too late. Template analysis was conducted to develop themes and subthemes.

Results

Five key themes were extracted: (1) communication, (2) fear, (3) personal beliefs about life and death, (4) ambiguity in terminology and (5) workload and time pressure. Barriers related to poor interdisciplinary communication were therapeutic obstinance, hierarchy, unawareness of the patient's wishes and fear of saying something inappropriate. Other barriers were patients' religious beliefs which often hindered the use of sedatives or morphine and led to discomfort and time restraints. A palliative support team in hospital and advance care planning (ACP) were enablers for early palliative care.

Study Limitations

This study started from a negative experience, leading to identification of a lot of barriers and only a few facilitators. The limited sample size and the restriction to two wards within one single hospital limit the diversity of perspectives and the generalisability of the findings.

Conclusion

More attention is needed for ACP and interdisciplinary communication. Palliative care, including ACP, and interdisciplinary communication should be included in the basic curricula of all healthcare professional courses. Further research is needed to explore barriers and facilitators to early initiation of palliative care in other healthcare settings and patient populations. This is crucial in order to develop and implement sustainable interventions for specific groups of patients.
Auslander‐type conditions and weakly Gorenstein algebras
Authors: Huang Zhaoyong
Published: August 2024

Let be an Artin algebra. Under certain Auslander‐type conditions, we give some equivalent characterizations of (weakly) Gorenstein algebras in terms of the properties of Gorenstein projective modules and modules satisfying Auslander‐type conditions. As applications, we provide some support for several homological conjectures. In particular, we prove that if is left quasi‐Auslander, then is Gorenstein if and only if it is (left and) right weakly Gorenstein; and that if satisfies the Auslander condition, then is Gorenstein if and only if it is left or right weakly Gorenstein. This is a reduction of an Auslander–Reiten's conjecture, which states that is Gorenstein if satisfies the Auslander condition.
A number‐theoretic classification of toroidal solenoids
Authors: Sabitova Maria
Published: August 2024

We classify toroidal solenoids defined by nonsingular ‐matrices with integer coefficients by studying associated first Ĉech cohomology groups. In a previous work, we classified the groups in the case using generalized ideal classes in the splitting field of the characteristic polynomial of . In this paper, we explore the classification problem for an arbitrary .
Methods to incorporate patient preferences into medical decision algorithms and models and their quantification, balancing and evaluation: a scoping review protocol
Authors: Fusiak Jakub , Mansmann Ulrich , Hoffmann Verena S.
Published: August 2024

Objective:

The objective of this scoping review is to identify and map methods used to incorporate patient preferences into medical algorithms and models as well report on their quantification, balancing, and evaluation in the literature. It will focus on computational methods used for incorporating patient preferences into algorithms and models at an individual level as well as the types of medical algorithms and models where these methods have been applied.

Introduction:

Medical algorithms and models are increasingly being used to support clinical and shared decision-making; however, their effectiveness, accuracy, acceptance, and comprehension may be limited if patients’ preferences are not considered. To address this issue, it is important to explore methods integrating patient preferences.

Inclusion criteria:

This review will investigate patient preferences and their integration into medical algorithms and models for individual-level clinical decision-making. The scoping review will include diverse sources, such as peer-reviewed articles, clinical practice guidelines, gray literature, government reports, guidelines, and expert opinions for a comprehensive investigation of the subject.

Methods:

This scoping review will follow JBI methodology. A comprehensive search will be conducted in PubMed, Web of Science, ACM Digital Library, IEEE Xplore, the Cochrane Library, OpenGrey, the National Technical Reports Library, and the first 20 pages of Google Scholar. The search strategy will include keywords related to patient preferences, medical algorithms and models, decision-making, and software tools and frameworks. Data extraction and analysis will be guided by the JBI framework, which includes an explorative and qualitative analysis.

Review Registration:

Open Science Framework https://osf.io/qg3b5
Operating Point Driven Improvements on the Eco-Efficiency of the Altitude Test Facility at the University of Stuttgart
Authors: Roth Christopher , Staudacher Stephan
Published: August 2024

In compliance with certification requirements, engine manufacturers must demonstrate the safe and reliable engine performance within a predefined flight envelope, including high altitude operation. Generally, high altitude testing of aero engines requires large amount of energy. With the aerospace supply chain continuously reducing its environmental impact, the requirements on the eco-efficiency on altitude testing increase as well. Consequently, the operation of Altitude Test Facilities (ATF) is subject to on-going improvements. Thermodynamic models that describe the generation of the altitude conditions are an important foundation for improvements of the altitude test procedures. One-dimensional network models are well suited to generate such models, since they are modular, standardized, and easy to configure. Yet, their calibration over the required wide range of configurations and operating conditions is a challenge. This results in a model which matches different operating points of the facility with varying precision. Modeling approaches which involve measured data promise an improvement in this respect and offer potentially real-time optimization of the facility operation. It is shown that the application of such models allows a transparent derivation of operating standards for altitude testing. The associated reduction of the environmental impact of altitude testing is significant.
CFD Modeling of Additively Manufactured Extreme Environment Heat Exchangers for Waste Heat Recuperation
Authors: Duggirala Vyas , Reddy Venkateswara , Muley Arun , Stoia Michael , Vanaffelen Doug
Published: August 2024

Advanced Brayton cycle-based Waste Heat Recovery (WHR) system for a targeted energy efficiency of 20–50%, and gravimetric power densities of 1.6–1.9 kW/kg are attractive propositions for future airplane designs. One of the critical challenges for the maturation of these technologies is the need to achieve highly compact heat exchangers capable of operation under extreme pressure and temperature environments. The current work presents CFD modeling strategies for the design and development of additively manufactured Extreme Environment Heat Exchangers (EEHX). Modeling and simulation-driven design improvements to the heat exchanger (HX) are implemented to achieve a power density of 15 kW/kg under the extreme environment of 800°C inlet temperature and 80 bar pressure with supercritical CO2 as the working fluid. Various CFD based modeling methods are described, starting from selecting, rating, and sizing heat transfer (HT) surfaces, followed by detailed core modeling through periodic and end-section models. Further, a novel porous media-based modeling approach with a high-fidelity manifold model is implemented to generate optimal manifold profiles while minimizing flow maldistribution through the core. Comprehensive physical testing of the additively manufactured heat exchanger prototypes has been used to validate the developed numerical models within 5–10% of pressure drop and heat transfer predictions.
Operation of FT4000® Single Nozzle Combustor With High Hydrogen
Authors: Locke Justin , Kim Wookyung , Smith Lance , Snyder Timothy , Dayton James
Published: August 2024

This paper reports initial results from an effort to develop a retrofittable fuel/air injector for the FT4000® aeroderivative gas turbine that enables use of hydrogen as a carbon-free fuel for efficient power generation. The FT4000 engine’s low-NOx combustor was developed by Pratt & Whitney and RTX Technology Research Center with core technology from the Pratt & Whitney PW4000 turbofan aircraft engine. The work reported here advances the technology readiness level of the FT4000 combustor for operation with hydrogen, starting with an experimental assessment of the current production hardware with increasing hydrogen content mixed with natural gas.

High-pressure single-sector combustor rig tests have been completed, demonstrating the ability for the dual fuel nozzle to operate an FT4000 combustor on 100% hydrogen with low nitrogen oxide (NOx) emissions. Metal temperature measurements and video images of the flame structure from zero to 100% hydrogen highlight opportunities to improve the fuel nozzle robustness for high hydrogen conditions.

The current FT4000 production engine operates on either natural gas or No. 2 fuel oil with water injection to achieve high thermal efficiency and low emissions. This engine is fielded by Mitsubishi Power Aero and delivers 70 MW of power with a simple-cycle efficiency of over 41% when operating with wet compression. Results from this study have cleared the current production FT4000 engines with dual fuel nozzles to operate at baseload power on blends of hydrogen mixed with natural gas and water.
Impact of Input Data Quality on the Uncertainties of a Compressor Blade Parametrization Process
Authors: Schulten Benedikt , Göing Jan , Lück Sebastian , Friedrichs Jens
Published: August 2024

In the wake of the push towards knowledge-based maintenance of jet engines, a process for analysing and evaluating the performance of deteriorated aero engine components was developed. This process automatically generates CFD-simulations from 3D-scans of compressor blades and inputs the calculated performance maps into a gath-path analysis of the jet engine. The uncertainties of such a process are important for the interpretation of its results. Therefore, the uncertainties of a specific part of the process, the geometric analysis, are investigated. Special focus is put on the impact the input data quality has on the uncertainties and how the specific process implementation responds to variations in quality. Test procedures are developed to calculate the uncertainties of individual process steps for specific input data qualities. It is shown, that the noise level of the 3D-scans has a significant impact on the uncertainties. The point-cloud density also has an influence on the uncertainties, which however is small as long as a certain minimum threshold of 189 per profile section is reached. It is also shown that the uncertainties are sufficiently small to capture real geometric variances of deteriorated compressor blades when input data with noise levels of 15 μm and 316 profile points or better is used.
Cooling System of a High-Pressure Centrifugal Compressor: Development and Impact on Wheel Temperatures
Authors: Weihard Stefan , Willeke Tobias , Božek Lukáš , Hort Vladimír , Münch Stefan , Spengler Sebastian , Winter Thomas
Published: August 2024

High power density, low fuel consumption, and a compact design with competitive total costs of ownership are key requirements for internal combustion engines for conventional fuels and carbon-free or carbon-neutral future fuels. These requirements influence the development targets of charging systems and call for single-stage charging systems with increased charge air pressures. However, high compressor pressure ratios of the turbocharger lead to challenging material temperatures in aluminum alloy wheels. Consequently, creep becomes the fundamental lifetime-limiting damage mechanism for these wheels. In order to meet customer requirements regarding total costs of ownership, the lifetime is of major importance for the development of aluminum compressor wheels for turbochargers with pressure ratios beyond 6. This paper focuses on a high-pressure compressor design with a water-cooling system for a new turbocharger generation. The development of its components and their validation based on numerically predicted and measured compressor wheel temperatures are discussed. After introducing the need for high-pressure ratios and the accompanying lifetime challenges, the paper presents the design strategy and methods of the development process. Finally, the paper summarizes the achievements obtained by this procedure. Detailed and rarely before documented temperature measurements from the rotating compressor wheel are published. As will be shown, the temperature measurements confirm the predictions from the pre-development phase. A comparison of the temperature measurements from the recently developed compressor wheel with measurements carried out for a state-of-the-art wheel reveals the technological improvements achieved by this new generation of high-pressure compressor wheels.
Bayesian Inference for the Calibration of Progressive Damage Model of Dovetail Specimens From Laminated Composite Fan Blade
Authors: Tang Xu , Chen Yong
Published: August 2024

Composite fan blades are the preferred alternative for the fan stage of most advanced high bypass ratio turbofan engines in the world. Under service operating conditions, the dovetail part bears a significant centrifugal load, and the ability of the dovetail to safely bear this load is one of the key points of the multi-level “test pyramid” approach of compliance demonstration for special airworthiness regulation. Debonding between adjacent layers is the main damage mode of laminated composite fan blades, and the Cohesive Zone Material model (CZM) is widely applied to characterize its elastic and progressive damage behavior. However, there is difficulty in measuring the as-manufactured interlaminar mechanical properties used in finite element models. In this study, tensile loading was applied to simulate the interacting centrifugal force and capture mixed-mode damage evolution. Structural responses and material damages were calibrated with measured tensile loads through Bayesian inversion, where interface and contact elements with distinct bilinear behavior were selected. Posterior probability distributions of maximum interface tractions and contact stresses were solved using Markov chain Monte Carlo sampler. Results indicated that the two bilinear cohesive material models had a capacity of predicting empirical means of longitudinal reaction forces as that in test considering additional discrepancy term (0.035 kN and 0.96 kN respectively), while they made an significant impact on the prediction of tensile load history especially when two delamination cracks initiated and propagated. Interface elements provided a higher matching quality in predicting loading history and capturing damage mechanism in association with in-plane progressive damage analysis. This calibrated parameter set could be functioned as benchmark in numerically determining the ultimate tensile load of dovetail elements and reducing the necessary number of physical tests at elemental length level.
Reverse Thrust Aerodynamics of Variable Pitch Fans With Inlet Distortion
Authors: Ma Kwun Yeung , Hall Cesare A. , Wang Tianhou , Williams Tim S.
Published: August 2024

Variable pitch fans can improve the operability of low pressure ratio fan systems by repitching the rotor blades. If a variable pitch fan can generate sufficient reverse thrust on landing it also eliminates the need for heavy, cascade-type thrust reversers. However, any reverse thrust generation is impacted by high levels of inlet distortion generated as air is drawn into the exhaust nozzle. This paper uses both RANS computations and low-speed rig experiments to explore how a representative inlet distortion from the engine installation affects the aerodynamics and performance of a variable pitch fan operating in reverse thrust mode. The simulations and the experiments both show that the distortion from the engine installation leads to a highly three-dimensional flow field with a large recirculation region within the bypass duct. This is in contrast to the primarily axial flow that is produced for a case with uniform freestream inlet conditions. The distortion substantially redistributes the mass flow, thrust and power in the engine. Streamline tracking combined with a power balance analysis reveals that there is highly radial flow within the fan rotor and almost all of the power from the fan is used to drive the recirculating flow in the bypass duct, which generates high loss and has a high total temperature. The recirculation reduces the net mass flow through the engine to around 5% of a uniform inflow case and the effective reverse thrust is greatly reduced. With uniform inflow the net reverse thrust was found to be 35% of the nominal takeoff thrust. With inlet distortion present this was reduced to 20%. This demonstrates the importance of designing and operating variable pitch fan systems to minimise the reverse thrust inlet distortion.
Simulation of Sand Erosion in a Transonic Fan Stage
Authors: Ghenaiet Adel
Published: August 2024

In desert regions, there is a high concentration of dust and sand particles carried by storms and sucked into aircraft engines, leading to severe erosion. This numerical study simulates the movement of sand particles and erosion process in the front components of a high-bypass turbofan engine (HBTFE). The components include the Pitot intake, spinner, fan, core flow inlet guide vanes (IGVs), and secondary flow outlet guide vanes (OGVs). The study focuses on the engine operating conditions during takeoff from a Saharan airfield. The flow field data is obtained separately, and exported to an in-house particle tracking code based on the Lagrangian approach. The finite element method (FEM) is used to track the particles as they move through the mesh cells and determine the precise impacts and conditions to calculate the local erosion rates and material removal.

The obtained results indicate large numbers of sand particles impacting the fan blade at high frequency from the hub up to approximately 80% of the span, due to their deflection by the Pitot intake lip and outer contour. The pressure side (PS) of the fan blade experiences extreme erosion rates, while the highest erosion rates occur at the leading edge (LE) and towards the trailing edge (TE). At the exit of fan blade a significant amount of particles pass through the OGVs and typically erode its PS, while fewer particles from the lower sections of the fan pass through the IGVs. These findings reveal the erosion-prone areas that need a special coating protection.
Steam Boiler Integrity Strategy for Complex Steam Generators in Thermal Operation Facility
Authors: Al Fazari Mohamed , Aulaqi Muatasam
Published: August 2024

Petroleum Development Oman LLC (PDO) is Oman’s premier oil producer and operates several fields. Thermal Development is one of key enablers in Oman for significant Oil Recovery. “A” facility is designed to receive Aquifer Pump-off (APO) water from a reservoir and utilize it for steam generation once treated in Water Treatment Plant (WTP).

Thermal Enhanced Oil Recovery application in Oman has been first operated in Gulf region back in 2012 with enormous lesson learned insights on selecting and operating water treatment facilities.

The Purpose of Water Treatment plant is to remove hardness of APO Well Water to make it suitable for Steam generation. The processes involve the removal of suspended solids and, traces of oil and dissolved minerals from water.

Quality of boiler (steam generator) feedwater is of critical importance in steam injection projects. Field experience indicates that most generators downtime is caused by water treatment performance concerns, hence operating outside water quality specification results in damaging mechanisms of the boiler tubes i.e., corrosion and scaling deposition.

The project steam consists of 10 steam boilers of various type with total steam production of 20k tones/day responsible to produce 30k net oil/day. Steam availability has been the most significant challenge for meeting oil productions target for Steam Enhanced Oil Recovery Fields. However, maintaining safe operation of boilers at “A” facility has come with huge annual OPEX cost of > $3mln annually from boilers inspection, tube repair, and associated oil deferment due to steam unavailability during maintenance.

A comprehensive engineering approach through setting detailed boiler integrity strategy and traffic lights criteria assessments development of API-530/ASME assessment while integrating that with detailed corrosion rate calculation and proper utilization of Fitness for Service API-579 in the right context.

The objective of this paper is to generate a robust integrity strategy management of steam boilers along with significant economic benefits of cost savings around $1.5mn/year. This has proven to be the standard boilers integrity strategy to be implemented for first time in Oman and has been cascaded for all other EOR applications.
Design and Verification of a Fully Interchangeable Additively Manufactured Production Injector
Authors: Ehlig Ryan , Fahme Tony , Ryan Daniel , Evans Timothy
Published: August 2024

The development of additively manufactured (AM) components via Powder Bed Fusion - Laser Beam (PBF-LB) has accelerated in recent years within the gas turbine industry. A desire to reduce manufacturing steps, assembly complexity, supply chain dependency, and development cycle time are all driven by efforts within the industry to reduce cost. At Solar Turbines®, AM technology development has focused on the design, print, and verification of AM injectors that can match the established performance of the legacy DLE production counterpart. The motivation for this focus is full interchangeability between the AM and non-AM produced injectors, allowing customers to either use existing injectors available off the shelf, on-demand AM produced injectors, or a combination of both.

Accordingly, the team has recently designed, 3D printed, and verified an AM produced injector that matches the performance of the production DLE counterpart. Using in-house developed AM technology that is not constrained by the traditional AM design rule of a 45° build angle limit, AM was used to produce matching flow feature geometries that are otherwise very difficult to print with traditional AM methods. Key combustion parameters were also matched, such as fuel-air mixing profiles, velocity profiles, and combustion exit profiles. These parameters all play an important role in emissions performance, lifing of downstream turbine hardware, and impact the potential for encountering thermoacoustic oscillations during engine operation. Through rig and full-scale engine testing, the design team has verified the interchangeability of AM and non-AM injectors and demonstrated that equivalent performance and emissions capability can be achieved with AM produced injectors without the need to compromise due to the complexity of the design.
Unsupervised Methodology for the Prognostics of Gas Turbine Abrupt Faults
Authors: Losi Enzo , Venturini Mauro , Manservigi Lucrezia , Bechini Giovanni
Published: August 2024

The current energy market requires that gas turbines (GTs) run efficiently and reliably, thus improving their sustainability. To this aim, condition monitoring is fundamental for GT manufacturers to track performance degradation and ensure fault detection in advance.

Thanks to the huge amount of data acquired during GT operation, data-driven methodologies can be successfully employed for fault detection and prediction.

Therefore, this paper develops an unsupervised data-driven methodology for the prognostics of GT abrupt faults. The methodology comprises i) an autoencoder (AE) neural network aimed at modeling GT operation in the absence of fault symptoms and ii) a threshold-based criterion for the detection of anomalous deviations between actual data and AE predictions. A sensitivity analysis on the anomaly threshold is carried out to identify the optimal set-up of the methodology.

The paper considers GT trip as archetypal of an abrupt fault. Since no labeled data are available in the case of trip occurrence, the time point at which trip symptoms arise has to be identified. Furthermore, the paper also investigates which measurable variables are most effective for predicting GT trip, in order to provide useful insights on trip prediction.

The methodology is validated by considering a real-world case study comprising data collected from six GTs before trip occurrence. The results prove that the optimally tuned methodology correctly classifies the 80% of data. Another relevant result is that fuel mass flow rate, exhaust gas temperature, and compressor discharge temperature are the most useful measurable variables for the detection of trip symptoms.
Numerical Investigation on the Robustness Assessment and Enhancement of Labyrinth Seal With Axial Displacement and Clearance Deviation
Authors: Jin Xin , Liu Chuankai , Liu Peng , Li Zijun , Ding Shuiting
Published: August 2024

The labyrinth is widely used in aero-engine, which experiences axial displacement and radial deformation due to the interaction of mechanical, aerodynamic, and thermal loads. The axial displacement and radial clearance variation of the labyrinth have a direct effect on its operating condition and then on the functions of the secondary air system. In order to evaluate the effect of axial displacement and radial clearance deviations on the mass flow rate of the labyrinth and the functions of the secondary air system, based on the fluid network method and the modular modeling method, this paper developed a low-dimensional simulation method of rotor axial displacement. In order to improve the robustness of the stepped labyrinth to axial displacement and radial clearance deviations, a new stepped labyrinth with negative feedback is proposed. Then, the effect of the structural parameters on the flow characteristics is studied, and the sealing performance of the new stepped labyrinth and the conventional stepped labyrinth is compared under different axial displacements and clearances. Finally, the robustness evaluation is performed in terms of the labyrinth sealing performance in the isolated boundaries and the environment of the secondary air system fluid network, respectively. The results show that the mass flow of the new stepped labyrinth is more sensitive to the axial displacement deviation than that of the conventional stepped labyrinth in the isolated boundaries. While in the fluid network environment, the mass flow rate and the axial bearing load variation range of the secondary air system with the new negative feedback stepped labyrinth are significantly smaller than that with the conventional stepped labyrinth. This shows that the new negative feedback stepped labyrinth has better robustness compared to the conventional stepped labyrinth when faced with axial displacement in a fluid network environment.
Investigation of NOx and Ammonia Slip in an Ammonia and Hydrogen Powered Aviation Gas Turbine Using Chemical Reactor Network Modelling
Authors: Garai Priyankar , Bobi Shahzad , Rahman Ramees K. , Zamora David , Ahmed Marzuqa , Urso Justin , Vasu Subith S.
Published: August 2024

Ammonia is a promising green fuel with several favorable attributes that could make it a replacement for current nonrenewable aviation fuels. The feasibility of using an NH3-H2 blend as the fuel in terms of the NOx emitted has been explored in this work, consisting of residence times of 10 ms and 5 ms which represent the residence times in modern aviation gas turbine combustors. Chemical reactor network (CRN) models have been simulated using the Ansys Chemkin-Pro software, implementing air-staging techniques like RQL (Rich-Quench-Lean) to efficiently combust the fuel and bring down the NOx while also minimizing ammonia slip. Various CRN configurations have been investigated for operating conditions reflecting take-off, while varying crucial parameters such as equivalence ratio, NH3-H2 fuel fraction, inlet temperature, and pressure. This exploration aims to understand the trends in NOx emissions and ammonia slip while ensuring that the reactor exit temperature remains within the cycle requirements to prevent any material damage to the components post combustion. The effect of varying the residence times in the individual CRN components on the NOx and ammonia slip was also investigated and discussed. The minimal NOx possible while varying the parameters was about 20 ppm for the 10 ms overall residence time simulations, and about 30 ppm for the 5 ms overall residence time simulations. The trends obtained from the parametric variations along with the understanding of the different CRN models explored can help in optimizing the NOx minimization further and assist in obtaining the optimal conditions for the NH3-H2 blend used, not just for take-off, but additionally for other flight operating conditions as well. Understanding the parametric trends for minimizing NOx emissions and controlling the NH3 slip from this study can help establish an understanding of using ammonia as aviation combustor fuel, serving as a basis for further computational and experimental research.
Design and Optimization of Leading-Edge Tubercles for a Transonic Axial Compressor
Authors: Schulz Yannik , Kohl Joop Moritz , Kuestner Christoph , Seume Joerg R.
Published: August 2024

In nature, the front of the flippers of humpback whales are structured with protuberances, so-called tubercles, giving them excellent manoeuvrability. Inspired by this, tubercles can be implemented on the leading edge of compressor blades as a form of passive flow control, improving performance and possibly stall margin.

In the present work, the effect of leading-edge tubercles in a single-stage transonic compressor is investigated numerically. The base compressor operates at a mass flow rate of up to 0.83 kg/s and is capable of reaching pressure ratios of up to 1.8 and isentropic efficiencies of up to 87% while the flow is accelerated to relative inlet Mach numbers of up to 1.5.

The tubercles are initially implemented on the leading edges of the rotor blades and stator vanes via a sinusoidal function and hence as a function of amplitude and wavelength. A genetic algorithm is then used to optimize the compressor aerodynamic performance by means of steady-state CFD at design-point conditions of a mass flow rate of 0.8 kg/s and a speed of 77,000 rpm. By computing and comparing the performance maps of the reference and the optimized compressor, off-optimization point performance can be assessed. An in-depth analysis of the flow field allows the identification of the underlying effects behind the performance improvement for the tubercle-shaped topology: the creation of counter rotating vortices, laminar separation bubbles and the reduction in tip leakage vortex size at suction side-incidence.
Study of Secondary Cooling Effect on the Endwall Region With Various Trailing Edge Cutback Configurations
Authors: Yang Xi , He Wenbin , Zhang Ke , Wu Junmei , Lei Jiang
Published: August 2024

Designing the cooling schemes for the endwall region of 1st stage vanes is a challenging task due to the requirement of low NOx emissions and the presence of strong secondary flows. Considering the adequate use of coolant, the coolant injections from the trailing edge cutback not only cool the vane surface but also protect the downstream endwall region. This is called the secondary effect of cooling and is worth studying. In the present paper, distributions of cooling effectiveness on the endwall surface are measured using the PSP technique. Discrete slots are implemented near the airfoil trailing edge to provide the coolant with three compound angles (β = 15°, 30°, and 45°). Two positions of cutback slots are studied: trailing edge pressure side cutback (PC) and central cutback (CC). Experiments are conducted in a five-passage linear cascade in a suction-type wind tunnel with the inlet Reynolds number of 1 × 105 based on the axial chord length. Effects of mass flow ratio (MFR = 1%–4%) are also considered. Aerodynamic losses are obtained by solving the Reynolds-averaged Navier-Stokes equations to assess the interaction of coolant and mainstream. Results show that, with the increase of MFR, the cooling performance on the endwall surface is improved greatly. At a higher MFR, as the compound angle increases, the coolant coverage is expanded significantly and the high cooling effectiveness region gradually shrinks towards the trailing edge. In addition, the influence of cutback slot position behaves differently.
Direct Numerical Simulation of Air-Cooled and Air-Heated Channels
Authors: Modesti Davide , Pirozzoli Sergio
Published: August 2024

We develop a theoretical framework for predicting friction and heat transfer coefficients in variable-properties forced-air convection, as typical of turbine blade cooling. To do this, we borrow concepts from high-speed wall turbulence, also featuring large temperature and density variations. Using the mean momentum balance and mean thermal balance equations we develop integral transformations that account for the effect of the variable fluid properties, and apply the inverse transformations to calculate the friction and heat transfer coefficients. The proposed theory is validated using a direct numerical simulation dataset spanning both heating and cooling conditions, and the predicted friction and heat transfer coefficients match DNS data with 1–2% accuracy.
Design and Testing of a Compact, Reverse Brayton Cycle, Air (R729) Cooling Machine
Authors: Teichel Sönke , Karaefe Renan Emre , Çokşen Ahmet
Published: August 2024

Efforts to reduce the contribution of refrigeration to global warming have resulted in a phase-down of the use of fluorinated refrigerants. The alternative, natural refrigerants, used in vapor compression refrigeration machines (VCR), such as propane (R290) and ethane (R170) have significantly lower Global Warming Potential (GWP) and are less harmful to the environment. However, these refrigerants are flammable, which does not make them the preferred choice for some applications like electronics cooling. An alternative refrigeration cycle, the so called Reverse Brayton Cycle (RBC), does not require a refrigerant that undergoes a phase change and can work with air as a refrigerant (R729). Air has the advantages that it is completely harmless and easily accessible. It can be used for direct cooling, which has the potential to allow more effective and uniform cooling, faster cooldown, and a less complex cooling cycle. Despite its significant efficiency disadvantage at cooling temperatures above −50°C, this can make R729 an attractive refrigerant for innovative and simple refrigeration systems in applications where efficiency is not the most critical parameter. In this paper, the design considerations of compact, electrically driven RBC cooling machines (about 2 kWe) are discussed. Preliminary system design is presented for two different potential applications, one at high cooling temperatures (25 °C), the other at low cooling temperatures (−90 °C). The design process of the turbine stage of a RBC cooling machine including a method for matching compressor and turbine are presented. A demonstrator was built and tested, achieving a cool down of about 28 °C. Despite the deviation to the simulation, the test data supports the applied methodology.
Effect of Tilt on Thermo-Hydrodynamic Model of a Thrust Air Foil Bearing
Authors: Pourashraf Talieh , Bonello Philip , Lancaster Craig
Published: August 2024

Air Foil Thrust bearings are essential parts of high efficiency turbomachinery and are often used to support rotating machines in the axial direction. Predicting the thermo-elastic behavior of hydrodynamic thrust bearings is particularly crucial because of the common heat management challenge. Previous research works demonstrate that the thickness of the lubricating gap is significantly influenced by the thermal deformation of the runner. They did not, however, consider the impact of the disk’s misalignment in addition to its thermally induced deformation. In this study, a thermo-hydrodynamic model for an air foil thrust bearing will be provided in order to predict the pressure and temperature distribution in the bearing while accounting for rotor disc misalignment. Based on the proposed model, the performance of the bearing has been investigated. The results show that ignoring the effect of thermally induced bending of the disk will lead to unreliable prediction of bearing behavior. The same applies to the neglect of tilt, although at this stage of the modelling the degree of tilt is prescribed, unlike the thermal bending of the disk.
Dimaxer: A Fast High Order Unsteady Simulating System on GPUs for Turbomachinery
Authors: Liu Boyang , Peng Jun , Lu Yi , Liu Kai , Zhang Yang
Published: August 2024

The space-time extension kinetic energy preserving flux reconstruction method (STE-KEP-FR) and the “Magazine” type computational model can achieve fast solution of high-order accuracy large eddy simulation (LES) on small-scale machine GPUs. In this paper, a completely autonomous CFD industrial software Dimaxer developed based on this method is used to perform 5th order accuracy LES on typical turbomachinery flow cases such as VKI LS59, VKI LS89, T106C, S809, and flat plate film cooling with cylindrical hole to assess the solution speed. As well as LES on coarse and fine meshes with lower order schemes are conducted on VKI LS59 and VKI LS89 to study the requirement of the mesh and order under a given error tolerance. All the simulations are conducted on multiple Nvidia-RTX4090 desktop GPUs. The results show that for typical flow problems of turbomachinery with Renolds number ranging from hundreds to millions, wall-resolved LES numerical simulation can be achieved at an affordable computational cost (∼1 GPU hour), showing good industrial application prospects.
Combustion Modelling of the T100 Micro-Gas Turbine Burner Including the Influence of the Stretch and Heat Loss/Gain Effects on the Flame
Authors: Generini Giulio , Andreini Antonio , Bianchi Enrico
Published: August 2024

This paper focuses on the application of an extension for Zimont’s Turbulent Flame Closure (TFC) model turbulent flame speed formulation to include stretch and heat loss and gain effects on the flame. The effects are introduced, by tabulating the consumption speed of laminar 1D counter-flow flames in a “fresh-to-burnt” configuration for different stretch and heat loss/gain values. The consumption speed look-up table is then used to compute the flame turbulent flame speed within the tabulated-chemistry Flamelet Generated Manifolds (FGM) combustion model. Existing models, such as the Extended Turbulent Flame Closure (ExtTFC), are able to account for stretch and heat loss effects downstream of the reaction zone. A new model, named ExtTFCcomplete, is presented taking into account, in the construction of the consumption speed look-up table, the heat loss and gain effects both on the combustion products and reactants.

The necessity of evaluating the heat loss/gain effects on the reactants derives from the flow and geometrical characteristics of the Ansaldo Green Tech AE-T100 micro-gas turbine (mGT) burner, the object of this study. The reverse-flow inlet air and the main line fuel distribution plenum geometry demand to consider the heat loss/gain effects on the mixture before entering the combustion chamber to correctly catch the flame characteristics.

In a first step, the performances of the proposed model are validated by comparing computational fluid dynamics (CFD) simulations predictions to experimental data of an atmospheric turbulent premixed bluff-body stabilized CH4/air flame. The model is then numerically applied to the AE-T100 burner, emphasizing how the extension significantly improves the flame shape prediction with respect to the original Zimont model.
Experimental Analysis on Performance of Air/Oil Centrifugal Breathers for Aircraft Engines Under Different Operating Conditions
Authors: Di Matteo Mariano , Berten Olivier , Hendrick Patrick
Published: August 2024

This paper investigates the separation efficiency of modern aeroengine air/oil breathers, focusing on identifying configurations that enhance existing geometries. The study systematically varies parameters such as air flow rates and rotational speed, using well-known particle size distributions for testing different configuration. The experimental campaign involves various breathers with metallic grids of different geometries and mesh sizes, evaluating performance parameters such as pressure drops, oil consumption, and droplet cut-off size. The insertion of a metallic grid with a narrow mesh is found to offer a favorable trade-off in terms of pressure drops, oil consumption, and particle size at the separator exit. Results indicate that while increasing pressure drops of a reasonable amount, the selected geometries significantly reduce oil consumption and size of droplet at the exit of the breather.
Insights Into Turbocharger Centrifugal Compressor Stability Using High-Fidelity CFD and a Novel Impeller Diffusion Factor
Authors: Liu Yiming , Spence Stephen , Horsley John , Mann Stuart , Stuart Charles
Published: August 2024

Turbocharger technologies are widely applied in the modern automotive industry to meet increasingly stringent carbon emission standards. To support the continuous enhancement of these tactics, delivering improvement to the performance and stability of turbocharger compressors at low mass flow rate regimes is of paramount importance.

The present paper investigated the stability of a turbocharger compressor stage equipped with a ported shroud, using high-fidelity CFD simulations. It was found that the recirculated flow passing through the ported shroud device had primary influence on the flow condition in the vicinity of the impeller tip region (80% to 100% span). This discovery facilitated the definition of a modified impeller diffusion factor (DF), which was applied to the CFD results for three different compressor geometry configurations to lead to the provision of quantitative metrics for impeller stability. Furthermore, the observed change in the limiting impeller DF along the compressor surge line indicated that the dominant components governing the instability of the entire stage had switched, i.e., the stalling behavior of the compressor stage had transitioned from impeller dominated stall to vaneless diffuser dominated stall. Additionally, the limiting impeller DF clearly showed that one of the compressor configurations with a change in the hub endwall recess around the rear of the impeller improved the impeller stability by 3%. By comparison, another configuration with a change to strut geometry in the ported shroud recirculation channel reduced the impeller stability by 10%.

The present work addressed the gap in the understanding about the stability of different compressor configurations equipped with a ported shroud, and was useful for determining the changes in compressor global and local instability through a quantitative parameter based on a modified definition of DF.
Large Eddy Simulations for the Prediction of Fuel-Bound NOx Emissions: Application to NH3 and NH3-CH4 Blends at Different Operating Conditions
Authors: Meloni Roberto , Mazzotta Luca , Pucci Egidio , Morris Steve , Goktepe Burak , Mashruk Syed , Borello Domenico , Valera-Medina Agustin
Published: August 2024

Ammonia and its blend with natural gas and/or hydrogen will play a significant role in decarbonizing the energy sector in the next decades. Moreover, green fuels can help in reducing the fluctuations introduced by intermittent renewable sources providing an interesting alternative to the storage by the adoption of P2x2P schemes. The challenge GT manufactures are asked to solve is mainly related to the minimization of NOx emissions and the discovery of the optimal operating windows of the engines taking into consideration the potential fuel composition fluctuations associated with the availability of ammonia and other carbon-free fuels. In this context, the definition of dedicated numerical tools able to predict the combustor performance becomes crucial for the re-design of burner architecture allowing detailed analysis of technical solutions prior to experimental tests. The availability of detailed measurements, even at lab scale, represents a milestone for the improvement of these tools, especially for the Computational Fluid Dynamics codes.

In the present paper, a Computational Fluid Dynamics (CFD) methodology for the calculation of NOx emissions is developed and validated against unique data collected at Cardiff University’s Gas Turbine Research Center for blends involving methane and ammonia, considering also different pressure levels. The novelty of this methodology, based on the switch between the “in-flame” – “post-flame” contributions, lies in its extension and application for the first time to the fuel-bound NOx formation path. Thus, the main goal of this investigation is the validation of the proposed approach in the framework of this NOx mechanism, hence allowing to overcome the limits of the pre-tabulated combustion models in the prediction of this pollutant. Further, the method is implemented along a computationally cheap model like the FGM, providing an additional benefit in terms of delivery time especially in the context of applied research.

Regarding the results, the findings show good agreement with the data: for most of the considered cases, not only the trend is captured, but the numerical results offer also a good quantitative prediction of the tests.