bluuebunny/crossref_metadata_2025 huggingface dataset:
Crystal structure of the GDP-bound human M-RAS protein in two crystal forms
Authors: Bester Stephanie M. , Abrahamsen Rebecca , Rodrigues Samora Luiza , Wu Wen-I , Mou Tung-Chung
Published: August 2024

M-RAS plays a crucial role in the RAF–MEK signaling pathway. When activated by GTP, M-RAS forms a complex with SHOC2 and PP1C, initiating downstream RAF–MEK signal transduction. In this study, the crystal structure of the GDP-bound human M-RAS protein is presented with two forms of crystal packing. Both the full-length and truncated human M-RAS structures aligned well with the high-confidence section of the AlphaFold2-predicted structure with low r.m.s.d., except for the Switch regions. Despite high sequence similarity to the available mouse M-RAS structure, the full-length human M-RAS structure exhibits unique crystal packing. This inactive human M-RAS structure could offer novel insights for the design of selective compounds targeting M-RAS.
Linking SMEs’ customer strategy to firm growth: the case of manufacturing suppliers in South Korea
Authors: Seo Eunjeong , Lee Euehun
Published: August 2024

Purpose

This study examines the customer strategies for small- and medium-sized manufacturing suppliers (SMMSs) in customer dominance markets, particularly regarding power asymmetry. It has two key objectives: (1) to identify factors impacting SMMSs' customer strategies, including technological and marketing capabilities and the importance of the main customer and (2) to examine the impact of these strategies on firm growth.

Design/methodology/approach

Using the survey data on 279 Korean manufacturing suppliers in B2B markets, nine hypotheses were verified through a structural equation model (SEM). It involved capturing the varied influence of organizational capabilities on the two types of customer strategies and the link between customer strategy and firm growth.

Findings

Technology and marketing capabilities affect new customer acquisition directly, while in the case of main customer retention, marketing capability affects main customer retention through the overall satisfaction about the existing relationship. Although the importance of the main customer suppresses new customer acquisition strategies, SMMSs should actively pursue both customer acquisition and retention to promote firm growth.

Originality/value

The findings reveal how SMMSs, leveraging technological and marketing capabilities, can concurrently pursue new customer acquisition and main customer retention. Additionally, it empirically demonstrates the impact of the main customer’s importance on these customer strategies and underscores the positive impact of both strategies on firm growth. This provides a blueprint for a value-creation process linking capabilities, customer strategies and firm performance.
Employee trainers’ self-efficacy and performance: the mediating role of trainer preparation
Authors: Dei Mensah Rebecca , Andoh Raphael Papa Kweku , Amfo-Antiri Dorothy , Essandoh Emmanuel , Tetteh Stephen
Published: August 2024

Purpose

This study aims to examine the mediating role of trainer preparation in the effect employee trainer self-efficacy has on trainer performance.

Design/methodology/approach

Using a census, data was collected from internal employee trainers in two universities in Ghana. In testing the hypotheses, a structural equation modelling based on 10,000 bootstrap samples was used, and the BCa confidence intervals were used to establish the significance of the hypotheses.

Findings

This study revealed trainer preparation as a complementary partial mediator in the effect trainee engagement self-efficacy and instruction self-efficacy had on trainer performance. In addition, the importance–performance map analyses demonstrated that the factor with the most importance in the model was instruction self-efficacy, yet it was not the highest-performing factor.

Originality/value

This study highlights the mediating role played by preparation in the effect of trainer self-efficacy on trainer performance. In addition, it adds to the dearth of studies that focus on employee trainers while at the same time using data from the trainers themselves.
The metaverse experience: a big data approach to virtual service consumption
Authors: Manthiou Aikaterini , Luong Van Ha , Ayadi Kafia , Klaus Phil
Published: August 2024

Purpose

The experience of leaving the real world and entering a virtual service environment makes many individuals happy. This study heeds the call by multiple researchers to conceptualize, interpret and illustrate the impact of the perceived service experience in the metaverse in a holistic way. In particular, this study aims to understand how the consumption of experiences is perceived in a metaversal space.

Design/methodology/approach

The authors analyze mega virtual live events with famous artists broadcast in virtual worlds. The authors take a big data approach and include two studies to gain insight into the online public audience’s perceptions and experiences in the metaverse. In the first study, the authors analyze text from YouTube with Leximancer. In the second study, the authors go one step further to refine the conceptual model from Study 1. The authors scrutinize additional Facebook comments using seeded Latent Dirichlet Allocation (LDA).

Findings

The findings reveal that the meta service experience (MEX) encompasses four dimensions: immersion, metascape, immediacy and hedonism.

Originality/value

This research provides important guidance not only for consumer behavior scholars but also for service marketers and event planners. The study proposes research opportunities to advance service experience research in the metaverse.
The impact of formal and informal credit institutions on entrepreneurship
Authors: Malkova Alina
Published: August 2024

Purpose

How do informal lending institutions affect entrepreneurship? This paper aims to investigates the role of formal and informal credit market institutions in the decision to become an entrepreneur over the life cycle.

Design/methodology/approach

The author developed a dynamic Roy model in which a decision to become an entrepreneur depends on the access to formal and informal credit markets, nonpecuniary benefits of entrepreneurship, career-specific entry costs, prior work experience, education, unobserved abilities and other labor market opportunities (salaried employment and nonemployment). Using detailed Russian panel microdata (the Russia longitudinal monitoring survey) and estimating a structural model of labor market decisions and borrowing options, the author assesses the impact of the development of informal and formal credit institutions.

Findings

The expansion of traditional (formal) credit market institutions positively impacts all workers’ categories, reduces the share of entrepreneurs who borrow from informal sources and incentivizes low-type entrepreneurs to switch to salaried employment. The development of the informal credit market reduces the percentage of high-type entrepreneurs who borrow from formal sources. In the case of default, a higher value of the social network or higher costs of losing social ties demotivate low-type entrepreneurs to borrow from informal sources. The author highlights the practical implications of estimates by evaluating policies designed to promote entrepreneurship, such as subsidies and accessibility regulations in credit market institutions.

Originality/value

This study contributes to the literature in several ways. Unlike other studies that focus on individual characteristics in the selection for self-employment [Humphries (2017), Hincapíe (2020), Gendron-Carrier (2021), Dillon and Stanton (2017)], the paper models labor and borrowing decisions jointly. Previous studies discuss transitions between salaried employment and self-employment, taking into account entrepreneurial earnings, wealth, education and age, but do not consider the availability of financial institutions as a driving factor for the selection into self-employment. To the best of the author’s knowledge, this paper shows for the first time that the transition from salaried employment to self-employment is standard and consistent with changes in access to financial institutions. Another feature of this study is incorporating both types of credit markets – formal and informal. The survey by the European Central Bank on the Access to Finance of Enterprises (2018) shows 18% of small and medium enterprise in EU pointed funds from family or friends. Therefore, the exclusion from consideration of informal credit markets may distort the understanding of the role of the accessibility of credit markets.
Artificial intelligence-powered tools and academic writing: to use or not to use ChatGPT
Authors: Al-Sofi Bakr Bagash Mansour Ahmed
Published: August 2024

Purpose

This study investigates the potential effectiveness of ChatGPT in enhancing the academic writing skills of Saudi EFL undergraduate students. It also examines the challenges associated with its use and suggests effective ways to address them in the education sector.

Design/methodology/approach

The study employed a sequential mixed-methods approach, which involved distributing questionnaires to gather data from students, followed by conducting semi-structured interviews with a purposeful selection of eight students and six teachers.

Findings

The findings revealed that students were generally satisfied with the effectiveness of ChatGPT in enhancing their academic writing skills. However, they also pinpointed some challenges associated with using ChatGPT, including plagiarism, overreliance, inadequate documentation, threats to academic integrity, and inaccurate information. To alleviate these challenges, effective strategies include deploying detection tools, equipping students and educators with training sessions, and revisiting academic policies and assessment methods. It is recommended that ChatGPT be used responsibly as an assistant tool, in conjunction with students' ideas and teachers' feedback. This approach can significantly enhance students' writing skills and facilitate completing their research projects and assignments.

Practical implications

ChatGPT can be a valuable tool in the educational landscape, but it is essential to use it judiciously. Therefore, teachers' effective integration of ChatGPT into their classrooms can significantly enhance students' writing abilities and streamline their research process.

Originality/value

This study contributes to recent AI-based research and provides practical insights on the responsible integration of ChatGPT into education while addressing potential challenges.
Trehalose attenuates testicular aging by activating autophagy and improving mitochondrial quality
Authors: Xi Huaming , Shan Wenjing , Li Minghui , Wang Ziqian , Li Yuan
Published: August 2024

Background

Reproductive aging can adversely affect male fertility and the health of offspring. The aging process is accompanied by impaired autophagy. Recent studies have shown that Trehalose plays an important role in the prevention of various diseases by regulating autophagy. However, the roles of Trehalose in testicular aging and reproductive decline remain to be clarified.

Objective

The present study aimed to evaluate the protective effects of Trehalose on testes in an aging mouse model.

Materials and methods

In this study, an in vivo aging model in mice by administering D‐galactose was established to explore the protective effect of Trehalose on testicular aging. We examined histological changes and related indicators of apoptosis, autophagy, mitochondrial biogenesis, and sperm quality.

Results

D‐galactose treatment induced oxidative stress, apoptosis, and impairment of autophagy of testicular cells in mouse testes. Trehalose administration significantly reduced germ cell apoptosis and DNA damage caused by D‐galactose‐induced oxidative stress. Notably, Trehalose activated autophagy activity and improved mitochondrial function in testicular cells. Furthermore, Trehalose treatment increased the expression level of the tight junction protein ZO‐1, and accelerated clearance of damaged mitochondria in Sertoli cells, indicating that Trehalose ameliorated Sertoli cell function in D‐galactose‐induced aging testes.

Discussion and conclusion

These findings suggest that Trehalose administration activated the autophagy activity in testicular cells and improved mitochondrial function, thereby effectively preventing testicular aging. Trehalose and its activated autophagy are crucial for preventing testicular aging, thus restoring autophagy activity by administering Trehalose could be a promising means to delay aging.
Toward a Truly Universal Catholicity?
Authors: Vivier‐Muresan Anne‐Sophie
Published: August 2024

This article discusses the latest document by the Francophone ecumenical group the Groupe des Dombes. The document advocates a “reformed catholicity” through the conversion of the churches, where catholicity is not seen as the exclusive property of the Roman Catholic faithful but encompasses the entire Christian church, and in which the word “reformed” also concerns the whole Christian church and not only Protestant churches. This article first explores the contribution of this text to ecumenical dialogue. It then discusses the “bold thesis” at the centre of the document, according to which the Catholic Church and the churches of the Reformation “form one Church, although in imperfect communion.” The article then goes on to highlight the eschatological dynamic of the document and the relationship between catholicity and mission. The article concludes with some thoughts about the path toward a truly universal catholicity.
Associations Between Severe Influenza‐Complicated Thromboembolism Events, Intensive Care Unit Stays and Mortality, and Associated Risk Factors: A Retrospective Cohort Study
Authors: Lee Wei‐Chun , Chang Che‐Chia , Ho Meng‐Chin , Lin Chin‐Kuo , Lin Chieh‐Mo , Fang Yu‐Hung , Huang Shu‐Yi , Lin Yu‐Ching , Chuang Min‐Chun , Yang Tsung‐Ming , Hung Ming‐Szu , Chou Yen‐Li , Tsai Ying‐Huang , Hsieh Meng‐Jer
Published: August 2024

The association between influenza infection and thromboembolism (TE) events, including cardiovascular events, cerebrovascular events, pulmonary embolism, and deep vein thrombosis, is supported by compelling evidence. However, there is a disparity in the risk factors that impact the outcomes of severe influenza‐complicated TE in intensive care unit (ICU) patients. The objective of this study was to evaluate the outcomes of severe influenza‐complicated TE in ICU patients and identify any associated risk factors.

Methods

A retrospective cohort study was conducted, recruiting consecutive patients with TE events admitted to the ICU between December 2015 through December 2018 at our institution in Taiwan. The study included a group of 108 patients with severe influenza and a control group of 192 patients with severe community‐acquired pneumonia. Associations between complicated TE, length of ICU stay, and 90‐day mortality were evaluated using logistic regression analysis, and risk factors were identified using univariate and multivariate generalized linear regression analyses.

Results

TE event prevalence was significantly higher in ICU patients with severe influenza than in ICU patients with severe CAP (21.3% vs. 5.7%, respectively; p < 0.05). Patients with severe influenza who developed TE experienced a significant increase in the ratio of mechanical ventilation use, length of mechanical ventilation use, ICU stay, and 90‐day mortality when compared to patients without TE (all p < 0.05). The comparison of severe CAP patients with and without TE revealed no significant differences (p > 0.05). The development of thromboembolic events in patients with severe influenza or severe noninfluenza CAP is linked to influenza infection and hypertension (p < 0.05). Furthermore, complicated TE and the severity of the APACHE II score are risk factors for 90‐day mortality in ICU patients with severe influenza (p < 0.05).

Conclusions

Patients with severe influenza and complicated TE are more likely to have an extended ICU stay and 90‐day mortality than patients with severe CAP. The risk is significantly higher for patients with a higher APACHE II score. The results of this study may aid in defining better strategies for early recognition and prevention of severe influenza‐complicated TE.
Effect of high‐flow nasal and buccal oxygenation on safe apnea time in children with open mouth: A randomized controlled trial
Authors: Ji Sang‐Hwan , Park Jung‐Bin , Kang Pyoyoon , Jang Young‐Eun , Kim Eun‐Hee , Lee Ji‐Hyun , Kim Hee‐Soo , Kim Jin‐Tae
Published: August 2024

Background

High‐flow nasal oxygenation is reported to prolong duration of apnea while maintaining adequate oxygen saturation with the mouth closed. Also, buccal oxygenation is known to have similar effects in obese adults. We compared the effect of these two methods on prolongation of acceptable apnea time in pediatric patients with their mouth open.

Methods

Thirty‐eight patients, aged 0–10 years were randomly allocated to either the high‐flow nasal oxygenation group (n = 17) or the buccal oxygenation group (n = 21). After induction of anesthesia including neuromuscular blockade, manual ventilation was initiated until the expiratory oxygen concentration reached 90%. Subsequently, ventilation was paused, and the patient's head was extended, and mouth was opened. The HFNO group received 2 L·min−1·kg−1 of oxygen, and the BO group received 0.5 L·min−1·kg−1 of oxygen. We set a target apnea time according to previous literature. When the apnea time reached the target, we defined the case as “success” in prolongation of safe apnea time and resumed ventilation. When the pulse oximetry decreased to 92% before the target apnea time, it was recorded as “failure” and rescue ventilation was given.

Results

The success rate of safe apnea prolongation was 100% in the high‐flow nasal oxygenation group compared to 76% in the buccal oxygenation group (p = .04). Oxygen reserve index, end‐tidal or transcutaneous carbon dioxide partial pressure, and pulse oximetry did not differ between groups.

Conclusion

High‐flow nasal oxygenation is effective in maintaining appropriate arterial oxygen saturation during apnea even in children with their mouth open and is superior to buccal oxygenation. Buccal oxygenation may be a good alternative when high‐flow nasal oxygenation is not available.
Wear it like armor and it can never be used to hurt you: Reappropriation, identity change, and collective action
Authors: Uysal Mete Sefa , Acar Yasemin Gülsüm
Published: August 2024

Reappropriation has been discussed as an identity management strategy as a means to reevaluate oneself in a context that will not allow for large‐scale social change. There are, however, numerous examples of reappropriation of stigmatizing labels as connected to political movements. This research examines whether reappropriation of stigmatizing labels can function as a precursor to collective action. In Study 1, we conducted semi‐structured interviews on the reappropriation of çapulcu identity with 20 Gezi Park protesters in Turkey. Interviews focused on how they recall the reappropriation of the word to have started, how they gave subsequent meaning, and how çapulcu identity predicted their protest participation and their broader politicization during and after the protests. In Study 2, we conducted a cross‐sectional survey on the reappropriation of fat identity by collecting data from fat liberation and body positivity activists in North America (n = 479). Reflexive thematic analysis (Study 1) and structural equation modeling (Study 2) showed that reappropriation of stigmatizing labels among activists is associated with a greater willingness to participate in collective action through increased agency, empowerment, and identity change. Findings provide important insights on identity management strategies and social change, and open new avenues to discuss reappropriation as a possible political strategy that might mobilize oppressed groups.
Development of an Efficient Compressor and Turbine for a 2MW-Class Emergency Gas Turbine
Authors: Kohama Takao , Anzawa Shuichi , Seki Yutaro
Published: August 2024

Emergency gas turbine generators manufactured by IHI Power Systems can promptly deliver large amounts of electricity during power outages, thereby playing a vital role in supporting society. When introducing these power generation devices into buildings located in city centers where installation space is constrained, a reduction in size becomes essential. As such, we have outlined a plan to downsize the existing 2 MW engine from NGT3 type to NGT2 type. To accomplish this, it is necessary to increase the output from the NGT2 type 1.6 MW to 2 MW, which entails a redesign of the compressor and turbine. This paper provides a detailed account of our efforts and the resulting outcomes of this undertaking.
Who Won the Race to Fracture – Torque Tube or Air Separator?
Authors: Gowreesan Vamadevan , Greaves Wayne
Published: August 2024

A gas turbine failed catastrophically at a process plant during operation. The failure resulted in the torque tube and air separator breaking into multiple pieces. The bolts connecting the torque tube to the air separator, the bolts connecting the torque tube to the turbine discs and the bolts connecting the torque tube to the compressor section also failed.

A detailed metallurgical root cause failure analysis was performed to understand what happened. The analysis included reconstruction of the torque tube and air separator from the broken pieces, and evaluation of all fracture surfaces. Based on the patterns seen on the fracture surfaces, the fracture mechanisms and crack propagation paths were determined for the torque tube and the air separator. Mechanical properties were tested using specimens extracted from the broken pieces. Microstructural evaluation was also performed. Similar analyses were performed on the broken bolts. Based on the fracture surface evaluation of the bolts, the bolt fractures were believed to be collateral damage.

Multiple preexisting cracks and a material defect were found in the torque tube. Fracture had propagated from one of these preexisting cracks in the torque tube. The question was if the torque tube fractured first, or the air separator fractured first.
The Effect of O-Ring Compression Set on the Rotordynamic Behavior of Turbomachinery
Authors: Simpson Christopher , Shakil Ali
Published: August 2024

For some aerospace applications, radial load support for high-speed turbomachinery is provided by gas foil journal bearings mounted on elastomeric O-rings. O-ring mounting provides several benefits including energy dissipation, thermal growth compensation, and higher bore misalignment tolerance. O-ring material selection requires careful consideration of application-specific factors to properly manage the synchronous and sub-synchronous response of the rotor bearing system over the lifetime of the application. O-ring material stiffness, bearing stiffness, operating temperatures, and environmental exposure are all relevant factors. Long-term exposure to operating environments can result in evolution of O-ring properties over time, including changes in stiffness, damping, and permanent compression set.

The objective of this work was to empirically characterize O-ring compression set behavior for a range of materials at a subscale level and to evaluate the associated effects on rotordynamic behavior at the assembly level. Subscale characterization efforts identified two materials with unique characteristics which were selected for further evaluation via full-scale assembly level rotordynamic testing. O-ring material characterization and high-speed rotordynamic test results are quantitatively evaluated, compared, and discussed to assess the suitability for use in future applications. Additional opportunities for continued validation efforts are also discussed.
Effect of Flexible Rotor Bucket Design on Savonius Turbine Performance
Authors: Grönman Aki , Bashyal Srijit
Published: August 2024

Savonius wind turbines are simple and robust devices suitable for a variety of climate conditions. Due to their low noise emission, they can be used in urban areas close to end users. However, their biggest drawback is their relatively low aerodynamic performance. One solution to this challenge is to use flexible rotor buckets. Public literature has shown that a wing’s aerodynamic performance can be improved by introducing flexible material; however, this idea has not been widely studied in the case of a Savonius turbine. Therefore, this work presents an experimental and analytical study determining how turbine performance is affected by the flexibility of the rotor bucket. In particular, the effect of the leading edge design is examined. In total, three rotor designs are studied in a continuously operated wind tunnel to reveal the effects of rotor design on the rotational speed and rotor deformation at different flow velocities. In addition, a correlation is developed to predict the turbine power coefficient under the measured operating conditions. The results suggest that a flexible membrane bucket can improve the performance of a Savonius turbine compared to a conventional rigid design. It is also found that the amount of leading edge flexibility can affect the optimal operating range. High-speed camera studies provide further insights into the bucket deformations during the operation of different rotor designs.
High Resolution Probe Measurements in a Multi-Stage Turbine Rig
Authors: Weggler Philipp , Bachner Johannes , König Franz-Xaver , Stephan Robert , Gmelin Christoph
Published: August 2024

This paper introduces the Rotating Turbine Rig (RTR) and presents the results of its first measurement campaign. The turbine test facility, NG-Turb, situated at DLR Göttingen, is described and a detailed description of the RTR setup is given. The measurement equipment and its associated uncertainties are examined. The focus of the results presented is on the aerodynamic design point of the 2½ stage high-pressure turbine. A typical test day operation and its stability and repeatability of the operational points are presented. Additionally, the investigation delves into the homogeneity of inflow and outflow. The reproducibility of measurements across different test days is compared, thereby illustrating the consistency and reliability of the experimental data. Finally, inter-blade flow fields measured by pneumatic probes is presented. Specifically, the study of the flow structures associated with tip flow leakage, purge flows, and cooling flows, and their interactions with the main flow is described. The high-resolution data is used to foster the understanding of multi-stage turbine flow.
Novel Alloying Strategy to Improve Brazing Properties on Nickel Based Superalloys for Aircrafts Turbine Application
Authors: Reker Dirk Wilhelm , Sowa Roman , Schwalbe Caspar , Seidel Frank , Moehwald Kai , Nicolaus Martin , Wackenrohr Steffen , Tillmann Wolfgang
Published: August 2024

The continuous improvement of high potential repair technologies is an essential driver for cost-effective and sustainable aviation. To withstand extreme forces and temperatures the turbine section of aircraft engines is made from Nickel-based superalloys. This class of materials routinely develops cracks and geometrical deviations in service which require a brazing repair, thus making brazing an indispensable key technology. This study seeks to improve brazing properties on Nickel-based superalloys for aircraft applications. Facilitated by materials simulation, a novel alloying strategy is outlined to design the braze alloy chemistry. The design criteria are established on the optimization of major microstructural properties influencing the mechanical properties known for repair brazed joints. The proposed design criteria were applied to the development of two new braze alloys. The new alloy design approach is validated experimentally by using the developed alloys. Mechanical properties of brazed samples made from Nickel-based superalloys were investigated at a service equivalent temperature of 871 °C. Results indicate that the ultimate tensile strength at 871 °C is 20.5 % higher than that published for legacy braze alloys. This study provides a basis for the development of repair technologies applicable to further superalloys.
Analysis of Irreversible Thermochromic Paints for High Temperature Applications Using Specular Reflectance and Roughness Measurement
Authors: Kossakowski Robert , Gier Stefan , Endrulat Benjamin , Voigt Matthias , Mailach Ronald
Published: August 2024

During the development process of a jet engine, it is critical to validate the thermal- and secondary air system. The validation requires an adequate measurement of the temperature distribution on hot end components, as combustor parts, turbine blades and vanes. Rolls-Royce is using irreversible thermochromic paints for measuring the spatial temperature distribution. The paint is a sensitive coating which irreversibly changes its characteristics with temperature and time on condition. For the prior art analysis process, the visual appearance of the paint is assessed and compared to calibration references for temperature prediction. This process requires special trained personnel and a standardised working environment. Previous research investigated the automation of the analysis process using imaging techniques. It is vital to explore these methods to increase the accuracy and precision of the measurement and accelerate the analysis process. However, especially for high temperatures, the change in colour is difficult to distinguish.

To supplement the visual analysis process, it is proposed to measure the specular reflectance and roughness of the surface in addition to the colour change. This paper investigates the correlation of these surface characteristics to temperature. Three frequently used paint types for high temperature application have been coated onto Nimonic®75 reference material, which have subsequently been heat-treated in a calibration furnace to generate solid state test pieces. The specular reflectance and roughness of the test pieces was measured with non-intrusive optical measurement devices. For all three paints, a correlation between reflectance and temperature was found. For roughness, the measurement suggests a correlation with temperature in higher ranges between 900 to 1200 °C. For validation, test pieces with a gradual temperature profile have been investigated. To include the effect of curvature, turbine blade test pieces have been measured and evaluated. The results show that measurement of the surface characteristics, like reflectance and roughness, contribute and supplement the analysis process especially in the high temperature range of irreversible thermochromic paints and hence aid the robustness and accuracy of the assessment.
Cluster Analysis of Acoustic Emission Signals From SiC/SiC CMCs Including the Introduction of Waveguides and the Effect of Material Changes Under Thermal Exposure
Authors: Quiney Zak , Gale Louise , Pattison Steven , Garcia-Luna Gonzalo , Newton Christopher , Bache Martin , Jeffs Spencer
Published: August 2024

Ceramic matrix composites (CMCs) have received significant attention due to their advantageous material properties for engineering applications where temperatures approach or exceed the working limits of traditional metals and alloys. An understanding of the damage mechanisms that accumulate within the material under complex mechanical and thermal stress conditions is therefore essential. Acoustic emission (AE) is one form of non-destructive evaluation (NDE) that is routinely used for such assessment. This paper investigates the application of pattern recognition tools to AE data obtained from monotonic tensile testing of SiCf/BN/SiC CMCs under thermal exposure in a range between room temperature (RT) and 1100°C.

Unsupervised pattern recognition in the form of k-means clustering was subsequently applied to the AE datasets in efforts to link different AE signal characteristics with damage mechanisms anticipated at specific stresses within the CMC. Due to elevated temperatures, AE waveguides were used in all tests. At RT, commonly occurring clusters were attributed to damage modes such as matrix cracking and interfacial debonding/sliding. At increasing temperatures, cluster activity remained broadly consistent until the effects of oxidation and thermally induced degradation of the material occurred between the temperature steps of400° and 600°C. Further differences were observed at 1100°C.
Comparison of Vortex Detection Methods on the Numerical Simulation of Tip Leakage Flow of a Low-Speed Axial Fan
Authors: Balla Esztella , Kovács Kinga Andrea , Lendvai Bálint
Published: August 2024

The present paper investigates the capabilities of the Lagrangian-Averaged Vorticity Deviation (LAVD) vortex detection method for turbomachinery applications. The tip leakage vortex of a low-speed axial fan is identified with multiple vortex detection methods. The investigation is carried out on a numerical simulation of a ducted fan. The results from the LAVD method are compared with the outcomes of the following vortex detection techniques: Q criterion, VR helicity density, vortex core distance technique of Li and Carrica, and Banks’ vorticity predictor-pressure corrector vortex core identification method. The position and extension of the vortex region and the location of the vortex core line are considered during the comparison. The results show that the vortex region and core detected by the LAVD technique are in great accordance with the outcome of the other methods. Compared to other methods, the advantage of the LAVD technique is that its parameters can be objectively defined from geometrical features of the flow field, e.g., blade chord length. The LAVD is also able to detect the core and the perimeter of the vortex region.
Experimental Characterisation of Surge Cycles and Second Quadrant Operation for a Centrifugal Compressor
Authors: Pronk Ola Ilseth , Bakken Lars Eirik
Published: August 2024

Accurate characterisation of compressor responses is critical for simulation studies involving flow instabilities. The positive-slope and second quadrant characteristics of a compressor dictate the performance of the compression system as the machine operates in an unstable condition. Conventional process simulation tools do not fully describe system behaviour beyond the surge line, as the compressor unit models omit performance losses incurred by surge and stall phenomena. The simulated response of events featuring flow instabilities will deviate from the actual system response unless the model is altered accordingly.

A major challenge of dynamic simulations at off-design conditions is related to the establishment of performance characteristics beyond the surge line. It is not possible to extrapolate correct transient responses without such characteristics. Empirical data quantifying key features of characteristics obtained at different operating conditions and system geometries are needed to resolve this challenge.

In this work, the performance characteristics of a single-stage centrifugal compressor operating in the first and second quadrants of the compressor map are exposed through an experimental test campaign. The trajectories of the operating point in the second quadrant and the development of surge cycles as the machine approaches and recovers from zero flow are highlighted. The impact of different discharge volumes on the transient and semi-steady compressor characteristics is documented. The volume of the plenum is shown to affect the response of the system in terms of oscillation amplitudes, frequencies, and phase shifts. Notably, it has little impact on the time-averaged semi-steady characteristics of the machine but greatly impacts the emergence of surge cycles. The experimental results provide a solid empirical basis on which novel modelling routines can be developed.
Multi-Stage Cyclic Symmetry Analysis of an Industrial High Pressure Turbine Assembly – Comparing Structural, Modal, and Solve Statistics
Authors: Bronson Jeffrey
Published: August 2024

Structural analysis of rotating turbomachinery geometry typically can take advantage of cyclic symmetry reduction to facilitate faster solve times and reduced result file size requirements. Historically, these analyses have been limited to decomposing the geometry to a single cyclic sector that shares a common sector count. Concessions are often made in these analyses (eliminating features that do not share a common sector count, artificially changing airfoil counts to force sector counts that are factors of each other, or modelling multiple sector that share a common factor together in a large segment — i.e. model a 1/3 sector) because the savings in solve time and file size reduction are invaluable versus trying to solve a full 360° representation of the geometry.

Multi-stage cyclic symmetry is a theoretical technique to create and analyze geometric models that consist of multiple cyclically symmetric structures that have different sector counts. This technique has been demonstrated on many simpler academic cases and has been shown to provide accurate results for a properly setup analysis model. The aim of this paper is to use the multi-stage cyclic symmetry approach on a full two row high pressure turbine assembly (consisting of non-proprietary geometry representative of an industrial assembly) to analyze both a static structural analysis for stress, as well as a modal analysis for natural frequencies and mode shapes. The paper will compare the results from running the same geometry as a full 360° reference case to check the multi-stage analysis for accuracy. Solve times, memory usage, and result file sizes will also be compared to show the benefits of using the multi-stage cyclic symmetry technique.
Evaluating the Energy Recovery Potential in Industrial Gas Pipeline Networks: A Preliminary Analysis of Gas Expander Applications for Nitrogen, Oxygen and Hydrogen
Authors: Baiguini Mattia , Doninelli Michele , Di Marcoberardino Gioele , Iora Paolo Giulio , Invernizzi Costante Mario
Published: August 2024

The aim of this work is to analyse the potential electrical energy that can be produced from the installation of expanders in the gas pressure reducing stations of industrial gases networks (oxygen, nitrogen and hydrogen). This solution is well established in natural gas grid but not yet implemented in existing technical gases networks. In the first part, the theoretical energy recovery potential is investigated by calculating the isentropic expansion specific power under different expander inlet temperatures and pressure ratios. Then the evaluation of adopting radial or axial expander is considered according to typical operating conditions: in particular, the design of axial expander is carried out with an open-source code. Eventually the design and the impact of the gas expanders solution is evaluated in selected industrial processes for each investigated technical gas. A discussion on practical issues is proposed. Radial expander could reach an isentropic efficiency of 89% while efficiency of 94% is obtained with an axial configuration with compact machinery. The application of gas expander in possible scenarios leads to annual energy production up to 19 GWh (O2 expander in blast furnace) with an utilization factor of 90% and cost of production ranges from 16 to 37 $/MWh with an avoided emission up to 1062 tCO2,eq/y. Results show an interesting potential for the proposed solution: however, the application strongly depends on adequate gas flow rate and operating pressure with a niche market now.
Introduction of Axisymmetric Grooves As a Tip Seal Treatment for Small-Core Turbines
Authors: Wiese Connor J. , Berdanier Reid A. , Thole Karen A.
Published: August 2024

The aerodynamic penalties associated with the tip gap flow in axial turbines remains a challenging problem for turbine manufacturers. As modern gas turbines with small-core architectures are brought online, the influence of the tip gap continues to grow. While technologies to reduce the losses associated with the tip gap flow have been implemented into the blades themselves, little attention has been paid to the stationary tip seal, or casing, around the rotor wheel. In this study, an introduction to the use of axisymmetric groove enhancements for the casing of the rotor tip are examined computationally. These studies use the National Experimental Turbine (NExT) geometry, an engine-representative high-pressure turbine blade.

Steady, Reynolds-Averaged Navier-Stokes simulations are used to assess the basic characteristics of axisymmetric grooves, such as depth, location, and arrangement. The objective of this introductory study was to determine the feasibility of impacting the tip leakage vortex formation and the associated losses in rotor efficiency. Furthermore, analyses were done with different tip gap heights along with both flat- and squealer-tipped blades.

Tip seals with a single groove are demonstrated to improve rotor aerodynamic efficiency relative to ungrooved seals by up to 0.4 points when applied to flat-tipped rotor blades and up to 0.15 points with squealer tips. Alternating arrays of grooves show improvements for flat-tipped blade performance by up to 0.76 points, while having little additional aerodynamic effect on squealer tip compared to the best single-groove designs. Finally, grooved tip seals appear to exert greater influence on the aerodynamic performance of the turbine rotor when at larger tip gaps, indicating that grooved tip seals alter the sensitivity of rotor performance to the tip gap.
Case Study of User Defined Element Integration in Rotor Dynamics Software
Authors: Mathuria Parag H. , Savela Gregory
Published: August 2024

Gas turbine engine companies often employ home-grown or internally developed computer programs for rotor dynamics design-analysis. Developing, and maturing these sometimes over decades to support day-to-day design execution and some of the more specialized problems in Rotor Dynamics. As some problems now require higher fidelity modeling or visualization, along with the incorporation of more physics-based capabilities, the employment of commercially available, general use software becomes attractive to predict general engine dynamic behavior with these additional features. These are found to be important in predicting rotor dynamic system behavior accurately.

Three case studies are presented in this paper, namely (1) squeeze film dampers with inertia terms in addition to conventional stiffness and damping, (2) speed/thrust dependent bearing stiffness in transient analysis and (3) the explanation of side-banding in the response utilizing transient analysis solutions. The approach described in this paper seeks to make use of already proven general finite-element nonlinear analysis (transient and harmonic analyses) which are available in the market. This process of integration will allow us to include system nonlinearities (particularly at the damper for case #1 and bearings stiffness for case # 2 and 3) appears to be necessary if analytical predictions are to be realistic. The work is applied to Nelson-McVaugh model to validate for squeeze file damper element for harmonic analysis and other two cases for transient analysis. This paper will be useful for the end user for implementing and enhancing the capability in house as well as commercial software where user defined element is possible.
Applicability of Volume of Fluid Method to Two-Phase Flow Turbomachinery Application
Authors: Salpingidou Christina , So Kwok Kai
Published: August 2024

Hydrodynamic bearings, based on lubrication oil, are commonly used in turbomachinery. The understanding and modeling of the air-oil two-phase flows in the bearing casing, piping and drain are important during the design phase. Given the limitations of the analytical methods and experiments, the use of robust and fast numerical methods, which can aid the engineers to assess various designs, is significant. In this paper, the use of VOF method for the air-oil flows for turbomachinery is reviewed. The paper first scrutinizes the use of VOF method for certain flow regimes from the perspective of the underlying VOF numerical method. Then, based on a detailed investigation using test rig observation of the bearing casing of a radial bearing of a turbocharger, the corresponding two-phase flow simulations using VOF are presented. Sensitivity studies are carried-out to understand the role of the key parameters and determine an appropriate CFD model. With the proper numerical setup, the CFD results are in good agreement with the test rig. The numerical setup is further applied to a common use case of air-oil two-phase flows of turbomachinery, namely the oil drain. The CFD model of the oil drain leads to realistic results and illustrates the applicability of the VOF method.
A Simplified Injection Model for Variable Area Turbine Fluidic Throttling
Authors: Spens Alexander , McFadden Evan J. , Westrick Cole D. , Bons Jeffrey P.
Published: August 2024

Previous studies have demonstrated the effectiveness of using fluidic actuators to throttle the flow through a nozzle guide vane, enabling a variable area turbine (VAT) with no moving parts. A simplified model was developed to assess the driving design factors that influence the blocked flow fraction and throttling effectiveness of the actuators. The model approximates slot injection using a simplified stream tube analysis, neglecting mixing with the primary passage flow. Throttling performance is predicted for fluidic actuators with different widths, orientations, streamwise locations, and pressure ratios. This simplified model evaluates these actuators in a constant width straight duct and a variable width duct. Two-dimensional CFD of injection in the nozzle guide vane passage reported strong agreement with the results of the simple model using the variable width duct. Higher injection pressure ratios result in more injected mass flow but not significantly higher throttling effectiveness. Wider slots retain the effectiveness and block much more primary flow. Upstream oriented injection proves best for both effectiveness and blockage capabilities. Finally, there is an optimal injection location relative to the passage throat, which is extracted by both the model and CFD. This model has potential application for optimizing fluidic VAT throttling designs while saving on the cost of high-fidelity testing and production of these configurations.
Undergraduate Hypersonics Research: the Fourth Year of the REU Site HYPER
Authors: Kauffman Jeffrey L. , Gordon Ali P.
Published: August 2024

Progress towards future modes of transportation and energy production has uncovered significant knowledge gaps impeding technical progress. Realizing aircraft that regularly operate in supersonic and even hypersonic regimes and turbomachinery supporting carbon neutrality can be addressed only through multi-disciplinary research. The University of Central Florida (UCF) equips future engineers and scientists for research-oriented careers through a variety of programs and initiatives. One key initiative is a Research Experiences for Undergraduates Site housed within the Center for Advanced Turbomachinery and Energy Research and the Department of Mechanical and Aerospace Engineering. Now hosting its fifth cohort, the site unites multi-disciplinary projects around HYpersonic, Propulsive, Energetic, and Reusable Platforms (HYPER). Beyond graduate-level research with expert faculty, participants engage in a professional development series, industry tours, and computational software training. UCF plays a key role in preparing a workforce of young scientists for research careers in hypersonics. This paper presents data drawn from the four completed cohorts of HYPER participants on how exposing participants to the various disciplines has impacted their self-efficacy, as well as a brief summary of lessons learned along the way. With this site, UCF plays a key role in preparing a workforce of young scientists for research careers in hypersonics.