bluuebunny/crossref_metadata_2025 huggingface dataset:
Cytomegalovirus‐related sepsis‐like syndrome in very premature infants in Japan
Authors: Namba Fumihiko , Nakagawa Ryota , Haga Mitsuhiro , Yoshimoto Seiji , Tomobe Yutaro , Okazaki Kaoru , Nakamura Kenji , Seki Yoshiko , Kitamura Souya , Shimokaze Tomoyuki , Ikegami Hitoshi , Nishida Kosuke , Mori Shigehiro , Tamai Kei , Ozawa Junichi , Tanaka Kosuke , Miyahara Naoyuki
Published: September 2021

Background

Very premature infants are at high risk of developing a symptomatic postnatal cytomegalovirus (CMV) disease, such as CMV‐related sepsis‐like syndrome (CMV‐SLS). To address the limited data regarding its clinical features, a nationwide survey of CMV‐SLS was conducted.

Methods

A questionnaire regarding CMV status and the clinical outcomes of CMV‐SLS was sent to centers with reported cases of CMV‐SLS.

Results

Twelve CMV‐SLS cases, nine confirmed and three probable cases, were reported during the 3‐year survey period. The median gestational age and birthweight were 25 weeks and 547 g, respectively. At disease onset, the median age was 49 days, and the corrected age was 31 weeks. Untreated breast milk was given in four cases (33%), whereas frozen breast milk was given in nine (75%). No specific symptoms and laboratory data regarding CMV‐SLS were found.

Conclusions

Very premature infants developed CMV‐SLS after 1 month of age. There are no symptoms and signs specific for the diagnosis of CMV‐SLS, so CMV‐SLS should be considered as a differential diagnosis for premature infants who have unexplained sepsis‐like symptoms during the convalescent phase.
Audiovisual and printed technology to prevent childhood diarrhea: A clinical trial
Authors: Melo Emanuella Silva Joventino , de Oliveira Brena Shellem Bessa , Melo Francisca Mayra de Sousa , da Silva Maria Jocelane Nascimento , de Oliveira Rhaiany Kelly Lopes , Bezerra Jallyne Colares , Braga Hévila Ferreira Gomes Medeiros , de Sabino Leidiane Minervina Moraes , do Nascimento Ludmila Alves , da Penha Jardeliny Corrêa , Freitas Débora Joyce Nascimento , Mendes Elizamar Regina da Rocha , Martins Isabelle Melo , Barbosa Lorena Pinheiro
Published: September 2021

Objective

To compare the effect of using an educational booklet and a video alone or together in promoting maternal self‐efficacy to prevent childhood diarrhea.

Design and sample

Randomized multicenter clinical trial with 522 mothers of children under 5 years of age from northeastern Brazil. They were allocated into eight groups, according to the city: metropolis − video alone (N = 61), booklet alone (N = 60), booklet and video along (N = 60), without intervention (N = 60); countryside − booklet alone (N = 70), video alone (N = 70), booklet and video along (N = 71), without intervention (N = 70).

Measurements

A sociodemographic form and the Maternal Self‐Efficacy Scale for preventing early childhood diarrhea.

Results

Increases in self‐efficacy scores were observed in all experimental groups after the educational intervention. Urban mothers living had greater self‐efficacy than rural mothers. This result was verified in the video alone group (p = .036) and without intervention group (p = .003). Mothers in all intervention groups, regardless of the educational intervention used, had higher self‐efficacy scores than the comparison group mothers (p < .05).

Conclusion

The tested educational technologies promoted maternal self‐efficacy to prevent childhood diarrhea, regardless of whether they are applied alone or in combination.
Depressed mood and frailty among older people in Tokyo during the COVID‐19 pandemic
Authors: Okamura Tsuyoshi , Sugiyama Mika , Inagaki Hiroki , Miyamae Fumiko , Ura Chiaki , Sakuma Naoko , Edahiro Ayako , Taga Tsutomu , Tsuda Shuji , Awata Shuichi
Published: September 2021

Background

The study aim was to identify depressed mood and frailty and its related factors in older people during the coronavirus disease 19 pandemic.

Methods

Since 2010, we have conducted questionnaire surveys on all older residents, who are not certified in the long‐term care insurance, living in one district of Tokyo municipality. These residents are divided into two groups by birth month, that is those born between April and September and those born between October and March, and each group completes the survey every 2 years (in April and May). Study participants were older residents who were born between April and September and who completed the survey in spring 2018 and in spring 2020, the pandemic period. Depressed mood and frailty were assessed using the Kihon Checklist, which is widely used by local governments in Japan. We had no control group in this study.

Results

A total of 1736 residents responded to both surveys. From 2018 to 2020, the depressed mood rate increased from 29% to 38%, and frailty increased from 10% to 16%. The incidence of depressed mood and frailty was 25% and 11%, respectively. Incidence of depressed mood was related to subjective memory impairment and difficulty in device usage, and incidence of frailty was related to being older, subjective memory impairment, lack of emotional social support, poor subjective health, and social participation difficulties.

Conclusions

Older people with subjective memory impairment may be a high‐risk group during the coronavirus pandemic. Telephone outreach for frail older people could be an effective solution. We recommend extending the scope of the ‘reasonable accommodation’ concept beyond disability and including older people to build an age‐friendly and crisis‐resistant community.
Winners and losers in dryland reforestation: species survival, growth, and recruitment along a 33‐year planting chronosequence
Authors: Albrecht Clifton , Contreras Zarek , Wahl Kimberly , Sternberg Mitch , Christoffersen Bradley
Published: September 2021

Reforestation in the Lower Rio Grande Valley (LRGV) of Texas began in the 1960s and to date over 6,475 ha of land has been reforested. However, there has been minimal assessment to understand differential species success, compositional trends, and the aboveground carbon sequestration potential of these developing forests. We coupled quantitative planting information of >50 native woody tree and shrub species with surveys of 5,223 stems of 4,606 individuals in a chronosequence of restored forests ranging in age from 1 to 33 years to estimate species‐specific mortality rates, biomass accumulation and recruitment, as well as compositional trends in the herbaceous understory. We show that 7–15 years are required for mortality rates of the transplanted cohort to stabilize to background levels observed in other dry forests. A small number of species, mostly N‐fixing trees with a deep rooting habit, persisted on the landscape beyond 15 years. Even so, aboveground biomass (corrected for differences in initial planting density) accumulated at an average rate of 1.41 Mg ha−1 yr−1 compared to 0.35 Mg ha−1 yr−1 for a fallow old‐field. Species biomass growth rates increased with decreasing mortality, as did the abundance of recruits, suggesting a degree of reproduction by initial planted cohorts. However, a suite of highly competitive exotic grasses increases in density over a 25‐year period, which we link to suppressed seedling recruitment. This poses a serious challenge to the long‐term sustainability of planted forests in the LRGV. We highlight potential avenues of research and modification to restoration methodologies.
Policy success: What is the role of implementation support programmes?
Authors: Peckham Stephen , Hudson Bob , Hunter David , Redgate Sam
Published: September 2021

The policy implementation process is often overlooked when policy is introduced potentially leading to policy failure. This is particularly relevant in complex policy areas where there is a lack of collaborative policy‐making and where implementation is in dispersed governance. This paper discusses the findings of a study examining a novel policy implementation support programme developed by the English Department of Health for the Care Act 2014, the most significant changes to the provision of social care for 60 years. Given the complexity of the changes, the Department of Health and its key partners introduced an Implementation Support Programme to increase the likelihood of effective implementation. As part of a suite of research studies, we examined the effectiveness of the implementation support programme in helping local authorities, responsible for social care delivery, implement the key Care Act priorities. We found that the support programme was effective in supporting ‘implementation readiness’ particular in situations where the context and policy itself are complex. We found that while important for the delivery of policy, such support programmes do not necessarily in themselves guarantee successful implementation. However, future evaluations of policy should include examining how the implementation is, or is not supported, in order to fully understand reasons for policy success and failure.
Incontestable: Imagining possibilities through intimate Black geographies
Authors: Hirsch Lioba A. , Jones Naya
Published: September 2021

This editorial takes the form of a dialogue between the editors of this Themed Intervention on Black intimate geographies. It frames the voices of the Black geographers from the USA and the UK assembled here as speaking to both the incontournability of anti‐blackness as a political reality and to Black ways of knowing, imagining, and dreaming our presents and our futures against and beyond resistance to anti‐blackness. The editorial celebrates the diasporic collaboration on which this Intervention is grounded and points to the possibilities of Black life and knowledge production.
Highly Sensitive Nonlinear Identification to Track Early Fatigue Signs in Flexible Structures
Authors: Habtour Ed , Di Maio Dario , Masmeijer Thijs , Cordova Gonzalez Laura , Tinga Tiedo
Published: September 2021

This study describes a physics-based and data-driven nonlinear system identification (NSI) approach for detecting early fatigue damage due to vibratory loads. The approach also allows for tracking the evolution of damage in real-time. Nonlinear parameters such as geometric stiffness, cubic damping, and phase angle shift can be estimated as a function of fatigue cycles, which are demonstrated experimentally using flexible aluminum 7075-T6 structures exposed to vibration. NSI is utilized to create and update nonlinear frequency response functions, backbone curves and phase traces to visualize and estimate the structural health. Findings show that the dynamic phase is more sensitive to the evolution of early fatigue damage than nonlinear parameters such as the geometric stiffness and cubic damping parameters. A modified Carrella–Ewins method is introduced to calculate the backbone from nonlinear signal response, which is in good agreement with the numerical and harmonic balance results. The phase tracing method is presented, which appears to detect damage after approximately 40% of fatigue life, while the geometric stiffness and cubic damping parameters are capable of detecting fatigue damage after approximately 50% of the life-cycle.
RANGE-GAN: Design Synthesis Under Constraints Using Conditional Generative Adversarial Networks
Authors: Heyrani Nobari Amin , Chen Wei (Wayne) , Ahmed Faez
Published: September 2021

Typical engineering design tasks require the effort to modify designs iteratively until they meet certain constraints, i.e., performance or attribute requirements. Past work has proposed ways to solve the inverse design problem, where desired designs are directly generated from specified requirements, thus avoid the trial and error process. Among those approaches, the conditional deep generative model shows great potential since 1) it works for complex high-dimensional designs and 2) it can generate multiple alternative designs given any condition. In this work, we propose a conditional deep generative model, Range-GAN, to achieve automatic design synthesis subject to range constraints. The proposed model addresses the sparse conditioning issue in data-driven inverse design problems by introducing a label-aware self-augmentation approach. We also propose a new uniformity loss to ensure generated designs evenly cover the given requirement range. Through a real-world example of constrained 3D shape generation, we show that the label-aware self-augmentation leads to an average improvement of14% on the constraint satisfaction for generated 3D shapes, and the uniformity loss leads to a 125% average increase on the uniformity of generated shapes' attributes. This work laid the foundation for data-driven inverse design problems where we consider range constraints and there are sparse regions in the condition space.
Development and Validation of an End-Effector for Mitigation of Collisions
Authors: Tommasino Domenico , Bottin Matteo , Cipriani Giulio , Doria Alberto , Rosati Giulio
Published: September 2021

In robotics, the risk of collisions is present both in industrial applications and in remote handling. If a collision occurs, the impact may damage both the robot and external equipment, which may result in successive imprecise robot tasks or line stops, reducing robot efficiency. As a result, appropriate collision avoidance algorithms should be used or, if it is not possible, the robot must be able to react to impacts reducing the contact forces. For this purpose, this paper focuses on the development of a special end-effector that can withstand impacts. It is able to protect the robot from impulsive forces caused by collisions of the end-effector, but it has no effect on possible collisions between the links and obstacles. The novel end-effector is based on a bi-stable mechanism that decouples the dynamics of the end-effector from the dynamics of the robot. The intrinsically nonlinear behavior of the end-effector is investigated with the aid of numerical simulations. The effect of design parameters and operating conditions are analyzed and the interaction between the functioning of the bi-stable mechanism and the control system is studied. In particular, the effect of the mechanism in different scenarios characterized by different robot velocities is shown. Results of numerical simulations assess the validity of the proposed end-effector, which can lead to large reductions in impact forces. Numerical results are validated by means of specific laboratory tests.
Multiobjective Monotonicity Analysis: Pareto Set Dependency and Trade-Offs Causality in Configuration Design
Authors: Sigurdarson Nökkvi S. , Eifler Tobias , Ebro Martin , Papalambros Panos Y.
Published: September 2021

Multiobjective design optimization studies typically derive Pareto sets or use a scalar substitute function to capture design trade-offs, leaving it up to the designer’s intuition to use this information for design refinements and decision-making. Understanding the causality of trade-offs more deeply, beyond simple postoptimality parametric studies, would be particularly valuable in configuration design problems to guide configuration redesign. This article presents the method of multiobjective monotonicity analysis to identify root causes for the existence of trade-offs and the particular shape of Pareto sets. This analysis process involves reducing optimization models through constraint activity identification to a point where dependencies specific to the Pareto set and the constraints that cause them are revealed. The insights gained can then be used to target configuration design changes. We demonstrate the proposed approach in the preliminary design of a medical device for oral drug delivery.
srMO-BO-3GP: A sequential regularized multi-objective Bayesian optimization for constrained design applications using an uncertain Pareto classifier
Authors: Tran Anh , Eldred Michael S. , McCann Scott , Wang Yan
Published: September 2021

Bayesian optimization (BO) is an efficient and flexible global optimization framework that is applicable to a very wide range of engineering applications. To leverage the capability of the classical BO, many extensions, including multi-objective, multi-fidelity, parallelization, and latent-variable modeling, have been proposed to address the limitations of the classical BO framework. In this work, we propose a novel multi-objective BO formalism, called srMO-BO-3GP, to solve multi-objective optimization problems in a sequential setting. Three different Gaussian processes (GPs) are stacked together, where each of the GPs is assigned with a different task. The first GP is used to approximate a single-objective computed from the multi-objective definition, the second GP is used to learn the unknown constraints, and the third one is used to learn the uncertain Pareto frontier. At each iteration, a multi-objective augmented Tchebycheff function is adopted to convert multi-objective to single-objective, where the regularization with a regularized ridge term is also introduced to smooth the single-objective function. Finally, we couple the third GP along with the classical BO framework to explore the convergence and diversity of the Pareto frontier by the acquisition function for exploitation and exploration. The proposed framework is demonstrated using several numerical benchmark functions, as well as a thermomechanical finite element model for flip-chip package design optimization.
Dynamic Modeling and Experimental Validation of a Domestic Refrigeration Cycle
Authors: Caglayan Akin , Husain Salman Mustafa , Ipek Mutlu , Aynur Tolga Nurettin , Cadirci Sertac
Published: September 2021

Performance analysis and design optimization of refrigerators are primarily carried out by time-consuming experiments. The current study presents an alternative method to analyze refrigerators by modeling the refrigeration cycle using a software called dymola, based on an object-oriented programming language, called modelica. The main components of a domestic refrigerator, i.e., compressor, condenser, evaporator, cabinet, and capillary tube-suction-line heat exchanger are first individually modeled and validated. The full dynamic refrigeration cycle model is then created. Both the simulations and the experiments are conducted using R600a as the refrigerant with on-and off-modes of the reciprocating, single speed compressor. An algorithm block is also included to represent the dynamic cyclic behavior of the refrigerator. The algorithm controls the operation using two set-point temperatures of the cabinet. To validate the one-dimensional dynamic model, experiments are carried out on a single door refrigerator with an internal volume of 343l. Results show that the cabinet air, evaporation temperature, condensation temperature, power and energy values deviate from experimental values by less than 2 °C and 2%, respectively. The dynamic modeling is found to be in good agreement with the experiments in the on-mode of the compressor and a promising and rapid tool to represent the transient behavior of the refrigerator.
Influence of Coolant Density on Turbine Blade Tip Film Cooling at Transonic Cascade Flow Conditions Using the Pressure-Sensitive Paint Technique
Authors: Ullah Izhar , Alsaleem Sulaiman M. , Wright Lesley M. , Shiau Chao-Cheng , Han Je-Chin
Published: September 2021

This work is an experimental study of film cooling effectiveness on a blade tip in a stationary, linear cascade. The cascade is mounted in a blowdown facility with controlled inlet and exit Mach numbers of 0.29 and 0.75, respectively. The freestream turbulence intensity is measured to be 13.5% upstream of the blade’s leading edge. A flat tip design is studied, having a tip gap of 1.6%. The blade tip is designed to have 15 shaped film cooling holes along the near-tip pressure side (PS) surface. Fifteen vertical film cooling holes are placed on the tip near the pressure side. The cooling holes are divided into a two-zone plenum to locally maintain the desired blowing ratios based on the external pressure field. Two coolant injection scenarios are considered by injecting coolant through the tip holes only and both tip and PS surface holes together. The blowing ratio (M) and density ratio (DR) effects are studied by testing at blowing ratios of 0.5, 1.0, and 1.5 and three density ratios of 1.0, 1.5, and 2.0. Three different foreign gases are used to create density ratio effect. Over-tip flow leakage is also studied by measuring the static pressure distributions on the blade tip using the pressure-sensitive paint (PSP) measurement technique. In addition, detailed film cooling effectiveness is acquired to quantify the parametric effect of blowing ratio and density ratio on a plane tip design. Increasing the blowing ratio and density ratio resulted in increased film cooling effectiveness at all injection scenarios. Injecting coolant on the PS and the tip surface also resulted in reduced leakage over the tip. The conclusions from this study will provide the gas turbine designer with additional insight on controlling different parameters and strategically placing the holes during the design process.
Collaboration Between Academia and Industry to Advance Industrial Gas Turbines
Authors: Winkelmann Bernhard , Kurz Rainer , Voss David , Thole Karen A.
Published: September 2021

Most collaborations between academia and industry involve industry funded and defined research projects. There are, however, many more opportunities for activities that lead to a stronger partnership that benefits both. Moving from individual projects to a wider collaboration aligned along industry needs and academic strengths, to form academic centers of excellence provides a more involved collaboration. This paper provides an example of how companies can become more than a research partner but, instead, can get involved in the curriculum and educational efforts of the academic partner.
Advanced Processing of a Blade Vibratory Response Obtained With Tip Timing Method Using Hyperparameter-Free Sparse Estimation Method
Authors: Kharyton Vsevolod , Zachariah Dave
Published: September 2021

The study presents the application of a sparse estimation method which enables explicit identification of spectrum components of a vibratory signal of a blade obtained by means of blade tip timing measurement. The method exploits the sparse frequency content of the blade vibratory response and uses a data-adaptive weighting to achieve sparsity. In contrast to other approaches, this method obviates the need for any parameter tuning during the identification process and admits an online formulation that renders it capable of real-time data processing.

In the study only experimentally acquired data from either prototype testing or field measurements are used to evoke the method applicability. For some considered test cases there were no strain gauges available, therefore proposed method was the only means to study blades vibratory response.
Experimental Investigation of Gas Turbine Axial Diffuser Performance: Part II — Effect of Inlet Flow Profiles at On- and Off-Design Conditions
Authors: Brown Kenneth , Guillot Stephen , Ng Wing , Iksang Lee , Dongil Kim , Hong Giwon
Published: September 2021

An experimental investigation of the effect of inlet flow conditions and improved geometries on the performance of modern axial exhaust diffusers of gas turbines has been completed. The first article in the two-part series [1] leveraged a scaled model to examine parametric variations in both diffuser geometry and inlet flow conditions with the latter having significant consequences for diffuser performance. This second article pivots on the conclusions of the companion article and offers findings and physical insight on diffuser performance for on- and off-design inlet flow conditions. Using a high-performing diffuser design from the companion article, an experimental investigation is carried out with tailored distributions of inlet Mach distribution, inlet swirl angle, and inlet radial flow angle which are designed to replicate conditions of an industry diffuser at various loads. Six different inlet distributions were investigated including a design condition and five other conditions which feature mass flows both greater than and less than the design condition. The measurements were taken at near full-scale turbine exit Reynolds number (ReH roughly 39% of the value for an H-class diffuser) and at full-scale turbine exit Mach number. The study was accomplished in a blow-down, cold-flow wind tunnel facility, and measurements included 5-hole probe traverses at planes of interest, axial pressure distributions, strut pressure distributions, and oil-flow visualization. Over the range of inlet conditions studied, pressure recovery at the exit varied by up to 68.5% from that of on-design operation. Tracking of performance coefficients along the axial direction suggested the existence of flow phenomena which were in some cases able to be confirmed with on-strut pressure measurements and flow visualization. In addition to physical insight, the results presented here offer an experimental benchmark for the sensitivity of diffuser performance to inlet flow conditions.
Method and Verification for Material Calibration of the Chaboche Plasticity Model for Multiple Material Directions
Authors: Krouse Charles R. , Musgrove Grant O. , Kim Taewoan , Lee Seungmin , Lee Muhyoung , Jeong Seongyong
Published: September 2021

The Chaboche model is a well-validated non-linear kinematic hardening material model. This material model, like many models, depends on a set of material constants that must be calibrated for it to match the experimental data. Due to the challenge of calibrating these constants, the Chaboche model is often disregarded. The challenge with calibrating the Chaboche constants is that the most reliable method for doing the calibration is a brute force approach, which tests thousands of combinations of constants. Different sampling techniques and optimization schemes can be used to select different combinations of these constants, but ultimately, they all rely on iteratively selecting values and running simulations for each selected set. In the experience of the authors, such brute force methods require roughly 2,500 combinations to be evaluated in order to have confidence that a reasonable solution is found. This process is not efficient. It is time-intensive and labor-intensive. It requires long simulation times, and it requires significant effort to develop the accompanying scripts and algorithms that are used to iterate through combinations of constants and to calculate agreement. A better, more automated method exists for calibrating the Chaboche material constants.

In this paper, the authors describe a more efficient, automated method for calibrating Chaboche constants. The method is validated by using it to calibrate Chaboche constants for an IN792 single-crystal material and a CM247 directionally-solidified material. The calibration results using the automated approach were compared to calibration results obtained using a brute force approach. It was determined that the automated method achieves agreeable results that are equivalent to, or supersede, results obtained using the conventional brute force method.

After validating the method for cases that only consider a single material orientation, the automated method was extended to multiple off-axis calibrations. The Chaboche model that is available in commercial software, such as ANSYS, will only accept a single set of Chaboche constants for a given temperature. There is no published method for calibrating Chaboche constants that considers multiple material orientations. Therefore, the approach outlined in this paper was extended to include multiple material orientations in a single calibration scheme. The authors concluded that the automated approach can be used to successfully, accurately, and efficiently calibrate multiple material directions. The approach is especially well-suited when off-axis calibration must be considered concomitantly with longitudinal calibration. Overall, the automated Chaboche calibration method yielded results that agreed well with experimental data. Thus, the method can be used with confidence to efficiently and accurately calibrate the Chaboche non-linear kinematic hardening material model.
Impact of a Centrebody on the Unsteady Flow Dynamics of A Swirl Nozzle: Intermittency of PVC Oscillations
Authors: Gupta Saarthak , Hemchandra Santosh , Shimura Masayasu , Shanbhogue Santosh , Ghoniem Ahmed
Published: September 2021

The precessing vortex core (PVC) is a self-excited flow oscillation state occurring in swirl nozzles. This is caused by the presence of a marginally unstable hydrodynamic helical mode that induces precession of the vortex breakdown bubble (VBB) around the flow axis. The PVC can impact emissions and thermoacoustic stability characteristics of combustors in various ways, as several prior studies have shown. In this paper, we examine the impact of centrebody diameter (Dc) on the PVC in a non-reacting flow in a single nozzle swirl combustor. Time resolved high speed stereoscopic PIV (sPIV) measurements are performed for combinations of two swirl numbers, S = 0.67 and 1.17 and Dc = 9.5 mm, 4.73 mm and 0 (i.e. no centrebody). The bulk flow velocity at the nozzle exit plane is kept constant as Ub = 8 m/s for all cases (Re ∼ 20,000). The centrebody end face lies in the nozzle exit plane. A new modal decomposition technique based on wavelet filtering and proper orthogonal decomposition (POD) provides insight into flow dynamics in terms of global modes extracted from the data. The results show that without a centrebody, a coherent PVC is present in the flow as expected. The introduction of a centrebody makes the PVC oscillations intermittent. These results suggest two routes to intermittency as follows. For S = 0.67, the vortex breakdown bubble (VBB) and centrebody wake recirculation zone (CWRZ) regions are nominally distinct. Intermittent separation and merger due to turbulence result in PVC oscillations due to the de-stabilization of the hydrodynamic VBB precession mode of the flow. In the S = 1.17 case, the time averaged VBB position causes it to engulf the centrebody. In this case, the emergence of intermittent PVC oscillations is a result of the response of the flow to broadband stochastic forcing imposed on the time averaged vorticity field due to turbulence.
In-Stall Compressor Performance and the Effects of Reynolds Number
Authors: Hutchings Jack , Hall Cesare
Published: September 2021

Previous research into axial compressor stall has mainly focused on stall inception and methods to extend the stable operating range. This paper considers the performance of an axial compressor beyond stall and investigates how the characteristics of stall cells depend on Reynolds number. An experimental study has been conducted using a single-stage axial compressor capable of operating across the Reynolds number range of 10,000–100,000. Detailed unsteady measurements have been used to measure the behaviour across a range of install flow coefficients. These measurements have been used to extract the stall hysteresis and to determine the size, speed, number, and spanwise extent of the stall cells. The results show that for the stalled compressor, as Reynolds number increases, the size of the minimum stable stall cell decreases. This means that a larger change in throttle area is needed to reduce the stall cell down to a size where the compressor can recover from stall. At Re = 100,000, the stall hysteresis is six times greater than at Re = 20,000. At the design Reynolds number, the number of stall cells that form transitions from one, to two, and then to four stall cells as the flow coefficient is reduced. At lower Reynolds numbers, the two stall cell state becomes unstable; instead, a single stall cell transitions directly into five cells. In all cases, as the number of stall cells increases, so do the speed of the stall cells and the total size. Further reductions in the flow coefficient cause an increase in the total size of the stall cells and a decrease in the stall cell speed.
Toward Machine Learned Highly Reduced Kinetic Models for Methane/Air Combustion
Authors: Kelly Mark , Dooley Stephen , Bourque Gilles
Published: September 2021

Accurate low dimension chemical kinetic models for methane are an essential component in the design of efficient gas turbine combustors. Kinetic models coupled to computational fluid dynamics (CFD) and chemical reactor networks (CRN) provide quick and efficient ways to test the effect of operating conditions, fuel composition and combustor design compared to physical experiments. However, detailed chemical kinetic models are too computationally expensive for use in computational fluid dynamics (CFD). We propose a novel data orientated three-step methodology to produce compact kinetic models that replicate a target set of detailed model properties to a high fidelity. In the first step, a reduced kinetic model is obtained by removing all non-essential species from the NUIG18_17_C3 detailed model containing 118 species using path flux analysis (PFA). This reduced model is so small that it does not retain fidelity in calculations to the detailed model. Thus, it is numerically optimised to replicate the detailed model’s prediction in two rounds; First, to selected species (OH,H,CO and CH4) profiles in perfectly stirred reactor (PSR) simulations and then re-optimised to the detailed model’s prediction of the laminar flame speed. This is implemented by a purposely developed Machine Learned Optimisation of Chemical Kinetics (MLOCK) algorithm. The MLOCK algorithm systematically perturbs all three Arrhenius parameters for selected reactions and assesses the suitability of the new parameters through an objective error function which quantifies the error in the compact model’s calculation of the optimisation target. This strategy is demonstrated through the production of a 19 species and a 15 species compact model for methane/air combustion. Both compact models are validated across a range of 0D and 1D calculations across both lean and rich conditions and shows good agreement to the parent detailed mechanism. The 15 species model is shown to outperform the current state-of-art models in both accuracy and range of conditions the model is valid over.
The Tip Leakage Vortex Breakdown and its Possible Relationship With Rotating Instability in a Subsonic Compressor Rotor
Authors: Yang Fan , Wu Yanhui
Published: September 2021

The unsteady flow in the compressor at small mass flow rate has an important impact on the safety and efficiency of the compressor. Rotating instability was found in the experiment at near stall condition. Through URANS simulation, the origin of unsteady flow in an isolated subsonic rotor is studied. And the relationship between unsteadiness of tip leakage flow and rotating instability is revealed. With the deepening of the throttle, the flow field in the rotor changes from steady to unsteady. The intermittent spiral type breakdown of tip leakage vortex is considered to be the origin of the unsteady flow. Quantitative analysis of the tip leakage vortex shows the breakdown cycle caused by the interaction of the tip leaked vortex with the adjacent blade. When the tangential velocity and axial velocity of the leakage vortex reach a critical value, the tip leakage vortex will break. A radial vortex called back flow vortex will appear periodically after breakdown happens, which plays an important in rotating instability. The back flow vortex at upstream causes an overflow at adjacent blade leading edge, which results the next breakdown happens at downstream. Due to such feedback, the tip leakage vortex breakdown at two location alternately. A possible cause of RI was proposed: The spiral breakdown of the tip leakage vortex at different positions resulted in a cross-passage structure, which propagates into circumferential direction.
A Mathematical Model for Windmilling of a Turbojet Engine
Authors: Abdulhamitbilal Erkan , Şal Sinan , Jafarov Elbrous M.
Published: September 2021

The transient windmilling characteristic of a modern turbojet engine under different flight conditions and altitudes is obtained with numerous tests conducted at an Altitude Test Facility (ATF). A simple and practical mathematical model for predicting the transient and steady-state rotational speed of a simple turbojet engine in flight has been developed. The method is derived from Froude’s momentum theory or disk actuator theory and implemented to a turbojet engine. A correction factor is introduced to match with test results of KTJ-3200 being indigenously developed by Kale R&D Inc. The present model’s predictions are compared with the test data of Microturbo TRI 60 engine and KTJ-3200 engine. The estimation of the present windmilling model fits very well with test results of two different engines within an error band of ±1.2% for various atmosphere conditions depending on flight speed, altitudes and temperature. The present model is compared with loss modeling windmilling estimation methods described in literature which requires large amount of inputs as blade angle, blade pitch and component efficiencies. The comparison with the available windmilling model at literature shows that both models capture the terminal speed estimation very well. However, the model in literature is not able to capture the transient engine speed, which is important for missile applications as the missile can be fired before the engine reaches to terminal speed. The difference between the test data and the available model during transients is up to 50%. The present model matches perfectly with test data even at transients. It is more practical and much simpler than the available windmilling model in the literature to estimate the both transient and terminal windmilling speed of the turbojet engines.

The agreement between the present model, KTJ 3200 test data, windmilling method available in the literature and test data of Microturbo TRI 60 is very good for most of the ranges investigated.
Experimental Studies on Dry Gas Seals With Time-Resolved Film Thickness Measurements
Authors: Luo Jingjing , Brillert Dieter
Published: September 2021

Dry gas lubricated non-contacting mechanical seals (DGS) are acknowledged as the sophisticated shaft end sealing solution which is most commonly found in turbo-compressors. Especially under demanding conditions where high speed is combined with high pressure, DGS becomes the preferred choice over other sealing alternatives. A reliable operation of DGS, due to the non-contact running between its rotating and stationary rings, is secured by the gas film in the region of a few microns in thickness. This paper presents the measurement method of obtaining the thickness of the running gap in two radial positions, namely the inner and outer diameter of the sealing gap, by integrating the proximity sensors in the stationary ring. The experimental investigations concerning film thicknesses, pressure distributions in the gas film and axial vibrations are carried out in an industry DGS up to 50 bar and 10,000 rpm, whereby a good insight into the dynamic behaviour of the sealing gap is provided. The results demonstrate the practicability of obtaining the gas film parameters in a grooved gas seal, bridging the gap between theory and practice. In combination with the experimental work presented in this paper, the numerical model for simulating the seal performance programmed in MATLAB is compared and validated. The comparisons for various operating conditions and groove profiles are discussed with the focus lying on the hydrodynamic effect in the gas film.
Periodic Unsteady Kinematics of Hub Flows in a Shrouded Multistage Compressor
Authors: Lee Jaehyoung , Lim Sungkyung , Shin Hyoun-Woo , Lee Sungryong , Song Seung Jin
Published: September 2021

Periodic unsteady flow kinematics in a shrouded multistage low-speed axial compressor has been measured for the first time. Data have been acquired at the inlet and exit of a shrouded 3rd-stage stator with a particular focus on the hub flows. The newly found features of the hub flow in a shrouded multistage compressor are different from those at the midspan or in unshrouded (i.e., cantilevered) compressors. First, the merging of the 2nd-stage stator and 3rd-stage rotor wakes causes positive radial migration near the rotor wake pressure surface at the hub of the 3rd-stage stator inlet. Second, the low-momentum labyrinth seal leakage flow of the 3rd-stage stator merges with the 3rd-stage rotor wake to create streamwise vorticity at the 3rd-stage stator inlet hub. Third, contrary to unshrouded stators, suction side hub corner separation in the shrouded 3rd-stage stator reduces rotor wake stretching. Thus, velocity disturbances are attenuated less, and amplitudes of periodic fluctuations in flow angles are larger at the 3rd-stage stator exit hub than at midspan. The positive radial migration of the rotor wake hub flow and wake stretching reduction are expected to decrease efficiency, whereas streamwise vorticity generation is expected to increase efficiency.
Evaluation of Performance Gain by Interstage Injection in a Four-Stage Axial Compressor
Authors: Doerr Tobias , Schuster Sebastian , Brillert Dieter
Published: September 2021

Recently, the energy market has seen a shift towards renewable energies due to changing demands. Gas turbines are used as a transitional technology to cope with grid fluctuations. The changing conditions have increased the interest in applying Wet Compression in order to increase the power output during peak demands.

The novelty of this paper arises from the experimental results of Interstage Injection by analysing the stage and overall pressure ratios at different operating points in the four stage axial compressor “eco.MAC” (“evaporative cooling Multiphase Axial Compressor”). An innovative injection design is realized with twin jet nozzles in the trailing edge of SLM printed stator blades. A variation of water mass fraction, inlet temperature and rotational speed is performed and shows a gain in pressure ratio up to 1.5 %. Moreover, a polynomial approach is used for the dry data to compare wet and dry results at equal air mass flow rates. For the first time, a linear dependency of the pressure gain on the compressor’s gas temperature is experimentally found.

It can be concluded that Interstage Injection is an effective technology to be applied in later stages of axial compressors due to the strong influence of local gas temperatures on the evaporation rate and thus the pressure gain. Furthermore, reducing the local injection rate decreases aerodynamic losses between the liquid and gas phase. Hence, a multiple injection and reduced local injection rates should be targeted.
Robust Design Optimization of an Industrial 1.5 Stage Axial Compressor Under Operational and Geometrical Uncertainties
Authors: Gouttière Alexandre , Wunsch Dirk , Nigro Rémy , Barbieux Virginie , Hirsch Charles
Published: September 2021

A robust design optimization of a 1.5 stage axial compressor with secondary flows from Safran Aero Boosters is investigated. A total of 9 simultaneous operational and geometrical uncertainties are propagated for the nominal design point as well as for two off-design points, close to stall and choke conditions respectively. These uncertainties, including mass flow rates of the secondary flows, tip gap size of the rotor and highly correlated profiles on the inlet condition, are propagated by the Non-Intrusive Probabilistic Collocation method. In order to understand the effects of the uncertainties on the performances and to minimize the computational cost of the robust optimization, a preliminary uncertainty quantification (UQ) study of the original design is performed to identify and rule out less influential uncertainties. Contrary to what was expected, the imposed geometrical uncertainties on the tip gap are identified to have the relatively smallest influence on the performances by means of scaled sensitivity derivatives. The global objective of the robust design optimization is to minimize the standard deviations of the main compressor performances at all three operating points and to preserve the mean values of these performances. Because the objective functions are standard deviations, this study is only possible in a robust optimization setting, by propagating the simultaneous operational and geometrical uncertainties. A total of 9 stochastic objectives and 15 stochastic constraints are taken into account. The best optimal design preserves the mean performances of the compressor, while the standard deviations are minimized compared with the original design, ensuring a more robust operation. This effect is very pronounced in the off-design points.
Adjoint-Based Inverse Design of Axial Compressor Airfoils
Authors: Geuens Christophe , Verstraete Tom
Published: September 2021

Design methodologies for axial compressor airfoils have undergone significant changes over the past decades. While inverse design methods have played a significant historical role, today they are mostly replaced by direct methods. Inverse methods do impose either the desired pressure or velocity distribution and search for the corresponding blade profile, in contrast to direct methods which modify directly the blade shape to reduce losses. Inverse methods therefore require the designer to know pressure or velocity profiles which provide low losses, and are as such mostly effective only in the hands of an experienced designer.

Inverse methods, however, pose some advantages: through setting velocity profiles which feature good off-design performance, the computational cost for the design of profiles can be significantly reduced compared to direct methods, which require to simulate multiple operating points. Additionally, inverse methods offer a way to adapt blades for experimental testing if the wind tunnel imposes restrictions on e.g. Mach number, allowing for similar boundary layer conditions. Finally, inverse methods can be used to deduce the blade geometry from measured or published velocity distributions.

Within this article, we aim to verify the use of inverse methods by applying more recent optimisation techniques to the inverse problem. Specifically, we test the performance of an inverse method that uses a gradient based technique to solve the inverse problem. The merits of the inverse method are investigated for different use cases. It is found that conventional, direct design methods are preferred for design improvement, although more expensive. The inverse method is, however, well-suited for adapting existing profiles to altered operating conditions, and for reproducing the blade shape based on published data.
Numerical Calibration and Investigation of the Influence Of Reynolds Number on Measurements With Five-Hole Probes In Compressible Flows
Authors: Schäffer Christian , Speck Konstantin , Gümmer Volker
Published: September 2021

This paper presents an investigation into the numerical and experimental calibration of a five-hole probe and effects of Reynolds number variations on the characteristics of the probe. The test object is a cone-type drilled elbow probe with a head diameter of 1.59 mm and a cone angle of 60°. The experimental calibration maps of four different probes of the same type and nominal geometry are compared. A significant variation of the curves can be observed especially at high yaw angles. This led to a visual inspection of the probes with a 3D measurement system. The actual geometry of the three used probes and the surface and radii in particular varied significantly from that of the unused spare probe.

Furthermore, a numerical calibration map of the ideal probe was generated for a Mach number of Ma = 0.3. A comparison between the experimental and numerical calibration coefficients revealed that total pressure, yaw and pitch angle were reproduced reasonably well. The dynamic pressure coefficient, however, has a considerable offset.

Finally, a parameter study of the effect of varying the Reynolds number over different yaw angles was conducted. The calibration Reynolds number is of the order of Re = 1 · 104 and was varied between 0.5 · 104 < Re < 6 · 104. While the results suggest that only minor measurement errors occur for yaw angle, total pressure and static pressure, a relatively large error was observed for pitch angle measurements.