bluuebunny/crossref_metadata_2025_split huggingface dataset:
Enhancing Turbine Deposition Prediction Capability With Conjugate Mesh Morphing
Authors: Bowen Christopher P. , Bons Jeffrey P. 
Published: September 2021

Abstract
A framework for performing mesh morphing in a conjugate simulation in the commercial Computational Fluid Dynamics (CFD) software ANSYS Fluent is presented and validated. A procedure for morphing both the fluid and solid domains to simulate the protrusion of deposit into the fluid while concurrently altering and adding to the solid regions is detailed. The ability to delineate between the original metal sections of the solid and the morphed regions which represent deposit characteristics is demonstrated. The validity and predictive capability of the process is tested through simulation of a canonical impingement jet. A single over-sized impingement jet (6.35 mm) at 894 K and an average flow velocity of 56.5 m/s is used to heat a nickel-alloy target plate. One gram of 0-5 μm Arizona Road Dust (ARD) is delivered to the target and a Particle Shadow Velocimetry (PSV) technique is used to capture the transient growth of the deposit structure on the target. Thermal infrared images are taken on the backside of the target and synchronized with the PSV images. The experiment is modeled computationally using the Fluent Discrete Phase Model (DPM) and the Ohio State University (OSU) Deposition Model for sticking prediction. The target is morphed according to the particulate volume prediction. The deposit regions are assigned an effective conductivity (keff) representative of porous deposit, and the fluid and thermal computations are reconverged. 10 mesh morphing iterations are performed accounting for the first half of the experiment. The morphed deposit volume and height are compared to the experiment and show reasonable agreement. The backside target temperatures are also compared, and the simulations show the ability to predict the reduction in temperature that occurs as the growing deposit insulates the metal surface. It is demonstrated that the assignment of unique thermal conductivities to the deposit and metal cells within the solid is critical. With a more robust and accurate implementation of the deposit keff, this conjugate mesh morphing framework shows potential as a tool for predicting the thermal impact of deposition.
Acoustic Pyrometry Robustness to Time of Flight Estimation Errors
Authors: Caposciutti Gianluca , Ferrari Lorenzo 
Published: September 2021

Abstract
Acoustic pyrometry is a widely used technique for contactless temperature measurement. It may be used in several applications, especially when high temperatures and harsh environments are involved. For instance, it has been applied to measure the temperature distribution at gas turbine outlet. This technique is based on the measurement of the time of flight of an acoustic wave through a medium. If multiple emitter-receiver couples are used, by using a computational procedure a reconstruction of a temperature map is possible. On the other hand, a full assessment of the robustness of this technique to potential errors in time of flight estimation is still missing. In this study, the impact of an inaccuracy in time of flight estimation on the reconstruction of a correct temperature map is investigated by means of a statistical approach. As a general result, it was found that when the time of flight was measured without inaccuracies, temperature estimation errors may be lowered by simply increasing the number of cells in which the estimation is performed. However, when the estimation of the time of flight is affected by errors, an optimal configuration exists that minimize the temperature estimation errors.
Conjugate Heat Transfer Simulation of an Industrial Gas Turbine Blade With Harmonic Balance Method
Authors: Zwiener Kim , Carpenter Cassie , Hodges Justin 
Published: September 2021

Abstract
The performance of turbomachines is often dependent on the unsteady flow fields they naturally produce, owing primarily to row-to-row interactions from both moving and stationary components, as well as the unsteady nature of the turbulent flow. When it comes to computational fluid dynamics, a disparity exists between steady state and transient simulation as far as accuracy is concerned, albeit the computational cost of transient simulation on fully complex industrial hardware can be overwhelming. This study bridges the gap by presenting a harmonic balance conjugate heat transfer simulation approach in Simcenter STAR-CCM+, to model the unsteady flow phenomena while also providing accurate temperature predictions throughout the gas turbine blade solid bodies. The harmonic balance method used is a mixed time domain and frequency domain technique, which is suitable for periodic unsteady flows and is much less expensive than transient simulation. With this method, the impact of capturing these unsteady flow structures, such as the wake interactions and secondary cooling flows, is quantified on the resulting metal temperature distribution. Such is investigated and characterized throughout an industrial gas turbine blade with fully complex internal cooling passages, as well as film cooling for the external blade surface. Comparisons to steady simulation and transient simulation are also made to quantify the relative fidelity of each approach. Regarding the final resulting blade heat transfer, analysis is also provided to differentiate between important sources: the unsteadiness in the primary gas path flow and the classical unsteady nature of turbulence. Often these effects are lumped together when analyzing the resulting heat transfer, which is incorrect and can be better understood with more detailed analysis.
Optimum Multi-Nozzle Configuration for Minimizing the Rayleigh Integral During High-Frequency Transverse Instabilities
Authors: Acharya Vishal , Lieuwen Timothy 
Published: September 2021

Abstract
This paper develops a formalism for optimizing nozzle location/configuration with respect to combustion stability of high-frequency transverse modes in a can combustor. The stability of these acoustically non-compact flames was assessed using the Rayleigh Integral (RI). Several key control parameters influence RI – flame angle, swirling strength, nozzle location, as well as nozzle location with respect to the acoustic mode shape. In this study, we consider a N-around-1 configuration such as typically used in a multi-nozzle can system and study the overall stability of this system for different natural transverse modes. Typically, such nozzles are distributed in a uniformly circular manner for which we study the overall RI and for cases where RI &gt; 0, we optimize the nozzle distribution that can reduce and minimize RI. For a fixed geometry such a circular configuration, the analysis shows how the flame’s parameters must vary across the different nozzles, to result in a relatively stable system. Additionally, for a fixed set of flame parameters, the analysis also indicates the non-circular distribution of the N nozzles that minimizes RI. Overall, the analysis aims to provide insights on designing nozzle locations around the center nozzle for minimal amplification of a given transverse mode.
Influence of Working Fluid Composition on the Optimum Characteristics of Blended Supercritical Carbon Dioxide Cycles
Authors: Crespi F. , Martínez G. S. , Rodriguez de Arriba P. , Sánchez D. , Jiménez-Espadafor F. 
Published: September 2021

Abstract
The supercritical Carbon Dioxide power cycle technology has attracted growing interest from the scientific community, becoming one of the most important options currently considered for CSP applications. This is thanks to its high thermal efficiency, even at moderate turbine inlet temperatures, and small footprint. Nevertheless, sCO2 power cycles require a fairly low compressor inlet temperature to exploit their full thermodynamic potential. When this cannot be achieved, as it is usually the case for Concentrated Solar Power plants where ambient temperatures are high, the interest of the technology is compromised. To compensate for this effect, the SCARABEUS project is working on the development of certain chemical dopants that could be added to the raw CO2, obtaining new working fluids with the same or even better performance than pure CO2 even at higher minimum cycle temperatures.
This paper studies the impact of using CO2 mixtures blended with Hexaflurorobenzene (C6F6) and Titanium Tetrachloride (TiCl4). It is found that these mixtures enable thermal efficiencies that are higher than if pure CO2 were used. The efficiency gain can be as high as 3 percentage points, depending on the dopant used and the operating conditions considered.
In addition to this absolute performance gain, the paper reveals that there are additional degrees of freedom that enable more effective cycle optimisation. These are the dopant molar content, not only its composition, and the cycle layout used. When this is studied, it is found that the optimum molar content ranges from 10 to 20% and that the layouts of interest when using mixtures are simpler than if plain CO2 were used. These results open the way for a significant performance enhancement of Concentrated Solar Power plants.
Effect of the Axial Casing Groove Geometry on the Production and Distribution of Reynolds Stresses in the Tip Region of an Axial Compressor Rotor
Authors: Koley Subhra Shankha , Saraswat Ayush , Chen Huang , Katz Joseph 
Published: September 2021

Abstract
Stereo PIV measurements performed in a refractive index matched facility examine the effect of axial casing grooves (ACGs) geometry on the turbulence in the tip region of an axial compressor rotor. The ACGs delay the onset of stall by entraining the Tip Leakage Vortex (TLV), and by causing periodic changes to incidence angle as their outflow impinges on the rotor blade. To decouple these effects, measurements have been performed using a series of grooves having similar inlets, but different outflow directions. The performance and flow structure associated with three grooves, namely a semi-circular ACG, as well as U and S shaped grooves have been presented in several recent papers. This paper focuses on the impact of passage flow-groove interactions on the distribution, evolution, and production rates of turbulent kinetic energy (TKE) and all the Reynolds stress components. The analysis is performed at flow rates corresponding to pre-stall conditions and best efficiency point (BEP) of the untreated end wall, and for different blade orientations relative to the groove. Interactions of the tip flow with the ACGs modifies the magnitude and spatial distribution of the highly anisotropic and inhomogeneous turbulence in the passage. Owing to TLV entrainment into the grooves, at low flowrate, the ACGs actually reduce the turbulence in the passage compared to that in the smooth endwall. However, the geometry -dependent tip flow-groove interactions introduce new elevated turbulence centers. In all cases, the TKE is high in the: (i) TLV center, (ii) corner vortex generated as the backward tip leakage flow separates at the downstream end of the groove, and (iii) shear layer connecting the TLV to the rotor blade suction side tip. The location of peaks and the dominant components vary among grooves. For example, the axial component is dominant for the semicircular ACG, and its peak is located in the shear layer. The radial component is the dominant contributor for the U and S grooves, and it peaks inside the grooves at different locations. The circumferential component peaks in the TLV for the U and semicircular ACG, but inside the S groove. The shear layers generated as the flows jet out from the upstream ends of the grooves also bring varying elevated turbulence. At BEP, interactions of the TLV with secondary flows generated by the U and semi-circular grooves, for which the outflow is oriented in the negative circumferential direction, generate high turbulence levels, which extend deep into the passage. In contrast, the interactions associated with the S grooves are limited, resulting in a substantially lower turbulence level. Many of the various trends can be readily explained by examining the corresponding spatial distributions of the turbulence production rates. Such understanding elucidates the different mechanisms involved and provides a unique database for modelling turbulence in the passage.
Combustion and Oxidation of Lube Oils at Gas Turbine Conditions: Experimental Methods
Authors: Petersen Eric L. , Mathieu Olivier , Thomas James C. , Cooper Sean P. , Teitge David S. , Juárez Raquel , Gutierrez Nobel , Mashuga Chad V. 
Published: September 2021

Abstract
Because of the high temperatures involved, undesirable ignition events can happen during gas turbine operation, often necessitating expensive down time and repairs. The ignition events are frequently linked to the lubricant, a flammable mixture of large hydrocarbons with a very low vapor pressure. To understand better the role of the lubricant in such ignition events, increased understanding of the fundamental thermal and oxidation characteristics of such oils is needed. To this end, a suite of different tests has been set up and demonstrated at the TEES Turbomachinery Laboratory at Texas A&M University (TAMU) to study various aspects of lubrication oil breakdown and oxidation at elevated temperatures, mostly those related to their coking and ignition behaviors. Five types of tests have been implemented: ignition delay time measurements using a shock tube; hot surface ignition (HSI); autoignition temperature (AIT) determination; thermal cook-off under controlled heating; and a high-temperature coking experiment. Such tests can be used both for fundamental understanding of how lube oils burn and for comparing the reactivity of various types and grades of oil. Each technique at TAMU is briefly described in this paper as they pertain to gas turbine lube oils, and sample results are presented for a common lubrication oil, Mobil DTE 732. For this oil, the HSI tests produced a lowest temperature without ignition of 510°C, and in shock-tube measurements, lower-temperature ignition kinetics are observed below about 1300 K, even at 1 atm. Typical AIT values for oils have been found to be around 370°C but do vary amongst brands, types, and level of degradation. The measured temperatures for the exothermic and boiling events were measured as 166±2 °C and 277±4 °C using the cook-off rig.
Investigating Heat Transfer in a Straight Cooling Passage Using Transient Infrared Temperature Data and URANS Conjugate Heat Transfer Analysis
Authors: Christensen Louis , Celestina Richard , Sperling Spencer , Mathison Randall , Aksoy Hakan , Liu Jong , Nickol Jeremy 
Published: September 2021

Abstract
Experimental work measuring heat transfer due to internal convection on a smooth straight passage is recreated using unsteady Reynolds averaged Navier-Stokes conjugate heat transfer simulations. The experimental work utilizes 1-dimensional and 3-dimensional conduction models to determine internal heat transfer rates from external surface temperature measurements collected with an infrared camera. The numerical simulations recreated these experiments to verify the conduction model and investigate the differences between the k-ω shear stress transport turbulence model, Reynolds stress turbulence model, and the k-ε turbulence model. It is found that the conduction model can accurately predict the heat transfer in the passage within an average error of 6% but with reduced spatial accuracy. The lower spatial accuracy can be accounted for by utilizing both the conduction model to predict the magnitude of the heat transfer and the numerical simulations to capture the spatial distribution. No one turbulence model was found to provide consistently superior heat transfer predictions, but rather each model excelled in some scenarios and underperformed in others. Overall, the k-ε model was found to best match the experimental heat transfer calculations with an average error of 5.9% of the total heat transfer, and it takes a more conservative approach as it can over predict the external surface temperatures by approximately 0.4 K. The end goal of this study is to develop a way to derive heat-flux data from infrared measurements on a range of geometries. A simple and well-understood geometry is investigated here to provide a firm foundation for future work.
Validating clinical practice guidelines for the management of febrile infants presenting to the emergency department in the UK and Ireland
Authors: Waterfield Thomas , Lyttle Mark D , Munday Charlotte , Foster Steven , McNulty Marc , Platt Rebecca , Barrett Michael , Rogers Emma , Durnin Sheena , Jameel Nida , Maney Julie-Ann , McGinn Claire , McFetridge Lisa , Mitchell Hannah , Puthucode Deepika , Roland Damian 
Published: September 2021

ObjectiveTo report the performance of clinical practice guidelines (CPG) in the diagnosis of serious/invasive bacterial infections (SBI/IBI) in infants presenting with a fever to emergency care in the UK and Ireland. Two CPGs were from the National Institutes for Health and Care Excellence (NICE guidelines NG51 and NG143) and one was from the British Society for Antimicrobial Chemotherapy (BSAC).DesignRetrospective multicentre cohort study.PatientsFebrile infants aged 90 days or less attending between the 31 August 2018 to 1 September 2019.Main outcome measuresThe sensitivity, specificity and predictive values of CPGs in identifying SBI and IBI.SettingSix paediatric Emergency Departments in the UK/Ireland.Results555 participants were included in the analysis. The median age was 53 days (IQR 32 to 70), 447 (81%) underwent blood testing and 421 (76%) received parenteral antibiotics. There were five participants with bacterial meningitis (1%), seven with bacteraemia (1%) and 66 (12%) with urinary tract infections. The NICE NG51 CPG was the most sensitive: 1.00 (95% CI 0.95 to 1.00). This was significantly more sensitive than NICE NG143: 0.91 (95% CI 0.82 to 0.96, p=0.0233) and BSAC: 0.82 (95% 0.72 to 0.90, p=0.0005). NICE NG51 was the least specific 0.0 (95% CI 0.0 to 0.01), and this was significantly lower than the NICE NG143: 0.09 (95% CI 0.07 to 0.12, p<0.0001) and BSAC: 0.14 (95% CI 0.1 to 0.17, p<0.0001).ConclusionNone of the studied CPGs demonstrated ideal performance characteristics. CPGs should be improved to guide initial clinical decision making.Trial registration numberNCT04196192.
Lipid accumulation product (LAP) as a potential index to predict risk of insulin resistance in young, non-obese Asian Indian males from Southern India: observations from hyperinsulinemic-euglycemic clamp studies
Authors: Anoop S Shajith , Dasgupta Riddhi , Rebekah Grace , Jose Arun , Inbakumari Mercy Prem , Finney Geethanjali , Thomas Nihal 
Published: September 2021

IntroductionWe aimed to compare the predictive accuracy of surrogate indices namely the lipid accumulation product (LAP) index, homeostatic model of assessment of insulin resistance (HOMA-IR), fasting glucose-insulin ratio (FG-IR) and the quantitative-insulin sensitivity check index (QUICKI), against theMvalue of hyperinsulinemic-euglycemic clamp (HEC), and to determine a cut-off value for the LAP index to predict risk of insulin resistance in non-obese (body mass index <21 kg/m2), normoglycemic, Asian Indian males from Southern India.Research design and methodsData of HEC studies performed in 108 non-obese, normoglycemic, Asian Indian males was obtained retrospectively and theMvalue (a measure of whole-body insulin sensitivity) was calculated. TheMvalue is the rate of whole-body glucose metabolism at the hyperinsulinemic plateau (a measure of insulin sensitivity) and is calculated between 60 and 120 min after the start of the insulin infusion in the HEC procedure. The LAP index, the HOMA-IR, FG-IR and QUICKI were calculated. Spearman’s correlation and logistic regression analysis were performed. Cut-off value for the LAP index was obtained using receiver operating characteristics with area under curve (AUC) analysis at 95% CI. P value <0.05 was considered to be statistically significant.ResultsSignificant negative correlation was observed for theMvalue with LAP index (r=−0.39, p<0.001) while significant positive correlation was noted with FG-IR (r=0.25; p<0.01) and QUICKI (r=0.22; p<0.01). The LAP index cut-off value ≥33.4 showed 75% sensitivity and 75% specificity with AUC (0.72) to predict risk of insulin resistance in this cohort.ConclusionThe LAP index showed higher predictive accuracy for the risk of insulin resistance as compared with HOMA-IR, QUICKI and FG-IR in non-obese, normoglycemic Asian Indian males from Southern India.
Beta-cell failure rather than insulin resistance is the major cause of abnormal glucose tolerance in Africans: insight from the Africans in America study
Authors: Ishimwe M C Sage , Wentzel Annemarie , Shoup Elyssa M , Osei-Tutu Nana H , Hormenu Thomas , Patterson Arielle C , Bagheri Hadi , DuBose Christopher W , Mabundo Lilian S , Ha Joon , Sherman Arthur , Sumner Anne E 
Published: September 2021

IntroductionUncertainties exist on whether the main determinant of abnormal glucose tolerance (Abnl-GT) in Africans is β-cell failure or insulin resistance (IR). Therefore, we determined the prevalence, phenotype and characteristics of Abnl-GT due to β-cell failure versus IR in 486 African-born blacks (male: 64%, age: 38±10 years (mean±SD)) living in America.Research design and methodsOral glucose tolerance test were performed. Abnl-GT is a term which includes both diabetes and prediabetes and was defined as fasting plasma glucose (FPG) ≥5.6 mmol/L and/or 2-hour glucose ≥7.8 mmol/L. IR was defined by the lowest quartile of the Matsuda Index (≤2.98) and retested using the upper quartile of homeostatic model assessment of insulin resistance (HOMA-IR) (≥2.07). Abnl-GT-IR required both Abnl-GT and IR. Abnl-GT-β-cell failure was defined as Abnl-GT without IR. Beta-cell compensation was assessed by the Disposition Index (DI). Fasting lipids were measured. Visceral adipose tissue (VAT) volume was obtained with abdominal CT scan.ResultsThe prevalence of Abnl-GT was 37% (182/486). For participants with Abnl-GT, IR occurred in 38% (69/182) and β-cell failure in 62% (113/182). Compared with Africans with Abnl-GT-IR, Africans with Abnl-GT-β-cell failure had lower body mass index (BMI) (30.8±4.3 vs 27.4±4.0 kg/m2), a lower prevalence of obesity (52% vs 19%), less VAT (163±72 vs 107±63 cm2), lower triglyceride (1.21±0.60 vs 0.85±0.42 mmol/L) and lower FPG (5.9±1.4 vs 5.3±0.6 mmol/L) and 2-hour glucose concentrations (10.0±3.1 vs 9.0±1.9 mmol/L) (all p<0.001) and higher DI, high-density lipoprotein (HDL), low-density lipoprotein particle size and HDL particle size (all p<0.01). Analyses with Matsuda Index and HOMA-IR yielded similar results. Potential confounders such as income, education, alcohol and fiber intake did not differ by group.ConclusionsBeta-cell failure occurred in two-thirds of participants with Abnl-GT and may be a more frequent determinant of Abnl-GT in Africans than IR. As BMI category, degree of glycemia and lipid profile appeared more favorable when Abnl-GT was due to β-cell failure rather than IR, the clinical course and optimal interventions may differ.Trial registration numberNCT00001853.