bluuebunny/crossref_metadata_2025 huggingface dataset:
An Understanding of Stress and Pretension Behavior of Aero Engine Rotor Bolted Joint
Authors: Mogullapally Venkateshwarlu , Jyoth Shine , Kumar Sanju , Rao Rashmi , B. A. Rajeevalochanam
Published: September 2021

Bolted joints in gas turbines are used commonly to connect the parts of dissimilar materials to facilitate assembly, dis-assembly, and also to achieve modularity for advanced aero engines. In gas turbine engine, there are many rotating and stationary parts that are subjected to an extreme working environment. Bolted joints should have sufficient strength to support the mating parts such as safety critical fan/turbine discs, drums, and shaft assembly. Bolted joints are designed to avoid flange separation and slippage. This paper attempts to understand the challenges faced in designing a typical fan disc rotor plain flange type bolted assembly and structural integrity aspects under various thermo-mechanical operating loads. The understanding of stiffness of the bolt and joint members is necessary to evaluate the performance of the joint assembly. Based on literature, different approaches are used for estimating member stiffness to compare with finite element results. The effect of external loads such as thermo-mechanical loads on pretension behavior of bolted joint is studied with the help of standard commercial software platform ANSYS. Bolted joint preload loss has been assessed via the standard analytical method and validated with 3D finite element approach. This paper enables designer a quick understanding of rotor bolted joint behavior for finalization of gas turbine rotor layout, before going into complex and time consuming 3D finite element modelling and nonlinear stress analysis.
Turbocharger Radial Turbine Response to Pulse Amplitude
Authors: Mosca Roberto , Lim Shyang Maw , Mihaescu Mihai
Published: September 2021

Under on-engine operating conditions, a turbocharger turbine is subject to a pulsating flow and, consequently, experiences deviations from the performance measured under continuous flow. Furthermore, due to the high exhaust gas temperatures, heat transfer further deteriorates the turbine performance. The complex interaction of the aerothermodynamic mechanisms occurring inside the hot-side, and consequently the turbine behavior, is largely affected by the shape of the pulse, which can be parameterized through three parameters: pulse amplitude, frequency, and temporal gradient. This paper investigates the hot-side system response to the pulse amplitude via a Detached Eddy Simulation (DES) approach of a radial turbocharger turbine system including exhaust manifold. Firstly, the computational model is validated against experimental data obtained under gas stand continuous flow conditions. Then, two different mass flow pulses, characterized by a pulse amplitude difference of ≈ 5%, are compared. An exergy-based post-processing approach shows the beneficial effects of increasing pulse amplitude. An improvement of the turbine power by 1.3%, despite the increment of the heat transfer and total internal irreversibilities by 5.8% and 3.4%, respectively, is reported. As a result of the higher maximum speed, internal losses by viscous friction are responsible for the growth of the total internal irreversibilities as pulse amplitude increases.
High Efficiency Active Damping on a Fan Rotor Blade in Case Of Resonant Vibrations by Means of Piezoelectric Actuators
Authors: Rossi Andrea , Botta Fabio , Giovannelli Ambra , Belfiore Nicola Pio
Published: September 2021

Severe resonant vibration is one of the main roots of turbomachinery blades failure. Forced response issues arise when the blades work in non-uniform flow fields. As a result unsteady aerodynamic pressures occur on the surfaces of the blade. If the frequency of the aerodynamic excitation matches an eigenfrequency of the blade, the vibration level may considerably increase and a drop in the life-cycle of the component could be entailed. The resonant vibration conditions could be identified at the design level by means of the Campbell diagram. Unfortunately, it is not possible to avoid all the resonant conditions, hence the mitigation of vibration has always been of the utmost importance for turbomachinery designers. Moreover an active damping system based on piezoelectric (PZT) actuators which is capable of tuning its behavior according to the resonant excitation, may be considered very attractive. In this work the forced response of a fan rotor blade, due to a stationary inlet flow distortion resulting from the presence of upstream struts, is taken into account. Some resonant conditions have been analyzed by means of Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) simulations. Thereafter a novel approach based on a proper distribution of the potential supplied to the electrodes of each PZT pair, in order to maximize the damping efficiency, is applied to the case of a plausible fan blade. The outcomes show that the proposed system is able to efficiently damp each resonant excitation and enhance the structural integrity of the blade.
Vortex Breakdown and Recirculation Bubble Formation in Counter Swirl Flows
Authors: Bompelly Ravi K. , Ponduri Sai Phani Keerthan , Maddila Sriharsha
Published: September 2021

For achieving better fuel-air mixing within a short distance or for improved atomization of liquid fuels counter rotating swirler designs are preferred in gas turbine engine combustors. In this study, vortex breakdown phenomenon is investigated in co and counter rotating swirlers using CFD. The swirler assembly consists of two axial swirlers, an inner and an outer swirler both with straight vanes. Swirler vane angles are varied from 30° to 60° in steps of 10° while keeping inner and outer swirler vane angles equal. CFD simulations are performed with air at ambient conditions as the working fluid at a constant mass flow rate. It is observed that strong shear layers are created in counter swirl flows due to the opposite flow rotation. The shear layers result in rapid decay of inner swirler tangential velocities for the counter swirlers compared to the co-swirlers. The tangential velocity decay is characterized with a parameter named tangential velocity integral (TVI). TVI was observed to decay faster for the counter swirl flows compared to the co-swirl flows. The faster decay in TVI for the counter swirlers is found to result in a stronger adverse pressure gradient in the axial direction at the center. The strong adverse pressure gradient resulted in higher pressure excess ratios (PER) for the counter swirlers. The higher PERs are observed to induce vortex breakdown in counter swirlers even at low vane angles whereas in co-swirlers vortex breakdown is not observed except for the highest vane angle. It is demonstrated that vortex breakdown could be suppressed in counter swirlers using a converging mixer passage. The converging mixer passage creates a favorable pressure gradient that counters the adverse pressure gradient due to swirl decay, resulting in breakdown suppression.
Effects on Film Cooling Performance in the Showerhead From Geometric Parameterization of Shaped Hole Designs
Authors: Moore Jacob D. , Easterby Christopher C. , Bogard David G.
Published: September 2021

The high heat loads at the leading-edge regions of turbine vanes and blades necessitate the most robust thermal protection, typically accomplished via a dense array of film cooling holes, nicknamed the “showerhead.” Although research has shown that film cooling using shaped holes provides more reliable thermal protection than that using cylindrical holes, the effects on cooling performance from varying the geometric details of the shaped hole design are not well characterized. In this study, adiabatic effectiveness and off-the-wall thermal field measurements were conducted for two shaped hole geometries designed as successors to a baseline hole geometry presented in a previous study. One geometry with a 40% increase in area ratio exhibited only a marginal improvement in adiabatic effectiveness (∼10%). A second design with a 12° forward and lateral expansion angle with a breakout area 40% larger performed marginally worse than its matched area ratio counterpart (∼15% lower), suggesting a negative sensitivity to breakout area. Such changes in performance for different shaped hole designs were small compared to the boost in performance gained by switching from a cylindrical hole to a shaped hole, which suggests cooling performance is insensitive to specific shaped hole details provided the exterior coolant flow is well-attached.
Aerodynamic Prediction on the Off-Design Performance of a S-CO2 Turbine Based on Deep Learning
Authors: Wang Yuqi , Liu Tianyuan , Zhang Di
Published: September 2021

The research on the supercritical carbon dioxide (S-CO2) Brayton cycle has gradually become a hot spot in recent years. The off-design performance of turbine is an important reference for analyzing the variable operating conditions of the cycle. With the development of deep learning technology, the research of surrogate models based on neural network has received extensive attention. In order to improve the inefficiency in traditional off-design analyses, this research establishes a data-driven deep learning off-design aerodynamic prediction model for a S-CO2 centrifugal turbine, which is based on a deep convolutional neural network. The network can rapidly and adaptively provide dynamic aerodynamic performance prediction results for varying blade profiles and operating conditions. Meanwhile, it can illustrate the mechanism based on the field reconstruction results for the generated aerodynamic performance. The training results show that the off-design aerodynamic prediction convolutional neural network (OAP-CNN) has reduced the mean and maximum error of efficiency prediction compared with the traditional Gaussian Process Regression (GPR) and Artificial Neural Network (ANN). Aiming at the off-design conditions, the pressure and temperature distributions with acceptable error can be obtained without a CFD calculation. Besides, the influence of off-design parameters on the efficiency and power can be conveniently acquired, thus providing the reference for an optimized operation strategy. Analyzing the sensitivity of AOP-CNN to training data set size, the prediction accuracy is acceptable when the percentage of training samples exceeds 50%. The minimum error appears when the training data set size is 0.8. The mean and maximum errors are respectively 1.46% and 6.42%. In summary, this research provides a precise and fast aerodynamic performance prediction model in the analyses of off-design conditions for S-CO2 turbomachinery and Brayton cycle.
A Study on Fundamental Combustion Properties of Oxymethylene Ether-2
Authors: Ngugi John N. , Richter Sandra , Braun-Unkhoff Marina , Naumann Clemens , Köhler Markus , Riedel Uwe
Published: September 2021

Oxymethylene ethers (OMEn, n = 1–5) are a promising class of synthetic fuels that have the potential to be used as additives or substitutes to diesel in compression ignition engines. A comprehensive understanding of their combustion properties is required for their safe and efficient utilization. In this study, the results of a combined experimental and modeling work on oxidation of OME2 are reported: (i) Ignition delay time measurements of stoichiometric OME2 / synthetic air mixtures diluted 1:5 with nitrogen using the shock tube method at pressures of 1, 4, and 16 bar, and (ii) laminar flame speeds of OME2 / air mixtures using the cone angle method at ambient and elevated pressures of 3 and 6 bar. The experimental data sets obtained have been used for validation of a detailed reaction mechanisms of OME2. The results of ignition delay times showed that OME2 exhibits a two-stage ignition in the lower temperature region. There is a good match of the measured data compared to the predicted ones using three reaction mechanisms from the literature. The mechanism from Cai et al. (2020) best predicted the temperature and pressure dependence of ignition delay times. For laminar flame speeds, the experimental data were well matched by the mechanism from Ren et al. (2019) at p = 1, 3, and 6 bar and for all equivalence ratios considered. From sensitivity analyses calculations, it was observed that chain reactions involving small radicals, i.e., H, O, OH, HO2, and CH3 control the oxidation of OME2. The comparison of the results of this work and our previous work (Ngugi et al. (2021)) on OME1 show that these two fuels have similar oxidation pathways.

The results obtained in this work will contribute to a better understanding of the combustion of oxymethylene ethers, and thus, to the design and optimization of burners and engines as well.
A Comprehensive Model for Cetane Number Prediction Using Machine Learning
Authors: Abdul Jameel Abdul Gani
Published: September 2021

Machine learning based predictive models are being extensively applied for predicting combustion properties like derived cetane number (DCN), which is the measure of a fuels ignition quality. In the present work, a comprehensive model was developed using artificial neural networks (ANN) that can predict the DCN of fuels containing a large number of chemical classes like paraffins, iso-paraffins, olefins, naphthenes, aromatics, alcohols, ethers, aldehydes, ketones and esters. Experimental DCN’s of 275 fuels was used as a dataset and the composition of the fuels expressed in the form of twelve functional groups and two structural parameters namely, branching index (BI) and molecular weight were used as the input features for the model. A feed forward neural network with two hidden layers with 40 neurons in each layer was developed using Levenberg-Marquardt algorithm. The developed model was validated with 15% of the data points that were randomly generated and kept aside for validation. A regression coefficient (R2) of 0.99 was observed between the predicted and the experimental values along with an average absolute error of 1.1. The results showed that the developed model was successful in predicting the DCN of fuels and can be applied to pure compounds, blends and real fuels containing diverse chemical functionalities.
Performance of a Long Smooth Multiphase Pump Seal in Different Flow Regimes
Authors: Zhang Min , Childs Dara W.
Published: September 2021

Demanding for multiphase pumps introduces new challenges to the pump design. To prevent machine failures, the performance of the pump (non-contact) annular seal under multiphase conditions needs to be studied. The air addition into the oil flow not only changes the properties of the fluid but also can change the flow status in the seal clearance. The flow status can significantly affect the performance of the pump seal and thereby impact the pump vibration performance. Within the seal annulus, the axial direction flow is dominated by the pressure drop through the seal and can be considered as a Poiseuille flow. The circumferential direction flow is driven by the rotor rotation and can be considered as a Couette flow. The regime of the flow in the seal is controlled by the axial Reynolds number and the circumferential Reynolds number. Published test results on the boundaries between the laminar, transitional, and turbulent regimes in an annular seal are scant. This paper will first draw these boundaries based on the test data for long smooth pump seals. Then, this paper will show the performance of the long smooth pump seal in different flow regimes. Predictions will also be presented to compare with test results under different flow conditions.
Method of Coupled Vibration Control for Dual Rotor System With Inter-Shaft Bearing
Authors: Ma Yanhong , Shi Chenglong , Sun Bo , Hong Jie
Published: September 2021

Structural layout scheme of dual rotor system with inter-shaft bearing plays an important role in reducing the bearing frame and structure weight of areo-engine. This kind of scheme is often used in the design of high thrust-weight ratio turbofan engine. However, the inter-shaft bearing will cause the direct interaction of the force and displacement between the high and low pressure rotor systems, contributing to the coupling of the dynamic characteristics of two rotor systems. The coupling may eventually lead to the failure of the rotor displacement control, loss of the robustness of the connection structure or excessive dynamic load of the bearing. The main purpose of this paper is to, firstly study and quantitatively evaluate the coupling characteristics of the dual rotor system, secondly obtain the correlation between the structural feature parameters such as the position of the inter-shaft bearing and the coupling vibration or interactive excitation characteristics of the system, finally propose the coupling vibration control method of dual rotor system.

The dynamic model of dual rotor system with inter-shaft bearing is established. The modal frequencies and modes of dual rotor system with or without coupling are analyzed and compared. The results illustrate the complexity of coupled vibration of high pressure and low pressure rotors. Then modal coupling characteristics evaluation parameter of dual rotor system based on energy distribution relationship is proposed. Using the coupling factor defined, the correlation between the inter-shaft bearing support feature and the modal coupling characteristics is discussed. The results show that, placing the inter-shaft bearing near the mass center of low pressure turbine can effectively restrain the mode coupling, meanwhile the proportion of bearing strain energy can also reflect the mode coupling characteristics of dual rotor system to a certain extent. Then a method of controlling the response coupled vibration of dual rotor system with inter-shaft bearing, based on the principle of mode superposition, is proposed. An example verifies the method can control the response coupling vibration of dual rotor system in wide speed range and under complex excitation conditions.
Rotating Cooling Performance of Two-Pass Rectangular Channels With Cross Bridge and Oval-Shaped Dimple
Authors: Jing Qi , Zhu Fahui , Liu Zhufeng , Xie Yonghui , Zhang Di
Published: September 2021

In order to adapt to the high-efficiency and low-resistance performances required by the new generation of gas turbine, a new type of two-pass rectangular channel with cross bridge and oval-shaped dimple structure is proposed for internal cooling of blade mid chord region. Firstly, the flow structure, heat transfer and friction characteristics of the novel channels under stationary and rotating conditions are numerically analyzed and compared in detail. Then the effects of cross bridge type/layout and dimple dimension/arrangement on the cooling performance are discussed. And the coupling mechanism of cross bridge, turning bend, oval-shaped dimple and rotation effect is revealed. The results show that the introduction of the cross bridge enables the coolant flow into the second pass in a distributed manner, which weakens the flow aggregation and extrusion in the tip turning bend region, thus the flow structure is optimized. Although the heat transfer is slightly weakened, the friction factor is reduced by 66.3% and 51.4%, and the overall thermal performance is improved by 16.7% and 11.6% (different cases) at most, for stationary and rotating conditions, respectively. The oval-shaped dimple achieves local heat transfer enhancement by controlling flow separation and reattachment. Furthermore, the optimized cross bridge type/layout and dimple dimension/arrangement are also obtained. This research will provide important reference data for the development of high-efficiency mid chord cooling technology for gas turbine blade.
Design, Development and Validation of Additively Manufactured First Stage Turbine Vane for F Class Industrial Gas Turbine
Authors: Torkaman Alex , Vogel Gregory , Houck Lonnie
Published: September 2021

Emerging additive manufacturing technology offers many opportunities for improved cooling design in gas turbine components by enabling design of cooling passages and shapes that are not manufacturable with conventional methods. Many combustion components have already taken advantage of these design opportunities however adaptation of this technology in turbine hot gas path components has been slower due to challenges with demanding environment and restriction on material properties obtained from additive manufacturing. This paper represents application of additive manufacturing technology in an F class industrial gas turbine including design, development and validation steps of a 1st stage turbine vane. A systematic design approach was undertaken to examine all aspects of operation and cooling of the component to down-select the appropriate design, material and processing. Detail characterization of multiple relevant material properties such as LCF, fracture toughness and creep was conducted to obtain material data and generate elastic and viscoplastic models for component design. Subsequent microstructural analyses of creep specimen were conducted to evaluate creep mechanism. Cooling design studies and coupon specimen testing were conducted to determine heat transfer and flow characteristics of micro channels used in the airfoil design. Detailed conjugate heat transfer analyses were used to iterate and optimize the cooling design. Once final design requirements were achieved, a number of prototype engine components were manufactured and tested in continuous engine operation for a predetermined duration of more than 6 months. These prototype components were removed from the engine after successful operation for validation purposes. Uniform crystal temperature sensors (UCTS) were used to validate the new cooling design. Destructive microstructural evaluations were performed to determine the impact of in-service operation on additive manufactured material. Details of the design and development steps as well as the results of prototype tests and microstructural evaluations are presented and discussed in this paper. It is demonstrated that with proper considerations of the resulting material properties, adaptation of additive manufacturing technology in turbine components is feasible with a comprehensive development process.
Experimental Investigation on Nonlinear Response of a Low-Swirl Flame to Acoustic Excitation with Large Amplitude
Authors: Liu Weijie , Zhang Liang , Xue Ranran , Yang Qian , Wang Huiru
Published: September 2021

Thermoacoustic instability is a major issue in developing high-efficiency low emission gas turbine combustors. In order to predict the amplitude of limit cycle oscillation, an understanding of the amplitude dependent response of the flame, i.e. the nonlinear response, to large acoustic excitation is needed. In the present study, the nonlinear response of a low-swirl CH4/air premixed flame to acoustic excitation is experimentally studied. Amplitude dependences of flame dynamic at 75 Hz and 195 Hz are discussed in detail over a wide range of excitation level. Experimental results show the gain of flame describing function of the low-swirl flame has a peak value at 65 Hz and a local minimum at 105 Hz which is caused by the destructive (out of phase) and constructive (in phase) of the axial and azimuthal velocity fluctuation. At low perturbation level, flame heat release fluctuation is in linear relationship with the normalized velocity driving level. Heat release fluctuation begins to saturate at a certain level which depends on the driving frequency. The low-swirl flame oscillates mainly in the axial direction at 75 Hz while it is in the radial direction at 195 Hz. The non-linear flame heat release response is a result of combination effect of flame rollup process and harmonic responses.
Low-Emissions Technology Development for Auxiliary Power Unit Combustion Systems
Authors: Bronson Thomas , Dudebout Rudy , Rudrapatna Nagaraja
Published: September 2021

The aircraft Auxiliary Power Unit (APU) is required to provide power to start the main engines, conditioned air and power when there are no facilities available and, most importantly, emergency power during flight operation. Given the primary purpose of providing backup power, APUs have historically been designed to be extremely reliable while minimizing weight and fabrication cost. Since APUs are operated at airports especially during taxi operations, the emissions from the APUs contribute to local air quality. There is clearly significant regulatory and public interest in reducing emissions from all sources at airports, including from APUs. As such, there is a need to develop technologies that reduce criteria pollutants, namely oxides of nitrogen (NOx), unburned hydrocarbons (UHC), carbon monoxide (CO) and smoke (SN) from aircraft APUs.

Honeywell has developed a Low-Emissions (Low-E) combustion system technology for the 131-9 and HGT750 family of APUs to provide significant reduction in pollutants for narrow-body aircraft application. This article focuses on the combustor technology and processes that have been successfully utilized in this endeavor, with an emphasis on abating NOx.

This paper describes the 131-9/HGT750 APU, the requirements and challenges for small gas turbine engines, and the selected strategy of Rich-Quench-Lean (RQL) combustion. Analytical and experimental results are presented for the current generation of APU combustion systems as well as the Low-E system. The implementation of RQL aerodynamics is well understood within the aero-gas turbine engine industry, but the application of RQL technology in a configuration with tangential liquid fuel injection which is also required to meet altitude ignition at 41,000 ft is the novelty of this development. The Low-E combustion system has demonstrated more than 25% reduction in NOx (dependent on the cycle of operation) vs. the conventional 131-9 combustion system while meeting significant margins in other criteria pollutants. In addition, the Low-E combustion system achieved these successes as a “drop-in” configuration within the existing envelope, and without significantly impacting combustor/turbine durability, combustor pressure drop, or lean stability.
On sCO2 Compressor Performance Maps at Variable Intake Thermodynamic Conditions
Authors: Romei Alessandro , Gaetani Paolo , Persico Giacomo
Published: September 2021

Unconventional aero-thermodynamic phenomena affect the performance of compressors that operate with carbon dioxide (CO2) close to its thermodynamic critical point. As a consequence, whether compressor performance maps based on conventional scaling parameters, such as flow coefficient and peripheral Mach number, still posses general features remains an open question.

In this work, we show that additional dimensionless parameters are needed to ensure full similarity conditions when intake thermodynamic conditions vary. Thanks to a combination of three-dimensional turbulent flow simulations, analytical developments and physical flow considerations, three main phenomena are shown to affect compressor operation when changing the upstream total state: (i) non-ideal effects that can modify the fluid compressibility from liquid-like to gas-like and vice versa, (ii) the extent of the two-phase region within the blade channel, (iii) the resulting compressibility of the two-phase mixture. Three dimensionless parameters are introduced to separately account for these effects and their relationship is highlighted. The influence of these parameters on compressor performance maps is widely discussed, shedding light on the way they act in the modification of the ideal similarity based only on the flow coefficient and the peripheral Mach number.

As a general result, two additional dimensionless parameters are needed to guarantee similarity conditions in presence of non-ideal flows of CO2 subject to phase change. These findings are expected to be relevant for the plant regulation in off-design conditions and for planning experimental campaigns at different thermodynamic conditions.
Life Limiting Aspects of an MI SiC/SiC Ceramic Matrix Composite (CMC) in Interlaminar Shear at Elevated Temperature
Authors: Kane S. , Stanley A. , Sanchez L. , Faucett D. C. , Choi S. R.
Published: September 2021

Life limiting behavior of an MI SiC/SiC ceramic matrix composite (CMC) was determined under interlaminar shear at 1316°C in air using double-notch-shear (DNS) test specimens. The three different shear loading configurations of dynamic fatigue, static fatigue, and cyclic fatigue were employed to assess their individual respective lives. The MI SiC/SiC CMC exhibited low susceptibility to fatigue (‘slow crack growth’) regardless of loading configuration. A Life prediction model for interlaminar shear in cyclic fatigue was developed based on the fracture mechanics framework. The newly developed cyclic fatigue model as well as the previously developed dynamic and static fatigue models were all in good agreement with the experimental data, indicating that the governing failure mechanism under interlaminar shear was consistent, independent of fatigue loading configuration.
Effective Evaluation of Rotordynamic Performance Within Rotor-Bearing System Design Bounds
Authors: Luo Zhusan , Schwarz Carl L.
Published: September 2021

This paper presents a study on the effective evaluation of rotordynamic performance for multiple analysis cases within rotor-bearing system design bounds. The variations in rotordynamic design variables and operating conditions are usually considered in a rotordynamic analysis. This can provide useful information about the current design, potential for modification, and the capability of off-design operation. Typical design bounds of a tilting pad journal bearing are discussed to show the complexity of multiple design cases and a demand for a method to postprocess the analytical results.

Rotordynamic performance is conventionally assessed by examining undamped critical speed maps, damped modes, stability, and unbalance responses. Evaluating rotordynamic performance for multiple cases is a tedious task for both rotordynamicists and reviewers. A new approach is studied to effectively extract, present and evaluate analytical results. A theoretical study shows the analytical results can be synthesized to determine key performance parameters. It is proposed that the amplification factors at critical speeds can be converted to equivalent logarithmic decrements. Based on the two studies, a new rotordynamic performance diagram is created to present damped modes, critical speeds and relevant acceptance criteria. With this informative diagram, one can quickly and effectively evaluate the acceptability and robustness of multiple design cases. This diagram can also convey the trends of key performance parameters, comparisons between cases, and the sensitivities of key performance parameters to design variables more clearly and concisely. This synthesizing approach and the rotordynamic performance diagram may be useful in modifying an existing design, determining a proper off-design operation range, and investigating rotordynamic issues.
Computed Tomography Wall Thickness Inspection to Support Gas Turbine Blade Life Extension
Authors: Hastie Scott , Chan Anthony , Wiens Kevin , Nagy Doug , Tollett Robert , Lowden Paul
Published: September 2021

The inclusion of Full Solution Rejuvenation (FSR®) in repairs of flight and aero-derivative gas turbine blades has shifted the primary cause for blade retirement from creep life consumption which is a function of service hours to primarily geometric limitations that are more governed by the cumulative number of repair cycles. For internally cooled components, one of the most significant causes for rejection is the remaining wall thickness of the airfoil. Operating blades with under-sized wall thickness can reduce the load-bearing capability and can increase the stresses that develop under transient thermal conditions found in operation.

Typically, ultrasonic wall thickness measurement techniques are used during repair processing for determining remaining wall thickness on components but a number of limitations to obtaining accurate results with this process have been identified. Computed Tomography (CT) wall thickness inspection has addressed these limitations and become an important tool for extending the life of components beyond the typical OEM limits during repair.

Entirely from the CT equipment user’s perspective, this paper explores a number of technical findings in the development of a highly accurate CT wall thickness inspection process for flight and aero-derivative gas turbine blades for utilization during repair after one or more service intervals. The importance of the accuracy of these wall thickness measurements is to ensure undersized blades are rejected and blades above the minimum wall thickness are accepted. Reducing uncertainty in the wall thickness measurements allows reconsideration of the acceptance limit and can result in more repairable blades returned for full service intervals. The target accuracy for measurements process was .002”. The findings described include aspects of equipment configuration, process parameters for the initial CT scanning, post-processing and interpretation, results validation specific to the component being measured and process limitations encountered.
Optically Observed Turbulence In Thrust Collars at Low Critical Reynolds Number Including Numerical Predictions
Authors: Kerr Thomas , Delgado Adolfo
Published: September 2021

Critical Reynolds number is a dimensionless parameter defining a transition between laminar and turbulent flow that can only be experimentally determined. As machine design pushes towards higher efficiencies, individual components such as bearings operate at higher speeds and loads. Proper modeling of bearing elements, especially at higher speeds requires accurate turbulence modeling. This paper presents the first critical Reynolds number for a Thrust Collar (TC). A high-speed camera observes the oil flow of a TC through a specially designed transparent window. The optical results show a consistent area in the entrance region of the flow field that increase in overall area with increasing spin speed, and decreasing axial load. The areas of turbulence correspond to a critical Reynolds number between 300 and 500. Additionally, the experimental results show that increasing the inlet velocity of the oil initially increases the turbulent area, until the speed of the oil surpasses the surface speed of the TC, at which point the turbulence disappears. Finally, the paper also presents a Computational Fluid Dynamics (CFD) turbulence model based on the k-ϵ equations. The model investigates the possible cause of the turbulence, and also matches the experimental results well. The CFD model predicts a slight increase in load capacity and power loss (< 1%) that could become more significant for larger spin speeds and axial loads.
Experimental Analysis and Material Characterization of Ultra High Temperature Composites
Authors: Ghoshal Anindya , Walock Michael J. , Nieto Andy , Murugan Muthuvel , Hofmeister-Mock Clara , Pepi Marc , Bravo Luis , Wright Andrew , Luo Jian
Published: September 2021

Ultra high temperature ceramic (UHTC) materials have attracted attention for hypersonic applications. Currently there is significant interest in possible gas turbine engine applications of UHTC composites as well. However, many of these materials, such as hafnium carbide, zirconium carbide, and zirconium diboride, have significant oxidation resistance and toughness limitations. In addition, these materials are very difficult to manufacture because of their high melting points. In many cases, SiC powder is incorporated into UHTCs to aid in processing and to enhance fracture toughness. This can also improve the materials’ oxidation resistance at moderately high temperatures due to a crack-healing borosilicate phase. ZrB2-SiC composites show very good oxidation resistance up to 1700 °C, due to the formation of SiO2 and ZrO2 scales in numerous prior studies. While this may limit its application to hypersonic applications (due to reduced thermal conductivity and oxidation resistance at higher temperatures), these UHTC-SiC composites may find applications in turbomachinery, as either stand-alone parts or as a component in a multi-layer system.

The US Army Research Laboratory (ARL), the Naval Postgraduate School (NPS), and the University of California – San Diego (UCSD) are developing tough UHTC composites with high durability and oxidation resistance. For this paper, UHTC-SiC composites and high-entropy fluorite oxides were developed using planetary and high-energy ball milling and consolidated using spark plasma sintering. These materials were evaluated for their oxidation-resistance, ablation-resistance, and thermal cycling behavior under a DoD/OSD-funded Laboratory University Collaborative Initiative (LUCI) Fellowship and DoD Vannevar Bush Fellowship Program. In the present paper experimental results and post-test material characterization of SPS sintered ZrB2, ZrB2+SiC, ZrB2+SiC+HfC, HfC+SiC, and HfC+ZrB2 pellets subjected to ablation test are presented.
Instabilities Everywhere! Hard Problems in Aero-Engines
Authors: Spakovszky Zoltán S.
Published: September 2021

Many of the challenges that limited aero-engine operation in the 1950s, 60s, 70s and 80s were static in nature: hot components exceeding temperature margins, stresses in the high-speed rotating structure approaching safety limits, and turbomachinery aerodynamic efficiencies missing performance goals. Modeling tools have greatly improved since and have helped enhance jet engine design, largely due to better computers and improved simulations of the fluid flow and supporting structure. The situation is thus different today, where important problems encountered past the design and development phases are dynamic in nature. These can jeopardize engine certification and lead to major delays and increased program cost. A real challenge is the characterization of damping and the related dynamic behavior of rotating and stationary components and assemblies, and of the fluid-structure interactions and coupling. The theme of this lecture is instability in the broadest sense. A number of problems of technological interest in aero-engines are discussed with focus on dynamical system modeling and identification of the underlying mechanisms. Future perspectives on outstanding seminal problems and grand challenges are also given.
Do you have COVID-19? An artificial intelligence-based screening tool for COVID-19 using acoustic parameters
Authors: Vahedian-azimi Amir , Keramatfar Abdalsamad , Asiaee Maral , Atashi Seyed Shahab , Nourbakhsh Mandana
Published: September 2021

This study aimed to develop an artificial intelligence (AI)-based tool for screening COVID-19 patients based on the acoustic parameters of their voices. Twenty-five acoustic parameters were extracted from voice samples of 203 COVID-19 patients and 171 healthy individuals who produced a sustained vowel, i.e., /a/, as long as they could after a deep breath. The selected acoustic parameters were from different categories including fundamental frequency and its perturbation, harmonicity, vocal tract function, airflow sufficiency, and periodicity. After the feature extraction, different machine learning methods were tested. A leave-one-subject-out validation scheme was used to tune the hyper-parameters and record the test set results. Then the models were compared based on their accuracy, precision, recall, and F1-score. Based on accuracy (89.71%), recall (91.63%), and F1-score (90.62%), the best model was the feedforward neural network (FFNN). Its precision function (89.63%) was a bit lower than the logistic regression (90.17%). Based on these results and confusion matrices, the FFNN model was employed in the software. This screening tool could be practically used at home and public places to ensure the health of each individual's respiratory system. If there are any related abnormalities in the test taker's voice, the tool recommends that they seek a medical consultant.
Glimpsing keywords across sentences in noise: A microstructural analysis of acoustic, lexical, and listener factors
Authors: Fogerty Daniel , Ahlstrom Jayne B. , Dubno Judy R.
Published: September 2021

This study investigated how acoustic and lexical word-level factors and listener-level factors of auditory thresholds and cognitive-linguistic processing contribute to the microstructure of sentence recognition in unmodulated and speech-modulated noise. The modulation depth of the modulated masker was changed by expanding and compressing the temporal envelope to control glimpsing opportunities. Younger adults with normal hearing (YNH) and older adults with normal and impaired hearing were tested. A second group of YNH was tested under acoustically identical conditions to the hearing-impaired group, who received spectral shaping. For all of the groups, speech recognition declined and masking release increased for later keywords in the sentence, which is consistent with the word position decreases in the signal-to-noise ratio. The acoustic glimpse proportion and lexical word frequency of individual keywords predicted recognition under different noise conditions. For the older adults, better auditory thresholds and better working memory abilities facilitated sentence recognition. Vocabulary knowledge contributed more to sentence recognition for younger than for older adults. These results demonstrate that acoustic and lexical factors contribute to the recognition of individual words within a sentence, but relative contributions vary based on the noise modulation characteristics. Taken together, acoustic, lexical, and listener factors contribute to how individuals recognize keywords during sentences.
Teachers’ Engagement With Professional Development to Support Implementation of Meaningful Physical Education
Authors: Beni Stephanie , Fletcher Tim , Ní Chróinín Déirdre
Published: September 2021

Purpose: The purposes of this research were to design a professional development (PD) initiative to introduce teachers to a pedagogical innovation—the Meaningful Physical Education (PE) approach—and to understand their experiences of the PD process. Method: Twelve PE teachers in Canada engaged in an ongoing PD initiative, designed around characteristics of effective PD, across two school years as they learned about and implemented Meaningful PE. Qualitative data were collected and analyzed. Findings: This research showed that teachers valued a community of practice and modeling when learning to implement Meaningful PE. While teachers were mostly favorable to the PD design, there were several tensions between ideal and realistic forms of PD. Discussion: This research offers support for several characteristics of effective PD to support teachers’ implementation of a novel pedagogical approach and highlights the need to balance tensions in providing forms of PD that are both effective and practical.
Human microphysiological systems for drug development
Authors: Roth Adrian ,   MPS-WS Berlin 2019
Published: September 2021

Organs-on-chips could be used to assess drug efficacy and support personalized medicine
Observation of fragmentation of a spinor Bose-Einstein condensate
Authors: Evrard Bertrand , Qu An , Dalibard Jean , Gerbier Fabrice
Published: September 2021

Fragmenting the condensate

In a Bose-Einstein condensate, a sizable fraction of particles occupies a single quantum state. In some systems, it is in principle possible to have more than one such macroscopically occupied state. Evrard
et al
. observed this so-called fragmented condensate in an ultracold gas of bosonic sodium atoms with three spin states. Starting from a single condensate in a static magnetic field, the researchers decreased the field to zero, resulting in a three-fragment condensate. —JS
The adaptive immune system is a major driver of selection for tumor suppressor gene inactivation
Authors: Martin Timothy D. , Patel Rupesh S. , Cook Danielle R. , Choi Mei Yuk , Patil Ajinkya , Liang Anthony C. , Li Mamie Z. , Haigis Kevin M. , Elledge Stephen J.
Published: September 2021

Defining tumor cell immune evasion

Mouse models used to study cancer often lack a full immune system, allowing implantation of human tumors into the mice. By contrast, naturally evolving tumors must contend with a fully functional immune system and its destruction of some of the cells (see the Perspective by Ho and Wood). Two groups now report studies on mouse models with a fully intact immune system. Martin
et al
. started with preexisting murine tumor cell lines and examined their continued evolution in vivo, whereas Del Poggetto
et al
. examined the development of new pancreatic tumors in the context of inflammation, as is often seen in human patients. In each study, the authors found that the immune system exerted a selective pressure on cells that would give rise to tumors, promoting the survival of those that had lost expression of tumor suppressor genes or activated a specific oncogene. The findings suggest a major role for the immune system in driving tumor evolution across multiple types of cancer. —YN
Comment on “Aberrant type 1 immunity drives susceptibility to mucosal fungal infections”
Authors: Puel Anne , Casanova Jean-Laurent
Published: September 2021

Break
et al
. (Research Articles, 15 January 2021, eaay5731) suggest that chronic mucocutaneous candidiasis in humans with inborn errors of
AIRE
and autoimmune polyendocrine syndrome type 1 is due to excessive interferon-γ production and not to autoantibodies neutralizing interleukin-17 cytokines. We argue that both claims are not conclusively supported by their data and are at odds with 35 years of study.
Response to Comments on “Aberrant type 1 immunity drives susceptibility to mucosal fungal infections”
Authors: Break Timothy J. , Oikonomou Vasileios , Dutzan Nicolas , Desai Jigar V. , Swidergall Marc , Freiwald Tilo , Chauss Daniel , Harrison Oliver J. , Alejo Julie , Williams Drake W. , Pittaluga Stefania , Lee Chyi-Chia R. , Bouladoux Nicolas , Swamydas Muthulekha , Hoffman Kevin W. , Greenwell-Wild Teresa , Bruno Vincent M. , Rosen Lindsey B. , Lwin Wint , Renteria Andy , Pontejo Sergio M. , Shannon John P. , Myles Ian A. , Olbrich Peter , Ferré Elise M. N. , Schmitt Monica , Martin Daniel ,   Genomics and Computational Biology Core, Barber Daniel L. , Solis Norma V. , Notarangelo Luigi D. , Serreze David V. , Matsumoto Mitsuru , Hickman Heather D. , Murphy Philip M. , Anderson Mark S. , Lim Jean K. , Holland Steven M. , Filler Scott G. , Afzali Behdad , Belkaid Yasmine , Moutsopoulos Niki M. , Lionakis Michail S.
Published: September 2021

Puel and Casanova and Kisand
et al
. challenge our conclusions that interferonopathy and not IL-17/IL-22 autoantibodies promote candidiasis in autoimmune polyendocrinopathy–candidiasis–ectodermal dystrophy. We acknowledge that conclusive evidence for causation is difficult to obtain in complex human diseases. However, our studies clearly document interferonopathy driving mucosal candidiasis with intact IL-17/IL-22 responses in
Aire
-deficient mice, with strong corroborative evidence in patients.
Common ground and the climate crisis
Saving Us: A Climate Scientist’s Case for Hope and Healing in a Divided World
Katharine Hayhoe
Atria, 2021. 320 pp.
Authors: Aczel Miriam
Published: September 2021

Invoking shared values can help convince skeptics of the need to mitigate climate change
A silver assist for microbial fuel cell power
Authors: Gaffney Erin M. , Minteer Shelley D.
Published: September 2021

Silver nanoparticles in
Shewanella
membranes boost electron transfer to graphene electrodes
Homogeneous neuromorphic hardware
Authors: Rao Feng , Tao Xutang
Published: September 2021

Bifunctional ferroelectric transistors enable collocation of memory and processing
In Other Journals
Authors: Zahn Laura M. , McCartney Melissa , Kelly Priscilla N. , Lavine Marc S. , Ray L. Bryan , Smith Keith T. , Jiang Di
Published: September 2021

Editors’ selections from the current scientific literature
Clearing the tinderbox
Authors: Cornwall Warren
Published: September 2021

As the climate warms, a huge forest experiment aims to reduce wildfire risk and find common ground between loggers and environmentalists
Forget oil or water. Icelandic drillers seek magma
Authors: Voosen Paul
Published: September 2021

Probe of volcano could reveal magma composition and guide early warning systems