bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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 (&lt; 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

Abstract
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

Abstract
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.