bluuebunny/crossref_metadata_2025_split huggingface dataset:
Finite Element Analysis of APU Mounting (3-2-1) in Aircraft/Helicopter Application Using Lumped Mass Modal Analysis
Authors: Savela Gregory , Mathuria Parag H. , Taubler James , Belotto Daniel , Masloski James 
Published: September 2023

Abstract
The mounting of the auxiliary power unit (APU) and gear box in Aircraft/Helicopter is discussed in the paper. The APU is usually connected to a Gear box to drive other components. The APU is exposed to shock and vibration environments. The shock and vibration concerns dealing with the design of a stiff support system to achieve target frequency. A frequency margin criterion is selected to ensure fundamental system frequencies are at least 15% away from dominant vibration inputs such as harmonics of helicopter blade passing frequency. A lumped parameter dynamic model is formulated to perform the modal analysis and 1g load static analysis. Modal analysis will help to identify the mounting frequencies, while static analysis will help to identify distribution of the load at each mount, driving the design of supports and identifying design equivalent loads for shock and vibration input. A detailed finite element analysis was performed to validate the lumped mass finite element model. The lumped mass model approach helps in quick turnaround in the preliminary phase of the design, to optimize the mount locations and identify required stiffnesses. The connection stiffness between the APU and Gear box was found to be the controlling stiffness for the mounted frequencies. Hence a short-term (compromise) solution and long-term (lower risk) approach were provided to achieve the target frequency.
Effect of Inert Species on the Static and Dynamic Stability of a Piloted, Swirl-Stabilized Flame
Authors: Rodriguez Camacho Javier , Akiki Michel , Blust James , O’Connor Jacqueline 
Published: September 2023

Abstract
Carbon sequestration and utilization has been proposed as a method for decarbonizing high-efficiency industrial gas turbines operating on natural gas fuels for power-generation and industrial markets. To increase the efficiency of the carbon removal process from the exhaust stream of the turbine, exhaust gas recirculation (EGR) can be used. EGR recycles a portion of the engine exhaust into the inlet, increasing the concentration of inert species in the exhaust stream to improve the performance and cost effectiveness of CO2 separation systems. This strategy can, however, reduce the oxygen concentration in the air, leading to changes in flame stabilization in the combustor. In this study, we investigate the effect of air diluted with inert gases of different compositions and the impact that these mixtures have on flame static and dynamic stability. A swirl-stabilized flame in a single-nozzle, variable-length combustor is used to measure the flame behavior for oxygen concentrations of 15% to 21% by volume. A constant adiabatic flame temperature test matrix is conducted to mimic operation in an industrial gas turbine. High-speed chemiluminescence imaging is used to determine the change in flame shape and dynamics for each gas composition. As the oxygen concentration decreases, the flame lifts from the centerbody, resulting in an aerodynamically-stabilized flame at the lowest O2 concentrations. Different compositions of gases result in different flame shapes, where higher levels of N2 in the diluents result in more flame stabilization in the outer recirculation zone as compared to those with higher levels of CO2. The flame oscillation mechanisms also change with oxygen concentration, where the lifted flames at low O2 levels exhibit an ignition/extinction oscillation mode as compared to a vortex-shedding-coupled oscillation mode at high O2 levels where the flame is stabilized on the centerbody. Companion chemical kinetics simulations are used to explain changes in the flame’s shape and behavior.
Evaluation of Torque Transmission Capacity for Centrifugal Compressor Impellers With Pre-Generated Data From Finite Element Analysis
Authors: Jin Hanxiang , Pettinato Brian , Shoup Frank 
Published: September 2023

Abstract
The evaluation of torque transmission capacity for centrifugal compressor impellers can be complicated due to the unique geometric characteristics of the impeller wheels. The existing analytical method for keyless interference fit only works for simple geometries like cylinders. In general, finite element analysis (FEA) simulations are needed to obtain the torque capacity of centrifugal compressor impellers for a specific setup (rotational speed/geometric scale/interference fit rate). However, when the torque capacity needs to be evaluated in multiple working conditions, the time cost of FEA simulations can be an issue if each case is evaluated individually. In this study, a methodology is provided to obtain the torque capacity of centrifugal compressor impellers instantly for any given working conditions with pre-generated data from FEA simulations, especially with scaling of the interference fit rate. If the interference fit rate (ratio of interference fit to diameter) is kept the same as the pre-generated FEA data, the results can be directly scaled by rotational speed and geometric scale factor which is covered by the existing method and not the focus of this study. If the given interference fit rate is different than the setup in pre-generated FEA simulations, then an engineering approximation is used to calculate the contact pressure and torque capacity based on impeller bore deformation. In this methodology, the FEA simulations are performed before knowing the working conditions which can be very useful in many time-sensitive industrial applications.
Windage Loss and Flow Characteristics in Back Gap of Radial Inflow Impellers With Steam Medium
Authors: Zhao Zhuobin , Deng Qinghua , Hu Lehao , Li Jun , Feng Zhenping 
Published: September 2023

Abstract
The impeller back gap of radial inflow turbines generates disk-type windage loss, and it is necessary to accurately predict and minimize the loss. In this paper, a steady-state numerical analysis for a two-stage radial inflow turbine with steam as working medium is carried out, and a modified model for predicting the windage loss is proposed and validated. Under the design condition, the windage loss affects obviously the turbine power output, the power of the Stage 1st and Stage 2nd reduced by 6% and 5%, respectively. The back gap makes the vortex structure of the impeller leading edge enhanced, and pressure distribution turns different at the blade inlet section. With the increase of rotational speed and mass flow rate, the vortex structure near the outlet expand and moves radially to the center of the gap. Finally, models from Daily and Coren indicate that Reynolds number and throughflow Reynolds number are important influencing parameters for windage loss in disk-type gap with throughflow. And the results show that the Daily model is more accurate. Therefore, based on the simulation results, a model is proposed to improve the accuracy of windage loss model. And the model containing these two parameters can accurately predict the windage loss with a maximum deviation of 10.6 %. Despite its preliminary character, the model has an important reference value for the design of radial inflow turbomachinery.
Influence of Elevated Temperature Solid Particle Erosion on Strength Degradation of Oxide/Oxide Ceramic Matrix Composites
Authors: Mirza Farhan , Panakarajupally Ragav P. , Rassi J. E. , Morscher Gregory N. , Abdi Frank , Choi Sung 
Published: September 2023

Abstract
The erosion behavior of an oxide/oxide ceramic matrix composite was characterized at 800 °C and 1200 °C. The effect of erodent particle velocity and temperature were investigated. Microscopic analysis was performed to understand the intensity of damage through depth profiling. The room temperature tensile strengths with digital image correlation were performed to evaluate retained mechanical properties of oxide composites. The results indicate that erosion rate increases with increase in particle velocity and temperature, the former being more consequential. Residual strength tests indicate that specimens impacted at higher velocity and temperature showed lower strengths due to increasing crater depth. The erosion behavior was similar to previous results on oxide/oxide composites.
CFD Analysis and Experimental Validation of a sCO2 Pocket Damper Seal
Authors: Ganiger Manjush , Vannini Giuseppe , Bigi Manuele , Vidyasagar R. , Cangioli Filippo 
Published: September 2023

Abstract
Supercritical CO2 (sCO2) used as a closed loop fluid for power cycles in waste heat recovery or small energy production services significantly reduces the size of turbomachinery due to high operating pressure and density of sCO2 fluid above its critical point. For this reason, this OEM is working to develop the relevant centrifugal compressor technology.
A damper seal like a Pocket Damper Seal (PDS) is a very effective choice for a sCO2 compressor balance piston both in design conditions and in a potential transient scenario operating in multiphase regime. The leakage and rotordynamic coefficients predictions for such a seal are very critical when this is operating close to CO2 critical point due to the large variation in gas properties.
In this paper, a PDS with upstream shunt-holes is the subject of the study. A Bulk Flow Model (BFM) approach was originally used to design the PDS for both leakage and rotordynamic coefficients. To verify the design of such a seal, a Computational Fluid Dynamics (CFD) based approach was employed at a later stage. The CFD approach outlines the use of various Equations of States (EOS) like Peng-Robinson, Redlich-Kwong, and Span-Wagner (NIST-Refprop) for the computation of leakage flow. Sensitivity study on the range of NIST-Refprop look-up table was also carried out to have a trade-off between leakage accuracy and computational time. The CFD based rotordynamic coefficients were also computed using the Integral Perturbation method (IPM) by leveraging NIST-Refprop EOS.
The experimental data are relevant to the sCO2 compressor prototype tested at the Authors’ internal test bench. Various parameters related to compressor performance along with balance piston leakages were measured. The leakage flows predicted by the CFD and BFM approaches were validated against the experimental results.
Leakage comparison results show that BFM approach predictions are underestimating the experimental results. The CFD approach, on the other hand, overpredicts the leakage flow especially for the high-pressure operating points. The CFD approach was also validated for 6 different operating points of the compressor. Rotordynamic coefficients prediction from the CFD approach shows very good agreement with the BFM results at the design point and both agree with the test results which always showed a very stable compressor behavior.
CFD Analysis of The Effect of a Cylindrical Probe Rod in the Axial Gap of the Last Stage on Rotating Instabilities in a Low-Pressure Model Steam Turbine Operating at Low Load
Authors: Ercan Ilgit , Vogt Damian M. 
Published: September 2023

Abstract
Steam turbines are sometimes operated at extreme part-load conditions, specifically when the energy balance in power grids featuring a high share of fluctuating energy sources necessitates such operation. At these extreme operating conditions, the last stage rotating blades of the low-pressure turbine are subject to highly unsteady flow. As the flow is heavily separated, Rotating Instabilities (RI) may develop, among other turbulent effects. These highly unsteady flow structures result in fluctuations of the flow field over a wide range of low frequencies.
This study is based on the findings of a previous study in which Improved Delayed Detached Eddy Simulation (iDDES) has been applied to low-volume flow operating conditions to simulate RI [1]. The analyzed domain consists of a three-stage low-pressure model steam turbine. To capture the resulting rotationally asymmetric effects of the RI in the flow field, the computational model spans the full annulus and comprises the non-axisymmetric inlet section, all three stages, the axial-radial diffuser as well as the exhaust hood.
In a second study, it was shown that rotating instabilities in this analyzed model turbine are formed when the vortices created during perpetual separation mechanisms interconnect due to the increased ratio of the circumferential velocity in relation to the decreasing axial flow velocity during low volume flow [2]. Furthermore, it was found that the frequency spectra of the pressure signals at various radial heights obtained during experimental probe traverse differed from the numerical results recorded from the CFD domain. The present study aims to understand the differences in the flow field caused by the probe rod used for the experimental traverse. The experimental results with and without the probe traverse rod were compared, showing a decrease in pressure amplitudes at the casing when the rod is present in the axial gap of the last stage. In order analyze the difference in unsteady pressure signals, the continuous wavelet transform method was applied to evaluate the changes in frequency content in the signals with time.
Additionally, a cylindrical probe rod spanning the full span from hub to casing was implemented into the CFD domain and this decrease in amplitudes was also replicated numerically. To examine the detailed mechanisms behind this change in the flow field, advanced visualization and quantitative methods were employed.
Development of an Hydrogen Fueled Gas Turbine Combustion System From Conceptual Through Full Scale Verification Test
Authors: Cerutti M. , Pucci E. , Romano C. , Dabiru V. R. 
Published: September 2023

Abstract
The development phases of an hydrogen fueled combustor for industrial gas turbine are presented in this paper, from the conceptual burner design definition to the verification phase in realistic environment.
The development strategy has been conceived to properly balance the market needs and the effort required to achieve them. The hydrogen combustion technology is mainly focused on flashback free burners and gas fuel injectors development, representing a significant fuel flexibility enhancement of the NovaLT gas turbines family.
The readiness of the currently available technology in dealing with hydrogen was verified in a dedicated testing session, in a full scale annular combustor rig. Stable flame windows were identified for different operating conditions, and characterized in terms of pollutant emissions, pressure pulsations and system component temperatures.
As matter of this work, a bunch of alternative burner solutions have been designed with the aim of reducing the NOx emissions while maintaining adequate limits to either blowout, flashback or thermoacoustic instabilities. To further mitigate the risk of high NOx emissions, the abatement though water injection has been investigated as well. An atmospheric reduced scale rig has been used to characterize the different viable burner solutions, ensuring fast and somehow iterative design changes, and arranged to mimic the main features of a industrial sized gas turbine combustor, namely the combustion air inlet temperature, the hot gases residence times and the equivalence ratio.
The results clearly indicate a viable candidate to be assessed in the more realistic environment represented by the full-annular rig. The main outcomes of such a test campaign are also reported in this paper, with focus on both the NOx emissions and the operability related aspects. Flashback and flame holding resistance tests have been thus performed, demonstrating that such a solution is technologically ready for the next verification step in a real engine.
The results, while indicating a design development paths for the investigated solutions, provide an exhaustive data set, useful to either the models validation or the identification of the developments needed for future detailed investigations.
Experimental and Computational Heat Transfer Study of sCO2 Single-Jet Impingement
Authors: Richardson John , Wardell Ryan , Fernandez Erik , Kapat Jayanta S. 
Published: September 2023

Abstract
The present study experimentally and computationally investigates the heat transfer capability of supercritical carbon dioxide (sCO2) single jet impingement. The evaluated jet Reynolds number range is between 80,000 and 600,000, with a non-dimensional jet-to-target surface spacing of 2.8. CO2 impinging jet stagnation conditions were maintained at approximately 200 bar and a temperature of ∼400 °C for most experiments. The goal is to understand how changes in the aforementioned parameters influence heat transfer between the working fluid and the heated surface. Additionally, due to the elevated Reynolds numbers and difference in thermodynamic properties between air and CO2, air derived impingement correlations may not be appropriate for CO2 impingement; these correlations will be evaluated against experimental sCO2 impingement data. At the time of this study, no sCO2 impingement data was available relevant to sCO2 power cycles. The target surface is a 1.5-inch diameter copper block centered on the 3 mm jet orifice. A mica heating element bolted to the bottom of the copper block provides a uniform heat flux. Thermocouples embedded in the copper block are used to determine the surface temperature. Nusselt numbers obtained from experimental sCO2 test data are compared to area averaged Nusselt numbers from air derived correlations. The comparisons showed that air correlations drastically underpredict the heat transfer when sCO2 is used as the working fluid. A modified sCO2 correlation using experimental data at discussed conditions, is derived based on an existing air correlation. A CFD study is also performed to further investigate sCO2 heat transfer characteristics, and asses the numerical model applicability to this problem type.
Pollutant Emissions Reporting and Performance Considerations for Ammonia-Blended Fuels in Gas Turbines
Authors: Douglas Christopher M. , Martz Thomas D. , Steele Robert C. , Noble David R. , Emerson Benjamin L. , Lieuwen Timothy C. 
Published: September 2023

Abstract
To limit climate change and promote energy security, there is widespread interest towards transitioning existing fossil fueled combustion systems to sustainable, alternative fuels such as hydrogen (H2) and ammonia (NH3) without negatively impacting air quality. However, quantifying the emission rate of air pollutants such as nitrogen oxides (NOx) is a nuanced process when comparing pollutant emissions across different fuels, as discussed in our paper GT2022-80971 presented last year. That study indicated that the standardized approach for measuring combustion emissions in terms of dry, oxygen-referenced volumetric concentrations (i.e. ppmvdr) inflates reported pollutant emissions by up to 40% for hydrogen combustion relative to natural gas. In this paper, we extend our prior analysis of these so-called “indirect effects” on emissions values to ammonia (NH3) and cracked ammonia (i.e., molecular hydrogen and nitrogen, 3H2 per N2) fuel blends. The results reveal that ppmvdr-based pollutant reporting approaches have a less prominent influence on emissions interpretations for molecular ammonia-methane blends than for hydrogen-methane blends. Nonetheless, we still find that ppmvdr reporting induces up to a 10% relative increase in apparent emissions when comparing 100% NH3 and 100% methane (CH4) fuels at an equal mass-per-work emission rate. Cracking the ammonia is shown to increase this relative bias up to 21% in comparison to a methane system. Further analysis shows how drying, dilution, thermodynamic, and performance effects each influence the relationship between ppmvdr and mass-per-work emissions across the spectrum of fuels and fuel blends. Following discussion of these findings, we conclude that quantifying combustion emissions using ppmvdr is generally inappropriate for emissions comparisons and advise the combustion community to shift towards robust mass-per-energy metrics when quantifying pollutant emissions.
A Novel Testing Methodology to Predict the Endurance of Ball Joints in Absence of Lubrication at High Temperature
Authors: Bucciarelli Federico , Macoretta Giuseppe , Monelli Bernardo Disma , Beghini Marco , Conforti Federico , Bellacci Michelangelo , Giusti Enrico 
Published: September 2023

Abstract
The enhancement of the operational flexibility of axial expanders can be obtained through the implementation of Nozzle Guide Vane (NGV). This design architecture includes moving parts typically sustained by ball joints, whose wear behavior might be important to define the maintenance interval of the expander and define its operational availability. This is especially true when considering challenging loading and temperature conditions. Usually, tribological tests are performed by pin-on disk or similar test methods. However, these techniques neglect important factors as actual sliding zone and contact morphology, which can be fundamental for ball joints.
This work deals with the design of an innovative experimental test procedure for the characterization of the tribological behavior of ball joints considering the actual operating conditions of a NGV at 500°C. The core of the methodology is a customized test bench specifically designed to investigate actual commercial ball joint in field conditions. Details on the design phase and on the commissioning of the experimental set-up are given. The results of the experimental campaign performed on this novel test bench are presented: the chosen test matrix explores a wide spectrum of load and sliding speed. Specimen pre-load and working velocity have been scaled-up to achieve viable testing duration. The test bench was employed on three different kinds of commercial ball joints for high-temperature applications in absence of lubrication. Measurement of diametral clearance and friction in worn conditions were also performed. The results discussion allowed to choose the most suitable solution for a specific design targeting 50000 working hours.
Design of a New Bench for High Temperature Static and Endurance Testing of Nozzle Guide Vane Bushing
Authors: Bucciarelli Federico , Giusti Enrico , Bellacci Michelangelo , Checcacci Damaso , Maestrale Francesco , Manconi Salvatore 
Published: September 2023

Abstract
Variable Guide Vanes such as Inlet Guide Vanes (IGVs) and Nozzle Guide Vanes (NGVs) are a typical design feature included in gas turbines and axial expanders to achieve improved performance in off-design conditions and, consequently, operational flexibility. In the last years the evolution of the energy market has challenged these components, which were already characterized by an intrinsic complexity, to achieve higher availability performances. For this reason, a deeper experimental characterization of the mechanical behavior of these assemblies has become of interest, especially when considering highly loaded nozzles. In particular, the investigation of the kinematic pairs of NGV is becoming very important in some design configuration. This paper describes the design and the commissioning of a novel advanced bench designed to test full-scale NGVs geometries constituted by stems supported by bushing couples. The bench is designed to perform the measurement of the friction coefficient of the kinematic chain and then to accomplish continuous endurance testing of the bushing/stem pair at high temperature. Details are given regarding the design of the bench components which allow testing of bushing different by size and manufacturing technology. The design verifications needed for the proper bench operation are presented. In addition, the testing procedure is also included which will provide in the upcoming months useful data regarding clearance evolution and, more in general, component lifing.