bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental Investigation of a Large Tilting-Pad Journal Bearing With a Direct-Bonded Sub-Millimeter PEEK Lining
Authors: Stottrop Michael , Engels Alexander , Weißbacher Christoph , Bender Beate 
Published: September 2023

Abstract
A novel coating technique allows direct bonding of polymer material to large plain bearings, enabling lower-cost manufacturing, more flexible running layer design and thin-layer coatings. In this publication, experimental results for a 500 mm tilting-pad journal bearing (TPJB) with a direct bonded sub-millimeter polyether ether ketone (PEEK) lining are presented. The five-pad TPJB in a non-flooded design is investigated on a test rig for original sized turbine bearings over a speed range of 1000 rpm – 3600 rpm. With the test rig, fluid film pressure and the distance between the shaft and the pads backing are measured from the rotating and axially shiftable shaft. By knowing the permittivity of the PEEK material and the thickness of the liner, the fluid film thickness is calculated from the data of a capacitive distance sensor. The experimental data are compared with those obtained with an identical bearing with Babbitt as lining material.
The results show markedly lower pad backing temperatures for the PEEK lined pads than for the Babbitt-lined pads and a reduction in their axial deflection is detected with the PEEK lined pads. Therefore, the test bearing can be loaded up to 4.75 MPa (at 3000rpm) in the experiments.
Numerical Investigation of the Interaction of a Circumferential Groove Casing Treatment and Near-Tip Modifications for a Highly-Loaded Low-Speed Rotor Under the Influence of Double Leakage
Authors: Reisinger Lukas , Eckel Jannik , von Jeinsen Philipp , Gümmer Volker 
Published: September 2023

Abstract
In [1], Eckel et al. proposed using a convex-profiled pressure side region close to the tip, known as belly, as an effective method of extending the operating range of low-speed axial compressor rotors. In the literature, circumferential grooves are another well-described technique for improving the stable working range of a compressor rotor. No research has been conducted to date to determine which modification is more effective and how they interact when used together.
This paper numerically investigates the influence of circumferential casing grooves and near tip modifications on the flow field in the tip region of a highly-loaded, low-speed axial compressor rotor. The simulated rotor consists of a hybrid blade configuration with a tandem profile in the mid-span region and single blade profiles near the endwalls. The single blade profile close to the tip features three different convex-profiled elements, which differ in their respective thicknesses. The aim of the numerical analysis is to explain the interaction of the secondary flow phenomena when applying the circumferential grooves and the belly geometries. For this purpose, eight different axial positions of the circumferential groove are investigated for each of the three belly configurations. These are arranged in 10 % increments from −7 % to 63 % along the axial rotor tip chord. The potential of the concept is evaluated by a numerical investigation in the 1.5-stage setup with an inlet guide vane and tandem stator.
It is shown that a circumferential groove can further increase the operating range for all belly configurations when positioned axially correctly. In this respect, equalization of the near-casing deceleration in the circumferential direction leads to an extension of the stall margin with both modifications. Concentrated regions of low momentum fluid with a large extent in radial direction should be avoided consequently. A tip vortex stability factor is introduced to quantitatively evaluate this effect. The operating range can thus already be estimated in a first approximation at the design point.
In general, the groove and belly should be positioned where the tip leakage vortex meets the pressure side of the adjacent blade. If the groove is used together with the belly, the leading edge of the former should be situated at the location of maximum thickness of the near tip modification. The effects of the circumferential groove and the belly are then superimposed. If using only one modification, the belly appears better suited for ensuring an extension of the operating range while maintaining high efficiencies.
Dynamic Modeling and Degradation Study of a Hybrid Electric Power System for Urban Air Mobility
Authors: Donateo Teresa , Ficarella Antonio , Spada Chiodo Ludovica 
Published: September 2023

Abstract
This investigation presents a model-based degradation study of a Hybrid Electric Propulsive System in parallel configuration for Urban Air Mobility. Literature studies on hybrid-electric aircraft are mainly devoted to the sizing and the management of hybrid systems and the energy flows are usually analyzed with a steady-state model applied to each flight phase while the role of hybridization in supporting the engine during transients has been only hinted at. In fact, the faster response of the electric drive can be used to stabilize the rotor shaft so that the dynamic response of a hybrid electric powertrain is quite different from a conventional configuration. To this scope, a complete model of the power system including the coaxial rotors, the mechanical connection, the turboshaft engine, the electric motors, and the battery is used in the present investigation. The inputs of the model are the pilot commands and the speed components of the rotorcraft. The model is used to highlight the degradation of the dynamic response as a consequence of component deterioration, with different degradation criteria, both on the thermal and the electric path. The results obtained in this work revealed how the torque contribution of the electric machine not only reduces fuel consumption and improves the dynamic response of the powertrain as already known in literature but also reduces the effect of engine deterioration on the performance of the power system. The outcome of the investigation is a dataset useful to train machine learning algorithms for the diagnostics and prediction of the state of health, especially considering the lack of experimental data in this field.
Optimized Casing Treatment to Improve Stall Margin Under Circumferential Pressure Distortion in a High-Speed Axial Flow Fan
Authors: Li Yihan , Li Jichao , Du Juan , Liu Yang , Zhang Min , Zhang Hongwu 
Published: September 2023

Abstract
Aviation fans often suffer from the negative effect of distorted inflow on the stall margin. An effective way to solve the aforementioned problem is to apply casing treatment for extending the stall margin. However, previously, it was observed that casing treatments often increase the stability but with reduced efficiency. Therefore, an optimized axial slot casing treatment (OPCT) was designed that improves the stall margin by 7.31% with 1.97% efficiency gain at a design speed of 100% in a high-speed axial flow fan. The stability-enhancing effect of the OPCT under distorted inflow was further evaluated. Based on the airworthiness standard, the distorted inflow with 9% of composite distortion index was tested with OPCT. At 100% design speed, the OPCT can still improve the stall margin by 6.19% with an improvement in efficiency by 1.63%. The stall margin improvement due to the OPCT at 80% design speed can be up to 13.31% with an improvement in efficiency by 0.87%. The unsteady measurement results under distorted inflow indicate that the location of the shock wave obviously moves forward towards the blade tip leading edge as the rotor blade rotates out of the distorted region. This in turn leads to an earlier stall of the fan compared to that at uniform inflow. When the OPCT is applied, although the fluctuation of the tip leakage vortex in the slot region is stronger than that in smooth casing, the strength of the interaction between the shock wave and tip leakage flow can be suppressed, and the location of the shock wave at the distorted region is pushed back towards the blade passage by the OPCT. Consequently, the transition from the disturbance downstream of the distortion region to the stall inception is postponed. It was experimentally discovered that the casing treatment does not alter the instability mode of the fan, and the fan eventually surges, which is consistent with B parameter value of 2.942. However, under the distorted inflow, B parameter can be reduced from 2.942 to 0.863, and thereby, the instability mode of the fan is changed from surge under uniform inflow to stall under distorted inflow. The aforementioned phenomena can guide the instability prediction when the fan encounters distortion or casing treatment is applied in future studies.
Non-linear Regression Model for Fitting Experimental Emissions Data
Authors: Ahrens Denise , Traub Sebastian 
Published: September 2023

Abstract
The measurement and reporting of non-volatile Particulate Matter (nvPM) emissions is now integral to aircraft engine emission certification. Akin to other gaseous emissions, CAEP11 sets a new LTO based standard. So far, the question how nvPM emission can be corrected for ambient conditions has to remain open. Addressing this, combustor rig tests may be consulted, where performance parameter such as Air-to-fuel ratio, pressure and temperature can be varied independently. However, results from selected tests may be misleading as nvPM emissions may show measurement uncertainties within actual sensitivities. The paper provides a novel approach utilising experimental data to investigate the prevailing sensitivities at different operation conditions and derive applicable correction factors. This methodology makes use of the fundamental assumption that each change measured in nvPM emissions is explainable with the relative change in combustor AFR, the combustion chamber inlet pressure P3, and combustor inlet temperature T3, for a given combustor design running on the same fuel. Computing the relative changes between all measurements of the same test for all performance and emission parameters enables the fitting of a nonlinear regression model to the experimental data. The fitted function consists of the product of the relative change of the performance parameters to the power of polynomial exponents. The methodology has the potential to be applied to a wide variation of emissions data obtained from different sources as combustor rig tests as well as from engine emission tests. The paper concludes with a first application of the methodology to experimental engine emissions data and a short discussion on AFR sensitivity. In order to set-up a more broadly applicable model nvPM pathways and mechanisms and their dependencies must be better understood helping to identify relevant parameters, e.g. characteristic AFR in the nearfield of the fuel spray nozzle.
Historical Developments in Fan Technologies for Aeroengines
Authors: Benini Ernesto , Mistry Chetankumar , Wadia Aspi R. 
Published: September 2023

Abstract
This paper reports on the evolution of fan aerodynamics starting with turbofan engines featuring moderate by-pass ratios (between 4 and 6) up to Ultra-High-By-pass-Ratio (UHBR) configurations which are currently being developed. The implementation of key enabling technologies for fan blades are discussed from a historical perspective, spanning from high-aspect ratio fan blades with part span shrouds (or snubber) to wide chord fan blades, from un-ducted (UDF) and propfan open rotors to highly swept blades. With continuous requirements for higher thrust and lower fuel consumption, bypass ratio demand has also increased leading to UHBR configurations (by-pass ratios higher than 13). Almost all engine companies have responded to these challenges by reducing the number of fan blades. To meet future performance and stability requirements of lower fan pressure ratios, new fan architectures are discussed.
Annular Liquid-Film Fragmentation Process Sheared by Developed Turbulent Gas Flow
Authors: Kamada Yoshiaki , Inoue Takuya , Wang Zhenying , Inoue Chihiro , Senoo Shigeki 
Published: September 2023

Abstract
Erosion by water droplets is a critical issue in steam turbines, but the detailed process is still unclear. In the present study, we investigate experimentally the sequential steps of liquid sheet instability when subjected to a developed turbulent gas stream, followed by droplet fragmentation. To control the boundary-layer thickness of the turbulent gas flow that determines the thin water-film instability, we employ a pipe flow. The liquid sheet slowly propagates along the inner wall and the gas flows at speeds of up to 100 m/s in the center. The liquid sheet sheared by the turbulent gas flow destabilizes intensely owing to both Kelvin-Helmholtz (KH) and Rayleigh-Taylor (RT) instabilities. At the trailing edge of the pipe, of thickness of 2 mm, the sheet stagnates. Liquid ligaments then elongate in the axial direction, which eventually disintegrate into droplets.
We construct a theoretical model describing the liquid-film instability, the properties of the ligaments, and the droplet size dispersed downstream. The circumferential wavelength at the trailing edge is determined by the RT instability, which is accelerated by the shear force of the gas flow and gravity. The ligament diameter is determined by the conservation of flow rate. We show that the droplet size dispersed downstream can be predicted from the diameter of the ligament. We also indicate the validity of this theory based on our experimental results and demonstrate its application to a practical condition.
Film Cooling Effectiveness and Flow Structures of Butterfly-Shaped Film Cooling Hole Configuration
Authors: Jeong Jin Young , Jo Ye Rim , Kang Min Seok , Kang Young Jun , Kwak Jae Su 
Published: September 2023

Abstract
Film cooling is applied to various high-temperature components of a gas turbine and greatly affected by the shape of the injection hole. Numerous studies have been conducted to investigate various film cooling structures to increase the film cooling effectiveness by inducing coolants toward the surface. In this study, a butterfly-shaped film cooling hole configuration is proposed, which consists of a pair of asymmetric fan-shaped holes installed adjacently. This novel structure enhances film cooling effectiveness by utilizing the interaction between coolant jets from the asymmetrical film cooling holes.
In this study, the film cooling effectiveness of the butterfly-shaped hole configuration was experimentally characterized under low-speed conditions on a flat plate, and was compared with that of widely used fan-shaped holes. Also, a numerical study was conducted to understand and visualize the flow structures generated by the butterfly-shaped film cooling configuration. As a result, an anti-vortex structure was observed near the hole exit. The film cooling effectiveness of the butterfly-shaped hole configuration was also compared with that of the fan-shaped hole. The film cooling effectiveness of the butterfly-shaped hole configuration was 1.9% higher than that of the optimized fan-shaped film cooling hole at its optimized condition. It was also found that the film cooling effectiveness increased with the blowing ratio for the butterfly-shaped hole configuration. It is expected that the film cooling effectiveness can be further improved by adjusting the shape parameters of the butterfly-shaped hole.
Vibro-Acoustic Responses and Pressure Signal Analysis for Early Surge Detection in a Turbocharger Compressor
Authors: Silvestri Paolo , Niccolini Marmont Du Haut Champ Carlo Alberto , Reggio Federico , Ferrari Mario Luigi , Massardo Aristide Fausto 
Published: September 2023

Abstract
High-speed centrifugal compressors may be exploited to pressurize fuel cell systems. Nonetheless, due to fuel cells significant interposed volumes, compressor behavior can lead to severe vibrations related to fluid-dynamic instabilities during part load operating conditions. In particular, surge strongly limits centrifugal compressors’ stable operating region when moving towards low mass flow rates due to a change in system working point. Therefore, compressor dynamic response must be adequately characterized for early surge detection. To this aim, a dedicated experimental activity was conducted on a vaneless diffuser turbocharger coupled to a solid oxide fuel cell emulator plant; compressor evolution towards surge was investigated. Several signal processing techniques were applied to pressure signals as well as vibro-acoustic responses to better predict compressor behavior and classify its status as stable or unstable.
Cepstrum, cross-correlation and wavelet transform have been identified as suitable techniques to define precursors able to detect incipient surge conditions early. By means of cross-correlation function, propagation phenomena in the ducts can be investigated to assess how they interact near compressor low-mass flow rate unstable conditions. Cepstrum provides a convenient way to determine pressure signal spectrum distortion in terms of further periodic components onset; they may be due to complex system responses generated by transient phenomena; indeed, it allows identification of hidden anomalous contributions in system response which may arise in incipient surge conditions. Wavelet transform was performed on both structural and pressure response signals to observe their dominant energy contents temporal evolution; indeed, such spectral pattern time-dependent variation can detect the rise of unstable conditions.
By doing so, a complete system identification is performed which allows a deeper investigation of the physical phenomena involved; moreover, a more complete set of surge precursors extracted from different probes’ physical signals were defined. The results obtained provide original diagnostic insights for monitoring systems suited to perform early surge detection. Indeed, compressor instability prevention can extend its operating range, performance, and reliability to allow better integration with other plant components. Finally, cepstrum application for compressor instability identification can be regarded as a novel method in the fluid machinery field.
Design, Multi-Point Optimization and Analysis of Diffusive Stator Vanes to Enable Turbine Integration Into Rotating Detonation Engines
Authors: Grasa Sergio , Paniagua Guillermo 
Published: September 2023

Abstract
Pressure gain combustion is considered a possible path toward improved thermal cycle efficiency and reduced carbon emissions. However, ad-hoc turbine designs are required to maximize the thermodynamic potential; the new turbomachinery should be suited for the oscillations in flow conditions generated by the detonation combustor, which are very different from conventional gas turbines. This manuscript investigates the design, optimization, and analysis of diffusive stator vanes operating under large inlet flow angles in the high subsonic regime.
First, the design methodology is outlined, focusing on the geometric requirements to ingest high Mach number flow and the parametric modeling of the endwall and the 3D vane pressure and suction sides. Then, the impact of the inlet flow angle on the flow field and vane design is studied through a multi-point, multi-objective optimization with three different inlet angles, performed using steady Reynolds Averaged Navier Stokes simulations. Remarkable reductions in pressure loss and stator-induced rotor forcing are attained while maintaining an extensive operating envelope and a high amount of turning. Finally, several design guidelines are provided based on analyzing the optimized geometries and the comparison with those optimized for axial inflows.
Development of a Hybrid Tabulated-Virtual Chemistry Model for Pollutant Formation Prediction
Authors: Luu Tan-Phong , Darabiha Nasser , Fiorina Benoît 
Published: September 2023

Abstract
In the context of energy transition, numerical models that can accurately describe pollutant formation are needed for designing novel combustion chambers. However, due to the stiffness of the chemistry describing pollutants, modeling chemical kinetics is a challenging issue. Simplified models such as flamelet-based tabulated chemistry allow a good resolution of the heat release rate and the temperature profile but usually fail in predicting pollutants in practical burners. The virtual chemistry method, recently developed at the EM2C laboratory, is an alternative technique to the tabulated chemistry method. It consists of first building a learning database using detailed chemistry solutions. Then, properties of “virtual” species and reactions are optimized to target key variables of interest. In that way, two virtual schemes are obtained: a main scheme trained to retrieve the main properties of the flame such as temperature and the flame speed, and a satellite scheme trained to retrieve pollutant formation. Although the virtual chemistry method is substantially cheaper than detailed chemistry, further cost reduction can be achieved. To that end, an innovative hybrid method coupling flamelet-based tabulated chemistry for the flame structure and virtual satellite mechanism for pollutant prediction is presented. By tabulating the inputs of the satellite mechanism as a function of the mixture fraction and progress variable, the number of transported variables is reduced by a factor of two. By comparison with detailed chemistry, flamelet-based tabulation, and virtual chemistry, the hybrid model is validated through the simulations of 3 configurations: 1-D freely-propagating premixed flames, 2-D premixed slot burner, and 2-D flame-vortex interactions. Results show the good performances of this model.
Investigating the Suitability of Multi-Scroll Volutes for Improving Spanwise Incidence of Mixed Flow Turbine Rotors With Varying Blade Cone Angles in Automotive Turbocharging Applications
Authors: Martin Peter , Spence Stephen , Stuart Charles , Starke Andre , Leonard Thomas , Geron Marco 
Published: September 2023

Abstract
Targets to reduce fuel consumption and reduce CO2 emissions have been met using engine downsizing and turbocharging. In automotive applications, it is important that the turbocharger responds well to transient events and operates efficiently at both the design and off-design conditions. A Mixed Flow Turbine (MFT) is not constrained to a radial inlet blade angle allowing the peak efficiency to be shifted to a lower U/C_is, providing additional freedom to the designer. As the MFT leading edge varies in radius, the spanwise incidence angle also varies, leading to additional separation on the suction surface (SS) of the blade near the hub because of increasingly positive incidence, which is most noticeable at off-design conditions.
A multi-scroll volute was previously paired with a MFT with 45° blade cone angle (Λ) which generated non-uniform spanwise flow that improved efficiency at off-design at the cost of peak efficiency. The current study identified the range of blade cone angles that benefitted from a multi-scroll volute to reduce incidence at the hub region. A numerical investigation was conducted which determined the influence a multi-scroll volute can have on MFTs with varying levels of blade cone angle.
When the MFT with large blade cone angle (Λ = 60°) was paired with a multi-scroll volute, the efficiency improved by 2.2%pts at design and 0.5%pts at off-design conditions. The incidence improved and the mass flow rate increased at the hub region. The MFT with smaller blade cone angle (Λ = 30°) had performance losses at both operating conditions because the multi-scroll volute increased incidence within the hub region, which reduced the peak efficiency by 1.3%pts. The off-design condition had an excessively positive incidence angle which was further increased at the hub region by the multi-scroll volute. This resulted in a 0.8%pts reduction in off-design efficiency. The multi-scroll volute concept was shown to offer efficiency improvements for MFTs with larger blade cone angles through better management of the non-uniform spanwise velocity distribution at rotor inlet.