bluuebunny/crossref_metadata_2025_split huggingface dataset:
Real Gas Effects on Autoignition Delay and Laminar Flame Speed Predictions for Direct-Fire sCO2 Combustion
Authors: Kinney Cory , Velez Carlos , Martin Scott , Forte Annalisa , Nassini Pier Carlo , Zucca Alessandro , Vasu Subith S. 
Published: August 2024

Abstract
Supercritical carbon dioxide (sCO2) power cycles are promising for improving the carbon footprint of natural gas based electricity generation through sequestration while also offering efficiency and size advantages; however, the cycle conditions pose challenges to in-situ experimental measurements needed for validating models due to extremely high working pressures (around 300 bar). There is still significant uncertainty in the best practices for modeling real gas effects at these conditions and the implications for optimal burner designs and configurations.
In this study, the impact of real gas models on chemical kinetic mechanism predictions for autoignition delay times, laminar flame speeds, and counterflow diffusion flames is assessed for conditions relevant to direct-fire sCO2 cycles. It is demonstrated that real gas effects result in a 15–20% decrease in ignition delay times at these conditions for the mechanisms studied. Additionally, laminar flame speed simulations were performed in Cantera to investigate the real gas effects and transport modeling with relevance to predicting flashback and blowout limits in combustors. Switching from an ideal gas equation of state to real gas only resulted in a 5–10% increase in flame speed predictions; however, flame speeds increased by a more significant 20–30% when a high-pressure transport model was implemented. The importance of equation of state consideration in chemical kinetic mechanism design is then discussed. The authors conclude that variations in density and transport properties are most important for simulation accuracy.
Blade Designs for Improved Multi-Phase Performance in sCO2 Compressors; Part II - Optical Diagnostics in sCO2 and Experimental Evaluation With Particle Image Velocimetry
Authors: Fernandez Erik , Gabriel-Ohanu Emmanuel , Vesely Ladislav , Kapat Jayanta , Hosangadi Ashvin , Cooper Paul 
Published: August 2024

Abstract
This paper presents the second part of a study in which the leading-edge and suction surface of a compressor blade was modified to delay onset of phase change for sCO2 compressors operating near the critical point. Using a first-of-its-kind apparatus for the measurement of sCO2 flow fields, Particle Image Velocimetry (PIV) is used for local flow field measurements of two compressor blade geometries: the modified “biased-wedge,” and a conventional constant thickness blade. Utilizing the developed hardware, the feasibility of a simple, laser-based diagnostic for qualitatively measuring liquid phase regions, is also presented. The design of the optical diagnostics rig, a discussion of numerous challenges, and necessary considerations involved in performing optical-based measurements like PIV, in sCO2, are discussed. Velocity field measurements for the modified compressor profile show a much lower suction peak compared to a conventional blade. These results validate numerical results at the tested conditions, where the suction side profile of the biased wedge works to minimize the local pressure gradient.
Characterization of the Swirl Velocity Field and Atomization Processes of a Lean Burn Gas Turbine Fuel Injector
Authors: Sahu Vivek , Jamod Preetam , K. P. Shanmugadas 
Published: August 2024

Abstract
The present work investigates the swirl velocity field and atomization processes of a lean burn gas turbine swirl injector. The injector includes a complex configuration of a pilot mixer and a main mixer with a mass flow split ratio of 31:69. The pilot and main mixer include a set of counter-rotating axial and radial swirlers of different swirl numbers. Incoming airflow from the pilot’s axial and radial swirler is separated by a prefilmer venturi. Jet in swirl cross-flow scheme is employed for injecting fuel into both pilot and main mixer. Particle image velocimetry (PIV) techniques are employed to investigate the air swirl flow field and atomization processes at the exit of the injector. Axial plane and transverse plane particle image velocimetry (PIV) experiments are conducted to obtain the three-component velocity of the gas phase at selected planes. Experiments are carried out at various air-to-liquid ratios ranging from 7.30 to 30.45, keeping the liquid flow rate constant, with three injector configurations: pilot, main, and pilot plus main mixer. Individual recirculating flow structures are observed in the case of both pilot and main mixer, and they merge to form a central toroidal recirculation zone in the case of the full injector assembly. The air momentum dominates the overall spray topology and droplet dispersion at higher air-to-liquid ratio conditions for all three configurations. Spray PIV measurements highlighted significant radial drifting of pilot spray droplets under the influence of main mixer swirl streams. Overall, swirl sense is controlled by the main mixer, and significant slip velocities are observed at the shear layer regions.
Parametric Study on the Duct Intake Reflection Coefficients for Fan Flutter Analyses
Authors: Perez Jose Miguel , Corral Roque 
Published: August 2024

Abstract
The coupling between the acoustic reflections of the intake and the fan vibration characterizes the fan flutter of aero-engines. Close to the intake cut-on/cut-off condition, the reflection of the intake is most significant and key to the appearance of the so-called flutter bite.
Rienstra’s model has been thoroughly used in this work to compute the amplitude and phase of the reflected acoustic wave in a zero-thickness intake. The methodology is based on the Wiener-Hopf technique, whereby close expressions involving the complex integration of several kernels are given. Because of its complexity, its usage has been hindered since Rienstra provided just a few results as examples.
Moreover, the existing results in the literature are intended for noise analyses, and the phase information of the reflected waves, which is critical for aeroelastic applications but irrelevant for most acoustic analyses, needs to be included.
This work presents a thorough data set of the modulus and phase of reflection coefficients for a zero-thickness intake, including variations of the inlet Mach number, inner-to-outer radius ratio, and circumferential wavenumber as a function of the dimensionless frequency. In addition, a simple-to-compute model is presented to help the characterization of the modulus and phase of the dominant waves scattered in the intake of aero-engines, easing the assessment of the flutter-bite occurrence.
Dynamic Characterization of a Low Drag Power Loss Tilting Pad Journal Bearing
Authors: Bradley Roarke , Delgado Adolfo , San Andrés Luis 
Published: August 2024

Abstract
High performance turbomachinery relies on tilting pad journal bearings (TPJB) for high-speed operation while maintaining acceptable stability margins. However, TPJBs can produce large drag power losses that increase with machine size and surface speed. In a conventional configuration, the unloaded pads will drag on the surface of the shaft while, presumably, having a minimum impact on the bearing dynamic performance. The effects of removing unloaded pads from a TPJB has been studied before but research has yet to describe the force coefficients of this bearing type. The present work aims to evaluate the effect on dynamic forced performance and power loss of a 4-pad TPJB configured as load on pad (LOP) and having the unloaded pad, opposite to the loaded pad, replaced by a fixed insert with a large clearance. The replacement insert has a significantly larger clearance (∼14.4 × nominal clearance), effectively making this a 3-pad bearing. The original 4-pad bearing was previously tested, hence allowing for an accurate comparison before and after the pad exchange. The experiments include operation at both 6 and 12 krpm (shaft surface speeds of 32 m/s and 64 m/s, respectively) with unit loads equaling 345 kPa, 862 kPa and 1379 kPa. The bearing is supplied with ISO VG 46 oil (inlet T = 50 °C) and flow equaling 50%, 100%, and 150% of a nominal flow set for the original 4-pad bearing. For the nominal flow and a unit load of 345 kPa, the modified bearing shows a substantial decrease in power loss, ∼38% at 6 krpm and ∼10% at 12 krpm. At the largest flow rate, however, the drag power loss reduction is less apparent, just ∼2% at 12 krpm. The 3-pad bearing shows signs of lubricant starvation due to the large volume created by replacing the unloaded pad with the large clearance fixed pad. Incipient sub-synchronous vibrations (SSV) appeared at 100% nominal flow, at both 6 and 12 krpm and a unit load of 1379 kPa. SSV hash is a common occurrence in bearings supplied with a low flow rate and low loads. During tests with the lowest flowrate, the modified bearing produced very small stiffness (∼75% reduction) and damping (∼57% reduction) coefficients along the unloaded direction, most likely due to lubricant starvation.
Improved Compressor Performance Prediction Using a Vortex-Reactive Turbulence-Model Extension
Authors: Mimic Dajan , Mahlstedt Janek , Herbst Florian 
Published: August 2024

Abstract
The accurate modelling of secondary-flow dynamics is a key aspect of reliable performance predictions for turbomachinery. This is due to the effect of secondary flow on the aerofoil boundary layers, as well as the overall energy budget.
In this paper, we assess the predictive performance of a vortex-reactive turbulence-model extension using integral performance data of a multi-stage compressor test rig. The model extension provides a more accurate prediction of multi-stage compressor characteristics, especially if cavities and squealer tips are considered. This is achieved by mitigating an underprediction of near-choke mass-flow rates, and of the total-pressure ratio and isentropic efficiency near stall. The analysis shows that this is achieved by affecting the formation and propagation of secondary flow.
Wake-Separation Bubble Interaction Over an Experimentally Simulated Axial Compressor Blade Under Low Reynolds Number Flow
Authors: Irps Thomas , Kanjirakkad Vasudevan 
Published: August 2024

Abstract
For the most part, the flow over an axial compressor blade is subjected to adverse pressure gradients. Under low Reynolds number conditions, the flow could separate off the blade surface especially on the suction side, where it first accelerates to a peak velocity and then decelerates to a higher-pressure condition at the blade exit. The ‘separation bubble’ thus formed could, in many cases, trigger flow transition from laminar to turbulent conditions on reattachment further downstream of the point of separation. Since blade profile losses depend on the transition location, the modification of the separation bubble due to any upstream generated disturbances is of great interest. In this paper the interaction between incoming wakes, that are generated periodically, and the separation bubble that exists on the blade surface is investigated. Results are presented from wind tunnel experiments conducted over a flat plate that is imposed with a surface pressure profile similar to that over a highly loaded compressor blade. The periodic wakes are introduced using an upstream bar passing mechanism that produces representative unsteady parameters. The spatial and temporal development of the flow along the mid-span region is described with the help of particle image velocimetry-based flow mapping at a relatively low Reynolds number of 210,000. Several interesting observations were made, but the most important one is the existence of a slow-moving thickened boundary layer feature that convects immediately behind the wake. While the calmed region that forms behind this feature can suppress the bubble, the thickened boundary layer itself is seen to have high unsteadiness and it contributes to a large momentum deficit.
Non-Synchronous Vibration: Characterisation of the Aerodynamic Disturbance and its Dependency on Local Tip Clearance
Authors: Tharreau Pierre , Hardy-Falch Magnus , Stapelfeldt Sina , Brandstetter Christoph 
Published: August 2024

Abstract
Non-synchronous vibrations (NSV) occurring near the stall boundary pose a major challenge to the design of safe and efficient compressors and fans. NSV occurs when aerodynamic disturbances which develop close to the aerodynamic stability limit couple with blade vibration. Despite its importance and a recent rise in research efforts, the exact nature of the aerodynamic disturbance is unknown and there are no robust modelling and prediction methods available. A characteristic parameter crucial to the successful prediction of NSV is the circumferential propagation velocity of the aerodynamic disturbance, which determines whether lock-in with a structural vibration mode is possible. This paper uses detailed aeroelastic measurements and coupled time-accurate simulations on the open-test-case composite fan ECL5, which was experimentally tested at Ecole Centrale de Lyon in project CATANA, to characterize the aerodynamic disturbance and determine the mechanisms responsible for its circumferential propagation. As part of this, the influence of blade-to-blade variations in tip clearance size is investigated.
The disturbance is identified as a vortical structure which originates in the tip clearance flow close to the leading edge and is convected across the passage to the trailing blade where it triggers the release of a new vortical structure. The tip clearance plays a crucial role in setting the convection speed across the passage and also influences the transfer mechanism across the blade. Overall, a larger tip clearance is found to increase the speed and strength of the disturbance in the subsequent passage. The implications of tip clearance variations for vibration are modelled and the results confirmed in the experimental analysis. It is shown that blade-to-blade variations in the tip clearance act as a form of aerodynamic mistuning, leading to vibrations in multiple nodal diameters.
Numerical Analysis and Design of New Exhaust Section Downstream of Constant Volume Combustor
Authors: Gallis Panagiotis , Misul Daniela Anna , Boust Bastien , Bellenoue Marc , Salvadori Simone 
Published: August 2024

Abstract
Pressure Gain Combustors (PGC) exploit either their iso-choric or detonative combustion increasing the theoretical thermal efficiency of a Gas Turbine cycle. On this basis, a Constant-Volume Combustor (CVC) is developed operating with rotary valves while the chamber is fed with mixture of air and liquid iso-octane. The present work describes the numerical design of a new exhaust section after the CVC. First, the design parametrization of the transition duct and the resulting Design of Experiments (DOE) of 81 samples are introduced. Every case is numerically tested and the election of the best sample is based on the pressure losses and the oscillations characterization. In the last part, the LS89-VKI vane is added at the aft part of the best transition duct and the ensemble exhaust system is analysed with the help of transient CFD analysis. Every component is evaluated in terms of pressure losses and oscillations, while the operation of the vane is investigated in details. The results of the stator’s performance are discussed and compared with steady experimental data. During a CVC period, the cycle average outlet flow angle remains close to the outlet metal angle denoting promising results for the future numerical analysis of the subsequent rotor.
Tribological Performance of Soft Magnetic Composite Materials for Gas Turbine Applications
Authors: Suman Alessio , Fortini Annalisa 
Published: August 2024

Abstract
Soft magnetic composites (SMCs) have gained attention in the last years of their usage in more compact and powerful electromechanical systems. These materials are used to combine the application of metallic material to the capability of generating (without external supply) a magnetic field. Automotive and aerospace technologies push the applications of these original materials to even higher power and mechanical stress to reduce the number of components, the size, and, in turn, the weight of complex systems. Considering gas turbine application, SMCs were formerly developed for bearings, but in the last decades, the new era of gas turbine electrification (e.g., hybrid-electric fly) has determined the need for mechanical improvement of such materials. At the same time, the reliability of soft magnetic material has to be discovered to avoid failure and reduce the maintenance schedule.
In the present work, tribological behaviors of SMCs were investigated by standard wear tests. In particular, two different types of SMSc were prepared through the powder metallurgy technique. Tests were conducted by a tribometer using a ball-on-disk configuration in lubricated condition. The effect of oil temperature and applied load were investigated. In addition to the tribological tests, an extensive post-mortem analysis was conducted on the worn surface to recognize the mechanisms responsible for the deterioration of the materials. The results showed the effects of the oil viscosity on the useful operating life of the SMCs. Removal mechanisms depend on the load conditions, and the proper selection of the oil characteristics and load was assessed.
Experimental Analysis of the Micro-Sized Particle Adhesion in a Subsonic Stationary Cascade
Authors: Suman Alessio , Zanini Nicola , Piovan Mattia , Pinelli Michele 
Published: August 2024

Abstract
The particle deposition phenomenon represents the critical factor for studying gas turbine fouling. Solid particle adhesion drives the contamination of the relevant surfaces of the power unit. Both compressor and turbine sides are affected by the performance degradation over time due to the contaminant adhesion. The performance losses are strongly related to the contaminants’ characteristics and the gas turbine’s operation. Solid contaminants like soil or soot coupled with environmental conditions such as temperature and humidity modify their stickiness, determining a difficult to predict effects on the gas turbine operation and reliability. According to the blade shape, surface characteristics, and flow field structures, particle impact determines the deposited layer growth process or the detachment/spallation of the previously deposited layer. This work analyzes the sticking and detachment processes generated by the interaction between solid substrate and micro-sized solid particles. The tests are carried out on a stationary linear subsonic cascade in which soil and soot particles are used to contaminate the flow field. A sensitivity analysis of the relative humidity values has shown how a slight increase in the relative humidity values determines the increment of the deposited contaminants by an order of magnitude. Blade regions and the overtime assessment of sticking and detachment processes are also assessed. Microsized contaminants interact with the blade surface, modifying the shape of the leading edge and the surface roughness, especially on the pressure side.
Modelling of Casing Containment in an Overspeeding Turbine Stage
Authors: Eryilmaz Ibrahim 
Published: August 2024

Abstract
This manuscript is on the structural characterization of a turbine casing in terms of blade containment. Gas turbines experience unintentional blade loss events in service for various reasons such as fatigue and the engines are certified on the basis that these events do not cause hazardous outcomes. In certain conditions, such as permanent loss of load after a shaft or transmission failure, the turbine stage(s) may accelerate to excessively high speeds creating the possibility of disk burst.
An LS-DYNA explicit finite element model of a bullet to plate experiment have been prepared with flat nose projectiles. Following the method verification, the procedure was applied for a turbine stage with a single layer and a multi-layer casing to assess the performance of those in a blade-off at overspeed conditions when turbine experiences permanent loss of load. The intention with the multi-layer casing is to allow penetration within the first layer to dissipate the energy of the fragments and to contain them within the second layer.
Calibration and Validation of a Novel Particle Rebound and Deposition Model
Authors: Jiang Lei-Yong , Patnaik Prakash , Suzuki Masaya 
Published: August 2024

Abstract
Environmental particles (e.g., sand, volcanic ash and other airborne dust) ingested into a gas turbine engine can significantly reduce engine performance, and even lead to complete power loss. This is particularly true for helicopters during taking-off, hovering, and landing. To predict this degradation quantitatively, a novel particle rebound/deposition model has been developed based on measured particle rebound characteristics and non-dimensional parameter analysis from more than seventy particle deposition tests relevant to engine hot-sections.
The model was calibrated/validated with the experimental data, where sand particles impinged on square ceramic coupons at a velocity of 215 m/s and a temperature range of 1300–1580 K. Numerical simulations were carried out for these testing cases, and the particle impact rate on the coupon for each test case was obtained with a user defined function. With the particle impact rates on the coupon, the experimental particle deposition rates based on the total released particles, and the operating conditions, the coefficient of a defined model formulation was obtained. The calibrated rebound and deposition model was compiled and linked to the flow solver, and the predicted results were in good agreement with the experimental data. With added model functions, the distributions of deposited particle parameters on the coupon surface are provided.
The Effect of Rotor Leakage Flows on Hot Gas Ingestion
Authors: Dawson Michael G. , Atkins Nicholas R. 
Published: August 2024

Abstract
The geometry of a turbine rotor disc has spaces through which parasitic leakage flows can leave the upstream disk cavity, affecting the purge flow required to maintain acceptable cavity temperatures. This paper presents a study of the effects of leakage flows through gas turbine rotors on hot gas ingestion into rotor-stator cavities. By modulating the area of rotor leakage paths, it is shown experimentally and numerically that, as expected, rotor leakage increases the purge flow required to maintain acceptable average cavity temperatures. However, the study also shows that through disc leakage exacerbates the effects of non-uniform ingestion, increasing the magnitude of local peaks in surface temperature for a given cavity average value. An empirical low-order model is proposed for the flow in the rotorstator cavity which captures the sensitivity of seal effectiveness to purge flow when leakage is present.