bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Investigations of Sector-Shaped Hybrid Fluid Film Thrust Bearing for High-Speed sCO2 Turbomachinery
Authors: Patel Ashutosh , Kumar Pramod 
Published: September 2023

Abstract
This paper proposes a sector-shaped taper-flat hybrid gas film bearing for high-speed supercritical carbon dioxide (sCO2) turbomachinery that experiences high axial load. In addition to proposing this new design, the study also develops a predictive model for hydrodynamic, hydrostatic, and hybrid gas film thrust bearings. The model takes into account the orifice coefficient of discharge at various clearance heights in order to accurately capture the impact of pressurized injection of bearing gas on hydrostatic and hybrid bearing lubrication. Full-fledged 3D CFD analysis is carried out to validate the accuracy of the model. The study also finds that there is an optimal orifice location, which varies with speed, at which the load on the bearing reaches its maximum value. The study investigates the effect of the tilt of the leading edge of the recess on the load capacity and stiffness of the thrust bearings. The developed model accounts for the fluid velocity field, hydrodynamic pressure, bearing load capacity, stiffness, reaction torque, and power losses within the lubrication layer due to the fluid shear.
Robust Design of a Vaned Diffuser in a Centrifugal Compressor Stage With a High Load Impeller
Authors: Agnolucci Andrea , Marconcini Michele , Biliotti Davide , Toni Lorenzo , Baroni Alberto , Romani Luca , Arnone Andrea 
Published: September 2023

Abstract
Centrifugal compressors are suited for high pressure applications. Generally, many centrifugal compressor stages are stacked together in order to guarantee the overall pressure ratio implying larger machines. With the aim of more compact machines, it is possible to design high pressure ratio stages, thus reducing the total number of components. In this case, the impeller rotates at high speed to obtain an adequate work input. That in turn implies that the flow exits the impeller and enters the following diffuser with a large tangential velocity.
Vaned diffusers are thus more effective in this context to obtain a high-pressure recovery keeping the widest operating range. Ideally, fixed diffuser vanes should not have any gap between the tip of the blade and the casing however, due to assembly tolerances, the diffuser has a clearance impacting performance.
On these premises, this paper presents the optimization of a vaned diffuser exploiting artificial neural networks as a surrogate model. The maximum clearance value allowed by the manufacturing tolerances is taken into account during the optimization. The optimized geometry shows a large improvement in the diffuser performance ensuring an extended operating range. Moreover, the optimized diffuser is more gap insensitive, since the performance lay in a narrow range of variability demonstrating an improved robustness with respect to the clearance values. The performance of the optimized geometry is assessed within a preliminary experimental campaign carried out on the compressor stage. Finally, the developed design rules are validated by means of an extensive experimental campaign on a full-scale model test.
Experimental Investigation of Forced Intermittency in Swirl-Stabilised Turbulent Methane-Air Flames
Authors: Rocha Nuno , Talibi Midhat , Mohni Izwan , Beita Jadeed , Balachandran Ramanarayanan 
Published: September 2023

Abstract
Thermoacoustic oscillations continue to be a major problem affecting combustor performance and operation in gas turbines. Acoustic forcing is often employed to simulate dynamical states in a combustor, however reproducing intermittent-like behaviour can be difficult. This paper, for the first time, reports a forced intermittent behaviour in a laboratory-scale, swirl-stabilised combustor burning methane-air mixtures that mimics the configuration of an industrial gas turbine. A frequency sweep using loudspeakers to generate velocity fluctuations identified 90, 220 and 320 Hz as the dominant frequencies of the burner. Amplitude sweeps were performed at these same frequencies and the flame response was obtained. At low forcing amplitude the acoustic flame response was in the linear range and the dominant frequency of the response matched the forcing frequency. Intermittency was observed beyond an amplitude threshold at 320 Hz, consisting of bursts of high-amplitude oscillations corresponding to broadband excitation around the forcing frequency. Further amplification resulted in excitation of a low frequency band. Wavelet analysis showed intermittent bursts to have a frequency signature matching the forcing frequency, and pressure and heat release oscillations were found to be coupled. In low amplitude regions between bursts, signals were found to be decoupled and response at forcing frequency was weak. Phase-space reconstruction showed acoustic modes to be consistent with those of self-excited flames found in literature. The outcomes of this work could provide further understanding on the causes of intermittency and its relationship with limit cycle oscillations.
Thermodynamic Optimization of the Cooling System of a High-Pressure-Turbine Blade
Authors: Fiedler Barbara , Muller Yannick , Voigt Matthias , Mailach Ronald 
Published: September 2023

Abstract
Designing efficient cooling systems for the highly thermally loaded blades and vanes of high-pressure-turbines requires minimizing cooling air consumption while maintaining cooling effectiveness. The complex interactions of the multiple design parameters makes the deterministic identification of the optimal cooling design extremely challenging. The application of mathematical optimization algorithms is key to automatically identifying the optimal design accompanied with enormous potential to significantly reducing development time.
In the present study, the cooling mass flow rate of a three-pass cooling system with rib-roughened walls is minimized while approximately preserving the initial temperature distribution in the blade component. Since the geometrical optimization is applied in the preliminary design phase, a 1D, correlation-based flow solver is coupled with a simplified 3D thermal model for the numerical evaluation of the cooling system performance. Prior to the optimization, a Monte-Carlo based sensitivity analysis of the system behaviour to geometric variability is performed. For the optimization the evolutionary, metamodel-assisted algorithm AutoOpti, developed at DLR, is used. Hereby, two sampling strategies, different base population sizes as well as the influence of a reduction of the parametric model are discussed. In all optimizations a significant reduction of the cooling mass flow rate of up to 12 % was achieved, whereas interestingly different design changes were observed between the optimizations.
Fleet Experience of SGT-600 (24 MW) DLE Gas Turbine With Over 60% H2 in Natural Gas
Authors: Berg Anton , Magnusson Rikard 
Published: September 2023

Abstract
Hydrogen is one of the leading options for energy storage from renewables and surplus electricity, as well as a major constituent in various streams in the chemical industry. Due to the difficulties in controlling the combustion of hydrogen, it is often flared or used for heat and power generation.
Siemens Energy identified the 24 MWe SGT-600 3rd generation DLE (Dry Low Emission) gas turbine as most suitable for a site where high hydrogen operation was requested due to its size, and two units were awarded to Siemens Energy for operating on natural gas mixed with hydrogen. The project was sold with emission guarantees of 25 ppmv dry NOx@15%O2 for hydrogen levels up to 60%, but also with the guarantee that the unit should not trip if the hydrogen level was higher than 60% (including up to 100% hydrogen).
The commissioning of the units during 2022 proved that NOx emissions below 20 ppmv15 (ppmv dry NOx@15%O2) could be achieved for hydrogen contents between 40–60%, which was well below the guaranteed values. Operation of the units have also been verified for hydrogen contents up to 90% at 50% load.
The 3rd gen. DLE burner is also used in the 33MWe SGT-700 and the 62MWe SGT-800, which will also benefit from the development of the increased SGT-600 hydrogen capability. The results open the possibility of using H2 rich gas more widely in all gas turbine configurations using 3rd gen. DLE burner.
Comparison of Subspace Identification Methods for Modal Estimation of Bladed Disks
Authors: Jorajuria Corentin , Esteves Cécile , Gibert Claude , Thouverez Fabrice 
Published: September 2023

Abstract
Bladed disks are critical parts of aeronautic turbojet engines requiring numerous dynamic analysis tests to fully achieve their design process. This work presents subspace state-space identification techniques for estimation of modal parameters of bladed disks using realistic although numerically generated test case data. Indeed, modal testing of bladed disks can exhibit high modal density leading to modal estimation issues. This study focuses on subspace state-space identification framework as it is an efficient way to process vector valued time series and thus to estimate modal parameters in a context of high modal density. In order to evaluate the techniques of interest, a versatile modal model has been specifically implemented to simulate data representative of full scale rotating aeronautic fan modal tests. This model is easily adjustable allowing to evaluate the identification methods in a more or less severe estimation context. The performance of the investigated methods are discussed and compared with the prescribed parameters of the model. Moreover, different techniques to estimate the order of the associated state-space model are reviewed and tested over several simulated configurations. Finally, a method to evaluate the uncertainties over the modal parameters using covariance of estimator results and pseudospectrum computation is proposed and discussed over the investigated test cases.
The Effect of Progress Variable Definition on Hydrogen Containing Fuel Gas Turbine Combustion Simulation Prediction
Authors: Kancherla Raghu , Giel David , Vogel Gregory , Yaquinto Matthew 
Published: September 2023

Abstract
The global push towards carbon free economy is more in focus than ever before, and there has been huge acceleration to the research and development of hydrogen fueled combustors to minimize or eliminate CO2 release into the environment. Therefore, there is a strong need for the community to investigate, verify the applicability, and validate various methodologies and models that are being used for Natural gas combustion simulation. Progress variable is a very critical parameter in modeling and understanding the combustion physics, and any inappropriate definition can lead to inaccurate predictions when applied in combustion simulations. The progress variable in the current combustion models is often defined based on the experiences of the model developers. Generally, these definitions are based on species composition in the reaction or based on the enthalpy of the reacting system. However, a universally accepted definition for progress variable is not available. This paper evaluates the impact of various definitions of progress variables and reactors, such as 0D, 1D strained flame, and 1D freely propagating flame, on FGM-RANS solution of a trapped-vortex gas turbine combustion system with methane and high-hydrogen fuels. The CFD simulations in this work are performed using Star-CCM+.
Adaptive Fuel Split Control for DLE Combustion Systems
Authors: Magnusson Rikard , Berg Anton , Nilsson Marcus , Kiss Maté 
Published: September 2023

Abstract
The industrial gas turbines must perform better and better with regards to emissions, fuel flexibility, load and ambient range and combustion stability. Industrial gas turbines with DLE (dry low emission) systems use a fuel split control to cope with most of these problems, but with the higher demand for fuel flexibility, it is not enough with fixed split values or quasi-active controls based on the root mean square (RMS) values of predefined filtered frequency bands of the combustion dynamics. An improvement can be done with the help of newer and better measurement systems with online spectral information and data acquisition capabilities used to control the fuel split. This will also allow accommodating a larger range of fuel compositions, variations in gas supply pressure and ambient operating conditions without additional gas turbine downtime.
This paper describes how the new adaptive fuel split control, named “emission control trim” has been implemented and tested in a full-scale gas turbine rig and field tested at a customer site with Siemens Energy 3rd generation DLE gas turbines.
The following full engine tests with the same burner type showed that the “emission control trim” controller is working as it was designed to, with safety measures included and the possibility to keep a NOx emission set point at different loads with optimized combustion dynamics. It also has the possibility to lower the emissions with up to 25% at certain conditions and still have the combustion dynamics under control. The robustness of the system has been satisfactory over the tested period.
The results open the possibility of using the system more widely in all gas turbine configurations using DLE burners.
Analytical Prediction of Acoustic Resonance in Labyrinth Seals
Authors: Mahlstedt Janek , Fischer Felix , Wein Lars , Seume Joerg R. 
Published: September 2023

Abstract
Labyrinth seals are an essential and widely used component of modern turbomachines and can contribute significantly to their efficiency. Their often complex geometry is intended to generate pressure losses to reduce leakage flow. Acoustic resonances can occur within the cavities used for this purpose, which, when combined with a matched source of excitation, can result in high noise emissions and vibration excitation of the mechanical components of the labyrinth seal. In this work, an analytical model is developed and validated with numerical data to predict the resonant frequencies of axial standing waves within the cavities for propagating acoustic modes. The model is based on a RANS simulation of the cavity flow and determines the axial characteristics of the acoustic modes propagating upstream and downstream at several axial positions. Two acoustic wave equations commonly used in turbomachinery applications are used to analytically estimate the sound propagation within the seal’s cavity. An overall axial wavelength across the cavity is estimated based on the wavenumbers determined at each axial position and a resonance condition is formulated to iterate the modal resonance frequency. This modeling approach is used to estimate the resonant frequency of an axial standing wave for different acoustic mode orders. Comparison of the models with numerical results in a generic labyrinth seal for three aerodynamic operating points shows a deviation between the analytically and numerically determined resonant frequency of approximately 0.68% on average with resonant frequencies occurring at Helmholtz numbers between 58.69 and 64.20 at Mach numbers of up to 0.4. Numerical setup studies regarding the influence of turbulence models, turbulent production limiters, and modeling of rotational effects on the turbulence in RANS simulations yielded in a deviation smaller than 1% of the numerically predicted resonance frequencies.
Corrosion of Rare-Earth Disilicate Environmental Barrier Coatings in Gas Turbine Environments—Part 1: Steady CFD Model
Authors: Cha Chong M. , Golden Robert A. 
Published: September 2023

Abstract
The volatization of ytterbium disilicate (YbDS) by water vapor is studied by experiment and computational fluid dynamic (CFD) simulation. The experiments use a standard testing procedure where a low Mach number, high-temperature steam jet impinges upon a YbDS coupon. The present, steady-state CFD model is based on the Deal & Grove theory of the thermal oxidation of silicon [1], generalized here to account for the second-order surface chemical reaction of YbDS and the fully-coupled gas transport processes of the outer zone. Comparisons between the experiment and CFD model include the coupon surface recession profiles at 150 hours of steam exposure and across three test conditions where the jet temperature has been varied within the range 1100–1450 ° C. The CFD model is also used to predict the scaling of the recession rate with the coupon surface partial pressures, jet exit velocity, and furnace operating pressure. These sensitivities are of primary importance for the gas turbine application, but are currently difficult to assess by experiment and the original Deal & Grove model alone.
Design of a Magnetic Array for Engine Order Excitation of Rotating Disks
Authors: de Brett Matthew , Schwingshackl Christoph , Edwards Garry 
Published: September 2023

Abstract
Blade vibration can significantly impact the performance, maintenance and safety of aero engines, hence a large research effort focuses on modelling the dynamic responses of bladed disks and blisks to ensure safe operation. Computational analyses of disk dynamics — for instance, quantifying mistuning or characterising friction dampers — require validation through experimental measurement of disks when subjected to realistic excitations. Engine order excitation constitutes a major source of steady forced vibration of fan and compressor disks during normal engine operation. In engine order excitation the disk rotates past a static pressure field, caused by upstream disturbances in the flow, that varies periodically with angular position. The blades of the disk rotate through the pressure field and are subjected to a periodic force. This paper presents the design of a magnetic array intended to simulate engine order excitation of a rotating disk. A model is developed that predicts the forces exerted between collections of magnets with simple geometries. The model is validated and used to predict the force applied to a rotating blade by different magnet array configurations. The aim of the research is to identify a magnet array with optimal forcing characteristics and the model is used to evaluate potential configurations according to some specified design criteria.
An Algorithm for Starved Lubricated Journal Bearings With Optionally Locked Lube Oil Feed Grooves
Authors: Hagemann Thomas , Vetter Daniel , Schwarze Hubert 
Published: September 2023

Abstract
Starved lubrication occurs intentionally or unconsciously in many journal bearing applications. However, the determination of its concrete distribution in a journal bearing is rather complex as the different lube oil feed grooves interact with each other due to their connection by the lubricant flow along the pad surfaces and the periodic geometric property of the entire bearing. A robust numerical procedure to determine the lube oil distribution between the different feed grooves in a starved lubricated fixed-pad journal bearing is presented as an extension to Elrod’s cavitation algorithm. The enhanced algorithm partly integrates flow rate boundary conditions into the linear system of equations for the solution of Reynolds equation and the transport equation. A strategy to couple these flow rate boundary conditions with the iterative procedure to determine the binary cavitation index is proposed. In particular, the algorithm enables an appropriate modeling of lube oil grooves with locked oil supply including the consideration of groove-specific dissipation or design features like bleed notches. The novel algorithm is implemented as a sub-module of a thermo-elasto-hydrodynamic (TEHD) bearing code and validated with test data for a high-speed two-lobe bearing with embedded arc. Furthermore, a comprehensive parametric study provides an insight on the robustness of the implemented numeric procedure. Results, current limitations and possible extensions to the algorithm are discussed.
The Effect of Hydrogen on Non-Linear Flame Saturation
Authors: Æsøy Eirik , Indlekofer Thomas , Bothien Mirko R. , Dawson James R. 
Published: September 2023

Abstract
We investigate the effect of increasing levels of hydrogen enrichment on the non-linear response and saturation of premixed bluff-body stabilised methane/hydrogen flames submitted to acoustic forcing. The thermal power is kept approximately constant to preserve the nozzle velocity whilst increasing the flame speed through hydrogen enrichment. The flame describing function (FDF) is measured for a fixed frequency and three hydrogen-methane blends ranging from 10% to 50% by power, corresponding to 25% to 75% by volume. We show that when the flame is forced at the same frequency at similar power and bulk velocities, increasing levels of hydrogen enrichment increase the saturation amplitude of the flame. To provide insight into the flame dynamics responsible for the change in the global nonlinear response and saturation amplitude, the flames were investigated using high-speed imaging in combination with OH-PLIF at a range of forcing amplitudes. At lower hydrogen concentrations, the flame is stabilised along the inner shear layer and saturation in the heat release rate occurs at lower forcing amplitudes due to large-scale flame-vortex interactions causing flame annihilation as observed in several previous studies. At increased levels of hydrogen enrichment, distinctly different flame dynamics are observed. In these cases, the flame accelerates and propagates across to the outer shear layer which acts to suppress large-scale flame annihilation during roll-up of both the inner and outer shear layers. This results in a coherent increase inflame surface area with forcing amplitudes significantly increasing the saturation amplitude of the flame. These results show that high levels of hydrogen increase the amplitude response to acoustic forcing leading to higher saturation amplitudes. This suggests that substituting natural gas with hydrogen in Gas Turbines increases the risk of much higher limit-cycle amplitudes if self-excited instabilities occur.
Ignition of Various Lubricating Oil Compositions Using a Shock Tube
Authors: Abulail Matthew , Cooper Sean P. , Sandberg Matthew G. , Petersen Eric L. 
Published: September 2023

Abstract
With new restrictions imposed on gas turbine efficiencies and power outputs, lubricating oils are used at higher temperatures and harsher conditions leading to potential, unintended combustion. To establish an understanding of a lubricating oil’s resistance to combustion, a new spray injector system was utilized in the High-Pressure Shock Tube Facility at the TEES Turbomachinery Laboratory at Texas A&M University. Two gas turbine oils (Mobil DTE 732 and Castrol Perfecto X32), a base mineral oil, and a surrogate (n-hexadecane) were tested at post-reflected-shock conditions at equivalence ratios near 2.5. Castrol Perfecto X32 was also characterized at an equivalence ratio near 1.2. All of the lubricating oils displayed ignition between temperatures of 1152 and 1383 K and near atmospheric pressures. To characterize combustion, two different definitions of ignition delay time were considered: sidewall OH* chemiluminescence and sidewall pressure. Both definitions were used to create temperature-dependent correlations for each of the lubricating oils. In general, both definitions provided similar results within the accuracy of the measurements. One trend from the data herein is that the brand-name oils (Mobil DTE 732 and Castrol Perfecto X32) provided ignition delay times that were similar to each other but slightly larger than the corresponding mineral oil and n-hexadecane results. This difference could be attributed to the additives that are present in the brand-name oils.