bluuebunny/crossref_metadata_2025 huggingface dataset:
Adaptation of VKI’s Isentropic Compression Tube Facility for High-Speed Low-Pressure Turbines Testing
Authors: Torre Antonino Federico Maria , Merli Filippo , Da Valle Lorenzo , Patinios Marios , Lavagnoli Sergio , Pintat Ludovic
Published: September 2023

This paper presents the commissioning of a newly designed High-Speed Low-Pressure Turbine (LPT) stage, operating at transonic exit Mach numbers and low Reynolds numbers, typical of modern geared turbofan (GTF) applications. The work falls within the scope of the Clean Sky 2 project SPLEEN (Secondary and Leakage Flow Effects in High-speed Low-pressure Turbines), which consists of an extensive experimental characterization of LPTs for GTFs. Geometries and measurements will constitute a valuable open-access database for the validation of simulation methods and data analysis tools.

At first, the characteristics of the research turbine are illustrated. The LPT stage is designed with an equal number of stationary vanes and shrouded rotor blades. The upstream and downstream hub cavities are purged and feature engine-realistic rim seals. The nominal operating condition of the stage is reported, along with a set of off-design conditions, obtained by varying rotor speed and purge mass flows.

The second part of the paper describes the substantial revamping of the CT3 large-scale compression tube at Von Karman Institute for Fluid Dynamics, traditionally employed for high-pressure turbine testing, now adapted to host a high-speed LPT stage.

The third section is an overview of the time-averaged and fast-response instrumentation. The test article is heavily instrumented, to maximize the amount of acquired data, while minimizing the number of blow-down tests. The dataset for each operating conditions includes aerothermal measurements in the annulus flow, in the hub cavities and in the shroud labyrinth seal. In addition, in this section is presented the design of an in-house traversing system for continuous probe traversing during the test.

Finally, the outcome of the commissioning phase is discussed, with particular emphasis on the operating conditions stability, as well as on the inlet and cavity injection uniformity. The commissioning of a traversing system for continuous probe traversing during the short-duration test is also discussed.
Research on Robustness Analysis and Evaluation Method of Inter-Shaft Bearing-Rear Journal of Low Press Turbine System
Authors: Liu Fangming , Hong Jie , Ma Yanhong , Chen Xueqi
Published: September 2023

The bearing outer ring with a flange is often used in advanced aero-engines, for the purpose of reducing weight of the engine and improve impact resistance. Cons and pros, in the working process, the rotor is subjected to complex loads such as centrifugal forces, periodic impact excitation and lateral inertia forces caused by overload on rotor. When the bearing is operating under heavy loads, a relatively large deflection occurs in the outer ring, causing deformation incoordination between the outer ring and rear journal. As a result, damage accumulation and structural failure such as wear, sliding and fatigue may occur on the contact interface.

This survey gives an insight to the deformation distribution and other contact characteristics of the interfaces in the Inter-shaft bearing outer ring — the low pressure turbine rotor system (ISBLPT) in detail, in order that stable contact in the connection structure is ensured with a reasonable structural design scheme. For typical ISBLPT, a dynamic model considering the interfacial contact characteristics of flange bolt was promoted. Then, based on possible failure modes, a contact damage assessment method and structural system robustness evaluation method is proposed.

The results show that different loads in inter-shaft bearing-rear journal system will lead to different damage failure modes, leading to uncertain damage failure modes in engine operation. And the change of interface contact characteristics will also have a significant impact on the stiffness characteristic.
Numerical Investigation of Flashing Flow in a Convergent-Divergent Nozzle
Authors: Kumar Amit , Tammone Carlotta , Haglind Fredrik
Published: September 2023

In order to reduce CO2 emissions, it is important to utilize renewable energy sources to their fullest. The output of renewable energy sources fluctuates which can be addressed through reliable storage. Liquid air energy storage can be used as an alternative energy storage method. Replacing the Joule-Thompson valve in the liquefaction process with a turbo-expander can increase the round-trip efficiency of the liquid air energy storage system. When the expansion occurs in two-phase conditions, the flow undergoes a flashing expansion with simultaneous acceleration and nucleation of vapor. To perform an efficient design of the turbo-expander, it is imperative to understand the flashing phenomenon and to model it accurately. The main objective of this paper is to identify the correct modeling approach available in commercial computational fluid dynamics software to predict the flashing phenomenon of water. Super Moby Dick and Abuaf nozzles were investigated using 2D Reynolds-averaged Navier-Stokes equations coupled with a two-phase mixture model. The Zwart-Gerber-Belamri model, Schnerr and Sauer model, and Lee model were used to model the interphase mass transfer. The results of the numerical simulations were compared with experimental data in order to evaluate which approach is the most suitable to model the flashing phenomenon. The results indicate that all models are strongly sensitive to the values of the model constants, as they govern both the onset of vapor nucleation and the vaporization rate. Therefore, in order to accurately predict the flashing phenomenon, a tuning of these parameters is needed. Overall, the error in the pressure profile increases as the inlet temperature increases, due to an increasing influence of non-equilibrium effects. Despite the fact that flashing and cavitation appear to have similar macroscopical characteristics, their underlying phase-change mechanisms are different. Additionally, owing to the absence of a wall nucleation model, it is not possible to accurately capture localized flow phenomena.
Design and Analysis of a Low Inlet Temperature Turbine Using a Supersonic Rotor
Authors: Martínez-Alvarado Luis Enrique
Published: September 2023

In this paper the study of an axial turbine with a supersonic rotor has been performed for a full stage turbine. The state-of-the art supersonic stages include supersonic stators that create shock waves that enter the rotor stage disturbing the flow. The current study proposes a semi-shockless approach which consists of using a supersonic rotor (altogether with a subsonic stator) and force the generation of the shockwave outside of the rotor passage. A method to design supersonic rotors is presented by using blade deflection angle and Mach number profiles along the blade length. Several 2D simulations using the SU2 solver were performed to evaluate the transition behavior at supersonic flow with different outlet pressures. The proposed rotor geometry allows to control by design the position and intensity of the generated shockwave. Thus, it was chosen to position the shock wave at the end of the rotor blade and to minimize its intensity. As an additional feature, the stator blades were replaced by a volute in order to reduce the quantity of components used in a full stage turbine for turbine designs having a volute just before the stator. A full stage 3D CFD analysis was performed using Ansys CFX solver. This approach has helped for the design of supersonic turbine stages with lower shock wave interactions between components.
Numerical Investigations of Reactive Reversible Blade Turbine for Slow Moving Currents
Authors: Patil Abhay , Nielson Jordan , Allison Tim , Cummings Scot
Published: September 2023

A reactive Reversible Blade Turbine (RRBT) is a drag-type hydrokinetic turbine consisting of movable blades designed to pivot around their axes to reduce drag and optimize the power coefficient. RRBT allows for reverse rotation of the opposing blades, with reduced drag during the rotation of the turbine. The blade “reverse slices” through the water to a neutral position and then rests against a stop which causes the turbine to rotate with reduced opposing drag on the opposite side of the turbine shaft. While the construction is simple, there is obscurity surrounding the quantitative gain in performance due to the proposed modification. The current study focuses on the development of a numerical model to quantify RRBT performance gain due to the reactive blade operation. The numerical model employs a sliding mesh model to simulate the single-blade motion in loaded positions to quantify the flow physics and performance estimation. The preliminary outcomes reveal power coefficient values comparable to the existing state of the art, however, peaking at a much lower tip speed ratio. The power coefficient (Cp) estimation of 0.219 using CFD agrees well with the test prediction of 0.2 at 0.32 Tip Speed Ratio. The study concludes with the evaluation and discussion of the performance gain using two different stop locations, and steady-state analysis to provide initial estimation of blade relative motion in reactive modes.
Simulating Part-Span Snubber in Low Pressure Steam Turbine Rotor With Simplified Methods for Aerodynamic and Aeromechanical Assessment
Authors: Mariotti Filippo , Lilli Leonardo , Pinelli Lorenzo , Arcangeli Lorenzo , Maceli Nicola , Brazzini Filippo , Marconcini Michele , Arnone Andrea
Published: September 2023

The present paper aims at investigating the impact of part-span snubber applied on a last rotating blade of an industrial low pressure steam turbine. The large increase in steam specific volume during the expansion forces low pressure turbine designers to develop high aspect ratio blades for the last stage. Considering also the relatively low thickness of the airfoil required to keep a high efficiency, the rotor becomes prone to aerome-chanical instabilities. Therefore, the design process must search for a tradeoff between aerodynamical and mechanical requirements that are usually conflicting. Part-span snubbers can be employed to grant additional mechanical stability to the blade thus avoiding the onset of vibrations which could lead to high cycle fatigue blade failure. In this work, a part-span snubber was introduced in the numerical model of an industrial rotor to assess its impact on the aerodynamic performance. The impact on the flow solution and on the computational cost was evaluated by using two different simplified approaches: firstly, the presence of the damping wire was introduced by means of a body forces model without any change in the aerodynamic geometry (that is blade without snubber). Then, the airfoil shape was modified to include the connections between the blade and the damping wire without a physical description of the damping wire itself which was once again modelled by the body forces. The CFD simulations were performed on hexaedrical structured grids, and a sensitivity with respect to the grid clustering near the damper devices was carried out to select a suitable tradeoff between computational cost and discretization accuracy. The aerodynamic analyses were performed with RANS computations and the flow distortions induced by the snubber are described in detail. In addition, uncoupled time domain flutter simulations were also performed to test the capability of the mesh deformation strategy to deal with snubber elements ensuring a smooth grid deformation without any cell interlacing. The simplified body forces model showed a good balance between results accuracy and computational cost, while the more complex model turned out to be more time consuming because of both the higher grid density required to correctly capture all the geometrical features of the connections, and for the higher efforts in generating a good quality mesh.
Numerical Investigations of Sector-Shaped Hybrid Fluid Film Thrust Bearing for High-Speed sCO2 Turbomachinery
Authors: Patel Ashutosh , Kumar Pramod
Published: September 2023

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

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

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

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

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

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

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

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

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

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

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

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

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

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.
Evaluation of NOx Emissions Associated to Non-Premixed Combustion of H2/Natural Gas Blends in a 40MW Heavy-Duty Gas Turbine
Authors: Carusotto Salvatore , Salvadori Simone , Baratta Mirko , Misul Daniela , Labrini Giovanni , Cardile Francesco , Toppino Marco , Valsania Massimo
Published: September 2023

The tightening in the international regulations is leading the energy production sector towards the usage of hydrogen, which is a zero-carbon energy carrier. In the field of gas turbine lifetime extension, a non-premixed approach including hydrogen blending with conventional fuels is the most promising. However, high-temperature spots might occur, thus increasing thermo-mechanical stresses and NOx emissions. Therefore, a reliable evaluation of the impact of hydrogen blends in combustors characterized by non-premixed flames is necessary. In the present work, a 40MW heavy-duty multi-can combustor belonging to EthosEnergy is investigated by means of steady, reactive simulations by using the ANSYS® FLUENT® solver. The combustor geometry is simplified by removing the casing volume, being the flow split among the holes already available. Such simplification allows for paying major attention to the chemical kinetics thanks to the use of the extended reaction mechanism for natural gas developed by NUI Galway. Simulations include the assessment of the natural gas base load configuration together with hydrogen blends up to 50% in volume, while maintaining unaltered the turbine inlet temperature. The obtained data provide some retrofitting guidelines in the field of hydrogen usage in non-premixed combustion and prove for a modified temperature field in the combustor core and close to the basket. A linear increase in NOx emission is also associated to hydrogen addition, thus suggesting the need for NOx abatement technologies (e.g., water injection).
Functionalization of All-Oxide CMC Elements Using 3D Braiding and Pressure Slip Casting for Composite Processing: Approaches to Reduce the Filter Effect of Dense Reinforcement Textiles
Authors: Jung Fabian , Grigat Niels , Vollbrecht Ben , Gries Thomas
Published: September 2023

A key element for the transition to sustainable energy lies in the transformation of the power plant fleet, which is dominated by fossil fuels, towards sustainable energy production from renewable energy sources. An increase in efficiency and reduction of exhaust gas emissions, especially the minimization of CO2 emissions, is possible through the use of new turbine materials which can withstand higher temperature levels. Oxide ceramics are well known for their high stability in aggressive environments, low density, high melting point, high stiffness and great creep resistance, but their brittleness has strongly limited their number of applications. Therefore, the implementation of fiber reinforcement using the 3D braiding process shows great potential to increase the damage tolerance of CMC and consequently the performance of thermal machines significantly.

Currently, the impregnation of 3D braids for the reinforcement of ceramic composites poses a challenge due to the high packing density of the textiles. In order to enable a homogeneous impregnation of the fiber structures using highly viscous ceramic slurries, the CMC research group at RWTH Aachen University’s Institute of Textile Technology (ITA) is investigating the combination of 3D braiding and pressure slip casting for an economical production of all-oxide CMCs. To increase the impregnation quality of dense textiles, this paper describes approaches to reduce the filter effect of braids. The results of an initial investigation into the functionalization of 2D braided reinforcement structures by using support structures and flow aids are described. The effectiveness of the impregnation ability is assessed by evaluating the residual porosity of generated green compacts via μCT analysis.
Effect of Impurities on the Compatibility of Steels in Supercritical CO2 at 450°-650°C
Authors: Pint Bruce A. , Lance Michael J. , Pillai Rishi , Keiser James R.
Published: September 2023

Direct-fired supercritical CO2 (sCO2) power cycles are a pathway to low-CO2 fossil energy but contain high levels of O2 and H2O in the sCO2. The effect of impurities on structural steels was investigated at 450°–650°C in 300 bar sCO2. The test matrix included 9 and 12%Cr ferritic-martensitic (FM) steels and conventional and advanced austenitic steels exposed for 1000–2000 h with and without additions of 1%O2 and 0.1%H2O to simulate the cycle after water removal. For FM steels, the mass gains and scale thicknesses were similar with and without impurities with the formation of thick, duplex Fe-rich scales in all cases including the observation that Fe2O3 only formed with 1%O2. For the austenitic steels, higher mass gains were observed at all temperatures with increased formation of Fe-rich oxides when impurities were added. Carbon ingress was assessed by bulk combustion analysis, glow discharge optical emission spectroscopy and measuring post-exposure room temperature tensile properties. Bulk C content was strongly increased at 650°C but not at 450° or 550°C.
3D Modelling of a Hydraulic Seal With an Oil Feed, Focussing on the Effect of the Jet on the Behaviour of Oil in the Trough
Authors: Warusevitane Achinie , Omar Rajab , Johnson Kathy , Ambrose Stephen
Published: September 2023

Hydraulic seals can be created between two shafts co-rotating at different speeds to provide a zero flow air seal across the annular cavity and these are often used as intershaft seals in aero-engines. These seals are formed between an oil filled trough on the higher speed shaft and a fin on the lower speed shaft that dips into the oil. Rotation is imparted to the sealing fluid within the trough due to the centrifugal force and the seal is able to balance a pressure difference similar to a manometer in operation. To minimize the effects of viscous heating generated by the interaction of the rotating surfaces and the oil, and to reduce oil residence time, a continuous jet-delivered oil feed is usual in aero-engine seals.

Previously published work, has established a successful modelling methodology to evaluate the maximum pressure capability of hydraulic seals when there is no oil feed. Expanding on prior studies, in this current research a relevant continuous through-flow oil feed is added to the seal modelled in Ansys FLUENT to create a model of the oil behaviour in the seal. The numerical simulations are based on a model representative of a hydraulic seal configuration investigated in an experimental study at the University of Nottingham. The CFD study shows the oil flow breaking up into droplets/ligaments followed by the oil film formed around the circumference of the trough using a Volume-of-Fluid (VOF) method when an operational differential pressure is maintained across the seal. Analysis on the size and trajectory of the droplets generated through splashing is reserved for future work.

This paper presents a quantitative evaluation of the disturbance created on the surface by the jet, demonstrating that the greatest disturbance is caused at the point of impact and the oil film thickness is only impacted by a negligible variation of +/− 0.1mm downstream. High quality CFD images of the jet impact behaviour compare with experimental results. The CFD results of the jet penetration and influence of the secondary flow are presented and discussed.

The second part of the paper comprises an investigation into thermal effects including oil-related heat transfer in the modelled hydraulic seal.
Development of a Needle Type Nanosecond Pulsed Plasma Actuator for the Enhancement of Blowout Limits in a Lifted Stabilized Combustor
Authors: De Giorgi Maria Grazia , Bonuso Sara , Mehdi Ghazanfar , Harth Stefan , Ficarella Antonio
Published: September 2023

The lift-off phenomenon in turbulent jet flames has garnered significant attention, but it also presents the risk of fuel leakage and flame blowout. Stabilizing flames remains a significant challenge in aeroengines and gas turbines. Plasma-assisted combustion (PAC) is considered a promising and active technology for practical applications as it has the potential to improve flame stability and reduce pollutant emissions. This study investigates the combustion characteristics of lifted methane/air flames using high-voltage nanosecond and sinusoidal plasma generators. While nanosecond pulsed excitation of cold atmospheric plasmas is thought to offer advantages over sinusoidal excitation, direct comparisons between the two are rare, especially in the field of PAC. A needle-type plasma actuator was used in a swirl combustor near the nozzle exit, and the electrical characteristics and LBO limits of the two different types of plasma generators were compared. The flame structures with plasma discharge were characterized using high-speed chemiluminescence from electronically excited CH* and OH* radicals. Proper Orthogonal Decomposition (POD) of CH* and OH* chemiluminescence images was used to identify the dominant flame structures using different plasma generators.
Study on the Transient Dynamic Characteristics of the Pitch-Regulated Device for Coaxilcopter Under Aerodynamic Loads
Authors: Meng Qingkai , Ke Zhifang , Wei Wei , Zhao Molei , Tu Jinghan , Yan Qingdong
Published: September 2023

Coaxilcopter with variable rotor space can dynamically adjust the parameters such as the angle of attack of blades through the pitch-regulated device, so it can adjust and change flight attitude. However, both the rotor aerodynamics and the structure of the pitch-regulated device are complex, and some of the forces generated by the rotor will act on such device in the form of a hinge moment, which would affect the realiablity of the variable pitch-regulated device and the whole craft.

Therefore, a coaxilcopter with a pitch-regulated device is designed, and the finite element numerical simulation method is promoted to calculate and analyze the transient aerodynamic loads of the rotor under different rotor spaces and unbalanced angle between blades. The hinge moment load results are further applied to the variable pitch-regulated device, and the dynamic characteristics of the variable pitch-regulated device under the action of hinge moment are further studied.

The results show that when the unbalanced angle between the left and right blade would lead to the increase of the hinge moment of both blade, and with the increase of rotor speed, the hinge moment of both the left and right blades gradually increases; When the hinge moment is applied to the variable pitch-regulated device, the steering gear load of the lower rotor is 1.57 times that of the rotor steering gear when the propeller spacing is 0.1R (R is rotor radius); When the propeller spacing is 1.2R, the actuator load of the upper rotor is 6%∼12% different from that of the single rotor mode, indicating that the influence of propeller spacing on the upper rotor is negligible at 1.2R, but the actuator load of the lower rotor is about 35% different from that of the single rotor mode, which has a significant influence. It also reveals that the aerodynamic interaction between rotors would affect the hinge moment, it provides a basis for the design of variable pitch-regulated device, and provides a reference for the variable pitch control strategy of aerodynamic performance, which has practical engineering significance.
Direct-Fired Liquid Air Energy Storage With Carbon Capture
Authors: Pryor Owen , Allison Tim , Conlon William , Thorp Joseph
Published: September 2023

This paper presents a hybrid liquid air energy storage system with a direct-fired gas turbine that incorporates liquid phase carbon capture. By liquifying air when energy prices are low, energy is able to be stored for long durations. It can then be pressurized and used as the oxidizer and primary working fluid in a natural gas combustion turbine system. By staging the post-combustion expansion, the air can be routed through a series of heat exchangers that serve to vaporize the liquid air and separate the carbon dioxide and water before the air is reheated and expanded down to atmospheric conditions. The key features of the cycle are the ability to store energy in the form of liquid air, generate power via using the liquid air in a direct-fired, high-pressure combustion process and extracting the carbon dioxide as a liquid via a staged expansion approach. A preliminary cycle model has been created to examine the potential benefits of the cycle using combustor exit conditions of 1150 °C and 30 MPa, and an intermediate extraction pressure of 1 MPa. The preliminary discharge cycle showed extremely high thermal efficiency of 65% with carbon capture and a stored energy rate of around 1.5 by utilizing liquid air as the storage medium.