bluuebunny/crossref_metadata_2025 huggingface dataset:
A Free Streamline Model for Fully Separated Turbomachine Flows
Authors: Prasad Dilip
Published: September 2023

This paper describes the use of the free streamline approach to determine flows in fully separated cascades, and to thereby provide a rational basis for estimating the performance of axial turbomachinery at severely off-design conditions. On the assumption of two-dimensional, incompressible flow, the free streamlines that bound the separated region are determined using the hodograph method, in which the methods of complex analysis are used to define a tractable numerical problem. The resulting jet-wake flow profile at cascade exit is then presumed to undergo mixing at constant-area, from which performance parameters for the cascade can be determined. The proposed method is verified by comparison against flat plate cascade solutions and by checks against momentum conservation. Validation of the free streamline approach is carried out by comparison against several cascade configurations for which experimental data and simulation results are available. In general, the predictions based upon the present theoretical model are found to be good, especially for negative incidences such as those that occur in the compressor section of an engine operating at sub-idle conditions. This suggests that the present approach can be used in the estimation of turbomachinery performance maps far from the design point, especially during early design phases.
Development of a 300 MWe Utility Scale Oxy-Fuel sCO2 Turbine
Authors: Moore J. Jeffrey , Neveu Josh , Bensmiller Jason , Replogle Cole , Lin Jianliang , Fetvedt Jeremy , Cormier Ian , Kapat Jayanta , Fernandez Erik , Paniagua Guillermo
Published: September 2023

A 300 MWe direct-fired supercritical carbon dioxide (sCO2) oxy-fuel turbine is being developed that will burn natural gas-fired, coal syngas and even hydrogen mixtures capable of 1,150°C turbine inlet temperature at 300 bar. This design will significantly improve the state-of-the-art for thermal efficiency and results in a high-pressure stream of CO2 with 98%+ carbon capture, making the power plant near emission-free and more efficient than Natural Gas Combined Cycle (NGCC) plants with carbon capture. This power plant will be capable of burning coal through gasification and cleanup of the synthesis gas (syngas). sCO2 power cycles are a transformational technology for the energy industry, providing higher efficiency heat source energy conversion for conventional and alternative energy sources. Oxy-fuel sCO2 cycles take these advantages even further, utilizing higher firing temperatures, improved efficiency, and simpler carbon capture strategies. This turbine will require cooled turbine nozzles and blades as well as advanced thermal management systems to accommodate these high temperatures. The cooled blade heat transfer correlations required new test programs at higher Reynolds number than air-breathing gas turbines for impingement, serpentine, and pin-fin regions. Novel blade optimization was performed to maximize aerodynamic efficiency, while minimizing cooling flows. A turbine layout was generated utilizing individual combustor cans with cooled liners feeding into a 6-stage axial flow turbine with cooled stator nozzles and turbine blades. The case design and thermal management preliminary design will be described. Experimental heat transfer and material testing will be presented as well. Finally material test results both with and without thermal barrier coatings at 780°C will be presented.
Coarse Droplet Measurement at the Last Stage Stator Exit of a Four-Stage Scaled Steam Turbine Using an Optical Backscatter Probe
Authors: Sasao Yasuhiro , Senoo Shigeki , Bosdas Ilias , Kalfas Anestis
Published: September 2023

Size and velocity distributions in polydisperse coarse droplets are important to estimate and reduce erosion damage and wetness losses in wet steam turbines. Diameters and velocities of coarse droplets are measured by an optical backscatter probe downstream of the last stage stator in a four-stage model steam turbine at the rated condition.

The droplet diameters distribute in the range from 30 to 90 micrometers. The Sauter mean droplet diameter is about 57 micrometers and the maximum droplet diameter is 88 micrometers. The corresponding Weber numbers are 11.4 and 17.6 respectively in the Sauter mean and maximum diameters. The Weber numbers are generally consistent with calculated values by both Kelvin-Helmholtz and Rayleigh-Taylor instability models. The mass flow rate and number of the coarse droplets is larger in the wake region from the stator, because the coarse droplets might be mainly generated by atomization of water films and rivulets on the stator. The larger droplets in diameter over 60 micrometers tend to axially deflect from steam flows. The Sauter mean diameters are slightly larger downstream from suction surface of the stator. The droplet velocities distribute in the range up to 40 m/s. The smaller droplets have the higher velocities as expected. Mean velocities are also consistent with predictions by the instability models. The measured number density distributions of coarse droplet diameters and velocities with the spatial resolution could improve the accuracy in models for blade erosion and wetness loss from models based on mean or maximum droplet diameter.
Economic Evaluation of Ceramic End Milling Tools for Rough Milling of Blisks Made of Inconel 718
Authors: Zimmermann Richard , Fricke Kilian , Ganser Philipp , Bergs Thomas
Published: September 2023

High-pressure compressor stages in modern aero-engines are commonly designed in the integral blisk (“blade-integrated disk”) configuration, due to their advantages regarding weight, blade density and freedom in airfoil design over conventional blade-disk assemblies. These components consist of thin-walled airfoils with high-aspect ratios, which result in a large weight percentage of the workpiece to be removed before achieving the final part. Because of their complex shape and tight dimensional tolerances, most of the machining is done by the conventional cutting technologies turning and milling. Thereby, first near-net-shape blanks are turned and then the blades are milled with end milling tools. As operating temperatures in the compressor section are rising to reach higher engine efficiencies, blisk components are increasingly made of heat-resistant superalloys (HRSA) such as Inconel 718. Machining processes for these components made of difficult-to-cut nickel-based alloys exhibit low productivity and high tool wear, which can be attributed to the conventionally used cemented carbide tooling. Innovative ceramic cutting materials such as SiAlON can be produced in the form of end milling tools and offer the potential to increase the productivity in the time-consuming roughing operation significantly. Due to the high hardness at elevated temperatures, the cutting velocity vc can be increased by a factor of 20 when using ceramic end milling tools compared to conventional strategies with cemented carbide. However, these innovative cutting tools are rarely applied in series production, which may be due to their high costs compared to cemented carbide tools. This study, therefore, aims at evaluating the economic potential of SiAlON end milling tools for roughing operations of blisk components made of Inconel 718. To reach this goal, a blisk milling process was designed and executed with both tool configurations, tool wear and machining times of all operations were measured and tool life as well as machine costs are evaluated.
Cooling and Sealing Design of Instrumentation Ferule for Annular Combustors
Authors: Rajesh Mavuri , Stefano Gori , Arun Ampi K
Published: September 2023

The Annular combustion system usually has an instrumentation system like flame detectors, spark plugs, and pulsation probes in the primary zone to investigate flame stability, ignition, and measuring the acoustic pulsations. The primary zone experiences the highest temperatures and sealing & cooling of an instrumentation system is critical to get timely combustion performance data. The location, and sizing of the instrumentation ferule that encompasses the instrumentation system are to be properly evaluated such that to avoid hot combustion gas injection in the ferule. The objective of the paper is to document the cooling and sealing requirements around the instrumentation ferule such that real-time data acquisition is maintained, and the structural integrity in terms of LCF/Creep life is the main design driver. System of flow, thermal, and structural is carried out to investigate unsteady flow recirculation/local peak temperatures to properly size the required cooling flow. The sealing flow injected around the ferule should be aligned with the core combustion flow to minimize the pressure drop. The first part of the paper presents the baseline configuration experiences the high static temperatures downstream of ferule system, then the thermal analysis process map is used to investigate different cooling schemes and impact on metal temperature reduction due to the conduction effect. The structural integrity of ferule system is also analyzed to verify the design requirements for various designs. To validate the numerical process, two potential configurations (Lifted ferule and Flat ferule) have been tested at high pressures and high temperatures keeping instrumentation around the ferule system. The numerical model is further tuned by implementing the film effectiveness and validated with test results. The flat and lifted ferule numerical results are quite aligned with the experimental data at most of the locations, however flat ferule shows a better cooling effect compared to the lifted system. Also, the paper presents the temperature spread on the ferule system from the experimental test data and presented it for all three configurations. The results indicate that the temperature spread is around 0 to 8% for the baseline and flat ferule cases, where the spread is high for the lifted ferule case. Due to limitation with current thermal process map inability to capture circumferential variation, only the test results (temperature spread) are presented.
Characteristic Secondary Flow Behavior in Ultra-Highly Loaded Turbine Cascade Under Transonic Condition
Authors: Tsujita Hoshio , Kaneko Masanao
Published: September 2023

A gas turbine is increasingly required to be enhanced in quick start capability as well as in aerodynamic performance to support variable energy output from renewable sources such as solar and wind powers. On the other hand, the diameter of core engine of a turbofan engine is demanded to be decreased for the improvement of propulsive efficiency by the increase of bypass ratio. Moreover, for the farther enhancement of the specific work output of micro gas turbines by the increase of the turbine inlet temperature, the application of a thick turbine blade will be required for the installation of any internal and external air-cooling system. These various requirements would be responded by an increase of blade loading of axial turbines.

In this study, the 3D computations were performed for the flows in an ultra-highly loaded linear turbine cascade (UHLTC) with the blade turning angle of 160 degrees under transonic condition with the assumption of steady compressible flow. The focus was on the characteristic secondary flow behavior and the associated loss generation. In the computations, the isentropic exit Mach number was varied in the range from 0.6 to 1.3 to examine the effects of the variation of shock wave formation on the secondary flow structure. The computed results for UHLTC were also examined by comparing with those observed in a typical transonic turbine cascade to highlight the characteristic secondary flow behavior caused by the increase of blade loading.
Prediction of the Influence of the Inlet End-Wall Boundary Layer on the Secondary Flow of a Low Pressure Turbine Airfoil Using RANS and Large-Eddy Simulations
Authors: Gisbert Fernando , Cadrecha David , Apoita Patxi
Published: September 2023

This paper analyses the effect of the inlet end-wall boundary layer on the secondary flow of a low pressure turbine airfoil cascade at Reynolds number 2 × 105 using RANS and implicit Large-Eddy Simulations. The results are compared against experimental data obtained at two low speed linear cascade facilities, one located at the Whittle Laboratory of the University of Cambridge and the other at the Polytechnic University of Madrid. The RANS turbulence model is the k-ω-γ-Reθt and no turbulence model has been used in the LES. An unstructured mesh of hexahedra and prisms is used, with high order elements used in the boundary layer region to better describe the airfoil shape in the LES. Two inlet end-wall boundary layers that produce different secondary flow patterns are analyzed: a laminar thin velocity profile and a turbulent thick velocity profile with several inlet turbulent intensities. The agreement between LES numerical predictions and experimental measurements of the position and intensity of the secondary vortices is excellent for both cases. RANS simulations are much cheaper in terms of computational cost and reasonably predict most of the flow features, except when the inlet turbulence is low and turbulent transition prediction becomes critical. The effect of the inlet velocity profiles and inlet turbulence on the secondary flow structure is quite pronounced. The velocity profile thickness determines the spanwise penetration of the passage vortex, and different inlet turbulence intensities modify its mixing. Higher inlet turbulence intensities lead to a decrease of the secondary losses due to the passage vortex and an increase of end-wall losses.
Overall Cooling Effectiveness of Effusion Cooled and Thermal Barrier Coated Swirl Stabilized Liquid Fueled Combustor Liner in Reacting Flow Conditions
Authors: Ozogul Hamdullah , Tin Ibrahim Edhem
Published: September 2023

The combination of effusion cooling and thermal barrier coating has enabled to reach higher combustor temperatures, hence more efficient and powerful gas turbine engines over the last two decades. Effusion cooling and thermal barrier coating are favored for their low amount of coolant demand, high effectiveness and uniform structure. Moreover, it is also utilized in afterburner systems to pursue desired thrust for sufficient time.

The main purpose of the present research is to provide overall cooling effectiveness and heat transfer calculation method for state-of-art effusion cooled and thermal barrier coated (TBC) gas turbine combustion chambers. The rig has been designed to run in a reacting flow and to provide realistic conditions of a swirl stabilized, liquid fueled can type combustor with TBC and effusion cooling. The test campaign covered equivalence ratio from 0.35 to 0.6 and with a static pressure drop of 1%. The liner is laser drilled to obtain shallow holes with an angle of 25 degrees to form the effusion cooling scheme. The hole density is set to have staggered arrays with s/d = 9, which is considered to be a high hole density for TBC coated liners. Metal temperature measurements are taken with thermocouples from five equidistant axial locations. To develop simple 1D heat transfer method, while Net Heat Flux Reduction coefficient is generated from test data, effective flow area of flame side is calculated from CFD analysis. 1D thermal solver and coefficients are validated by means of different equivalence ratio and adiabatic flame temperatures.
Analysis of the Bifurcating Duct of an Inlet Particle Separator in Transonic Flow Conditions
Authors: Castaldi Marco , Mayo Ignacio , Demolis Jacques , Eulitz Frank
Published: September 2023

To increase the reliability of turboprop and turboshaft engines in extreme operating conditions, filtering protections such as Inlet Particle Separators (IPS) can be installed at the intake. The flow inside an IPS is highly 3D and unsteady, with fluctuations especially pronounced when transonic conditions are reached. Locally, shocks can occur, increasing the pressure losses. In this paper, we aim at providing the transonic analysis of an industrial IPS designed for aerodynamic lab testing. As a first step, we define the threshold beyond which sonic conditions are reached in the boundary cross sections of the IPS, in terms of inlet total pressure and Reynolds number, by means of a 1D semi-empirical model. Second, we select a critical configuration, very close to these conditions, and we perform CFD simulations to analyze the locations and evolution of the transonic flow inside the IPS. Different models are presented, i.e. steady and unsteady Reynolds-Averaged Navier-Stokes, Detached Eddy Simulation and Large Eddy Simulation, characterized by three levels of resolution (based on the grid size). The results show the evolution of some transonic shocks: the steady-state model is only providing information on averaged quantities, while the time-resolved simulations offer a more precise overview in the time domain (velocity and Mach number fluctuations). The analysis in the frequency domain reveals the frequencies of the transonic fluctuations, which can negatively affect the IPS. Finally, we discuss three alternative designs to effectively improve the operating range and mitigate the risks related to the transonic instabilities, comparing the differences in separation efficiency with respect to the baseline case. The results prove that the optimal design choice is given by the trade-off between operating range, pressure losses and separation efficiency.
Effects of Ignition Position and Inlet Pressure on Ignition Performances of a Centrally Staged Combustor
Authors: Zhang Chi , Hu Yingqi , Wang Jianchen , Liu Yan
Published: September 2023

For a centrally staged swirl combustion chamber, ignition performance is a critical issue. Because of the significant influence of the main stage airflow located in the outer layer of the dome, fuel droplets are not easily transported to the tip of the igniter. Also, the outer air layer exerts a strong convective effect on the flame core. In this paper, we mainly explore the ignition performance of the centrally staged combustor under ambient temperature and low-pressure conditions. The effects of different spark axial positions on the ignition characteristics were experimentally investigated in the range of 30.8–70.3 kPa inlet pressure of the combustion chamber. The results of ignition fuel air ratio under different combustion chamber air pressure drop conditions were obtained.

The results show that the trend of ignition fuel air ratio with pressure drop is different under different inlet pressure conditions. When the inlet pressure was 35.7KPa and 30.8KPa, the ignition fuel air ratio increased with the pressure drop, while the trend became opposite when the inlet pressure increased to 70.1Kpa near atmospheric pressure. For the ignition position, when the igniter is located at different positions in the recirculation zone of the combustion chamber, it will directly affect the ignition fuel air ratio and even determine whether the ignition can be successful. The results showed that the best ignition performance was achieved when the igniter was located at 57.6 mm from the combustion chamber sleeve. In addition, CFD analysis was performed. The differences in ignition boundaries were further explained by analyzing the flow field and the propagation path of the ignition kernal. From the analysis results of numerical simulation, it can be concluded that when the ignition position is located in the middle of the edge of the recirculation zone, the flame propagation time to the dome of the combustion chamber can be shortened and thus a better ignition boundary can be obtained.
The Hybrid Pathway to Flexible Power Turbines: Part B, Fast Data Transfer Methods Between Varying Fidelity Simulations, to Enable Efficient Conjugate Thermal Field Prediction
Authors: Baker Mark , Rosic Budimir
Published: September 2023

The global drive towards renewable energy is imposing challenging operating requirements on power turbines. Flexible load-leveling applications must accept more frequent and demanding start-stop cycles. Full transient analyses are too computationally expensive for real-time simulation across all operating regimes so monitoring relies on sparse physical measurements. Alone, these sparse data lack the fidelity for real-time prediction of a complex thermal field.

A novel hybrid methodology is proposed, coupling data across a range of fidelities to bridge the limitations in the individual analyses. Combining several fidelity methods in parallel; low-order models, corrected by real-time physical measurements, are calibrated with high-fidelity simulations. A newly developed low-order thermal network code is used to predict the thermal field in real-time. High-fidelity flow characteristics are routinely transferred to the decoupled low-order solution. A critical enabling feature of this hybrid approach is the fast data interpolation between differing fidelity numerical simulations.

This paper evaluates a spatial Kriging method for robust data transfer between two different fidelity mesh, tested in the case of thermal profile prediction of a power turbine. Additionally, a novel coordinate-based hash mapping process is demonstrated for the fast high-to-low fidelity data transfer. Localized hashing allows independent, parallel, nearest neighbor search at significantly reduced computational cost. The demonstrated method facilitates fast mesh pairing, necessary to support the real-time hybrid method for thermal field prediction during turbine transient operation.
Experimental Evaluation of Damping for Torsional Dynamic Calculations of a Turbomachinery Shaftline
Authors: Carassale Luigi , Gillon Stephen , Pallini Giovanni
Published: September 2023

Standard torsional rotordynamics modelling of large turbines considers steady state frequency response calculations with assumed damping values for torsional natural frequencies. A degree of conservatism is applied since torsional vibration is rarely monitored or evaluated in a commercial engine. Of particular interest, and the primary focus of [1], are torsional modes in the vicinity of 1x and 2x line frequency, which are potential sources of torsional excitation in the event of an electric fault. Typical blade-rotor interaction (BRI) torsional modes for large turbine – generator shaftlines can occur close to these frequencies, requiring significant effort during the design phase to ensure adequate separation. [1] acknowledges that while significant steps have been made in recent decades to enhance prediction of torsional natural frequencies for coupled blade-rotor systems, challenges remain in estimating torsional damping, particularly for BRI modes. This paper aims to re-examine the assumed damping values currently applied.

Torsional vibration data recorded during steady state operating conditions in Ansaldo’s gas turbine test centre have been used to estimate damping of torsional modes through an algorithm involving the spectral estimation by the wavelet transform, the system identification by the eigensystem realization algorithm and an iterative clustering procedure. This paper presents a description of the test facility and torsional vibration measurements, description of the algorithm, and damping results harvested from its application for the first seven modes of the shaftline for various load conditions. Several aspects of the results are discussed, notably a comparison between measured and assumed damping and dependence of torsional damping on generator active load.
Tuning Modal Behaviour of Additively Manufactured Lattice Structures
Authors: Beghini Marco , Grossi Tommaso , Macoretta Giuseppe , Monelli Bernardo Disma , Senegaglia Ivan , del Turco Paolo , Fardelli Andrea , Morante Francesco
Published: September 2023

Thanks to the increasingly widespread additive manufacturing technology and promising properties, the use of Lattice Structures (LS) is becoming increasingly frequent. LS allows the components to be designed with tunable stiffness, which can unlock the control of natural frequencies. However, crucial challenges must be faced to integrate LS into the typical design process. In the present work, an experimental and numerical study of LS-enabled tuning of natural frequencies in mechanical components is proposed. In a first step, the difficulties arising with the large amount of FEM nodes, that are required to predict LS complex shapes in detail, are overcome by modeling LS with an elastic metamaterial whose stiffness properties are determined through ad hoc finite element analyses. After that, a simplified investigation can be conducted on the modal properties of components with fixed external shape and variable internal LS filling, based on Triply Periodic Minimal Surfaces (TPMS) lattices. In those conditions, the parameters of the LS core can be tuned to control and optimize the global modal frequencies of the entire geometry. In addition, the admissible range of frequencies can be estimated. Optimized plates results are validated through an experimental test campaign on additively manufactured specimens made with Selective Laser Melting (SLM) technology. The samples are hammer-tested with various boundary conditions while laser sensors measure the oscillation data of selected points. Finally, estimated and identified natural frequencies were compared. The described model is suitable to be implemented in an automated tool for designers.
Evaluation of Empirical Loss Models for Base Drag Prediction of sCO2 Axial Turbine Aerofoils
Authors: Kumaran R. Senthil , P. P. Sharath , Alone Dilipkumar B. , Kumar Pramod
Published: September 2023

Axial flow turbines can be efficiently designed and used in megawatt scale sCO2 closed Brayton power systems. Empirical loss models are required for design and optimization of axial turbines. Ample loss models are available in the open literature for air and steam based axial turbines. But no loss models have been reported so far exclusively for sCO2 applications. Constructing a complete loss model for sCO2 turbomachinery is farfetched until loads of data are generated from cascade tunnels and turbomachinery test rigs with sCO2 as the operating fluid medium. Unlike air and steam, which are approximated as ideal gases, sCO2 is a real gas. Nevertheless, designers and commercial turbomachinery design softwares use corrected versions of these existing loss models for sCO2 turbine design. The profile loss / base drag contributes to 50–60 % of overall losses in an axial turbine. Estimation of base profile drag is important at the beginning of the design phase of the turbine in order to maximize the power output and efficiency. An attempt has been made in this paper to evaluate some of the well proven axial turbine loss models like Ainley & Mathieson, Dunham & Came, Kacker & Ockappu, Aungier etc. for estimating base profile drag of an sCO2 axial turbine aerofoil. The aerofoil investigated in the present study has been designed for a 10 MW sCO2 axial turbine stator. Profile drag of the aerofoil was computed from full turbine 3D CFD and 3D cascade CFD simulations with sCO2 fluid medium. Turbine CFD simulations were carried out using pressure based ANSYS CFX RANS solver with SST turbulence model. 3D cascade CFD simulations were carried out using pressure based ANSYS Fluent RANS solver with SST k-ω turbulence model. sCO2 fluid properties were modelled using Refrigerant Gas Property tables generated from NIST Refprop database. It would of great interest to see if cascade wind tunnel data generated with air can be applied to sCO2 turbine design. In this context, cascade test experiments were carried out for a 10 bladed linear cascade model of the aerofoil in a high-speed cascade wind tunnel at CSIR-NAL. The aerofoil performance was investigated at the design condition and over a range of off-design conditions. The base profile drag data obtained using the loss models, CFD simulations and cascade test experiments are compared and discussed in detail. This study shows that loss models developed for air-based turbines can be efficiently used to predict base profile drag of sCO2 turbines with corrections. It is also inferred that the cascade wind tunnel data can be a useful tool to study sCO2 aerofoils.
Influence of Geometrical and Operational Parameters on the Leakage Flow of a Radial Labyrinth Seal for Application in Inward Flow Radial Supercritical CO2 Turbine
Authors: Lanjewar Saurabh Deorao , Fenil Arockia , Kumar Pramod , Gopi Pramod Chandra
Published: September 2023

Inward flow radial (IFR) turbines are preferred for small-scale power generation due to their compact and efficient design. The parasitic loss due to leakage of working fluid and disk friction at the back face of the turbine is a concern issue at smaller power scales. In the presented work, a radial labyrinth seal at the backface of the inflow radial turbine is used and analyzed to control the leakage rate. CFD studies are carried out to understand the influence of the geometric and operating parameters of the radial labyrinth seal on the leakage rate through the seal. CFD predictions reveal that for a particular pressure ratio of 1.26, the variation in axial clearance (c/s) varied from 0.025 to 0.0625, results in a ∼57.2 % increase in the leakage rate. However, the variation in height (h/s) from 0.25 to 0.75 results in a marginal 4.24 % leakage reduction. It is also observed that there exists an optimum number of teeth for a given effective seal length to improve seal performance. Furthermore, the increase in rotational speed from 10,000 rpm to 1,00,000 rpm results in a ∼67.16 % reduction in leakage rate with the temperature rise of s-CO2 through the seal by ∼62°C for the case with clearance (c/s) 0.05. The ratio Taylor to Reynolds number (Ta/Re) is found to be an essential parameter in deciding the evolution of tangential velocity. A critical value of 0.15 for the ratio is identified, beyond which the tangential velocity evolution is seen to be profound.
Gas Leak Ignition Study for 100% H2 Gas Turbine Package
Authors: Minotti Stefano , Nenciolini Andrea , Quartieri Eugenio , Rossin Stefano , Sorgonà Federico , Brekke Olaf , Holen Jens Kristian , Johannessen Bente
Published: September 2023

In the frame of CO2 footprint reduction towards energy transition, it is paramount developing solutions to safely convert existing gas turbine (GT) units to burn Hydrogen fuel blend potentially up to 100% H2. Equinor and Baker Hughes have collaborated to identify possible solutions for hydrogen fuel conversion of existing aeroderivative gas turbines. A feasibility study on an existing offshore package was carried out to understand the impact of the conversion of the GT and its auxiliary systems from a dual fuel (NG/Liquid Fuel) into a dual gas configuration (NG/100%H2) with water injection.

In-situ three-dimensional geometry scanning for the entire package, 3D model piping layout reconstruction and detailed CFD evaluation was needed for a better understanding of dispersion phenomena and ignition consequence due to H2 leakages. A sudden rupture of a fuel gas system tubing connection was considered the most severe failure that could occur inside the turbine enclosure during the gas turbine operation.

To shed additional light on the potential consequences of such events, several simulations of hydrogen leak dispersion were carried out using advanced computational methods like CFX and FLACS for ignition. Leakages were considered with different location, orientation and rate, and simulations results for dispersions and ignition on flammable clouds were compared including potential transition from deflagration to detonation. Potential development areas were identified to reduce the probability of such scenarios, including innovative technical solution both for installed fleet and for the next generation GT.
Impact of Engine Degradation on Contrail Formation of Long Range Aircraft Trajectories
Authors: Navaratne Rukshan , Laskaridis Panagiotis
Published: September 2023

Aircraft contrails are considered as one of the emissions towards climate change. Trajectory optimization is one of the methods that can be used to reduce contrail formation and a strategy that can readily be implemented. However, most of the trajectory optimization studies were performed only with clean engines, and engine degradation was not considered. This work provides a novel approach to aircraft trajectory optimization problem by including engine degradation and real aircraft trajectories within the optimization framework. Impact of engine degradation on long range optimum aircraft trajectories were assessed by quantifying the difference in fuel burn and contrail formation, when an aircraft is flying on a trajectory which has been optimized for clean engines and degraded engines. For this study, Contrail prediction model was developed with one clean and two degraded engines, integrated with aircraft performance model in an optimization framework to generate optimum aircraft trajectories. The optimum trajectories generated with degraded engines were compared with the trajectories generated with clean engines. The results have shown, for long range aircraft the persistent contrails can be reduced by 2.1% with low level degraded engines having 50°C EGT increase and 3.84% with highly degraded engines having 100°C EGT increase. However, to achieve zero persistent contrail for the same route there is a significant penalty of 2.3% and 4.2% increase of fuel with low level degraded engines and highly degraded engines. Therefore, impact of engine degradation on contrail optimum aircraft trajectories are significant and in order to reduce contrails aircraft need to fly on an optimized trajectory specifically customized for the degraded engine performance.
Assessment of Part-Load Operation Strategies of Supercritical Power Cycles Using Carbon Dioxide Mixtures in CSP Plants, Including Air-Cooled Condenser Optimisation
Authors: Rodríguez-de Arriba Pablo , Crespi Francesco , Sánchez Martínez David , García Rodríguez Lourdes
Published: September 2023

This manuscript, developed in the framework of SCARABEUS project, presents an assessment of the part-load performance of a transcritical Recompression cycle running on a 80%CO2-20%SO2 mixture under different load-control schemes.

The first part of the paper describes the computational platform of the integrated system, implemented in Thermoflex but with profuse use of in-house scripts, in order to accurately describe the off-design performance of key components when operating on CO2 mixtures with non-ideal gas behaviour. These off-design models make use of performance maps for turbomachinery — provided by the SCARABEUS partners — whereas the Conductance Ratio Method employed to model the counter-current heat exchangers is calibrated with in-house tools. The paper is specifically focused on the Heat Rejection Unit, for which a specific design tool accounting for accurate heat transfer between working fluid and cooling medium (air) and for auxiliary power consumption — both in off-design — has been developed by the authors.

In the second part of the paper, different operating strategies of the power cycle are considered, based on keeping one of the following three parameters constant: turbine inlet temperature, turbine outlet temperature or return temperature of molten salts. Globally, plant operation is constrained by the need to keep the temperature of cold HTF returning to the storage system as close as possible to its rated (design) value and by the need to keep turbine outlet temperature below 450°C to avoid the installation of an external cooling system in the low pressure section of this equipment. Therefore, the trade-off between these two parameters and system net efficiency are assessed in the paper. Regarding the Air-Cooled Condenser, the optimal operation strategy of this component found to be based on a combination of Single-speed and Variable Frequency Driver fans.

The results show that the operation at constant turbine inlet temperature leads to the highest net efficiency of the power block, closely followed by the control scheme based on constant return temperature of the heat transfer fluid. Nevertheless, this latter option enables a perfect control on the other two figures of merit. As a consequence, the identification of the best operation strategy must be addressed in future works by means of a thorough techno-economic assessment considering the annual yield of the plant.
Computationally Efficient Workflow for Conjugate Heat Transfer With LES for Gas Turbine Combustors
Authors: Verma Ishan , Prasad Sudhanshu , Zore Krishna , Shrivastava Sourabh
Published: September 2023

Typical Gas Turbine Combustor (GTC) and High-Pressure Turbine (HPT) stage generally employs 10,000 to 100,000 small passages of cooling holes. Such an arrangement protects the solid walls through impingement and effusion cooling. The former provides solid wall internal cooling, and the latter helps to reduce the metal temperature by developing a thin film around it. High-fidelity simulations are primarily utilized in the industry such that accurate prediction from numerical tools can aid advancement in the performance of such machines. In this paper, a numerical study using Ansys Fluent has been conducted with Large Eddy Simulation (LES), Conjugate Heat Transfer (CHT), and radiation to explore the relative benefits of implicit and explicit fluid-solid thermal coupling.

The simulations of LES with CHT are performed for well-documented experiments of heated nozzle exhaust passing over a film-cooled plate [12]. The accuracy of the modeling approach is assessed by comparing CHT predictions of fluid velocity and solid-plate temperatures with experiments. Acceleration techniques for LES-CHT simulations are explored in this paper with an emphasis on thermal coupling, radiation, etc. The effects of mesh sensitivity and flow solution approach are presented in detail. LES-CHT results generally match the experiments at various blowing ratios both qualitatively and quantitatively. The comparisons in the paper allow the selection of best practices for CHT modeling in GTC. A generic combustor model with effusion cooling hole arrays is used in the paper to establish the workflow for modeling LES with CHT in the industrial-type combustor. Various acceleration techniques are utilized to show an overall improvement in solution performance with the same level of accuracy.
HERMES Out of Balance Excitation System
Authors: Schwingshackl C. W. , Xu Y. , Szydlowski M. , Muscutt L. , Rix A. , Patsias S. , Ondra V.
Published: September 2023

Blade off events in an aero engine are one of the most critical failures, since they can lead to significant damage to the engine, and if not managed correctly, lead to uncontained failure. During development programs detailed simulations are conducted to understand the dynamic response of bladed discs and blisks in operation, to prevent blade off events. However, blade off events do still occur on rare occasions and it is critical to be able to detect and manage them. Modelling and validation of such events is very time consuming and expensive since a blade off test is a destructive test.

To provide a more effective way of investigating a sudden addition of out of balance excitation to a complex rotor system, the Holistic Engine Rotor MEasurement System (HERMES) at Imperial College London was fitted with a purpose built Out of Balance excitation system, that was embedded in the shaft of a helicopter engine. The Out of Balance excitation system design, functionality, and commissioning test results are discussed in detail in this paper to demonstrate the feasibility of the design and highlight the level of excitation that can be achieved with such a system.
Experimental Investigation of the Combined Effects of a Split-Ring Damper and an Intentional Mistuning Pattern on a Blisk Forced Response
Authors: Rodríguez-Blanco Salvador , Pagès Valdo , Guérin Nicolas , Blanc Laurent , Dumartineix Cécile , Gibert Claude , Thouverez Fabrice
Published: September 2023

Friction damping is one of the main mechanisms for dissipating vibration energy in turbomachinery. For assembled bladed disks, friction typically arises in the blade root — in the disk interface or, for shrouded blade configurations, in the interface between two consecutive shrouds. For integrally bladed disks, where no such interface naturally occurs, additional damping devices must be designed if energy is to be dissipated through friction. Split-ring dampers are such devices: they are located in a circumferential groove under the blisk platform, and pressed onto it by centrifugal loads. At low vibration levels and/or high rotating speeds, the split ring remains stuck to the disk, while at high levels, relative motion starts and dissipates vibrational energy.

Such devices are often designed to mainly target a given nodal diameter mode of vibration. Nevertheless, designing these dampers is a challenging task. Indeed, their behavior depends on the design of the ring (dimensions, material and interface properties, etc.) and on the location of implementation; many different phenomena are involved such as centrifugal and thermal loading, mistuning, etc. Realistic contact modeling and simulation are also difficult because the dynamical behavior is non-linear due to the friction interfaces.

In this work, the effect of a split ring damper is investigated experimentally on an industrial compressor blisk in a vacuum chamber. A traveling wave excitation with a prescribed nodal diameter index is produced using piezoelectric actuators. Blade vibrations are monitored through strain gauges. Forced responses are measured, first on a tuned configuration activating the split ring damping effect on the targeted specific nodal diameter. Then an intentional mistuning pattern is implemented, so that the split ring target nodal diameter appears in different modes of the new configuration. The experiments show that resonance peaks are damped for different modes from that targeted at the tuned design stage.
Liquid Rocket Engine Inducer Pump Design and Performance Evaluation
Authors: de Oliveira Igor , Bringhenti Cleverson , Takachi Jesuino T. , Adalgiza Garcia Maia Ana , Kapat Jayanta S. , Fernandez Erik
Published: September 2023

The inducer is an axial pump that is part of the propellant injection system of Liquid Propellant Rocket Engines (LPRE). It is located at the inlet of the turbopump assembly and is critical for designing high performance LPREs. Its geometric and operational characteristics allow it to operate at low inlet pressures, delaying the appearance of cavitation and allowing the propellant tanks to operate at lower pressures. This allows the tanks to be lighter due to a reduced wall thickness requirement. The inducer also needs to operate harmoniously with the other components of the turbopump, especially with the main impeller which is located just downstream in the system. Therefore, it is important that the flow conditions at the inducer inlet and outlet are known and integrated with the turbopump and tank design. The present work aims to develop a methodology for inducer design based on literature established methods in order to obtain geometry and evaluate the flow conditions in liquid-propelled rocket engine inducer pumps. This work will assess outlet flow and pressure conditions in a way that it is possible to match them with the main impeller inlet. Performance criteria are evaluated in terms of the outlet pressure coefficient, flow coefficient and efficiency focusing exclusively on non-cavitating conditions. Two established analytical methods were implemented, one to provide inducer geometry in terms of system operational requirements and another, from National Aeronautics and Space Administration (NASA), for performance prediction based on geometrical and operational parameters. Further analysis is complemented by simulating the generated geometry in a CFD software. The methods were validated using published experimental data and the performances of the analytical, numerical and experimental results were compared. Results showed that the 3D turbulent CFD simulations provided very good agreement of efficiency. Satisfactory results were obtained for the general trends of characteristic curves over a range of flow rates and the spanwise distribution of key performance parameters near design point. The pressure coefficient was significantly overestimated. The results of the analytical models showed good agreement with simulated CFD results, indicating appropriate calibration of loss coefficients.
Experimental Characterization of Two Low Aspect Ratio Stages With Scaling Effect for Small Core High Speed Axial Compressor
Authors: Babin Cedric , Fontaneto Fabrizio
Published: September 2023

Due to the increase of the overall pressure ratio, forthcoming aircraft engine designs will exhibit smaller core dimensions, compared to the state of the art. For the high-pressure compressor, this imposes the use of blade rows with aspect ratios well below unity. To assess the validity of current design tools for novel designs, two different stages representative of the last stage of a high-pressure axial compressor have been experimentally characterized at the von Karman Institute for Fluid Dynamics. They both share an identical design methodology, same blade count and rotor tip speed but different aspect ratio, yet well below unity. The current paper proposes a comparison between the stages in terms of overall performance and rotor and stator flow fields, at different Reynolds numbers, and for different operating points. The tip-gap influence has also been assessed by comparing scaled and realistic relative tip gap sizes for the low aspect ratio stage. This study aims at providing an identification of the phenomena driving the performance degradation associated with the reduction of the aspect ratio. This description also paves the way for improvement in existing design tools through a better modelling of the critical physics in this design space.
Cyber Security in Compression Stations, A Major Issue for Pipeline Gas Transport
Authors: Bainier Francis , Latreche Abdelbaset
Published: September 2023

Cyber-attacks on hospitals are regularly in the news. Less spectacular than hospitals, cyber-security is a vital issue to ensure the flow in gas pipelines. This paper presents the methodology applied in compression stations at GRTgaz.

Trusting manufacturers is not enough; cyber-security must be understood by asset managers. Asset managers need to understand the cyber-security protections of their suppliers, and in light of this knowledge, they must organize their strategy to cover all the risks they could be exposed to.

In some cases, manufacturers do not comply with the desired requirements. In this case, solutions must be implemented for short or long periods of time, depending on the solutions implemented to cover or reduce the risk.

Most Transmission System Operators (TSOs) do not require to carry out any shift work at their compressor stations. The stations are controlled remotely from a dispatching center, and maintenance teams have remote access to ensure the effective operation. The manufacturer can also have remote access when the location of the compressor units highly impacts the gas flow.

These conditions of operation designate the level of cyber-security required for each station studied.

This paper presents the cyber-security strategy developed and implemented at GRTgaz to minimize the cyber-risks.