bluuebunny/crossref_metadata_2025 huggingface dataset:
Historical Review and Performance Comparison of Hydrogen Oxyfuel Steam Cycles for Thermal Power Plants Considering Current Limitations of Turbomachinery
Authors: Bocandé David , Schatz Markus
Published: September 2023

To face the challenge regarding reconversion of stored green hydrogen into electricity, zero emission oxyfuel hydrogen cycles with steam as a working fluid are very promising in both thermal efficiency and large-scale applicability. Previous studies suggest that with Turbine Inlet Temperatures (TIT) of 1700 °C thermal efficiencies in excess of 70% based on Lower Heating Value (LHV) can be reached. This work starts with a historical review, from the early 80s until today, of the processes proposed in the literature which can be categorized in partly condensing and fully condensing cycles. Also, since the calculations in the literature are based on different assumptions of cycle parameters, component efficiencies and material limitations, a selection of state-of-the-art process and component parameters in the turbomachinery and power plant industry will be established to help identify the technically realizable and promising cycles. Those parameters will also be used as a common base for thermodynamic simulations of the selected cycles and can serve as a reliable reference for further calculations. The simulations show that thermal efficiencies up to 73% are achievable under conditions reflecting the present state-of-the-art and 75% in the near future, considering current development. Mitsubishi’s intercooled topping recuperation cycle shows the highest thermal efficiency with 75% based on LHV. Moreover, a higher TIT goes along with increased cooling demand and thus higher losses in the turbine, counteracting the efficiency increase due to the elevated temperature. A parametric analysis will identify the optimum operating point of each cycle regarding TIT with consideration of the cooling efficiency.
Robust Design of Herringbone Grooved Journal Bearings Using Multi-Objective Optimization With Artificial Neural Networks
Authors: Massoudi Soheyl , Schiffmann Jürg
Published: September 2023

Herringbone grooved journal bearings (HGJBs) are widely used in micro-turbocompressor applications due to their high load-carrying capacity, low friction, and oil-free solution. However, the performance of these bearings is sensitive to manufacturing deviations, which can lead to significant variations in their performance and stability. In this study, design guidelines for robust design against manufacturing deviations of HGJB supported micro-turbocompressors are proposed. These guidelines are based on surrogate model assisted multi-objective optimization using ensembles of artificial neural networks trained on a large dataset of rotor and bearing designs as well as operating conditions. The developed framework is then applied to a series of case studies representative of heat-pump and fuel cell micro-turbomachines. To highlight the importance of rotor geometry and bearing aspect ratio in the robustness of HGJBs, two types of optimizations are performed: one focusing on optimizing the bearing geometry, and the other focusing on both the bearing and rotor geometries. The analysis of the Pareto fronts and Pareto optima of each type of optimization and case study allows for the derivation of design guidelines for the robust design of HGJB supported rotors. Results suggest that by following these guidelines, it is possible to significantly improve the robustness of herringbone grooved journal bearings against manufacturing deviations, resulting in stable operation. The best design achieved ±8 μm tolerance on the bearing clearance, and designs optimized for both rotor and bearing geometry outperformed those optimized for bearing geometry alone. This work successfully identifies guidelines for the robust design of herringbone grooved journal bearings in micro-turbocompressor applications, demonstrating the strength of surrogate model assisted multi-objective optimization. It provides a valuable tool for engineers seeking to optimize the performance and reliability of these bearings.
Comparison of the Flame Dynamics of a Liquid Fueled Swirl Stabilized Combustor for Different Degrees of Fuel-Air Premixing
Authors: Kaufmann Jan , Vogel Manuel , Sattelmayer Thomas
Published: September 2023

This study investigates the flame dynamics of lean premixed kerosene combustion for two different degrees of fuel-air premixing using a swirl stabilized burner with an axially movable twin fluid fuel injection nozzle. Thermal power, equivalence ratio and atomizing air mass flow are varied systematically for both nozzle positions investigated. Measurements of the droplet size distribution at the nozzle exit are provided for all operation points. NOx emission measurements and OH*-chemiluminescence flame images show that stationary combustion characteristics significantly change with the nozzle position. Flame Transfer Functions (FTFs) are presented and interpreted for all operation points. The FTFs for the two configurations differ most in the low frequency range where the influence of the droplet dynamics is expected to be highest. For both configurations, a change in thermal power does not affect droplet size, flame shape, NOx emissions and FTF. The observed trends in response to changes in equivalence ratio and atomizing air mass flow are opposite for both configurations. NOx emissions and flame shape are independent of the atomization air mass flow in the highly premixed configuration but not in the partially premixed configuration. In contrast to this, the FTF is affected by changes of the atomization air mass flow in both configurations, but again the trends are opposite. The observed trends for the highly premixed configuration are modeled and reproduced by a change in the phase relation between the equivalence ratio fluctuations and other instability driving mechanisms.
Turbulent Flame Speed and Flame Characteristics of Lean Premixed H2-CH4 Flames at Moderate Pressure Levels
Authors: Faldella Filippo , Eisenring Sebastián , Kim Taesung , Doll Ulrich , Jansohn Peter
Published: September 2023

Carbon dioxide emissions in gas turbine power generation can be reduced by adding an increasing amount of hydrogen to the existing natural gas-fueled combustion systems. To enable safe operation, more insight on how H2 addition affects turbulent flame speed and other important flame characteristics is needed. In this work, the investigation of hydrogen addition effects on certain flame properties has been carried out in a high-pressure axial-dump combustor at gas turbine relevant conditions. OH planar laser induced fluorescence (PLIF) was applied to retrieve flame front contours and turbulent flame speed. The results show that as the concentration of hydrogen in the fuel mixture increases, turbulent flame speed and flame characteristics change drastically. Two main regimes can be identified: From 0 to 50% vol. hydrogen, the turbulent flame speed increases weakly in an almost linear fashion, while from 50% vol. to 100% vol. the trend sharply changes and the higher reactivity of hydrogen, combined with a lower Lewis number, cause thermal-diffusive instability and preferential diffusion effects to become increasingly strong, leading to very high burning rates. The presented results, help to understand and to define the relevant modifications that are necessary to successfully operate gas turbine combustor systems with high H2 content fuels.
Vibration Control of a Rotor-Magnetic Bearing System on the Moving Base Through H∞ Control
Authors: Zhang Guorong , Liu Mingyang , Zou Hansen , Wang Xikui , Xi Guang
Published: September 2023

Rotor-Active magnetic bearing (AMB) systems installed in an aircraft are supported by a moving base. An optimal controller is required to ensure the stability and ideal vibration response of the rotor-AMB system. In this paper, a rigid rotor-AMB system on an aircraft is modeled by the Lagrange principle. The moving base generates additional stiffness, damping and external forcing terms. H∞ control method is applied to design a controller and compare it with a decentralized PID controller. The flight maneuvers of the dive-pull up and horizontal turn are mainly studied. The results show that when the aircraft is in different flight maneuvers, the H∞ controller has a strong ability to resist base movement disturbance, and the rotor displacement of the H∞ controller is smaller than that of the PID controller. As the flight speed Va and maximum roll angle γm increase, the maximum rotor displacement of the H∞ controller remains almost unchanged, but the peak control current of the AMB also increases and may even exceed the maximum allowable value. Therefore, the effect of base movement disturbance should be fully considered during the design process of the AMB.
Quantitative Definition of Spray Edge With Extinction Diagnostics and Evaluation of Attenuation Coefficient for Liquid Jets in Supersonic Crossflow
Authors: McKelvy Aubrey J. , Braun James , Paniagua Guillermo , Andre Thierry , Choquet Etienne , Falempin Francois
Published: September 2023

We present a quantifiable, reproducible, and repeatable definition of the three-dimensional spray width and depth for a canonical jet in an open-source supersonic crossflow. An expanding Mach 2 dry-air crossflow is generated through a converging-diverging nozzle with a 25.4 mm by 230 mm wide throat area. A one-millimeter injector with ethanol seeding provides the liquid injection. Injector characteristics and losses are quantified through a calibrated cavitating venturi. Momentum flux ratios ranged from 0.1 to 20, and Reynolds number scaled by the injector diameter ranged from 5,000 to 40,000. A shadowgraph setup with a telecentric lens provides uniform magnification for precise and repeatable measurements from injection to 150 mm downstream of the jet. A Phantom v2012 camera with a frame rate of 20 kHz and shutter time of 285 ns was employed. Light transmittance is defined and calculated for each image pixel with a ratio method paired with no-spray images collected immediately before injection. These values are then related to an attenuation coefficient by incorporating spray width profiles collected with cross-sectional Mie-scatter imaging at multiple axial locations with a burst mode laser.
Investigation of the Effect of Blade Passing on Two-Phase Flow Within Discrete Compressor Casing Recirculation Channel Using Particle Image Velocimetry
Authors: Ribeiro Santa Cruz Mendoza Carlos Eduardo , Ozdemir I. Bedii , Helcig Christian , Gümmer Volker
Published: September 2023

Recirculation channels (RC) can improve the aerodynamic operational stability of axial compressors. The performance of compressors using RC is still unascertained during in-service operations, which might be subject to particle ingestion. Due to its inherent unsteadiness, little is known about the two-phase flow structure inside such discrete casing treatments.

The present study provides the first insight into the two-phase flow within an RC via Particle Image Velocimetry, characterizing air and particle motions. The ensemble correlation method is used to obtain averaged flow field data corresponding to different blade positions with respect to the RC, providing the periodic dynamic characteristics of the flow.

Measurements show that the blade passing frequency and operation condition impact the amount of recirculated air, the creation of stagnation and separation points, particle trajectories, and slip velocity inside the RC. As a result, this study shows that a robust RC design should consider the particle-wall interactions that can lead to significant erosion or fouling and possibility of blockage near the inlet.
Modelling and Control System Development of a Turbocharged Proton-Exchange Membrane Fuel Cell System
Authors: Cavo Matteo , Mantelli Luca , Crosa Silvia , Bozzolo Michele , Magistri Loredana
Published: September 2023

Pressurized Polymeric Electrolyte Membrane Fuel Cell (PEMFC) systems are growing among electrical power generation systems, as a zero-emissions technology. In this framework, the University of Genoa have been modelling an innovative concept for the application of low-temperature fuel cells. A turbocharged proton exchange membrane fuel cell (TC-PEMFC) plant layout with design output power higher than 200 kW is investigated. Pressurizing air before entering the stack can increase the stack efficiency and recovering the exhaust air within a turbocharger leads to better system performance. A crossflow flat pack membrane humidifier has been introduced between the air turbocharger and the PEMFC to guarantee proper operating condition into the stack. Finally, a Gas-to-Gas (GtG) heat exchanger enables cooling of the charging air while recovering the thermal energy through the turbine. In this paper, the authors present a dynamic model of an innovative turbocharged PEMFC system developed in Matlab/Simulink environment. The “RealTime” library, built by the University of Genoa, has been adopted: most of the models have been previously validated and a few new models have been customized for this application. The Matlab/Simulink model shown in this paper is used to aid the design process of the future plant, to evaluate the performance of the plant in many operating conditions and to design and test its control system. At the current stage, the model is ready to be used for on-design, off-design and transient analyses. It can be used to investigate the effect of different design choices, as well as to determine the specifications of the plant components. Some preliminary steady-state simulations are presented: the performance of the system in a wide operative range (cell currents between 150 A and 500A), with net power higher than 300 kW and system efficiency up to 58%.
Impact of Non-Axisymmetric Inlet Guide Vane Stagger Angle on the Performance and Stability of a Low-Speed Research Compressor
Authors: Xia Kailong , Deng Hefang , Zhu Mingmin , Qiang Xiaoqing , Teng Jinfang , Lu Shaopeng
Published: September 2023

The paper examines the impact of non-axisymmetric inlet guide vanes (IGV) stagger angle on the performance and flow behaviors of a 4-stage low-speed research compressor at Shanghai Jiao Tong University. The One-ninth entire annulus of the IGV row and the first stage are modeled as the computational domain. The stagger angle of one in nine IGV blades is varied by 1.5 and 3 degrees in the anticlockwise direction from the datum case. The sensitivities of these non-axisymmetric configurations to two different total pressure inlet profiles (the datum and defective ones) are analyzed using RANS and URANS numerical methods.

Results indicate that the impact of IGV stagger angle deviations on overall performance is negligible under the datum inlet. However, the performance and internal flow behaviors are significantly influenced by the defective inflow, especially in the 3-degree configuration. When stagger angle varies by 3 degrees, an approximately 2.39% efficiency penalty at the near stall condition and a 1.58% reduction in stall margin occur. The analysis on the internal flow behaviors shows that, with the datum inlet, only neutral trailing edge separations are observed in both design and near stall conditions. While under the defective inflow, a large corner separation exists near the rotor suction surface, resulting in a distinct performance degradation. The dynamic pressure signals at the rotor tip are examined to investigate the unsteadiness inside the rotor passage under both inlet conditions. It is demonstrated that for both inlet, the 3-degree deviation of IGV blade magnifies the intensity of the prominent frequency around the period of 2/3 blade-passing-frequency, which represents the generation, oscillation, and shedding of leakage vortices. Furthermore, a characteristic frequency 2044 Hz is newly observed in the 3-degree configuration under defective inflow. It might be brought by the radial migration and fluctuation of low-energy fluid separated from the rotor suction surface. Further investigations are required to study the effects of varied IGV staggers on rotor-stator matching and stall inception mode.
Influence of Air/Hydrogen Momentum Ratio, Equivalence Ratio and Dilution Hole Geometry on the Performance of a Micromix Combustor for a 100 kWe mGT
Authors: Devriese Cedric , Derks Sander , Kole Jasper , Schlösser Yarne , De Paepe Ward , Bastiaans Rob
Published: September 2023

Against the background of a growing deployment of renewable electricity production, like wind and solar, the demand for energy storage will only increase. One of the most promising ways to cover the medium to long-term storage is to use the excess electricity to produce hydrogen via electrolysis. In a modern energy grid, filled with intermittent power sources and ever-increasing problems to construct large power plants in densely populated areas, a network of Decentralised Energy Systems (DES) seems more logical. Consequently, building a previous work, there is a need for the design and optimisation of a hydrogen fuelled micro Gas Turbine (mGT). This paper focusses on our continued development and optimisation of the low-NOx hydrogen combustion chamber, using steady-state RANS CFD simulations. To further optimise the primary zone of the combustor, this work concentrates on the specific impact of the air/fuel momentum ratio, the primary zone equivalence ratio and dilution zone geometry on the combustor performance. First, the air mass flow rate and the hydrogen inlet pressure are varied within a specified control range. This results in a range for the momentum ratio and the equivalence ratio for which we can analyse the resultant NOx concentration at the combustor outlet. This allows the momentum ratio and the equivalence ratio to be optimally chosen for a new primary zone combustor geometry with lower NOx formation. In a second step, this primary zone design is completed with an initial and separately optimised design of the secondary air zone or dilution zone. An analysis was made on the variation of several key dilution zone design parameters such as; the diameter of a dilution hole, the number of dilution holes in a single row, the variation in size between the holes in the same row and the distance from the centre of the single row of dilution holes to the combustor head. This parameter variation study affected the secondary air mass flow rate, the average outlet temperature, the outlet temperature homogeneity and the NOx emissions at the combustor outlet, on the basis of which a first simple, single dilution hole row is proposed and optimised. Both the final optimisation of the primary zone and the optimisation of the secondary zone will come together a new micromix combustor geometry that will be part of the future work and will be included in the presentation at GT2023.
Cloud Based Predictive Monitoring System for Steam Industrial Turbogenerator
Authors: Sanguineti Antonio , Venuti Roberto , Violante Antonio , Busi Adriano , Malavasi Francesco
Published: September 2023

Steam turbogenerators have a wide application in the exploitation of thermal from the combustion of biomass, general waste to energy and natural gas.

In the current social and economic worldwide situation, ensuring the continuity of the industrial process, is a competitive advantage for biomass industries and waste incinerators.

In this context, Fincantieri has developed a cloud-based monitoring system, based on instrumentation installed together with virtual sensors with the aim of detecting deviations from the design, foreseeing the intervention of alarms and trips of the conventional control system. The outcome is the increasing machine availability.

The control system signals are published (via OPC server), processed to generate additional sensors (called ‘virtual sensors’) and distributed to a cloud, overcoming the limited memory capacity.

Thermo-fluodynamic quantities are evaluated to track the machinery aging. Rotor dynamics and bearing are monitored with an operational database to create dedicated monitoring algorithms.

Installation of additional instrumentation is forecasted to allow the updating and the monitoring of all the relevant parameters.

Once the development phase was completed, the system was installed and tested in a first prototype plant. Two powerplants are nowadays already monitored by remote.
Rework and Repair Options for Steam Turbine Components Subject to Flexible Operation
Authors: Biesinger Frank , Lorini Huascar , Shah Ritesh
Published: September 2023

The increase in renewable energy penetration on the grid has accelerated the need to transition conventional fossil-based energy sources from their traditional base load operation to more flexible operational regimes. The mode of operation changed dramatically in terms of number of starts, operating hours per annum and variation in load level. This results in greater thermal transients on operational equipment leading to an increase in Low Cycle Fatigue damage. To ensure the continued integrity of the steam turbine components, it is essential to assess the lifetime status by applying Residual Lifetime Analysis methods.

Depending on the amount of lifetime consumption and the extend of potential crack findings, different component repair options are possible. The rework or repair options can be divided into two main groups, namely cold- and hot-rework. These two options can also be carried out consecutively. All rework or repair options provide the opportunity to improve the application of a component by applying profiling with improved stress fields and even superior materials, in the case of hot rework.

The aim of the rework / re-conditioning is to ensure that the steam turbine component is suitable for future operation. This ensures that plants are well placed to deliver more flexible operation in the energy industry through carefully tailored refurbishments and reworks.
Enhancing the Damping Capability of Rib-Stiffened Structures With Additive Manufacturing
Authors: Scott-Emuakpor Onome , Johnson Philip , Celli Dino , George Tommy
Published: September 2023

The focus of this study is to determine the effectiveness of inherent vibration suppression via additive manufacturing (AM) of laser powder bed fusion (LPBF) Nickel Alloy 718 plates with stiffening structures. The prevalence of stiffening structures in many industries is a testament to their ability to improve part stiffness, shift natural frequencies of critical parts from operational ranges, and reduced system noises. Motivation for understanding stiffening structures in aerospace industries (specifically in turbine engines) comes from the potential to improve the designs of low-pressure compressor blades, rotor flange connections, and engine frames for next generation flight. The damping technology applied to the stiffening structures in this study is the Inherent Damping via AM Processes (i-DAMP™). Assessing the effectiveness of i-DAMP™ uses vibration experimentation results of plate components with low and high aspect ratio stiffening structures. The results from this assessment show significant vibration suppression with similitude to previous i-DAMPTM demonstrations, and the vibration suppression is realized while maintaining negligible changes in stiffening capabilities.
Best-Practice Guidelines for High-Fidelity Simulations Based on Detailed Analysis of a Highly-Loaded Low-Pressure Turbine Cascade
Authors: Rosenzweig Marco , Giaccherini Simone , Pinelli Lorenzo , Kozul Melissa , Sandberg Richard , Marconcini Michele , Pacciani Roberto
Published: September 2023

The highly-loaded, linear low-pressure turbine cascade T106C is a popular validation test case for direct numerical and large-eddy simulation solvers. In most previous high-fidelity simulations, the cascade’s geometry has been simplified by considering only a fraction of the spanwise extent. A periodic boundary condition in the spanwise direction is then typically used to analyze the flow in the mid-span region. However, it has proved challenging to numerically reproduce experimental data of the blade loading at engine-relevant conditions of isentropic exit Reynolds number of 80,000 and isentropic exit Mach number of 0.65 in the absence of a turbulent inflow. The discrepancies between high-fidelity simulations and experiments have mostly been attributed to an insufficient spanwise domain extent in the numerical setup. The present paper resolves these differences by including spanwise end-walls in the numerical setup using a dedicated high-fidelity computational fluid dynamics solver. Both the blade loading and the wake loss are thus adequately predicted by the present numerical study, which had not previously been achieved in the literature. Furthermore, a series of highly-resolved large-eddy simulations have been performed proving that spanwise periodicity cannot capture the underlying flow physics determining the blade’s mid-span performance at the considered operating point. For these cases, grid resolution and spanwise domain extent were systematically varied to highlight their combined effect on the blade loading along the suction side and wake loss prediction. Finally, a rigorous comparison between different flow solvers and numerical setups summarizes best-practice guidelines for conducting high-quality, scale-resolving simulations of highly-loaded low-pressure turbine blades.
Centrifugal Compressor Surge in Innovative Heat Pump – Part 1: Fluid Dynamic and Vibrational Analysis
Authors: Ferrando Marco , Reboli Tommaso , Reggio Federico , Niccolini Carlo Alberto , Silvestri Paolo , Traverso Alberto , Sishtla Vishnu
Published: September 2023

In the current energy scenario, it is necessary to reduce fossil fuel consumption to achieve the far-sighted and stringent decarbonization goals. To date, heat is mainly produced through fossil fuels. Alternatively, electrically driven heat pumps can exploit renewable power to recover environmental and waste heat, offering energy efficient and environmentally friendly heating and cooling for applications ranging from domestic and commercial buildings to process industries. For this reason, they are expected to play a primary role in complementing or displacing natural gas boilers in the residential and industrial sectors in the near future.

Centrifugal compressors are already used as prime movers of the working fluid in heat pumps, thanks to their industrial replicability, compact size, affordable costs, and good performance in terms of efficiency and low noise. However, they are subject to instabilities such as surge and stall like any other dynamic compressor and these phenomena develop quite differently than in classic open-loop systems such as gas turbines. In fact, such peculiarity is mainly due to the closed-loop configuration with real gases in two-phase conditions, occurring in typical heat pump cycles. In addition, heat exchangers also contribute to make these phenomena different from what is commonly studied. Compressor surge in closed loop heat pump systems has received lower attention than other applications by the engineering community, lacking dedicated experimental characterization and clear exposition of the phenomenon.

The aim of this paper is to experimentally investigate the behavior of a centrifugal compressor installed into an innovative close loop heat pump system under stable and unstable conditions from both vibrational and fluid-dynamic points of view. The impact of the main process parameters on the evolution of the instability is shown, highlighting how surge cycles change by varying system operating conditions. The energy contents of surge cycles and pressure fluctuations are highlighted, using data post-processing techniques such as Fast Fourier Transform and Phase Locked Average.

The vibroacoustic analysis enrich the comprehension of the phenomena. The experimental results shown in this paper can be a basis for the future development of validated mathematical models of closed loop heat pumps systems equipped with dynamic compressors operating under stable and unstable operating conditions.
Quantification of Geometric Variability Effects Through a Viscous Through-Flow Model: Sensitivity Analysis of the Manufacturing Tolerance Effects on Performance of Modern Axial-Flow Compressor Blades
Authors: Budo Arnaud , Hillewaert Koen , Le Men Thibault , Arnst Maarten , Terrapon Vincent E.
Published: September 2023

An important question for turbomachine designers is how to deal with blade and flowpath geometric variabilities stemming from the manufacturing process. The challenge consists in identifying where stringent manufacturing tolerances are absolutely necessary and where looser tolerances can be used, as some geometric variations have little or no effects on performance, while others do have a significant impact. Because numerical simulations based on Reynolds Averaged Navier-Stokes (RANS) equations are computationally expensive for a stochastic analysis, an alternative approach is proposed, in which these simulations are complemented by cheaper through-flow simulations to provide a finer exploration of the range of variations, in particular in a context of robust design. The overall goal of the present work is to assess through a sensitivity analysis the ability of through-flow modeling to predict geometric variability effects on compressor performance and, in particular, to capture the main trends. To do so, through-flow simulations are compared to RANS simulations applied to a modern low-pressure compressor designed by Safran Aero Boosters. Within the scope of this preliminary study, perturbations of the three-dimensional position of undeformed stator blades and deformations of the hub and shroud contours are introduced one-factor-at-a-time per simulation. Their range is defined based on the tolerance limits typically imposed in the industry and on observed manufacturing variability. It is found that the through-flow model broadly provides realistic predictions of performance variations resulting from the imposed geometric variations. These results are a promising first step towards the use of the through-flow modeling approach for geometric uncertainty quantification.
Characterising the Unsteady Flow-Field in Low-Flow Turbine Operation
Authors: Kim Hye Rim , Stania Lennart , Maroldt Niklas , Oettinger Marcel , Seume Joerg R.
Published: September 2023

Current operational considerations require steam turbines to operate in a more flexible way, with more frequent and faster start-up and an increasing part-load operation. For very low mass-flow rates, the interaction of highly separated flow with the high speed rotor blades causes windage flow. This type of flow is characterized by increased temperature and highly unsteady flow, which forms vortex structures that rotate at a fraction of the rotor speed. If their magnitude is sufficiently high and the frequency is close to the blade eigenfrequency, non-synchronous vibration (NSV) can be induced. In this paper, low-flow turbine operation is investigated using a three-stage turbine rig that features an instrumentation concept focused on capturing aerodynamic and aeroelastic phenomena. Extensive steady probe, unsteady pressure, and tip-timing measurements are utilized. The experimental scope covers a wide range of operating points in terms of rotational speed and mass flow rates. Low-flow regimes are detected by a reversal in torque and increase in temperature. Unsteady measurements during transient operation identified large-scale vortical flow structures rotating along the circumference, so called rotating instabilities (RI). The onset, growth, and breakdown regimes of RI are characterized for different low-flow conditions. The quantitative characteristics of RI with regards to nodal diameter and rotational speed are derived by a cross-correlation of multiple unsteady sensors. The blade vibration measurements show a moderate structural response from unsteady aerodynamic excitation, indicating no significant NSV occurring in the present experimental setup. Later in the study, an acoustic excitation system has been applied to trigger a locked-in NSV without interrupting the coherent flow structures. From that, significant blade response has been observed, revealing a high degree of mistuning and damping of the rotor blading.
An Experimental Study of the Stability and Nearfield Structure of Oxyfuel Jet Flames at Elevated Pressures
Authors: Bukar Muhammad , Basnet Suman , Wu Bin , Magnotti Gaetano
Published: September 2023

This study presents experimental results of the stability limit and the nearfield structure of oxy-methane jet flames at pressures ranging from 2–5 bar. The oxidizer used in this campaign consists of 40% O2 and 60% CO2. Two sets of cases were studied: one where pressure increase was achieved by keeping the fuel Reynolds number constant and the other where the velocity was kept constant while increasing pressure. Stability limits (lift-off velocity) are reported for various coflow velocities at different operating pressures. Natural flame luminosity imaging with a DSLR camera and combined CH* chemiluminescence using an ICCD (PIMAX 4) are used to characterize the nearfield structure of the flame. The CH* results were then processed to extract the attachment location, defined in terms of attachment height and radius. The study mainly investigates the effect of pressure on the flame attachment height and radius. The DSLR images complement the study with qualitative information on the flame appearance and sooting propensity. Results show that at constant Reynolds number, the attachment height decreases with pressure for all cases considered while the attachment radius increased with pressure increase. At constant velocity, however, both the attachment height and radius were observed to decrease with increased pressure.
Numerical Investigation on Combustion Characteristics and Emissions of Hydrogen/Methane Blends in Flamesheet Combustor
Authors: Vo Duy-Tan , Jung Jine-Sung , Ryu Jaiyoung
Published: September 2023

Flamesheet is a novel head-end combustor component design that can accommodate up to 40% H2 in volume fraction while maintaining a low NOx emission at 9 ppm. It is compatible with many popular combustors, including 501F DLN, 7F DLN 2.6, and 7F DLN 2.6+. This study used a numerical investigation to examine the combustion characteristics of methane blended with hydrogen at various compositions in a lean premixed swirling flame in a W501F Flamesheet combustor. The volume of hydrogen enrichment ranged from 0 to 40%. A numerical approach using the partially premixed flamelet model and turbulent SST k-omega model was adopted to simulate the Flamesheet combustor. The flamelet-generated manifold was used to analyze the effect of hydrogen enrichment and equivalent ratio on flame operation, temperature distribution, CO and CO2 emissions, and species concentrations. The operating principle of this Flamesheet model was described, and details of flow characteristics and heat transfer were discussed. The results show that the Flamesheet combustor can operate stably with up to 40% hydrogen. The outlet temperature can be maintained at a constant by controlling the equivalent ratio as the hydrogen concentration increases. The effect of adding hydrogen on species concentrations was also discussed in detail.
Aerodynamic Design, Study, and Performance Mapping of a Radial-Axial Machine for Geothermal Power Plants in Energy Transition Applications
Authors: Lottini Fabrizio , Marconcini Michele , Arnone Andrea , Biliotti Davide , Foschini Alice
Published: September 2023

Energy transition has become one of the most discussed topics of the current times. Turbomachinery still plays a key role in the power generation field, but the machines must meet very high standards in terms of performance levels, compactness, and cost reduction. In this perspective, new design configurations need to be explored. This paper presents a procedure for the aerodynamic design of a radial-axial stage turbine for geothermal applications. Based on a real set of possible power plant conditions, a dedicated CFD campaign has been carried out to assess the performance of the radial-axial machine — at design and off-design conditions. The main goal of the presented work is to exploit the benefit of combining radial and axial stage architectures, providing a compact, flexible, and efficient machine, capable to maintain high performance levels even at off-design conditions, which is a crucial requirement for renewable energy applications. Since organic fluids with high molecular weight are used in these applications, in addition to the common design procedure based on RANS CFD analyses, real-gas calculations are mandatory to correctly predict the behavior of the machine. All the CFD analyses are performed using the TRAF code, while the design of the radial-axial stages is carried out based both on in-house and commercial tools as per Baker Hughes best practice. The paper highlights the feasibility of the unusual radial-axial architecture as an effective way to combine the benefits of both the radial and the axial configurations, resulting in an efficient, robust, and compact machine.
A CFD-Based Throughflow Solver Using Cascade Potential Theory for Axial Compressor Flow Modeling
Authors: Kravtsoff Florent , Schvallinger Michaël , Ottavy Xavier
Published: September 2023

This paper describes the use of the Hess & Smith cascade potential method as an additional feature for throughflow modeling. This method is incorporated inside ASTEC, a CFD-based throughflow solver developed by Safran Tech providing local blade loading information for blade force and loss modeling. The test cases are all subsonic, composed of two compressors cascades and a low speed compressor. The two profile families for the cascades are a classical NACA 65 009 and a controlled diffusion cascade designed by the Whittle Laboratory. The compressor is the well studied CME2, a research single stage designed by Safran Aircraft Engines. From the potential calculation, boundary layers and wakes are calculated on the blades providing deviation angles and profile losses. The tip leakage losses are also estimated from blade loading at the tip of a rotor. The results are compared to MISES code predictions, RANS simulations, experimental data and classic Lieblein empirical correlations. This work aims to model compressors flow with geometry-based classic analytical methodologies for a minimal use of empiricism. The predictions are good on bi-dimensional cascades cases compared to several other methodologies and at mid-span for the multiple incidences considered compared to experimental cascade results. For the compressor case, the blade loading near mid-span of the rotor blades show good agreement compared to RANS results leading to an overall good capture of the performance characteristic trends near design point. There is still room for improvements near the end-walls, mostly due to the lack of hub boundary layer model in the actual methodology. These results still build a step on which the enrichment of the flow model can be pursued.
Structure and NOx Emissions of Stratified Hydrogen-Air Flames Stabilized on a Coaxial Injector
Authors: Leroy Maxime , Mirat Clément , Renaud Antoine , Puggelli Stefano , Zurbach Stephan , Vicquelin Ronan
Published: September 2023

In recent years, the need for low-carbon power has seen hydrogen emerge as a potential fuel to replace conventional hydrocarbons in combustion to limit CO2 emissions in several sectors, including aeronautics. The challenges posed by hydrogen combustion are similar to the issues of kerosene flames but more challenging, like nitrogen oxide (NOx) emissions and flame flashback. One potential solution to address these problems is to burn a rich mixture of hydrogen and air in globally lean conditions on a coaxial injector to obtain a stable and staged combustion and attempt to reduce emissions. In this article, the evolution of NOx production as more air is mixed into the fuel is studied, as well as the changes in flame size and structure. In particular, the appearance of a secondary flame front is observed and increasing the proportion of air in the fuel mixture both shortens the flame and reduces the NOx emission index. Additionally, the effect of the global equivalence ratio and flame thermal power are studied. Finally, existing models for NOx emission of hydrogen flames on a coaxial injector based on average flame residence time and strain rate are tested and shown to have promising results.
Conjugate Modelling of a Closed Co-Rotating Compressor Cavity
Authors: Parry James , Tang Hui , Scobie James A. , Lock Gary D. , Carnevale Mauro
Published: September 2023

Robust methods to predict heat transfer are vital to accurately control the blade-tip clearance in compressors and the radial growth of the discs to which these blades are attached. Fundamentally, the flow in the cavity between the co-rotating discs is a conjugate problem: the temperature gradient across this cavity drives large-scale buoyant structures in the core that rotate asynchronously to the discs, which in turn governs the heat transfer and temperature distributions in the discs. The practical engine designer requires expedient computational methods and low-order modelling. A conjugate heat transfer methodology that can be used as a predictive tool is introduced here. Most simulations for rotating cavities only consider the fluid domain in isolation and typically require known disc temperature distributions as the boundary condition for the solution.

This paper presents a novel coupling strategy for the conjugate problem, where unsteady Reynolds Averaged Navier-Stokes (URANS) simulations for the fluid are combined with a series of steady simulations for the solid domain in an iterative approach. This strategy overcomes the limitations due to the difference in thermal inertia between fluid and solid; the method retains the unsteady flow features but allows a prediction of the disc temperature distributions, rather than using them as a boundary condition. This approach has been validated on the fundamental flow configuration of a closed co-rotating cavity. Metal temperatures and heat transfer correlations predicted by the simulation are compared to those measured experimentally for a range of engine-relevant conditions.
Improvement and Validation of an Autonomous Experimental System to Identify BLISK Mistuning
Authors: Denis Sophie , Hoffait Sébastien , Ligot Jérôme , de Cazenove Jean , Salles Loïc
Published: September 2023

This paper presents an autonomous mistuning identification method for single BLISKs. The proposed methodology relies on the ICMM identification methodology. The required inputs are obtained thanks to measurements of the system mode shapes and natural frequencies carried out with a dedicated test rig. The BLISK is excited by an electrodynamic shaker. An infrared Laser Doppler Vibrometer attached to a robotic arm is used to perform the measurements on the blades. The use of a robotic arm enables the reduction of human interventions and significantly limits the positioning error which increases the accuracy of the identification. The proposed setup thus permits to perform repeated characterization campaign, to increase the number of measurements with low human resources cost, and to perform 3D modal analysis. This opportunity makes the test bench suitable for next generation of engines which are composed of one-piece multi-stages compressor, the Bladed druM (BluM). Indeed, the overlay of the blades could reduce the accessibility of vertical measurement.

In this work, the proposed method is firstly presented. The robust experimental input data selection procedure which has been developed and which allows for the optimization of the mis-tuning identification is then described. This procedure reduces the sensitivity of the result with respect to bad experimental content. At last, the usefulness of the method is demonstrated on the 1B and 1T mistuning evaluation of an industrial BLISK.
Integrated Hybrid Air Foil-Magnetic Thrust Bearing (i-HFMTB) Part II: Possibility of Rigid Mode Control for 250HP Air Compressor System
Authors: Lee Yongbok , Ha Yunseok , Kim Jungwan , Jeong Keonwoo
Published: September 2023

This study aims to verify the effectiveness of the 250 HP class compressor system to which the integrated hybrid air foil magnetic thrust bearing (i-HFMTB) proposed in part I is applied, and the vibration and instability problems of air foil journal bearing (AFJB) occurring in the rigid mode are controlled by i-HFMTB. The compressor rotor is supported by two AFJB (journal diameter = 60mm) and an i-HFMTB, and the length and mass of the rotor are 550mm and 15.24kg, respectively. i-HFMTB has a structure in which air foil thrust bearing (AFTB) pads are inserted into eight slotted active magnetic thrust bearings (AMTB), and PD control (proportional gain: 4,000 /differential gain: 10) is applied. The operating area was identified through AFJB’s dynamic coefficients and rotordynamic analysis. As a result with the experiment of the 250 HP compressor system supported only by two AFJB, sub- and super-synchronous vibrations were generated owing to the AFJB’s insufficient load capacity and damping in the rigid mode (7,000rpm) region, and this instability did not disappear even upon increasing the speed to 15,000rpm. However, when i-HFMTB was turned on in rigid mode, it was confirmed that the sub- and super-synchronous vibrations were significantly reduced. The thrust collar tilt angle was calculated through orbit trajectory analysis of the impeller and cooling side, and it was confirmed that the tilt angle of the thrust collar was reduced during i-HFMTB operation. Thus, the coupled moment acting on AFJB could be reduced, this can not only affect the load distribution of AFJB, and but also improve the performance degradation problem of AFTB caused by thrust collar tilt.