bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparative analysis and trends in liver transplant hospitalizations with Clostridium difficile infections: A 10‐year national cross‐sectional study
Authors: Ali Hassam , Patel Pratik , Pamarthy Rahul , Fatakhova Karina , Bolick Nicole Leigh , Satapathy Sanjaya Kumar
Published: October 2022

Goals and background

Clostridium difficile infection (CDI) is the leading cause of antibiotic‐associated diarrhea in the United States. We aimed to determine comparative trends in inpatient outcomes of liver transplant (LT) patients based on CDI during hospitalizations.

Methods

The national inpatient sample database was used to conduct the present retrospective study regarding CDI among the LT hospitalizations from 2009 to 2019. Primary outcomes included 10‐year comparative trends of the length of stay (LOS) and mean inpatient charges (MIC). Secondary outcomes included comparative mortality and LT rejection trends.

Results

There was a 14.05% decrease in CDI in LT hospitalizations over the study period (p = .05). The trend in LOS did not significantly vary (p = .9). MIC increased significantly over the last decade in LT hospitalizations with CDI (p < .001). LT hospitalizations of autoimmune etiology compared against non‐autoimmune did not increase association with CDI, adjusted odds ratio (aOR) 0.97 (95% confidence interval [CI] 0.75–1.26, p = .87). CDI was associated with increased mortality in LT hospitalizations, aOR 1.84 (95% CI 1.52–2.24, p < .001). In‐hospital mortality for LT hospitalizations with CDI decreased by 7.75% over the study period (p = .3). CDI increased transplant rejections, aOR 1.3 (95% CI 1.08–1.65, p < .001). There was a declining trend in transplant rejection for LT hospitalization with CDI from 5% to 3% over the study period (p = .0048).

Conclusion

CDI prevalence does not increase based on autoimmune LT etiology. It increases mortality in LT hospitalizations; however, trend for mortality and transplant rejections has been declining over the last decade.

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An Upgraded Chemical Kinetic Mechanism for Iso-Octane Oxidation: Prediction of Polyaromatics Formation in Laminar Counterflow Diffusion Flames
Authors: Hernandez Astrid Ramirez , Kathrotia Trupti , Methling Torsten , Braun-Unkhoff Marina , Riedel Uwe
Published: October 2022

Iso-octane is widely recognized as a prominent candidate to represent the oxidation of iso-alkanes within jet fuel and gasoline surrogates. This work evaluated a chemical kinetic mechanism for iso-octane focusing on the model's capability to predict the formation of polycyclic aromatic hydrocarbons (PAHs). As the model is intended to be further coupled with soot models, the chemical kinetic mechanism must supply good predictability of the formation and consumption of PAHs considered as major soot precursors. A first validation of the iso-octane submodel as incorporated within ESTiMatE-Mech, using experimental data from literature, reveals the need to improve the submodel. Considerable deviations were observed in the prediction of the PAHs, although concentration profiles of major species and fundamental combustion properties, here ignition delay time and laminar flame speed, were accurately predicted. Through rate of production and sensitivity analyses of the mechanism, nine reactions were identified to have a strong impact on the (over) prediction of the PAHs. These reactions have been modified based on information gathered from literature resulting in an updated version of the mechanism called ESTiMatE-Mech_mod. Simulation results with this modified mechanism showed that this updated mechanism is now capable of predicting well the targeted PAHs, while retaining the good initial prediction of the major species concentration profiles as well as of laminar flame speeds and ignition delay times.
Flametube Evaluation of a Lean-Lean Combustor Concept Developed for Supersonic Cruise Aircraft
Authors: Tacina Kathleen M. , Podboy Derek P. , Guzman Francisco J.
Published: October 2022

Gaseous emissions were measured in single-cup flametube tests of an advanced low-NOx combustor concept at simulated supersonic cruise conditions. The combustor concept is a low technology readiness level (TRL), lean front-end design developed under the NASA Fundamental Aeronautics/Supersonics project to minimize NOx emissions at supersonic cruise. The flametube conditions matched or approached combustor conditions at supersonic cruise, with combustor inlet temperatures up to 920 K, inlet pressures up to 19 bar, and combusted gas temperatures up to 2,120 K. Whether these conditions met or just approached supersonic cruise conditions depended on the type of engine the combustor would be installed in. Two types of engines were considered here: a “derivative” engine based on a current technology and an “advanced” engine with a higher operating pressure ratio and higher temperature limits. For the “derivative” engine, the combustor is expected to be at least close to meeting the NASA NOx emissions goal of 10 g-NOx/kg-fuel at supersonic cruise. However, with the higher combustor inlet and flame temperatures of the advanced engine, NOx emissions are expected to be well above the goal.
A Model-Free Kullback–Leibler Divergence Filter for Anomaly Detection in Noisy Data Series
Authors: Zhou Ruikun , Gueaieb Wail , Spinello Davide
Published: October 2022

We propose a Kullback–Leibler divergence (KLD) filter to extract anomalies within data series generated by a broad class of proximity sensors, along with the anomaly locations and their relative sizes. The technique applies to devices commonly used in engineering practice, such as those mounted on mobile robots for nondestructive inspection of hazardous or other environments that may not be directly accessible to humans. The raw data generated by this class of sensors can be challenging to analyze due to the prevalence of noise over the signal content. The proposed filter is built to detect the difference of information content between data series collected by the sensor and baseline data series. It is applicable in a model-based or model-free context. The performance of the KLD filter is validated in an industrial-norm setup and benchmarked against a peer industrially adopted algorithm.
Effects of Clearance and Operating Conditions on Tip Leakage Vortex-Induced Energy Loss in an Axial-Flow Pump Using Entropy Production Method
Authors: Kan Kan , Li Haoyu , Chen Huixiang , Xu Hui , Gong Yan , Li Tianyi , Shen Lian
Published: October 2022

Tip leakage flow (TLF) is a typical flow phenomenon in the internal flow of axial-flow pumps that has a serious impact on their safety and stability. In this study, numerical simulations are performed to investigate the influence of various tip clearances and operating conditions on the characteristics of the tip leakage vortex (TLV) and energy loss of a prototype of a vertical axial-flow pump. First, based on entropy production theory, the TLV-induced energy loss is quantitatively studied. The entropy production rate caused by turbulence dissipation (EPTD), which is caused by pulsating velocity, contributes the most to the total energy loss. The EPTD at the impeller is principally distributed on the leading edge of the blade due to the influence of the tip clearance. Then, the spatial shape and trajectory of the core of the TLV are discussed, and their correlations with pressure and vorticity are investigated to reveal the spatial distribution characteristics and formation mechanism of TLVs. With increasing tip clearance, the trajectory of the vortex core extends radially outward, and the low-pressure area near the blade tip is consistent with the trajectory of the core of the TLV, which accompanies high vorticity. Fundamentally, pressure gradients and flow separation at the leading edge are the root causes of the TLVs. Lastly, the spatial evolution of TLVs under different calculation schemes is discussed by utilizing the vorticity transport equation, demonstrating that the Coriolis force (CORF) is the main factor that affects the location of a TLV, whereas the vorticity stretching term (VST) has a greater influence on the vorticity variation rate of the TLV than the CORF and plays a predominant role in the spatial development of the TLF.
Machine-Learning Assisted Optimization of Generalized K-Omega (GEKO) Turbulence Model Parameters for Turbocharger Radial Compressor
Authors: Amstad Patrick , So Kwok Kai , Fischer Magnus
Published: October 2022

This paper presents a complete and general machine-learning assisted optimization framework for the Generalized k-ω (GEKO) turbulence model based on experimental measurements. The optimization framework is applied to the use case of a turbocharger radial compressor for three different operating conditions including design and surge conditions. The first optimization of the GEKO turbulence model is performed w.r.t measured global thermodynamic quantities, including the isentropic efficiency and pressure ratio. A second optimization is performed w.r.t local experimental flow quantities, i.e. wall pressure distribution along the diffuser vane. The testing errors of the machine-learning models are compared and analyzed, and the best performing algorithms are Support Vector Regression (SVR) and Artificial Neural Network (ANN) for modeling the response surface of the GEKO parameters, based on which the turbulence model is optimized by Genetic Algorithm (GA). The aforementioned 2 optimizations result in an equivalent GEKO parameter set, where the optimized GEKO model agrees well with the measurements and the more computationally expensive Explicit-Algebraic Reynold Stress Model (EARSM), and outperforms the Shear Stress Transport (SST) in terms of relative error, and the prediction of onset of surge and flow separation. The optimized GEKO model also generalizes well to different operating conditions as well as another radial compressor with a different diffuser geometry. In addition, a data-based approach is used to quantify the influence of the six GEKO parameters on different flow phenomena in the radial compressor. The result of the data-based approach aligns well with heuristic loss mechanism in turbomachinery.
Hybrid Air Foil Thrust Bearings Design and Performance Measurement
Authors: Xu Fangcheng , Qiu Shuoxian , Chu Jianhua
Published: October 2022

Air foil bearings (AFBs) are widely used in high speed and low duty turbomachinery such as fuel cell air compressors, turbo blowers and micro gas turbines due to its high-speed operation, low power loss and good temperature adaptability. However, the applications of air foil thrust bearings to large power compressors such as closed-cycle supercritical CO2 turbines and high power single stage compressors still have many technical challenges due to load capacity limitation. Hybrid air foil bearing (HAFB) combines the benefits of AFB and hydrostatic air bearing. Compressed air is injected through a pipe behind the top foil to enhance pressure inside the thin film to increase bearing load capacity which can be controlled by changing source pressure. This paper presents the manufacturing process of hybrid air foil thrust bearings (HAFTBs) and measurements of bearing performance with three different orifice locations. The experiment was conducted to test the effect of orifice location and air supply pressure on bearing load capacity, friction torque and temperature. The experimental result shows that HAFTBs have significant bearing load capacity enhancement in comparison to AFBs. Source pressure and orifice location are the key parameters of the hybrid air foil thrust bearing.
Hydrogen Compression - Towards a New Strategy for the Design of Hydrogen Compressors
Authors: Tiainen Jonna , Turunen-Saaresti Teemu , Mäki-Iso Mikko , Schuster Sebastian , Brillert Dieter
Published: October 2022

The growth of renewable energy resources increases the need for energy storage. Excessive energy could be stored into hydrogen, but its transportation in pipelines requires compression up to pressures of 70 bar and high volume flows. Due to several benefits, centrifugal compressors could be considered for hydrogen transportation.

Previous investigations indicate that the achievement of the required pressure rise needs high tip speeds, resulting in high mechanical stresses. This paper proposes forward-swept impeller blades to reduce the tip speed. 1D methods are used to design compressors with different outlet blade angles. The performance of three compressors is analyzed numerically. The performance maps are computed with an Euler-based through-flow approach. The results indicate that the forward-swept impeller with −15° could reduce the tip speed by 5% compared to the unswept impeller without negatively impacting the efficiency.
Numerical Observations of a Stall Phenomenon in the NASA CC3 Compressor
Authors: Ni Michael , Robles Vega Gregorio , Ni Ron Ho , Clark John , List Michael
Published: October 2022

Numerical analysis of the transonic NASA CC3 centrifugal compressor stage with vaned diffuser is undertaken and the mechanism for the onset of stall investigated. The analysis methodology employs standard practice numerical methods, the mixing-plane approximation at the rotor-stator interface and periodic boundary conditions within a given row. Simulation results were then compared against full annulus time accurate simulations and the methodologies evaluated for estimation for the onset of stall.

In the study, steady state and full annulus time accurate simulations were conducted at the 100% design speed, from choke to stall. Many time-resolved simulations “stalled” at pressure ratios where steady state mixing-plane solutions converged. One observation from the time-resolved simulations is that the number of revolutions required for the flow to stall was over 5 revolutions and increased to 9 revolutions closer to the last stable point.

Integrations of the time-resolved solutions at the onset of stall reveal that the flow field of both the impellers and diffusers are not circumferentially uniform, and a stall “cell” is rotating in the opposite direction of the rotor. However, the “cell” is stationary in the stationary frame of reference thus, it is not a conventional rotating stall.

There is a notable difference in choke flow between experiment and CFD results, which has been seen by others for this configuration. The reason for the miss is not a focus of this paper, and the numerically predicted unsteady stall point should not be viewed as the exact mechanism for stall within the NASA CC3 experiment, instead this work is to provide a review of standard practice numerical approximations and how cost effective full wheel unsteady analysis can be used to improve transonic compressor design.
Computational Fluid Dynamics Modeling of Fuel Properties Impact on Lean Blowout in the ARC-M1 Combustor
Authors: Dasgupta Debolina , Som Sibendu , Wood Eric , Lee Tonghun , Mayhew Eric , Temme Jacob , Kweon Chol-Bum
Published: October 2022

The flow and flame dynamics within liquid fueled gas turbine combustors are complex due to the interactions between the highly turbulent flow, spray dynamics and combustion. Computational tools help understand these governing processes. A computational fluid dynamics model for Army Research Combustor Midsize (ARC-M1) is developed to characterize the complex turbulent flow, multi-phase spray physics and hydrocarbon chemistry. Using high-quality X-ray data for the combustor, the spray is initialized in the near nozzle region. To understand the overall impact of liquid properties, the liquid properties corresponding to Jet-A and F-24 are tested. It is observed that F-24 has a higher LBO liquid flow rate compared to Jet A. To understand the impact of individual properties, liquid properties such as density, viscosity, specific heat, heat of vaporization, are changed one at a time. It was observed that an increase in density, viscosity, heat of vaporization and specific heat w.r.t Jet-A tends to increase the LBO liquid flow rate i.e. makes the flame blow-off at higher equivalence ratios. This is attributed to the altered flame shapes and the impact of these properties on fuel heating and its subsequent vaporization.
Internal Heat Transfer Measurement on Metal-Based Additively Manufactured Channels Using a Transient Technique
Authors: Lüscher Patrick , Deflorin Marin , Voggesser Manuel , Stuber Peter , Galoul Vincent , Ko Minseok
Published: October 2022

The advancements in additive manufacturing (AM) of metals open new possibilities in the design of gas turbine parts. Especially the cooling efficiency of internal channels can be improved with more complex geometries. Naturally, AM channels have a higher surface roughness than conventionally manufactured parts, which influences the cooling air pressure loss as well as the heat transfer. Implementing novel cooling designs using AM can be possible only if the effect of increased surface roughness on the flow and on the heat transfer can be predicted with an appropriate accuracy. The objective of the current study was to measure these parameters experimentally in simple AM channels to build a database for designing complex and efficient cooling designs using the AM technique. A test rig and post-processing method was elaborated to derive the local internal heat transfer distribution of metal-based AM channels. Six circular single channel coupons made by selective laser melting (SLM) were tested for Reynolds numbers ranging from 20000 to 50000. The coupon with the lowest relative roughness shows good agreement with the Dittus-Boelter correlation. All the other coupons show a consistent increase of internal heat transfer and flow friction with the increase of the internal surface roughness.
Validation of Hydrogen Boundary Layer Flashback Model on Gas Turbine Geometries and Conditions
Authors: Klein Sikke , Sarakatsanis Christos
Published: October 2022

Hydrogen is considered as a promising zero carbon battery fuel to deliver balancing power for the future electricity system with an increasing share of variable renewable power generation. Flame flashback is one of the main challenges for the application of hydrogen in gas turbines. Lean premixed hydrogen combustion is more prone to flashback than natural gas combustion due to higher flame speed and Lewis number effect.

The TU Delft developed a boundary layer flashback model based on a previous work by TU Munich. The TU Delft model includes amongst others the effect of the laminar flame speed, boundary layer profile, Lewis number and adverse pressure gradient of the mean flow. The model was successfully validated on academic experiments from TU Munich.

In the present paper the turbulent flame speed closure in the TU Delft flashback model is updated for gas turbine like conditions using experimental data from the University of California, Irvine (UCI). This updated model is validated against data from the Paul Scherrer Institute (PSI) and back tested on the original academic experiments from TU Munich.

The updated TU Delft boundary layer flashback model and the flashback model from the Paul Scherrer Institute (PSI) have been applied to a scaled version of the Flamesheet™ combustor. The outcome of the PSI flashback model correlates very well with test results from the TU Delft laboratory, the TU Delft flashback model only with the original flame speed correlation.
Estimation of Autoignition Propensity in Aeroderivative Gas Turbine Premixers Using Incompletely Stirred Reactor Network Modelling
Authors: Gkantonas Savvas , Jella Sandeep , Iavarone Salvatore , Versailles Philippe , Mastorakos Epaminondas , Bourque Gilles
Published: October 2022

The study of autoignition propensity in premixers for gas turbines is critical for their safe operation and design. Although premixers can be analysed using reacting Computational Fluid Dynamics (CFD) coupled with detailed autoignition chemical kinetics, it is essential to also develop methods with lower computational cost to be able to explore more geometries and operating conditions during the design process. This paper presents such an approach based on Incompletely Stirred Reactor Network (ISRN) modelling. This method uses a CFD solution of a non-reacting flow and subsequently estimates the spatial evolution of reacting scalars such as autoignition precursors and temperature conditioned on the mixture fraction, which are used to quantify autoignition propensity. The approach is intended as a “postprocessing” step, enabling the use of very complex chemical mechanisms and the study of many operating conditions. For a representative premixer of an aeroderivative gas turbine, results show that autoignition propensity can be reproduced with ISRN at highly reactive operating conditions featuring multi-stage autoignition of a dual fuel mixture. The ISRN computations are consequently analysed to explore the evolution of reacting scalars and propose some autoignition metrics that combine mixing and chemical reaction to assist the design of premixers.
Non-Linear Numerical Simulation of Pre-Loaded Turbine Blades With Frictional Shroud Contact Under Dynamic Conditions
Authors: de Filippis Hugo , Thouverez Fabrice , Blanc Laurent , Girard Patrick , Chevillot Fabrice
Published: October 2022

In a process of permanent innovation and increase of turbojet efficiency, the low pressure turbine is designed to run at higher rotational speed in future engines. Such an evolution requires a precise evaluation of their effects on dynamic behavior of the turbine. Low-pressure turbine blades in aeronautical industry are generally composed of a shroud, whose main purpose is to keep the tightness of the primal air stream, but it produces in consequence a mechanical damping into the dynamic response of the full blade turbine assembly through frictional contacts. Depending on the industrial design choices, the geometry of these blades can induce a pre-torsion effect which will straighten the shrouds during the assembly process, in this way they are brought into contact and the blades are pre-loaded. Predicting the dynamic behavior of such structure and calculating forced responses is a major challenge considering the complexity involved. The numerical model used in this article is based on the geometry of a test bench which was designed to reproduce the pre-torsion assembly loading on the blades through a geometrical interpenetration, and to evaluate the dynamics of the contact between the shrouds. It includes only three blades with a simplified geometry but represents the main dynamic characteristics of a real turbine. A static analysis on a commercial FE software of the test bench blades assembly has been carried out to evaluate the contact area on the shrouds, and determine the deformation related to the pre-torsion loading. Modal analyses were also realized to determine the natural frequencies of the structure and the modal shapes according to the imposed contact status. Then a reduced order model of the structure is generated, and is used into a specific numerical code. A procedure is implemented to handle the interpenetration generated by the pre-torsion of the blades, which is the key part of the static loading of the structure. In order to solve this non-linear dynamic problem in the frequency domain, based on the static loading results, the Harmonic Balance Method (HBM) is coupled to the Dynamic Lagrangian Frequency Time (DLFT) method or a classic penalty method to evaluate the non-linear contact forces. Numerical results around the first and third bending modes of the structure are computed and a parametric study is presented, pointing out the impact of the static normal load distribution depending of the method used, the friction coefficient between, the excitation force level, etc. The precision of the nodal coupling scheme used to manage the contact between the shrouds meshes for the numerical simulation is also evaluated by changing the meshing, in order to quantify such hypothesis.
Experimental Investigation of Twin Scroll Turbocharger Performance Under Pulsating Conditions
Authors: Brodbeck Philipp , Guse Eduard
Published: October 2022

The pulsating nature of automotive internal combustion engines (ICE) is one of the main challenges in the modeling of turbochargers in process simulation. Radial compressors and turbines are characterized by maps containing parameters such as wheel speed, mass flow rate, temperatures and pressure ratios. Those parameters are obtained by standardized test bench measurements, which require stationary flow conditions. In this paper an advanced experimental setup is introduced to investigate the turbine behavior under pulsating conditions. Pressure, temperature, mass flow and turbine torque are measured with an equivalent to a resolution of 0.1 degrees camshaft rotation to obtain working cycle resolved parameters. This way, the turbine performance can be evaluated under pulsating conditions.
Turbine Vane Passage Cooling Experiments With a Close-Coupled Combustor-Turbine Interface Geometry Part 1: Describing the Flow
Authors: Nawathe Kedar P. , Nath Aaditya R. , Kim Yong W. , Simon Terrence W.
Published: October 2022

Due to the proximity of the first stage gas turbine vanes to the combustor, coolant introduced to the combustor walls interacts with the endwall film coolant and changes the vane passage flow physics. Recent results show that combustor coolant contributes significantly to cooling the endwall and vane surfaces. In this paper, the traditional combustor-turbine interface was modified to improve overall cooling performance. The performance of this new injection cooling scheme on passage fluid dynamics and surface cooling is assessed. The first of this two-part paper reports detailed experimental tests that document secondary flows and coolant transport throughout the vane passage for four combustor coolant flowrates. The experimental facility imitates combustor coolant injection and engine-level turbulence and has a modified transition duct design, called the ‘close-coupled combustor-turbine interface.’ The ‘impingement vortex’ seen in previous studies with combustor cooling appears as the dominant secondary flow. It is observed in the present study over a wide range of flowrates, confirming its tie to the combustor coolant flowrate and not the combustor-turbine interface geometry. It was found, however, that the location and size of the impingement vortex are affected by coolant flowrate. The second of this two-part paper discusses the impact of the observed secondary flows on cooling vane passage surfaces.
Design of an Axial Flow Fan for a Unique Cooling Application
Authors: Boshoff Francois D. , van der Spuy Sybrand J. , Pretorius Johannes P. , Meyer Christiaan J.
Published: October 2022

A rotor-only axial flow fan is designed for use in a concentrated solar power application. The plant uses a supercritical carbon dioxide Brayton Cycle for power generation and an air-cooled heat exchanger (ACHE) for cooling.

Fan specifications are derived by considering the geometry and air flow rate requirements for the ACHE, using simple, circular finned tube bundles. The specifications lead to a fan design with a relatively large hub-to-tip ratio of 0.5102.

The fan’s performance is estimated numerically using a periodic three-dimensional model (P3DM) in both an annular computational domain and a computational domain representing a simplified ISO 5801 type A fan test facility. A 1:4.78 scale model of the fan was manufactured and tested in an ISO 5801 Type A fan test facility.

Numerical fan performance results for the annular domain show good agreement with those predicted by the design procedure, for both the cases with no tip gap and the design tip gap size present. It also demonstrates the effect of the tip gap on the overall fan performance. Numerical results for the simplified ISO 5801 type A fan test facility indicates that fan performance is significantly worse than in the annular domain, due to the hub size of the fan being considered in this domain.

The experimental results for the manufactured fan demonstrates the accuracy of the numerical methods used and provide the fan performance characteristics over a wide range of flowrates.
On the Use of Kinetic-Energy Balance for the Feature-Based Mesh Adaptation Applied to Large-Eddy Simulation in Complex Geometries
Authors: Grenouilloux Adrien , Balarac Guillaume , Leparoux Julien , Moureau Vincent , Lartigue Ghislain , Bénard Pierre , Mercier Renaud , Ferrey Paul
Published: October 2022

Static and dynamic feature-based mesh adaptation have gained momentum during the last decade as they allow to refine areas to capture specific flow features. These methods do not always guaranty that the budget of the kinetic energy of the mean field is mesh independent as it could be expected. In the present paper, a framework which uses the assessment of the kinetic energy budget to refine or coarsen the mesh resolution locally is presented in the framework of Large-Eddy Simulation (LES). The whole methodology is applied to two industrial configurations, namely the isothermal PRECCINSTA burner and a row of three jets impinging on a surface at Re = 23000 and a nozzle to plate distance of H/D = 5. Flow field quantities, including mean velocity and RMS or Nusselt number on the final grids are in good agreement with experimental data.
Unsteady Rotor-Stator Interaction in a Four-Stage Axial Turbine: An Experimental Investigation
Authors: von Gosen Florian , Winhart Benjamin , di Mare Francesca
Published: October 2022

This paper presents an experimental investigation of the transient rotor-stator interactions (RSI) in a four-stage axial flow turbine at design as well as off-design conditions. The pressure fluctuations recorded on the surface of a stator vane in stage 3 of the machine are phase-averaged to the rotor position and decomposed into the main contributing periodic components. The origins of the different fluctuations are identified by matching their frequency to the individual blade counts of the different blade rows which, in turn, allows to get insight into their interaction mechanisms and their inter-blade-row propagation mechanisms. Dependent on the operating point, the magnitude, and local distribution of the pressure fluctuation, components change significantly and components originating from different upstream and downstream blade rows become dominant. For operating points close to the design point both directly neighboring blade rows R2 and R3 are the main contributors to the RSI affecting the pressure fluctuations on stator vane 3 at mid span. For the intermediate off-design operating conditions the effect of the downstream blade row R3 diminishes and instead the blade row R1 further upstream beyond the directly neighboring R2 reaches magnitudes similar to that of R2. For strong off-design conditions the influence of the downstream blade row R3 diminishes further and instead of pressure fluctuations corresponding to the blade passing frequency of the immediate upstream blade row R2, a pressure fluctuation corresponding to the difference in blade counts of both upstream blade rows becomes the dominant component.
Power and Hydrogen Co-Production in Flexible “Powdrogen” Plants
Authors: de Cataldo Alessandro , Astolfi Marco , Chiesa Paolo , Campanari Stefano , Martelli Emanuele , Silva Paolo , Bedogni Stefano , Ottolina Luca , Tappani Marco , Romano Matteo C.
Published: October 2022

This study investigates the potential of “Powdrogen” plants for blue hydrogen and decarbonized electric power production, conceived to operate flexibly depending on the electricity price and to increase the capacity factor of the hydrogen production and CO2 separation units. The Hydrogen production is based on fired tubular reforming or auto-thermal reforming technologies with pre-combustion CO2 capture by a MDEA process. The power island is based on a combined cycle with H2-fired gas turbine and a triple pressure reheat heat recovery steam generator (HRSG). The analysis considers three main plant operating modes: hydrogen mode (reformer at full load with hydrogen export and combined cycle off) and power mode (reformer at full load with all hydrogen burned in the combined cycle), plus an intermediate polygeneration mode, producing both hydrogen and electricity. The possibility of integrating the HRSG and the reformer heat recovery process to feed a single steam turbine has been explored to allow keeping the steam turbine hot also in hydrogen operating mode. The economic analysis investigates the competitivity of the plant for different operating hours in hydrogen and power modes. Results suggest that these plants are likely to be a viable way to produce flexibly low-carbon hydrogen and electricity following the market demand.
Casing Treatment: Its Potential and Limitations
Authors: Yoon Sungho , Cargill Patricia
Published: October 2022

Casing treatment is an advanced design feature intended to improve the stability of a compressor. Various investigations have been conducted based on both experimental and numerical studies at least over the last fifty years. In general, it has been demonstrated that a careful design of a casing treatment can substantially improve the stall margin of a tip-limited compressor although this generally comes with an aerodynamic efficiency penalty. This review paper revisits important past studies on casing treatments to clarify findings on the sometimes-conflicting results and understand what lessons are generally applicable to a wider group of machines.

Circumferential grooves over a rotor tip have been in use for some time. Much recent work has focused on axial slots over a rotor tip, because of the significant stall margin improvement and the better efficiency potential of this configuration. This paper includes both configurations, with more emphasis on the latter.

The paper concludes that casing treatment offers powerful benefits to a compressor and deserves continuing research and development. Good benefits result from axial slots which start ahead of the rotor leading edge and cover the front part of the rotor tip and include skew (tangential lean in the direction of rotation). Contributing physical mechanisms include increasing the axial momentum of the casing flow casing and reducing the aerodynamic blockage to improve the casing boundary layer and the tip leakage flow. The role of impacting unsteadiness is yet to be further clarified.

Areas of further research are recommended, both experimental and analytical, including further work to understand and control the loss mechanisms, studying and controlling stage interaction effects in multi-stage compressors, and the simultaneous design optimization of the rotor blade with the casing treatment. Multi-disciplinary issues such as manufacturing cost, weight, length, durability, aeromechanics effects, tolerance to dust and ice, etc. also deserve further attention.
Improvement of Silicon Nitride Turbine Blade Impact Resistance Under Uniaxial Compression Loading
Authors: Beauchamp F. , Dubois P. K. , Plante J.-S. , Picard M.
Published: October 2022

The inside-out ceramic turbine (ICT), a novel microturbine rotor architecture, uses monolithic ceramic turbine blades held in compression by a rotating structural shroud instead of traditional superalloy turbine blades in order to increase its maximum turbine inlet temperature (TIT) and cycle efficiency. Previous work has shown that this microturbine architecture has potential to be viable for long-term operation in normal operating conditions. However, foreign object damage (FOD) has been a major concern for ceramic turbine rotor past development efforts, and its effects on the ICT ceramic turbine blades lifespan have not been studied thus far.

An experimental approach was used to characterize the effect of the ICT configuration on ceramic turbine blade impact resistance: spherical steel impactors were fired towards silicon nitride specimens simulating blade boundary conditions for both traditional and inside-out turbine layouts. Preload levels ranging from 100 MPa to 400 MPa were applied on the inside-out layout specimens to determine its effect on impact resistance.

Results indicate that the inside-out turbine configuration increases the resistance to FOD over a traditional turbine configuration. For the specific conditions of this study, the specimens resisted to over five times the impactor energy when fixed at both ends. Also, results show that applying a higher compression preload on the specimens helps to resist higher energy impacts by about 50% when far from the buckling limit.
A Study of Onshore Wind Turbine Property Damage
Authors: Jou Bin
Published: October 2022

As new capacity enters the wind energy market, property damage and forced outage losses of wind turbines are becoming more frequent. Risk assessment and property loss prevention for wind turbines are common goals for owners, operators, manufacturers, and insurers. In this work, wind turbine failures or damage from industry experience and literatures are reviewed and analyzed along with turbine property loss events at FM Global clients’ insured wind farms, with a focus on understanding the external and internal factors that drive the turbine damage through various failure modes, and for different modules or components. The types of property damage considered include breakdowns due to windstorms, lightning strikes, fires, as well as other mechanical and electrical breakdowns. The damage events are also analyzed from a component perspective including major items such as turbine blades, generators, gearboxes, other electrical and mechanical components etc. The risk of wind turbine property losses is discussed in terms of both frequency and severity of the events. The study reveals important trends of wind turbine property losses and indicates potential paths to effective loss prevention for various stakeholders in the wind energy industry.
Parametric Modeling and Economic Analysis of a 2MWth 3-Stream sCO2 Heat Exchanger
Authors: Neveu Joshua , Pryor Owen , Cich Stefan , Stechel Ellen
Published: October 2022

This paper presents the design and cost optimization of a novel 2MWth 3-stream sCO2 plate-fin heat exchanger. This heat exchanger design is unique in that it uses reduced metal oxide particle-to-sCO2 heat exchanger for cost-effective energy storage applications. The design uses low velocity, laminar air as the re-oxidizing reactant to transfer the heat of the re-oxidizing reaction to a sCO2 power loop. The design of the heat exchanger is based on a 2-D, 3-fluid plate/fin heat transfer model. The model parameterizes the size, shape, and number of passages of the heat exchanger to calculate the temperature profile, pressure drop, and fluid velocities of all three fluids. Global heat exchanger parameters such as the effectiveness and total heat transferred to the sCO2 are then calculated for overall performance. Due to the value and increased use of sCO2 heat exchangers in power cycles, a cost model of the system based on the unique high temperature/high pressure operating conditions was created using quotes from reference projects and market analysis. These quoted air-to-sCO2 heat exchangers are then processed using multiple weighting factors pertinent to heat exchanger design, including heat exchanger type, maximum temperature, differential pressures, fluids, duty, and more. These factors are then used in an exponential function in order to generate a parameterized cost curve. The design and cost of the heat exchanger are then optimized using the SMPSO genetic algorithm in Python. The optimization objectives for the system are to maximize the overall system effectiveness, including an air recuperator for preheating, and to minimize unit costs. Additional constraints are added to the system for the sCO2 and air pressure drops, air velocity to reduce particle entrainment, and the length and volume of the heat exchanger.
A Framework for Estimating Effects of Combustor Turbulence on Turbine Profile Loss Generation
Authors: Gakhar Kanika , Folk Masha , Greitzer Edward M. , Tan Choon S.
Published: October 2022

This paper describes a framework to quantify the effect of freestream turbulence, generated by mixing processes in a combustor, on turbulent boundary layer loss generation in the high pressure turbine downstream of the combustor. The regime of freestream turbulence common to gas turbine aero engines is identified and it is shown that the dissipation loss coefficient in this regime can be determined using existing measurements of the effect of freestream turbulence on skin friction. The paper shows that combustor-generated freestream turbulence can increase the profile loss coefficient of a typical high pressure turbine blade by as much as 28%. A relation has been derived between a non-dimensional turbulence parameter, which characterizes the freestream turbulence, and the increase in turbine boundary layer dissipation, which quantifies the decrease in turbine efficiency. The relation provides guidelines for combustor turbulence modifications that lead to turbine performance benefits. The framework has been applied in example trade studies which show that increasing the size of dilution ports and increasing the length of the combustor can decrease high pressure turbine profile loss generation to potentially increase stage efficiency up to 0.5%.
Vortex-Generators Reduce the Dynamic Axial Forces in the Model of a Steam Turbine Control Valve
Authors: Wallat Stefan , Musch Christian , Brillert Dieter
Published: October 2022

Control valves of steam turbines are exposed to large static and dynamic forces caused by pressure fluctuations, turbulence and other influences, especially in part-load operation. Excitation of acoustic modes in cavities is one of these causes that leads to fluctuating forces on parts of the valve especially the valve plug. In control valves, the acoustic mode can be excited by unstable periodic behaviour such as shear layer flow. This shear layer flow occurs behind the valve seat in the diffuser between the wall jet and a backflow region in the core of the diffuser.

This paper describes the occurrence of increased fluctuating axial forces on the valve plug in a control valve for steam turbines due to the excitation of an acoustic mode in the rear cavity between the valve plug and the valve cover. In the first step, an initial geometry is investigated in a test rig. The occurrence of an acoustic mode and the effects on the valve plug were measured using force, pressure and displacement sensors. The results are presented in this paper and compared to numerical results from previous studies.

In the second step, vortex-generators are installed in the same model valve and their effects on the excitation of the acoustic mode in the rear cavity are investigated. It is shown that the vortex-generators upstream of the valve seat effectively create vortices that affect the flow topology downstream of the valve seat. This weakens the excitation of the acoustic mode and reduces the axial forces.
Efficient Modelling of Blade Film Cooling in Gas Turbines
Authors: Penrose Justin , Zori Laith , Morales Juan Carlos , Patil Sunil , Pons David , Rida Samir
Published: October 2022

One of the most effective ways to mitigate thermal fatigue in a high-pressure turbine’s blades is by cooling the blade from inside and outside via an intricate cooling system. The cooling flow passes from the blade interior through many small holes to form a cooling film on the blade surface. In the early blade design phases, the designers must accurately determine the location, the pattern, the distribution density, the shape, and the size of cooling holes to maximize the blade film cooling whilst maintaining the external aerodynamics. Hundreds of simulation cycles may be needed to reach an optimal design.

In this work, a film-cooling model and associated workflow are proposed. The model implementation within Ansys-Fluent uses a virtual-boundary concept which does not require the explicit resolution of the holes. The benefit of this is its compatibility with existing turbomachinery solution methods, and the consistency with subsequent mesh refinement toward resolved hole geometry. The workflow will allow designers to dissociate the uncooled aerodynamic geometry and mesh from the hole/film-cooling design, during the early design iterations.

For verification of this approach, results for a simplified single hole-setup on a flat plate are first presented. A typical gas turbine vane configuration is then used to demonstrate industrial application. The results from an aerodynamic mesh refinement study show good agreement with the resolved model. Flexibility within the workflow for changing the location, shape and properties of the holes is also demonstrated. This approach, therefore, represents a useful design tool where multiple hole pattern configurations could be quickly assessed.
Explainable and Interpretable AI-Assisted Remaining Useful Life Estimation for Aeroengines
Authors: Protopapadakis Georgios , Apostolidis Asteris , Kalfas Anestis I.
Published: October 2022

Remaining Useful Life (RUL) estimation is directly related with the application of predictive maintenance. When RUL estimation is performed via data-driven methods and Artificial Intelligence algorithms, explainability and interpretability of the model are necessary for trusted predictions. This is especially important when predictive maintenance is applied to gas turbines or aeroengines, as they have high operational and maintenance costs, while their safety standards are strict and highly regulated. The objective of this work is to study the explainability of a Deep Neural Network (DNN) RUL prediction model. An open-source database is used, which is composed by computed measurements through a thermodynamic model for a given turbofan engine, considering non-linear degradation and data points for every second of a full flight cycle. First, the necessary data pre-processing is performed, and a DNN is used for the regression model. The selection of its hyper-parameters is done using random search and Bayesian optimisation. Tests considering the feature selection and the requirements of additional virtual sensors are discussed. The generalisability of the model is performed, showing that the type of faults as well as the dominant degradation has an important effect on the overall accuracy of the model. The explainability and interpretability aspects are studied, following the Local Interpretable Model-agnostic Explanations (LIME) method. The outcomes are showing that for simple data sets, the model can better understand physics, and LIME can give a good explanation. However, as the complexity of the data increases, both the accuracy of the model drops but also LIME seems to have difficulties in giving satisfactory explanations.