bluuebunny/crossref_metadata_2025 huggingface dataset:
Methanol-Fired Allam Cycle: Combining Oxy-Fuel Power Cycles With Synthetic E-Fuels
Authors: Manente Giovanni , Rahim Ahtasham , Ficarella Antonio
Published: August 2024

Direct-fired supercritical CO2 cycles combine oxy-combustion with supercritical CO2 to achieve high thermal efficiencies in power plants with carbon capture. The Allam cycle is a transcritical CO2 oxy-fuel cycle, named after its inventor. It achieves the highest thermal efficiencies compared to other oxy-fuel cycles, with a relatively simple configuration. Currently, most of the research and the commercial development of this cycle focuses on the use of natural gas or coal-derived syngas as a fuel, and oxygen obtained in cryogenic air separation units. Only recently, a few studies have investigated the integration of water electrolysis units that provide the oxygen for combustion. Instead, it appears that currently there are not studies about the use of biofuels or e-fuels in the Allam cycle. However, their use would allow to achieve net negative CO2 emissions and, possibly, to mitigate the issues of CO2 storage. This paper proposes and analyzes for the first time a methanol-fired Allam cycle. Methanol is produced from CO2 hydrogenation using hydrogen from an electrolyzer (e-methanol). Oxygen for methanol combustion is produced in the electrolysis unit. The methanol oxy-combustion generates a stream of flue gases composed uniquely by water vapour and CO2, being supercritical CO2 used as a combustion diluent. After turbine expansion and recuperation the water vapour is condensed and used as feed to the electrolyzer. Instead, the CO2 is partially recycled to the compressor and partially used for methanol production. The aim of the study is to evaluate the performance of the integrated system, and possibly its improvement by identifying any synergy between the Allam cycle and the methanol synthesis. Distinctive features of turbine expansion deriving from the use of methanol as a fuel are highlighted. The results show the optimum operating conditions of the overall system and the energetic and environmental performance, also in comparison with the natural gas fired Allam cycle.
RANS Prediction of Low-Pressure Turbine Tip Shroud Flows
Authors: Uncu Fatih , François Benjamin , Buffaz Nicolas , Le Guyader Sébastien
Published: August 2024

In low-pressure turbines, an attached tip shroud is often used to mitigate rotor tip leakage. The interaction between tip shroud’s bypass flow and the primary flow leads to mixing losses and amplifies vortex structures, which contribute to aerodynamic losses. Accurately predicting these losses remains a challenge with RANS approaches, especially for engine manufacturers aiming to design an efficient tip shroud geometry that ensures proper sealing while minimizing losses. This study aims to evaluate the capability of RANS simulations in tracking loss evolution with changes in tip shroud geometry. To do so, the present work assesses a second order Reynolds Stress Model (RSM), as well as an eddy-viscosity model, in a two stage low-pressure turbine with attached tip shrouds. Two different geometries (axisymmetric and non-axisymmetric) of the off-channel components have been simulated and their performance have been compared to relevant experimental measurements to understand the loss sources. The RANS simulations capture the correct trend in the isentropic efficiency: the non-axisymmetric tip shroud increases entropy production, resulting in poorer aerodynamic performance. The RSM simulations align better with the measurements and predict secondary structures that differ from those predicted by the linear model.
Rotordynamics of a Single-Stage Brush Seal in Isolation: The Effects of Variable Stiffness and Back Plate Geometry
Authors: Bird Joshua , Keogh Patrick S. , Sangan Carl M. , Bowsher Aaron A. , Crudgington Peter F. , Scobie James A.
Published: August 2024

Brush seals control leakage around rotating components from areas of high to low pressure inside turbomachinery. They are known to contribute to the overall stability of gas turbines, therefore their dynamic behaviour is of particular importance to engine designers. Despite this, limited research exists in the literature on the rotordynamic behaviour of brush seals. This paper aims to experimentally characterise the leakage and rotor-dynamic performance of two seals with different bristle diameters tested with both conventional and pressure-relieved back plates with a slight interference. A dynamic test facility was utilised to study the dynamic characteristics of an isolated seal with changes in excitation frequency, rotational speed and pressure drop.

Seal leakage increased with bristle diameter and with the use of the pressure-relieved back plate but reduced with increasing rotational speed for all tests. The direct dynamic coefficients were shown to increase with pressure difference. The back plate geometry influenced the change in stiffness coefficient with rotational speed. The larger bristle diameter resulted in a stiffer seal, however, the damping coefficient reduced with the reduction in packing density. The insight provided by these results will help inform engine manufacturers on the suitability of implementing brush seals in future gas turbine designs.
Integrated Performance Assessment and Decarbonising Potential for Aircraft Retrofitted With Sustainable Aviation Fuels
Authors: Rompokos Pavlos , Sasi Sarath , Mourouzidis Christos , Roumeliotis Ioannis , Pachidis Vassilios , Akure Michelle , Swindell Hannah
Published: August 2024

The aviation industry is transitioning towards sustainable fuels from conventional fossil-based jet fuels to make air travel sustainable and environment-friendly. Hydrogen, Ammonia, and Methane are all potential long-term solutions since their implementation relies heavily on the redesign of existing aircraft configurations. Sustainable aviation fuels (SAF) on the other hand, due to their similar physico-chemical characteristics with conventional fossil-based jet fuels, are an effective drop-in solution for both short and long term. This solution enables next, current, and older generation aircraft to reduce their carbon footprint.

This paper focuses on the retrofit application of SAF for an older-generation trainer jet aircraft for defence applications and aims to demonstrate the performance, economic and environmental impact of using the alternative fuels. A baseline high-manoeuvre mission profile with Jet A-1 is established, upon which all the SAF variants are compared. Reductions in fuel weight, in-flight CO2 as well as NOx emissions of up to 2–3% were observed, which are mostly attributed to the properties of the alternative fuels. Contrary to the fuel weight savings, higher operational costs are expected due to the higher SAF costs. At engine level, the fuel burn reduction enables a slight decrease in turbine entry temperatures. Finally, when switching to SAF, there exists shortcomings in terms of maximum operational range, mainly attributable to its lower density and consequently, lower energy stored in the fuel tanks.
Gas Turbine Design Point Definition Using Economics, Environmental and Optimization Aspects
Authors: Henrique De Paiva Pinheiro Carlos , Bringhenti Cleverson , Takachi Tomita Jesuíno , Jefferds Dos Santos Silva Franco , Roma Alexandre , Lopes Salgado Mayara
Published: August 2024

This work aims to provide a methodology for defining the design point for industrial gas turbine considering the economic, environmental, and engine performance aspects. The definition of the design point is a key step in the development project of a gas turbine since this definition involves the analysis of several operational points to verify if the desired performance can be obtained. Thus, to extend the methodology presented in the literature developed for micro-turbines to consider industrial gas turbines a computer program was developed in MATLAB®. This program is capable of performing thermodynamic calculations for design point definition and of performing single- and multi-objective thermoeconomic and thermodynamic optimizations using genetic algorithms. For the optimization process, total cost minimization, yield maximization, and gas turbine-specific work maximization were chosen as objective functions. The decision variables chosen were compressor pressure ratio, compressor polytropic efficiency, turbine polytropic efficiency, and maximum cycle temperature. For the calculation of economic aspects, fixed costs (equipment, installations, land acquisition cost, etc.) and variable costs (fuel, emissions, and operation and maintenance costs) were considered. The emission cost of NOx, CO, and UHC was considered for the environmental cost calculations. The thermodynamic calculations were based on enthalpy and entropy. The developed computer program was validated by simulating a commercial gas turbine and comparing the results obtained, also using a commercial program, GASTURB®. The presented optimization process shows results for a single objective, two objectives, and three objectives, where the results show a comparison between different design points obtained. The software developed will be of great assistance in the learning of engineering students.
Development of a Low-Pressure Section for Industrial Power Generation Application
Authors: Arcangeli Lorenzo , Aquilino Antonio , Brazzini Filippo , Cosi Lorenzo , Maceli Nicola , Rizzi Sara
Published: August 2024

The Low Pressure (LP) stages are critical components in any steam turbine product line, as their contribution has a significant impact on overall expansion and their specific operability design limits may pose restriction to the turbine operation.

The authors’ company designed a new family of LP stages for power generation applications aimed at improving the efficiency and the overall design of the existing low-pressure sections for 50 Hz and 60 Hz industrial power generation applications of a comparable annulus area.

Industrial power generation comprises a wide range of applications for fixed speed 50 Hz and 60 Hz LP stages, especially in Waste to Energy plants, Concentrated Solar Power plant, Geothermal plants, Combined Cycles plants, Captive Power plants and more recently, energy transition process power plants (e.g. green hydrogen production). This wide application mix establishes an ample set of requirements in terms, among the others, of off design performances, frequent start up, high exhaust pressure capability and capability to sustain operation in low load and erosion promoting conditions which poses a specific challenge in the definition of a single optimal design.

This paper will present a broad review of the typical operational and design requirements dictated by the various industrial power generation applications along with the summary of the all the phases of the design with focus on the technology related aspects of the different components developed, including exhaust system.
Experimental Measurements of Buoyancy Induced Flow in Rotating Cavities Under High Reynolds Number Conditions
Authors: Puttock-Brown Mark R. , Kanjirakkad Vasudevan
Published: August 2024

The buoyancy-induced flow structure and heat transfer in rotating cavities is a well-known conjugate problem. The disc temperatures affect the flow and vice versa. This creates a challenging environment to study as it is: three-dimensional, unstable, and unsteady. Further, the vast timescale range between the flow and thermal transients on the discs prove impractical to simulate within rapid engine design cycles, requiring validated reduced-order physics-based models. Literature has established the relationship between the temperature of the core and heat transfer and how this is affected by compressibility, resulting in a critical Reynolds Number at which disc Nusselt number is maximum.

This work presents new thermal measurements of a rotating cavity at engine representative conditions under elevated test section absolute pressure from the Sussex Multiple Cavity Rig. The axial throughflow temperature rise is recorded by shaft mounted thermocouple rakes, offering the opportunity for first-order energy balance estimates. By increasing the density of the throughflow air, this allows the investigation at Reθ and Gr rarely published from academic facilities, providing further insights into the interplay between the governing non-dimensional parameters. The results have shown, for all comparable cases of constant Ro, increasing Reθ has reduced disc surface temperatures. Despite elevated Gr ≥ 1013 and high temperature gradients, there is no conclusive evidence of thermal stratification and the associated sharp reduction in shroud heat transfer.
Multi-Objective Optimization and Chemical Reactor Network Modelling to Estimate the Minimum NOx and Ammonia Slip in an Aviation Combustor
Authors: Bobi Shahzad , Garai Priyankar , Rahman Ramees K. , Zamora David , Ahmed Marzuqa , Vasu Subith S.
Published: August 2024

Ammonia has been deemed an attractive option as a carbon-free fuel for power generation gas turbines to address greenhouse gas emissions and to deal with climate change. Recently, ammonia and its blends with hydrogen have been investigated as a prospective aviation fuel. However, high NOx emissions and unburnt ammonia slip during ammonia combustion make it challenging. This study explores chemical reactor networking (CRN) modeling and multi-objective optimization of NO emissions and NH3 slip for similar conditions of an aviation gas turbine. The parametric studies were considered for the equivalence ratio (0.9–1.4), ammonia fuel fraction (0.5–1.0), combustor inlet temperature (644–848 K), and inlet pressure (13–44 bar) at take-off, and high-altitude flight conditions. This simulation model was developed using Ansys Chemkin-Pro software, which consists of a rich burn stage as a network of ideal reactors. The results of CRN simulation indicate that a lean-to-rich equivalence ratio with 100% NH3/air combustion reduces NO emissions and raises NH3 slip trends in the primary stage. Adding hydrogen into the fuel mixture showed a slightly increased NH3 slip and decreased NO emissions at lower and higher inlet pressure and temperature. Moreover, results of optimization studies investigated minimum NOx emissions as low as 13, 38, and 100 ppm at take-off, cruise, and maximum altitude with 30 ms, 10 ms, and 5 ms, respectively, where NH3 slip was observed at less than 1 ppm in all cases of multi-objective optimizations.
CFD Study on the Effect of Rotor Leading Edge Erosion on the Performance of Single Stage Compressor
Authors: Jung Jin-sol , Son Changmin
Published: August 2024

As aircraft engines operate in various environments, they are subjected to adverse external factors, such as ice crystals, sand dust, corrosive gases, etc. which damage engine components. One common damage found in the engines is erosion in a compressor. Due to its rapid rotational speed, even minuscule particles can induce surface abrasions on the compressor airfoil, resulting in performance deterioration.

Considering the impact of compressor erosion, the sensitivity of the location and size of erosion in multistage compressors to its performance map remains an area for continuing research. However, there is very limited experimental data in the public domain, especially for multistage compressors. One and only experimental data available to the authors’ knowledge is a single-stage compressor test results with eroded NASA Rotor 35 airfoils. The rotor assemblies were built to represent three different combinations of nominal and eroded airfoils. The measured pressure fields at the downstream of rotor assemblies are compared. Noticeable difference in rotor performance is only shown near chocking region.

The present study aims to validate CFD against the measured performance of the single-stage compressor with eroded NASA Rotor 35 rotor assemblies. In addition, CFD analysis includes a ‘nominal’, non-eroded airfoil. The computational domain includes a full annular passage of the rotor and a single periodic passage of the stator. A commercial CFD package, Ansys CFX 2021 R2 was used for analysis.

As it was reported from experimental work, the predictions based on CFD showed negligible differences among the three configurations at the design condition. The review on the complete set of analysis matrix including off-design conditions will provide a more comprehensive understanding and useful guides for modelling the effect of erosion on compressor map.
A Modelica Based Integrated Air Vehicle - Novel Propulsor Architecture for Sustainable Aviation
Authors: Tristanto Indi , Thorpe Joseph , Palumbo Nunzio , Cino Andrea
Published: August 2024

To achieve the sustainable aviation target, the design of a novel propulsion architecture requires the ability to assess its performance and efficiency at air vehicle level. This is particularly important for those architectures requiring fuels with either low specific energy or low energy density, or even both.

This paper presents a consistent modelling tool to enable air vehicle level system performance to be considered during the design and operational analysis of a powerplant. A desirable feature is the ability to adjust the fidelity of each sub-system model according to the objective of a particular modelling phase. An equally important feature is the ability to protect intellectual properties owned by sub-system contributors. The paper is ended with an academic exercise comparing a conventional gas turbine, and a hybrid system of battery-boosted fuel cell powered regional aircraft to illustrate how the tool can be used to investigate challenges in designing a novel propulsion system.
A Hybrid Surrogate Modeling Approach for Data Reduction and Design Space Exploration of Turbine Blades
Authors: Ali Sazeed S. , Yadav Vikas S. , Nouri Behnam , Ghani Abdulla
Published: August 2024

The conventional iterative geometry optimization process for turbine blades using computer aided engineering (CAE) simulations is both cost and time consuming and has limitations in terms of computational requirements and data management. A particularly problematic aspect is that the generated 3D simulation data of computational fluid dynamics (CFD) and finite element analysis (FEA) cannot be fully reused for future optimizations. The data for multiple geometry variations of the turbine blade can range from several hundred gigabytes to multiple terabytes. This leads to difficulties in storing and accessing them for a longer period. To address this challenge, we introduce a methodology based on machine learning models for data reduction and forecast of 3D surface field data.

Specifically, we develop a convolutional variational autoencoder (VAE) that combines two models: the encoder and the decoder. The encoder transforms the input data into a representation of reduced dimensionality in a latent space, and the decoder reconstructs the input data from the given latent representation in its original space. The latent representation of the input data and the trained VAE together result in much smaller data amounts, solving the issue of data storage for future use. Furthermore, we train a fully connected feed-forward mutilayer perceptron (MLP) that learns the mapping of the geometry parameters, responsible for generating the variations, to the latent space. Thereby, we combine the MLP with the trained decoder of the VAE to our proposed multilayer perceptron variational autoencoder (MLP-VAE) hybrid neural network model. The MLP-VAE predicts the surface field data results for new and unseen blade geometry variations and generates their latent representations without any additional cost.
Combustor Operational Flexibility in the Ansaldo Energia GT36 Fleet
Authors: Sierra Sánchez Patricia , Pennell Douglas , Smith Richard L. R. , Wickström Anders , Gant Francesco , Boudy Frédéric
Published: August 2024

Ansaldo Energia has successfully introduced the GT36 H-class gas turbine to the market. The GT36 is equipped with a two stage Constant Pressure Sequential Combustion (CPSC) system, which consists of a premix burner system (Multi-Burner First Stage, MBFS) and a sequential burner (SB) in series within a can combustor architecture. The development and validation of the combustor system was accompanied by publications at recent ASME conferences, with a focus on fuel flexibility, turndown and future hydrogen applications.

In this paper, the optimized version of the CPSC system that is running commercially on various GT36 units will be described. Supported by field data, the paper will elaborate on important aspects of combustor operation, such as: Ignition and startup reliability, stable operation during engine load transients (including fast loading/de-loading, load rejection, and ancillary services such as primary frequency response), robustness against variable fuel properties, and operability under changing ambient conditions. Additionally, dedicated data is shown to demonstrate the extended turndown capability to below 20% relative load and the low emission levels from ignition to full load. The emission data covers fuel composition variation from virtually pure methane (< 0.5% C2+) to higher order hydrocarbon compound concentrations of up to 14% C2+.
Integrating Location-Specific Non-Destructive Inspection Simulation With Probabilistic Damage Tolerance Assessment
Authors: Enright Michael P. , Zaman Yasin , Foucher Fabrice , Lonné Sebastien , Dubois Philippe , Leberre Stephane , Calmon Pierre
Published: August 2024

Conventional probability of detection (POD) curve development is an expensive process that may not adequately capture local parameters that can influence POD outcomes. Non-destructive evaluation (NDE) simulation has the capability to consider these parameters but requires information regarding the anomaly sizes that must be found. Probabilistic damage tolerance (PDT) can be used to quantify anomaly sizes that are associated with failure at specific locations throughout a component. In this paper, a methodology is presented for integrating NDE simulation (via the CIVA software) with PDT analysis of turbine engine components (via the DARWIN® software). High risk locations are identified using PDT analysis. Anomaly sizes and orientations that lead to failure are identified for the NDE simulation. The resulting POD curves are applied to PDT assessments to quantify the influence of NDE on fracture risk enabling the analyst to identify the locations in a component that may benefit most from NDE inspection. The methodology is illustrated for a representative gas turbine engine component.
Laminar Burning Speed Measurements of Hydrogen/Natural Gas Mixtures at 10 atm
Authors: Safdari Ahmed F. , Yovino Louis , Kim Gihun , Rahman Ramees K. , Vasu Subith S.
Published: August 2024

Fossil fuels, when burned in the air, release large amounts of carbon dioxide (CO2) and greenhouse gases (GHG) into the air, causing a significant increase in pollution. To reduce exhaust emission of fossil fuels on the environment, we can use natural gas (NG). Extending the lean burn area similarly reduces emissions of greenhouse gases (CO and CO2) and NOx pollutants. Temperature, pressure, and reactive mixture composition all influence measuring laminar burning speed (LBS). LBS is helpful because it (i) provides a measure of combustion efficiency and heat release rate; (ii) makes it possible to validate chemical kinetic mechanisms; (iii) provides turbine design engineers with a metric for the anticipated amount of time needed to burn the fuel charge. While studies on natural gas and hydrogen combustion near atmospheric conditions exist, very few investigations exist on high pressures in the literature. Here, we report data on natural gas/hydrogen LBS measurements up to an initial pressure of 10 atm and initial temperature of 296 K. To investigate its impact on LBS, a wide range of equivalence ratios were used. As part of the validation procedure for the results, they are also contrasted with the performance of comprehensive kinetic models.
Experiments on Structurally Mistuned UHBR Open-Test-Case Fan ECL5/CATANA
Authors: Brandstetter Christoph , Schneider Alexandra P. , Fiquet Anne-Lise , Paoletti Benoit , Ottavy Xavier
Published: August 2024

The operational capabilities of turbofan engines encounter limitations due to instabilities arising from tightly coupled interactions among aerodynamics, acoustics, and structural mechanics. Modern fans and compressors exhibit Non-Synchronous Vibration (NSV), leading to safety-critical blade oscillations. In contrast to self-excited phenomena such as flutter, NSV stems from the convection of aerodynamic disturbances that synchronize with blade eigenmodes. Understanding this phenomenon is challenging, as its intricate interaction patterns and the occurrence of flow separations constrain the predictive capabilities of current state-of-the-art methods.

To establish a comprehensive benchmark dataset on the aeroelastic behavior of modern Ultra-High Bypass Ratio (UHBR) architectures, the European CleanSky-2 project CATANA aimed to examine a carbon composite fan stage, ECL5, utilizing multiphysical instrumentation. Recently, experiments on a structurally tuned reference configuration were conducted, revealing highamplitude Non-Synchronous Vibration (NSV) at multiple subsonic speedlines. The observed interaction modes and instability onset differed significantly from numerical predictions using both LRANS and URANS with prescribed harmonic blade motion.

In an effort to enhance the dataset, two additional fan configurations with identical blade profile geometries were investigated: one featured a structurally mistuned rotor with approximately doubled frequency variation of all eigenmodes compared to the reference, and the other involved a case with locally increased tip clearance on individual blades.

This paper presents the experimental results of a sensitivity study and explores the influence of structural mistuning and tip clearance variation associated with manufacturing tolerances.

Contrary to the intended outcome, it will be demonstrated that the mistuned case exhibited higher blade vibration amplitudes than the reference case during NSV. Detailed instrumentation reveals that the mistuning pattern was effectively transferred to the rotating system, but aerodynamic mistuning, particularly concerning tip clearance, emerged as a dominant factor. The non-synchronous forced-response nature of NSV during highly throttled operation ultimately dictates the observed response levels under different conditions, necessitating a thorough analysis to evaluate the robustness of a specific configuration.

These results contribute valuable insights to the open dataset for the ECL5 configuration, benefiting the research community. Particularly noteworthy is the detailed capture of blade-to-blade variations in this research, which will prove instrumental in validating numerical methods.
Techno-Economic Analysis of Emerging Energy Storage Technologies for a Microgrid
Authors: Schmitt Joshua , Hofer Douglas , Pryor Owen , Khawly George , Karg Bulnes Fernando , McClung Aaron
Published: August 2024

With the growing need for decarbonization, microgrids that independently produce carbon-neutral power will become an important part of the solution. An analytical model has been developed based on the historical demand at Southwest Research Institute (SwRI). This model incorporates general energy production and storage technologies into a flexible framework for assessment of scenarios for a microgrid. For solar photovoltaics (PV), the model incorporates time-series renewable data on solar PV performance from the NREL System Advisor Model (SAM). The capital cost and operating cost information for storage and generation were sourced from public studies and were escalated to 2023 costs using inflation. Using these inputs, the analytical model projects the 30-year performance of the power generating system and applies economic parameters to establish a blended cost of electricity that is a levelized cost of electricity (LCOE) for the capital and operating cost of behind the meter assets along with any purchased electricity or natural gas from utilities. A variety of electricity producing technologies were examined, including PV, gas generator with carbon capture and storage (CCS), lithiumion battery, hydrogen production and utilization, and pumped thermal energy storage. For shifting PV generation in daily cycles, the storage systems were implemented as long-duration energy storage (LDES) with a minimum duration of 6 hours.

The trends in blended electric cost showed how electric energy consumed on the SwRI campus can be decarbonized by 40%, while reducing costs by about 12% through the addition of behind the meter PV generation alone. Adding storage to utilize curtailed PV increased system cost, but it improved decarbonization to 55% before reaching parity with present electric costs. Reaching 90% decarbonization with PV and LDES came at the cost of an additional 37% increase of blended costs. The trends showed that costs beyond 90% decarbonization increase dramatically because LDES became very large to balance longer trends in PV power production and reach 100% decarbonization. A combined system that installed a gas generator with CCS showed how the last 10% of decarbonization can be achieved without the dramatically escalating costs of a PV with LDES system alone beyond 90%.
Numerical Analysis of Oscillating Blade in Linear Cascade at Transonic Flow
Authors: S. Ragupathy , Kushari Abhijit , Keerthi M. C.
Published: August 2024

This paper explores the numerical simulation of stall flutter in transonic compressor blades. The primary objective is to characterize the flutter patterns observed in oscillating blades impacting stationary blades in a linear cascade arrangement. The study focuses on the STC-5 airfoil configuration, utilizing a cascade assembly with five blades arranged in a linear manner. The oscillation amplitude is set at 2 degrees for the blades adjacent to the center blade (0 degrees) Both steady-state simulations and time-dependent analyses, considering three incidence angles and varying reduced frequencies and IBPA’s. The study underscores the significant role of surface pressure fluctuations induced by shock oscillation in determining unsteady aerodynamic forces affecting blade stability. These fluctuations primarily resulted from the movement of the shock impingement point on the blade surface. It reveals that the oscillation of the separated region, resulting from shock-boundary layer interaction, contributes to additional pressure fluctuations along the blade surface. Both shock oscillation and the movement of the separated region are identified as critical factors influencing unsteady aerodynamic behavior and vibration characteristics in the transonic compressor cascade.
Analysis and Optimization of the Fatigue Damage Accumulation Under Transient Vibrations of Mistuned Bladed Disks
Authors: Jing Tong , Zang Chaoping , Petrov Evgeny
Published: August 2024

This paper develops an efficient method for calculations of stress levels, accumulation of HCF and mistuning optimization aimed at the reduction of the fatigue damages for mistuned bladed disks under transient vibrations caused by variation of the rotation speed in the vicinity of resonance frequencies. The expressions for the sensitivities of the stress intensity at critical locations, and fatigue damage at loading cycles concerning the mistuning are derived analytically, providing high accuracy and speed of their evaluations. A gradient-based optimization method based on the sensitivities is applied to find the blade mistuning patterns providing the minimum and maximum fatigue damage accumulated during gas-turbine acceleration or deceleration of a mistuned bladed disk for extending the service life. The method uses realistic large-scale finite element modelling for bladed disks, accounting for the varying damping and excitation loads with amplitude and frequency spectrum changing with rotation speed. The method has been implemented in a computer code. The fatigue accumulation caused by the transient vibration has been studied using a realistic bladed disk model. The gradient-based optimization search for mistuning patterns providing the minimum and maximum fatigue damage accumulation during rotor acceleration is performed.
Conceptual Analysis on the Impact of Acoustic Liners in Fan Flutter
Authors: González-Monge Javier , Pérez José Miguel , Corral Roque , Zhao Fanzhou , Vahdati Mehdi
Published: August 2024

This work investigates the impact of acoustically treated intakes on fan flutter. The propagation of the fan acoustic perturbations is studied using a simplified model, where the frequency of the waves in the intake is the natural frequency of the fan blade in the stationary frame of reference. The model consists of a constant cross-section annular duct, where the acoustic modes are computed for hard wall and lined wall regions, assuming a uniform axial flow. The interfaces between the lined and hard wall sections are solved by doing mode matching. The acoustic reflections in the zero-thickness intake are computed using the WienerHopf technique following Rienstra’s model. Analytical results show that the waves propagating from the fan are reflected and scattered radially at the interfaces between the hard wall and the liner. Furthermore, the liner damps and changes the phase velocity of acoustic modes. Due to the low frequency of the flutter waves, the radial scattering can activate different cut-off modes, which need to be retained in order to make accurate predictions. The likelihood of fan flutter is estimated using the phase of the reflected cut-on waves reaching the fan. This strategy is used to assess the impact of the acoustic liners on the stability of a realistic fan. It is concluded that the impact of the phasing and reflections induced by the acoustic liners is comparable to that of the intake and can alter the flutter characteristics of the fan significantly.
The Effect of Temperature on the Forced Response of a Blisk Rotor With Inherent Mistuning
Authors: Dodda Jhansi , Leng Yujun , Key Nicole L.
Published: August 2024

Rotor forced response is a major cause of high-cycle fatigue (HCF) in gas turbine engines. Blade-to-blade variations in natural frequency, known as mistuning, can cause significant variations in the blade-to-blade vibrational response. Individual blade resonant response, primarily the peak frequency, has been used as a ‘fingerprint’ to identify a rotor blisk, and the change in frequency is widely used as a failure detection technique.

The frequency data from a forced response investigation of an embedded rotor in the Purdue 3-stage axial compressor research facility is the focus of this work. The forced response of the embedded rotor was measured with both strain gauge and blade tip timing systems. During a repeatability study of the vibrational response, a notable shift in blade peak response frequency was observed. Despite a shift in the peak frequency, the overall shape of the individual blade resonant response curve remained similar, even with the inherent mistuning of the rotor. Factors affecting the frequency and dynamic response were investigated to address this shift.

A major difference between these tests was the ambient temperature, which was different on different days and at different times of the day. Material properties are generally temperature-dependent, which has the potential to change natural frequencies. A cyclic symmetric FEM modal analysis showed a modal frequency shift at different temperatures. An analytical study was conducted based on the Fundamental Mistuning Model, considering the effect of temperature. The analytical results correlate well with the experimental results, showing similar blade peak response shifts without significantly changing the blade resonant response curve for the considered temperature range.
Ignition Characteristics of Fully Premixed Hydrogen/Air and Methane/Air Flames With High-Speed Chemiluminescence and Schlieren Imaging
Authors: Tiwari Pratik , Premchand C. P. , Palies Paul
Published: August 2024

This article investigates the ignition of hydrogen/air and methane/air premixed flames in a laboratory scale experiment. It focuses on an initial characterization of the ignition transient sequence comparing the effects of fuel, equivalence ratio, and bulk velocity as well as geometry (bluff-body vs swirler, confined or unconfined). Transient evolution of the flame through high-speed flame chemiluminescence imaging are recorded for selected pre-mixture injector bulk velocities ranging from 5 to 15 m/s in the lean equivalence ratio range. Additional high-speed data include schlieren imaging. The chemiluminescence data are utilized to generate integrated flame light time-series to estimate ignition delay time. A comparison of the experimentally determined ignition delay time is conducted with results from literature and chemical kinetic data. The observed differences are discussed. Results from the high-speed schlieren imaging at speed up to 140 000 frames per second (fps) capturing the spark ignition dynamic sequence are documented next for three specific cases. These selected ignition transient sequences leading to stabilized flames are characterized in the premixed turbulent combustion flamelet regime near unity Karlovitz number. The flame front is tracked by identifying flame edges as the flame surface expands during the earliest instants of the ignition sequence. The method documented in this article is an initial step that can be used in future work to describe the evolution from ignition to flame stabilization. This work is motivated to fill the gap on ignition studies in the fully premixed regime and especially for hydrogen/air premixture where spark igniter is utilized.
Aerodynamic Study of a Horizontal Axis Wind Turbine in Surge Motion Under Angular Speed and Blade Pitch Controls
Authors: Firpo Agnese , Sanvito Andrea G. , Dossena Vincenzo , Persico Giacomo
Published: August 2024

Floating offshore wind turbines experience dynamic conditions due to platform motion, requiring specific control strategies to mitigate loads and promote the wake diffusion improving overall wind farm efficiency. These problems can be appropriately modelled by medium-fidelity solvers, which rely on a CFD resolution of the flow while avoiding its detailed resolution around the blades, preserving high-fidelity in simulating the wake at an acceptable computational cost. This work adopts a medium-fidelity Actuator Line Model, implemented in the OpenFOAM environment, previously validated against experiments and multi-fidelity models in the frame of the OC6 Phase III project. The study analyses several operating conditions during surge motion: a variable angular speed in below-rated condition, conceived to maximise the turbine efficiency, and a collective blade pitch control employable in above-rated conditions to limit surge-induced loads fluctuations. The effect of each control strategy is assessed individually through a systematic comparison with the baseline case with constant angular speed and blade pitch. Results indicate that the angular speed control succeeds in increasing the turbine power, and reduces the spanwise variability of the induction factor amplitudes. Conversely, the pitch angle control reduces the force amplitude but does not alter the spanwise trend of the induction factor amplitude.
Design and Analysis of High-Temperature, High-Pressure Seal Test Rig
Authors: Kerr Thomas , Bensmiller Jason
Published: August 2024

As the power density of turbomachinery increases, individual components such as seals are subject to more extreme conditions. The maximum working fluid temperature and pressure are increasing, as is the operating speed. Seal performance has always had a large impact on machine efficiency, but with new working fluids and higher temperatures, this is especially true. Designing component level test rigs at these conditions presents challenges. Material compatibility at high temperatures, rotordynamics, thermal expansion, and a cooling scheme must be balanced in order to yield satisfactory designs.

This paper presents the design of a new test rig capable of testing seals to 700° C and 250 bar at speeds up to 21,000 rpm. The test rig measures leakage and estimates drag loss. While designed to test dry gas seals for sCO2, the test rig can accommodate a variety of seal types, geometries, and working fluids. A direct drive 250 kW motor provides rotation to the test rig, and a separate spindle assembly provides a connection to ground. Thermal expansion in the seal housing is radially uniform due to a flexible attachment to the spindle assembly. The seal housing material is Alloy 625, and is rated for the full pressure range. Cooling is provided to the spindle shaft through an oil/air system.
Systems-Based Approach to Predicting TBC Delamination due to CMAS Infiltration
Authors: Teglas Matei , Bojdo Nicholas , Elms Jacob , Pawley Alison , Covey-Crump Stephen , Jones Merren
Published: August 2024

CMAS infiltration and attack is difficult to simulate at real-world rates. To better understand the sensitivity of the process to engine operating parameters and CMAS chemical composition, a systems-based reduced order infiltration model that incorporates combustion gas properties, TBC microstructural properties, TBC heat transfer properties, and CMAS physical properties was developed. The aim was to predict the time to delamination for aircraft engines operating in non-benign environments. The penetration depths reached by a synthetic four-element CMAS mixture within a clean TBC were calculated by finite difference method. Engine operating conditions and TBC top coat types were varied to study the effects on the penetration depths and times. A larger difference between operating temperature and cold shock temperature was found to increase the risk of Mode I delamination. An increase in engine operating temperature had little effect on the critical penetration depth, but significantly influenced the actual penetration depth and time. An increase in EB-PVD TBC taper angle resulted in a decrease in the critical penetration depths, suggesting a greater risk of Mode I delamination. The time taken to reach the actual penetration depth increased with operating time, until the TBC was consumed, at which point penetration time decreased with operating temperature due to lower melt viscosity.
Model for Local Cavitation Instabilities in 2-Bladed Turbopump Inducers
Authors: Yoon Youngkuk , Song Seung Jin
Published: August 2024

Various local cavitation instabilities in turbopump inducers (e.g., alternate blade cavitation, super-synchronous rotating cavitation, etc.) have previously been experimentally identified. However, a model, which is capable of predicting such local instabilities is still lacking. Therefore, a new model, which models an N-bladed inducer as a system of N coupled mass-spring-damper systems, is presented to predict post-onset behavior of alternate blade cavitation instabilities. The model predicts alternate blade cavitation to occur. As the flow coefficient is decreased, the model predicts the magnitude of alternate blade cavitation to first increase and then decrease, and then finally vanish. If the flow coefficient is further decreased beyond the range of alternate blade cavitation, sudden increase in equilibrium incidence is predicted. All of these predictions agree with the previous experimental findings. Furthermore, simultaneous in-phase oscillations of the blade cavities are predicted during alternate blade cavitation. These in-phase oscillations of the cavities correspond to the surge mode oscillation, which had been previously mistakenly categorized as a global (system) instability. Finally, it is proposed that the above post-onset behaviors of alternate blade cavitations are general in two-bladed inducers, as long as the change in incidence on the following blade has a local minimum when it is expressed as a function of leading blade’s incidence.
Perception and imitation of period-doubled phonation: Pitch and voice quality
Authors: Huang Yaqian
Published: August 2024

Period-doubled phonation, henceforth, period doubling, characterized by voicing periods that alternate in amplitudes and/or frequencies, is often perceived rough and with an indeterminate pitch. Lower pitch percept has been suggested by past studies when the degree of amplitude or frequency modulation increases. However, how listeners use period doubling when identifying linguistic tones remains unclear. The current study uses tasks of categorization with training, followed by imitation of tones manipulated with period doubling (with amplitude and frequency modulation, both separately and jointly) in a novel language. Native Mandarin and English speakers with different levels of music experience were tested. I show that period doubling leads to a low-tone bias in perception and imitation, especially as the modulation degree, particularly that of frequency, increases. Interestingly, interactions with stimulus f0 and modulation type show that in amplitude-modulated tokens, when compared to lower f0 (200 Hz), higher f0 (300 Hz) drives more low-tone responses. Period doubling is also imitated with lowered f0 and creaky quality. Language and music experience does not affect perceptual and imitative responses, suggesting that the perception of period doubling is not language-specific or conditioned by tonal knowledge. Period doubling likely signals low tones, even when the original f0 is high.
Influencers de la Educación Física en Instagram: el Engranaje entre Conocimiento Experto, Estrategias de Microcelebridad y Funcionalidades de la Plataforma
Authors: Alcolea Lozano Alejandro , Camacho-Miñano Maria José
Published: August 2024

Propósito: Este estudio analiza el profesorado de Educación Física (EF) que adopta el rol de influencer en la red social Instagram. Método: Mediante un estudio de casos descriptivo, se han analizado durante siete meses los perfiles de tres influencers españoles (159 post y 73 stories) con un análisis temático. Resultados: El rol de influencer de EF es producto de un complejo engranaje en el que la difusión de su conocimiento y su identidad como personas expertas se desarrolla a través de estrategias de micro-celebridad y el manejo de las funcionalidades de la propia plataforma orientadas a potenciar su visibilidad y, en última instancia, monetizar su contenido. Conclusiones: Se concluye con las tensiones que existen para la EF en torno a este fenómeno dentro del contexto educativo neoliberal y la necesidad de que la formación del profesorado se adapte a esta nueva realidad educativa.
The TaWAK2-TaNAL1-TaDST pathway regulates leaf width via cytokinin signaling in wheat
Authors: Du Dejie , Li Zhaoju , Yuan Jun , He Fei , Li Xiongtao , Wang Naijiao , Li Renhan , Ke Wensheng , Zhang Dongxue , Chen Zhaoyan , Jiang Zihao , Liu Yunjie , Chai Lingling , Liu Jie , Hu Zhaorong , Guo Weilong , Peng Huiru , Yao Yingyin , Sun Qixin , Ni Zhongfu , Xin Mingming
Published: August 2024

Leaves play a crucial role in photosynthesis and respiration, ultimately affecting the final grain yield of crops, including wheat (
Triticum aestivum
L.); however, the molecular mechanisms underlying wheat leaf development remain largely unknown. Here, we isolated a narrow-leaf gene,
TaWAK2-A
, through a map-based cloning strategy.
TaWAK2-A
encodes a wall-associated kinase (WAK), for which a single Ala-to-Val amino acid substitution reduces the protein stability, leading to a narrow-leaf phenotype in wheat. Further investigation suggests that TaWAK2 directly interacts with and phosphorylates TaNAL1, a trypsin-like serine/cysteine protease. The phosphorylated TaNAL1 is then involved in the degradation of the zinc finger transcription factor TaDST, which acts as a repressor of leaf expansion by activating the expression of the cytokinin oxidase gene
TaCKX9
and triggering in vivo cytokinin degradation. Therefore, our findings elucidate a signaling cascade involving TaWAK2-TaNAL1-TaDST that sheds light on the regulation of wheat leaf development.
Real-world exoskeletons are better than those in the movie
Atlas
Authors: Murphy Robin R.
Published: August 2024

The recent movie
Atlas
misses fundamental robotics advances in self-stabilization and human-robot interaction.