bluuebunny/crossref_metadata_2025 huggingface dataset:
Best Practices From Hydrogen Fuel System Retrofit
Authors: Pigon Travis , Cloyd Scott , Springer Chaya , Boggs James , Shiraiwa Takashi , Yamazaki Shinichi
Published: September 2023

Hydrogen co-firing is increasingly being considered as a viable solution for the decarbonization of Gas Turbine Power Plants. Enabling this capability at existing natural gas-fired plants requires a hydrogen fuel system retrofit. Hydrogen has a higher propensity to leak and ignite when compared to natural gas. Additionally, when blending hydrogen, hazardous area classification and materials do not necessarily comply with the industry regulations and standards for power plants that run on 100% natural gas. Considering these challenges, the conventional procedures and tests used for natural gas must be reconsidered for the application of hydrogen to achieve a safe, compliant, and cost-effective retrofit.

This paper summarizes best practice recommendations and lessons learned from the successful retrofit and demonstration of a hydrogen fuel system for co-firing at a Southern Company/Georgia Power combined cycle plant featuring Advanced Class M501G gas turbines. As the paper discusses, the methods applied during the project are not new to the industry. However, it was necessary to employ a more controlled and, at certain points, inventive process to address the challenges presented by the unique properties of hydrogen.
Advanced Polytropic Efficiency and H-S Diagram Application
Authors: Wettstein Hans E.
Published: September 2023

The polytropic efficiency is the best quality measure for compressing or expanding engines for compressible fluids. Compressor- and gas-turbine 1D cycle performance simulation methods use it preferably. In steam expanding engine simulation the isentropic efficiency definition is dominating. However, the polytropic efficiency is well applicable for steam expansion based on recent papers of the author [1], [2]. Most applications of polytropic efficiency assume adiabatic change of state. In current turbomachinery, external heat exchange in the blading is often negligible due to short residence time and established external insulations. However, in (historic) reciprocating engines as well as in some current concepts external heat exchange plays an important role forcing to understand this effect as well. This paper aims at understanding the effects of external heat exchange on the polytropic efficiency calculated with a recursive numeric integration algorithm for any finite pressure ratio in expansion.

I select as a teaching appliance a historically well-documented reciprocating Uni-(directional)-flow steam engine involving steam condition with condensation (assuming equilibrium). The older reciprocating steam engines (with alternating flow direction in the cylinders) have both internal heat exchange and external heat losses during expansion. “Our” uniflow engine was a considerable historic improvement step including internal heat exchange in a documented manner. This allows demonstrating the features and the interpretation of the polytropic efficiency based on the use of the current IAPWS steam data.
The Role of Diffusive Mixing in Current and Future Aviation Fuels at Relevant Operating Conditions
Authors: Di Sabatino Francesco , Wan Kevin , Manin Julien , Capil Tyler , Hicks Yolanda , Gander Alex , Crua Cyril
Published: September 2023

With aviation’s dependence on the high volumetric energy density offered by liquid fuels, Sustainable Aviation Fuels (SAFs) could offer the fastest path towards the decarbonization of aircrafts. However, the chemical properties of SAFs present new challenges, and research is needed to better understand their injection, combustion and emission processes. While efforts such as the United States National Jet Fuel Combustion Program (NJFCP) that investigated several aspects in detail, certain processes were unfortunately beyond the reach of this program. One of them in particular is about droplet evaporation at relevant pressures and temperatures, and this represents the focus of the present manuscript. To address this gap we characterized the evaporation and mixing of spray droplets injected into well-controlled thermodynamic environments at conditions relevant to modern and next generation aero-engine combustors. We tested three fuels from the NJFCP, namely an average Jet A fuel (A-2), an alcohol-to-jet fuel containing highly branched dodecane and hexadecane type components (C-1), and a blend made of 40 % C-1 and 60 % iso-paraffins ranging from 9 to 12 carbon atoms (C-4). We also tested a single component normal alkane: n-dodecane, as well as an advanced bio-derived cyclo-alkane fuel: bicyclohexyl. The time evolution of fuel droplets was monitored using high-speed long-distance microscopy in a specific configuration that enabled sharp images to be acquired at these extreme conditions. The collected images were processed using a purposely-developed and trained machine learning (ML) algorithm to detect and characterize the droplets’ evaporation regime. The results revealed different evaporation regimes, such as classical and diffusive. In agreement with previous studies, evaporation regimes appear to be controlled by ambient pressure, temperature, and fuel type. The measurements demonstrate that diffusive evaporation is relevant at high-pressure conditions, such as take-off combustor pressures for modern commercial aircraft engines. However, classical evaporation mostly controls mixing at lower pressure, such as cruise altitude conditions. The ML analysis emphasized that multiple evaporation regimes co-existed at the same operating condition and no significant relationship was found between droplet size and evaporation regime. The findings of this work constitute a database for validating spray and droplet models that are necessary for implementing lower emissions fuels in aero-engines.
Characterization of High-Pressure Hydrogen Leakages
Authors: Cerbarano Davide , Lo Schiavo Ermanno , Tieghi Lorenzo , Delibra Giovanni , Minotti Stefano , Corsini Alessandro
Published: September 2023

Reduction of gas turbines carbon emissions relies on a strategy for fueling the engines with pure or blended hydrogen. The major technical challenges to solve are i) the adjustments to the engine and in particular the combustion chamber and ii) a series of issues to solve to guarantee safe operations. In fact, compared to natural gas, hydrogen fueling implies higher risks of explosion in case of leak in the turbine enclosure and a more careful design of the ventilation system. Thus, a deeper comprehension of hydrogen leak scenarios is needed to adjust the safe design strategy of the enclosure. To this aim, a series of numerical investigations was carried out to understand how different methane-hydrogen blends (from pure methane to pure hydrogen) behave when leaking from a pipeline with fuel pressure that span from 1.5 to 4.5 MPa. The different fuel blends leaks in form of under-expanded jets were studied under different cross-flow ventilation conditions, with ventilation velocity spanning from 0 m/s to 5m s.

When compared to pure methane, the outcome is a three times longer penetration distance for pure hydrogen axisymmetric flammable clouds, whereas in cross-flow conditions a more complex three-dimensional behavior was found, potentially opening a safety-related concerns discussed in the manuscript.
Swirl Enhancement Effect on Turbine Rim Seal Performance
Authors: Choi Mingeun , Goo Bonhan , Cho GeonHwan , Song Seung Jin
Published: September 2023

In gas turbines, sealing flow is extracted from the high-pressure compressor and supplied into the turbine wheel-space to suppress hot gas ingestion. Such hot gas ingestion is thought to be driven by the difference in either the static pressure or swirl between the mainstream and wheel-space flows. For the first time, experiments have been conducted in a low-speed single-stage axial turbine with a single-radial clearance rim seal and a “swirler” on the rotor disk. The objective is to evaluate the impact of enhanced wheel-space flow swirl on the rim seal performance. The swirler does not affect the mainstream flow. In the wheel-space, however, the swirler reduces static pressure; increases swirl; and improves rim seal performance (i.e., reduces the minimum sealing flow rate needed for hot gas ingestion prevention). Thus, the seal performance improvement occurs with increased difference in pressure and reduced difference in swirl between the mainstream and wheel-space flows. Therefore, it can be inferred that the rim seal performance depends more strongly on swirl than pressure. Preliminary gas turbine cycle performance studies indicate that net cycle efficiency benefits can be obtained.
Effect of Air-Liquid Homogeneous Mixture on the Linear Dynamic Characteristics of a Hydrostatic Journal Bearing
Authors: Voitus Anthony , Arghir Mihai , Hassini Mohamed-Amine
Published: September 2023

Water lubricated hydrostatic journal bearings are widely used to support radial load of pumps in nuclear power plants. In some situations, these pumps may be required to operate with a mixture of water and air. This compressible air-water mixture will alter the dynamic characteristics of the hydrostatic journal bearings and can have a significant impact on the vibration behavior of the entire pump shaft line. The present work is a parametrical investigation of the rotordynamic characteristics of these bearings relative to the volume fraction of the ingested air. The compressibility, the density and the viscosity of the air-water mixture depend on this volume fraction. In order to evaluate this influence, a homogeneous air-liquid mixture model was developed. Moreover, for low viscosity lubricants, inertia effects can also have an important impact on bearing rotordynamic coefficients. Therefore, the flow is modeled first with the Reynolds equation and then with the bulk flow system of equations to evaluate this impact. The results show the variation of the direct and cross-coupling stiffness and of the direct damping with the evolution of inertial effects and of the level of air contamination.
Application of a Multidisciplinary Design Process to Assess the Influence of Requirements and Constraints on the Design of Military Engines
Authors: Matuschek Tomasz , Otten Tom , Zenkner Sebastian , Becker Richard-Gregor , Zamboni Jacopo , Moerland Erwin
Published: September 2023

The design of supersonic military aircraft is a complex multidisciplinary optimization (MDO) process in which the dependencies and strong interactions between engine and aircraft must be imperatively considered. Applying a fully coupled propulsion-airframe design system is a highly challenging task, since it requires a set of numerically stable analysis tools capable of optimizing multiple design variables simultaneously. To improve computational efficiency, the application of low-fidelity design of experiment (DOE) methods aid in narrowing down the selection of suitable combinations of design parameters. This approach allows the division of the multidisciplinary process into subsystems, each of which can be served by specialized engineers. Interactions between the disciplines are then considered by exchanging DOE-based sensitivities.

This paper presents the multidisciplinary design process developed at the German Aerospace Center (DLR), — in which the airframe and propulsion system are designed simultaneously whilst effectively utilizing DOE-based sensitivities. Guiding the work is an application case on the preliminary design of military engine concepts considering its effects on overall integrated aircraft architecture. The design process is used to investigate the influence of important engine parameters such as overall pressure ratio (OPR), bypass ratio (BPR) and turbine entry temperature (T4) on the design of military aircraft. Furthermore, the impacts of thrust requirements and technological constraints of the engine are analyzed.
Viability of Fiber Optic Temperature Sensors Embedded Within Engine-Scale Turbine Blades
Authors: Berexa Emily K. , Fells Julian A. J. , Ireland Peter T.
Published: September 2023

Small variations in temperature across a gas turbine blade can have significant impacts on engine fuel efficiency, power output, and blade life. Therefore, an improved understanding of the temperature distribution on the surface of and within a gas turbine blade supports optimization of cooling systems and blade structures. While established methods exist for external blade surfaces, limited methods exist to capture the temperature distribution within the internal structure. Due to the small sizes of blades and the complex cooling configurations they contain, optical access is limited, and sufficient spatial resolution is difficult to obtain. This paper explores the viability of embedding fiber optic temperature sensors within engine-scale turbine blades. Given their minimally invasive nature, potential for multiplexing, and ability to operate in harsh conditions, fiber optic sensors present an opportunity to capture detailed temperature data for research and development or in-situ health monitoring. Specifically, fiber Bragg gratings (FBGs), or narrow band filters which reflect certain wavelengths of light, can be used to sense physical parameters such as strain and temperature. A single optical fiber with a diameter of less than 0.2 mm can contain many FBGs along its length, allowing for measurements with high spatial resolution. Additionally, the high temperature capabilities of FBGs create sensors well-suited for the harsh conditions present in turbine blades. This paper identifies and explores obstacles to the embedding of FBG sensors within engine-scale blades. Three primary challenges include routing through complex configurations, achieving thermal contact between the sensor and blade, and decoupling strain and temperature for embedded measurements. This study evaluates how routing and embedding fiber optic sensors within a blade impact the measurements acquired. Following this study, instrumentation of a cooled, engine-scale blade with fiber optic temperature sensors will be undertaken in a linear cascade at the Oxford Thermofluids Institute.
Initial Numerical Simulations of a Laboratory-Scale Premixed Hydrogen/Air High Swirl Experiment
Authors: Caulfield Christopher J. , Patil Sunil , Arguinzoni Carlo , Ansari Naseem , Palies Paul
Published: September 2023

As decarbonization of combustion systems is critically important, studies focusing on hydrogen combustion are required and undertaken for various future industrial applications. In this context, an experiment located at The Combustion and Propulsion for Aviation Research Center is studied with numerical simulations to get insights into both non-reacting and reacting flow-field. This article presents the computational results of a series of numerical simulations of this laboratory scale fully premixed hydrogen/air experiment. The design of the experiment is first discussed with key components of the setup being described. This setup includes water-cooled bluff-body and upstream plenum for flashback mitigation, axially translatable swirler for combustion instability passive control, and both partially-premixed and fully premixed operating conditions. The simulated operating point corresponds to an equivalence ratio of 0.6, an injector bulk velocity of 13.4 m s−1 and a thermal power of 9 kW. The article discusses results obtained with Reynolds-Averaged-Navier-Stokes (RANS) and Large-Eddy-Simulations (LES) for the non-reacting flow as well as obtained with Stress-Blended Eddy Simulations (SBES) for the reacting flow. State-of-the-art meshing and geometry capabilities are used and lead to a poly-hexacore mesh made for those simulations with a cell count of 6.2 million. The turbulence closure, the combustion and kinetic models used along with the simulations settings are described. The convergence is discussed with two main metrics: mass conservation and residuals monitoring. The results indicate that the current experimental design enables: (i) the formation of a strong inner recirculation zone (IRZ) and an outer recirculation zone (ORZ) as captured by the computations, (ii) the stabilization of a highly swirled premixed hydrogen/air flame which is observed to be compact.
Effect of Hydrogen Enrichment on Transfer Matrices of Fully and Technically Premixed Swirled Flames
Authors: Blondé Audrey , Schuermans Bruno , Pandey Khushboo , Noiray Nicolas
Published: September 2023

Knowledge of flame responses to acoustic perturbations is of utmost importance to predict thermoacoustic instabilities in gas turbine combustors. However, measuring transfer functions linking acoustic quantities upstream and downstream of flames is very challenging in practical systems and these measurements can significantly deviate from state-of-the-art models. Moreover, there is a lack of studies investigating the effect of hydrogen enrichment on the response of natural gas (NG) flames. In this work, measurements of flame transfer matrices (FTM) of turbulent H2/NG flames in an atmospheric combustor featuring an axial swirler burner have been performed, allowing us to unravel the transition between FTM in fully premixed (FP) and in technically premixed (TP) conditions. Furthermore, imaging of OH* chemiluminescence and OH-Planar Laser Induced Fluorescence are obtained for characterizing the topology of the flame for varying H2 fraction and mixing conditions. Transfer matrices are measured using the multi-microphone method for H2 fractions ranging from 12% to 43% in power. Afterwards, the flame transfer functions (FTF), which linearly relate the coherent fluctuations of the heat release rate to the acoustic velocity oscillations, are obtained from the FTM by using the Rankine-Hugoniot jump conditions across the flame. Using the OH* chemiluminescence intensity as a surrogate for the heat release rate, the FTF based on this optical measurement is also extracted and compared to the one exclusively obtained with the multi-microphone method. As expected, the two different methods are in very good agreement for the FP case and significantly differ for the TP case. Indeed, chemiluminescence fluctuations cannot be directly linked to heat release rate fluctuations when the acoustic forcing induces equivalence ratio fluctuations at the flame, making the optical method unusable for TP configurations. We also show that the two methods agree in the high end of the explored excitation frequency range and we provide an explanation to this intriguing finding. Moreover, we investigate the sensitivity of the FTM measurement to the estimate of the speed of sound in the rig in FP conditions. Finally, the measured FTFs are fitted with FTF models based on multiple distributed time delays. This allows us to explain the frequency dependence and the hydrogen fraction dependence of the gain and the phase in FP and TP conditions.
Surrogate-Based Robust Optimization of a Blade-Disk Interface
Authors: Emmrich Elmira , Voigt Matthias , Hörmann Julia Maria , Bruder Lukas , Mailach Ronald
Published: September 2023

The design of the blade-disk interface in a jet engine is of particular importance since the resulting stresses in both disk and blade represent limiting factors for the life of the engine. Hence, it is important to find an optimal design that fulfills lifing requirements and is robust with respect to uncertainties such as manufacturing variabilities.

In this paper, the challenges of performing such a robust optimization are analyzed and a solution strategy is proposed. Based on a numerical model of the blade-disk interface, involving a high-dimensional parametrization of the interface geometry, a surrogate-based optimization is carried out.

The surrogate model is created from a set of Monte Carlo samples covering the high-dimensional design space. Correlations among the input variables as well as nonlinearities in the numerical model require the use of Gaussian process surrogate models instead of simple polynomial approaches. Based on this, an efficient exploration of the design space is possible, minimizing the relevant stresses of the design. In the next step, the robustness of the optimized model is analyzed via the maximum stresses and the standard deviation as the robust optimum of the design. With this approach, lifing as well as robustness requirements can be incorporated into the design process.
Investigating the Cause and Threat of Lack of Fusion in 316L Parts
Authors: Scott-Emuakpor Onome , Warner Justin , Celi Dino , George Tommy
Published: September 2023

This study connects information from tensile strength data, fractography, computed tomographic (CT) scanning data, and previous additive manufacturing (AM) research to determine the cause of a unique lack of fusion (LOF) phenomenon in Laser Powder Bed Fused (LPBF) 316L parts. Motivation for the study comes from the need to understand the structural capability of an LPBF IBR operating under vibration excitation within a spin rig. A minimalist approach (limited data and analysis) is used to assess structural capability. Therefore, small amounts of information are leveraged within a systematic approach that is applied to the LOF root cause analysis. The results show a unique repeatability in LOF occurrences for a specific geometry within a build volume. Correlating the build strategies to previous AM research, the LOF phenomena appears connected to melt pool characteristics that are functions of geometric features and scan strategies. The important takeaway from this study is that the LOF in the specimen is not representative of the defect characteristics in the IBR and does not reflect the risk level of spinning the IBR in a vibratory environment.
Early Fault Detection Using Deep Learning on Compressed Cyclic Spectral Coherence Maps
Authors: Perez Sanjines Fabian , Peeters Cédric , Verstraeten Timothy , Vervlimmeren Ivo , Nowé Ann , Helsen Jan
Published: September 2023

Research nowadays takes advantage of the cyclostationary properties in the vibration waveforms of rotating machines for fault detection. For example, cyclic spectral coherence maps (CSCM) break down vibration signals into cyclic and carrier frequencies. However, the large size of the CSCMs and the enormous amount of data makes it challenging to identify the faults. Therefore this paper presents an approach that uses compressed CSCMs as input for a deep learning autoencoder, as a means to detect mechanical failures from vibration signals. The autoencoder learns to reconstruct a healthy version of the CSCMs, taking advantage of the generalization bias due to the unbalanced existence of healthy data. Furthermore, if the autoencoder receives a faulty CSCM as input, it reconstructs a healthy version. Alarms are triggered if the residuals between reconstruction and input CSCM exceed a calculated threshold. Next, the reporting step lists the cyclic order, carrier frequency band, and their respective alarm numbers. Five years of data from five different turbines in the field is used to train the autoencoder. The evaluation is validated on data from two faulty and eight healthy turbines. This work provides a fast, reliable and automated method to detect mechanical failures.
An Euler-Based Throughflow Approach for Axial Compressors
Authors: Martens Oliver , Schuster Sebastian , Brillert Dieter
Published: September 2023

Precise and fast performance map calculation of turbomachinery in the design process provides the basis for low-cost and efficient development of new machines. For this purpose, map calculation programs are needed that can calculate the complete performance map, including surge and choke limits, with limited geometry data. This paper presents a throughflow approach based on the inviscid Euler equations and the finite volume method. The governing equations are supplemented by models that account for the losses and the deflection of the flow. The presented approach offers flexibility regarding radial mass transport and can also solve locally choked blade channel regions. The paper utilises this approach to calculate the performance map of a four-stage axial compressor. Losses derived from profile polars are considered via a total pressure loss co-efficient. Furthermore, the results are compared with validated three-dimensional computational fluid dynamics (3D-CFD) results. A good agreement is achieved in terms of efficiency and pressure ratio. Finally, the results allow to conclude that Euler-based throughflow approaches allow a precise computation at the choke limit (suction line).
A Numerical Test Rig for Turbomachinery Flows Based on Large Eddy Simulations With a High-Order Discontinuous Galerkin Scheme - Part 1: Sliding Interfaces and Unsteady Row Interactions
Authors: Bergmann Michael , Morsbach Christian , Klose Björn F. , Ashcroft Graham , Kügeler Edmund
Published: September 2023

In this first paper of a three-part series, we present the extension and validation of the high-order Discontinuous Galerkin scheme in DLR’s CFD-solver TRACE for scale-resolving simulations of unsteady row interactions. The translational movement of rows in linear cascade experiments is represented in the numerical model by solving the equations in the relative frame of reference. To couple rows in different frames of reference, a sliding interface approach based on the mortar technique for non-conforming meshes has been developed. The verification of the approach is exemplified by three canonical test cases. First, the experimental order of convergence is verified for the isentropic vortex convection. Subsequently, the suitability of the sliding interface approach for scale-resolving simulations is tested on the Taylor-Green vortex flow and a turbulent cylinder flow. Finally, the LES solver is applied to the T106D cascade with upstream moving bars at an exit Reynolds number of 200, 000 and exit Mach number of 0.4. The flow physics with and without bars are discussed in terms of the instantaneous flow field, and time- and phase-averaged quantities. The comparison with experimental data shows overall a good agreement, especially for the total pressure losses in the wake, but also reveals uncertainties related to the reproduction of an experiment in the numerical model.
Mass-Heat Coupling in Film Cooling Experiments — The Influence of Temperature and Turbulence on the Dufour Effect
Authors: Wiese Connor J. , Rutledge James L.
Published: September 2023

The use of foreign gases in laboratory film cooling experiments is attractive since variable density ratios can be achieved with coolant-to-freestream temperature ratios near unity, often reducing the cost and difficulty of the experimental campaign. In adiabatic effectiveness experiments employing pressure sensitive paint along with the mass transfer analogy to heat transfer, isothermal surfaces are often an experimental requirement. Furthermore, low temperature laboratory experiments using thermal techniques often employ relatively close matches between the coolant and freestream temperatures. Using foreign gases, however, introduces off-diagonal couplings of heat and mass transport, which can produce unexpected results in film cooling experiments. In particular, the Dufour effect — also called the diffusion-thermo effect — which is the transfer of thermal energy by mass transfer processes, can manifest in surface temperatures that break the traditional bounds of thermal adiabatic effectiveness experiments: outside the upper and lower bounds of the coolant and freestream temperature. Beyond the expected confusion for the researcher, this effect can also be detrimental to those that assume that matching the coolant and freestream temperatures are the necessary and sufficient conditions to ensure isothermal surface conditions in traditional pressure sensitive paint experiments. In this work, the influence of cooling gas selection, experimental temperature, and experimental freestream turbulence conditions are explored on a simulated leading edge with compound injection from a cylindrical cooling hole. Air, argon, carbon dioxide, helium, and nitrogen coolants were analyzed due to their use in prior film cooling studies. The Dufour effect was found to be significant when using helium as the coolant, though temperature separation was also observed in argon and carbon dioxide cases. Additionally, elevated experiment temperatures generally increased temperature separation. Finally, high freestream turbulence intensity was found to reduce, but not eliminate, the Dufour effect in helium experiments.
Effect of Winglet Blade on the Performance of Small-Scale Horizontal Axis Wind Turbine
Authors: Al Hamad Saif , Abousabae Mohamed , Hasan Alaa , Habash Omar , Amano Ryoichi S.
Published: September 2023

Wind energy as a promising energy solution has drawn the attention of many researchers to enhance its generation efficiency. Understanding the aerodynamics of the new designs and configurations of airfoils is crucial in predicting the aerodynamic behavior of wind turbine rotors. Improving the aerodynamic performance of airfoils participates to a far extent in improving a turbine’s performance, hence increasing a turbine’s power output. Studying aerodynamic performance for both airfoils and wind turbines can be done either by wind tunnel testing, Computational Fluid Dynamics (CFD) techniques, or both. In this work, the effect of winglet direction and cant angle on the power production of a small-scale Horizontal Axis Wind Turbine (HAWT) was investigated numerically using CFD techniques after measuring the experimental Tip Speed Ratio (TSR) experimentally in the University of Wisconsin Milwaukee Wind Tunnel Facility. Suction side and pressure side winglets were studied over a wide range of cant angles between −90 degrees and +90 degrees using three wind speeds 5, 10, and 15 m/s. Blade Element Momentum (BEM) theory was used to design the optimum twisted blade as a baseline design. The output power was the key parameter in this study, where each design power output was compared to the baseline design without winglets. All winglet design parameters other than the cant angle (length, radius of curvature, and toe, twist, and sweep angles) were fixed throughout this study to isolate their effect. Computational Fluid Dynamics (CFD) methods were used to capture the aerodynamic performance for the most promising configuration. It was found that all the upstream and downstream wingletted turbines outperformed the baseline design except for the perpendicular downstream (−90°) winglet at low wind speed. Furthermore, it was found that the enhancement is more pronounced with higher velocities.
The Influence of the Confinement Ratio on the Precessing Vortex Core Dynamics in a Counter-Rotating Dual Swirler
Authors: Link Sarah , Dave Kaushal , Eitelberg Georg , Gangoli Rao Arvind , de Domenico Francesca
Published: September 2023

Lean-premixed swirl-stabilized combustion is a successful strategy to reduce pollutant emissions. However, these combustion systems are especially prone to thermoacoustic instabilities. The precessing vortex core (PVC) plays a significant role in suppressing or exciting those instabilities. Therefore, it is necessary to predict the PVC dynamics in different operating conditions. The introduction of alternative aviation fuels like hydrogen in fuel-flexible gas turbines might require changes in the combustor geometry. However, the influence of particular geometric parameters on the PVC dynamics in less conventional combustion chamber configurations is not yet clear. To contribute to the knowledge of PVC dynamics in different combustor geometries, this paper presents an experimental study of the PVC dynamics in isothermal conditions in a counter-rotating dual swirler configuration in different confinement ratios. Additionally, a non-rotating axial air jet can be injected on the center line of the primary swirler as a provision for increased flashback resistance in the reacting case with H2. PVC frequencies and amplitudes are obtained by spectral proper orthogonal decomposition (SPOD) of time-resolved PIV measurements, and by time-resolved pressure measurements. The study shows that the frequency of the PVC scales with StPVC = 0.78, based on the diameter and the bulk velocity of the mixing tube. The PVC frequency is only determined by the conditions in the primary swirler and is fully independent of the amount of airflow going through the secondary counter-rotating swirler. Introducing an axial air jet on the center line decreases the PVC frequency significantly, which can be related to the change in effective swirl number. It is also shown that the smallest combustion chamber diameter results in the highest spectral energy for the PVC mode for all investigated points, hence the PVC motion is the strongest. Meanwhile, the biggest combustion chamber diameter shows the weakest pressure fluctuations. The results obtained in this study provide evidence that the periodic oscillations arising in the swirling flow field can be predicted and follow a Strouhal scaling independent of the geometry, even for more unconventional configurations.
Methodology to Monitor Early Warnings Before Gas Turbine Trip
Authors: Losi Enzo , Venturini Mauro , Manservigi Lucrezia , Bechini Giovanni
Published: September 2023

The current energy scenario requires that gas turbines (GTs) operate at their maximum efficiency and highest reliability. Trip is one of the most disrupting events that reduces GT availability and increases maintenance costs.

To tackle the challenge of GT trip prediction, this paper presents a methodology that has the goal of monitoring the early warnings raised during GT operation and trigger an alert to avoid trip occurrence. The methodology makes use of an autoencoder (prediction model) and a three-stage criterion (detection procedure). The autoencoder is first trained to reconstruct safe operation data and subsequently tested on new data collected before trip occurrence. The trip detection criterion checks whether the individually tested data points should be classified as normal or anomalous (first stage), provides a warning if the anomaly score over a given time frame exceeds a threshold (second stage), and, finally, combines consecutive warnings to trigger a trip alert in advance (third stage).

The methodology is applied to a real-world case study composed of a collection of trips, of which the causes may be different, gathered from various GTs in operation during several years. Historical observations of gas path measurements taken during three days of GT operation before trip occurrence are employed for the analysis.

Once optimally tuned, the methodology provides a trip alert with a reliability equal to 75% at least ten hours in advance before trip occurrence.
Application of Transfer Learning for the Prediction of Gas Turbine Trip
Authors: Losi Enzo , Venturini Mauro , Manservigi Lucrezia , Bechini Giovanni
Published: September 2023

One of the most disrupting events that reduces gas turbine (GT) availability and also significantly increases maintenance costs is trip. Given its nature, data-driven methodologies, which are becoming more and more widespread for diagnostic and prognostic purposes, are best suited for its prediction. However, one of the major limitations of data-driven models is their partial extrapolability.

To overcome such limitation, this paper exploits a transfer learning approach for sharing knowledge about GT trip among different GT fleets. The transfer learning approach applied in this paper employs a Long Short-Term Memory (LSTM) neural network that is pre-trained by using the data of a given fleet and then finetuned on the data of another fleet running in a different site. The case study is represented by a collection of field measurements referring to real-world trips taken from two GT fleets during several years of operation. The field data cover multiple ambient and operating conditions, thus providing a challenging test for the transfer learning approach.

The analyses performed in this paper demonstrate that the loss of accuracy between the source domain model (trained and tested on trips that belong to the same domain) and the predictions made on the target domain can be less than 7%. Thus, in general, the results prove that transfer learning is possible and allows comparable (though necessarily lower) accuracy to that of the source domain model.
Validation of Thermal History Coating Technology on Two Stage-One Turbine Blades
Authors: Karagiannopoulos Solon , Taniguchi Tomoki , Peral David , Tanaka Ryozo , Araguas-Rodríguez Silvia , Feist Jörg P.
Published: September 2023

Small and mid-size gas turbines for distributed power generation have been widely used in recent years, with designers constantly seeking to improve efficiency by increasing operating temperatures. Therefore, accurate thermal mapping is now more critical than ever for validating new designs, but also very challenging in such a dynamic environment as a gas turbine. A novel advanced off-line temperature mapping technology has been developed called Thermal History Coating (THC). Thermal History technology has distinct advantages including wide temperature measurement range (150°C to > 1,600 °C), high durability, high temperature resolution, single or multi-cycle operation, high spatial resolution (thousands of measurement points per component) and fully digitized CAD compatible data. Additionally, THC materials are REACH compliant and can be used for both moving and stationary components. High resolution thermal maps of the surface of 3D CAD components can be delivered at the end of the process.

For the first time ever this paper directly compares Thermal History technology with other methods such as Type-K sheathed thermocouples and Uniform Crystal Temperature Sensors (UCTS) and pyrometry on two stage-1 blades of mid-size Kawasaki gas turbine engine test. Temperature data obtained from the different temperature methods were compared qualitatively and quantitatively. Measurement data were also compared with the Conjugate Heat Transfer (CHT) model for the particular internal cooling design of these blades. Further, the application of the THC on two identical blades allowed a direct comparison of component-to-component variations and indicated excellent repeatability of the THC data.
Full Rejuvenation Heat Treatment of MGA 1400DS
Authors: van Esch Hans , Pietersen Stijn , Greaves Wayne , Bridges Alex , Scheibel John
Published: September 2023

Directionally Solidified (DS) nickel-base superalloys have been extensively used for power generation turbine blades. These blades are exposed to high stresses and temperatures for extended periods of time and aging the microstructural and reducing the mechanical properties. After an operational cycle a repair is typically performed to restore dimensional and coating integrity as well as restore metallurgical and mechanical properties of the base material to extend the life of components manufactured from DS alloys. These repair methods can include heat treatments for stress relieving weldment, application of braze, coatings and rejuvenation of the aged base material. Industry standard heat treatments (ISHT) for these DS alloys do not always provide a (full) rejuvenation. Therefore TEServices, Sulzer and EPRI improved ISHT for DS alloys, such as MGA 1400DS and GTD 111DS, for obtaining a full rejuvenation these base materials and obtaining metallurgical and mechanical properties that, in some cases, exceeds the new material properties [1].

The study in this paper focuses on modifying MGA 1400DS ISHT to obtain a full rejuvenation (solutioning the gamma prime during solution heat treatment in the dendritic and inter-dendritic regions) without negatively impacting the metallurgical structure (such as incipient melting) and mechanical properties. This study was performed using optical and scanning electron microscopy evaluating the microstructure of MGA 1400DS in as new, artificially aged and heat treated condition to establish the impact of full rejuvenation heat treatment (FRHT). Mechanical testing was performed on new, aged and FRHT MGA 1400DS to establish the impact of aging and FRHT compared to new material. For this, creep and stress rupture, fatigue, and combination of stress rupture and fatigue testing was performed.

The findings in this study show that FRHT provides superior metallurgical and mechanical properties of MGA 1400DS when compared to new and aged material.
Damping and Stiffness Mistuning Effects in a Bladed Disk With Varied Disk Coupling
Authors: Krizak Troy , Kurstak Eric , D’Souza Kiran
Published: September 2023

Component mode mistuning (CMM) is a well-known, well documented reduced order modeling technique that effectively models small variations in blade-to-blade stiffness for bladed disks. In practice, bladed disks always have variations, referred to as mistuning, and are a focus of a large amount of research. One element that is commonly ignored from small mistuning implementations is the variation within the blade-to-blade damping values. This work seeks to better understand the effects of damping mistuning by utilizing both structural and proportional damping formulations. This work builds from previous work that implemented structural damping mistuning reduced order models formulated based on CMM. A similar derivation was used to create reduced order models with a proportional damping formulation. The damping and stiffness mistuning values investigated in this study were derived using measured blade natural frequencies and damping ratios from high-speed rotating experiments on freestanding blades. The two separate damping formulations that are presented give very similar results, enabling the user to select their preferred method for a given application. A key parameter investigated in this work is the significance of blade-to-blade coupling. The blade-to-blade coupling study investigates how the level of coupling impacts damping mistuning effects versus applying average damping to the bladed disk model. Also, the interaction of stiffness and damping mistuning is studied. Monte Carlo simulations were carried out to determine the amplification factors, the ratio of mistuned blade responses to tuned blade responses, for various mistuning levels and patterns. The baseline parameters were chosen to match an actual bladed disk tested in a rotating experimental rig.
Reduced-Order Model of Aero-Thermal-Mechanical Interactions in Ultra High-Speed Micro Gas Turbines
Authors: Tiralap Aniwat , Tan Choon S.
Published: September 2023

Ultra high-speed micro gas turbine engines developed for high performance could experience substantial thermal-induced effects on engine operation due to high temperature gradients relative to those in conventional large gas turbine engines. A reduced-order model for quantifying thermal-induced differential expansion of the shaft-bearing housing system is developed based on insights obtained from unsteady computations. The key controlling non-dimensional parameters characterizing the aerothermal-mechanical interaction and response are identified using the reduced-order model that yields thermal-induced mechanical deformation in agreement with the computed results. For geometrically similar engine systems, the controlling non-dimensional thermal and structural parameters consist of: (1) shaft fin parameter, (2) housing fin parameter, (3) ratio of heat diffusivity of housing to that of shaft, (4) 3 cooling flow parameters, and (5) ratio of coefficient of thermal expansion of the housing to that of shaft. These non-dimensional parameters serve as a guideline for developing strategies for controlling bearing clearance variation within the acceptable margin, including selecting shaft and housing materials with appropriate properties as well as tailoring the cooling flow. An approximate scaling rule for thermal-induced shaft-bearing housing clearance variation in engines of various sizing is formulated; specifically, the rule provides a direct means for estimating the time instant and the design attributes under which a specific value of minimum shaft-bearing clearance would occur during the engine start-up process to steady-state operation. A design example is provided to illustrate that adjustment of thermal and structural characteristics through thermal conductivity and coefficient of thermal expansion of the housing material is adequate to mitigate the thermal expansion mismatch issue without engine structure redesign.
Aerodynamic Impact of Secondary Air Injection Flowrates on the Main Annulus Flow Field and Performance for a Transonic High-Pressure Turbine Stage
Authors: Okita Yoji , Kazawa Junichi , Fuchigami Kazutaka , Yamane Takashi , Tanaka Nozomi , Sato Hiroki , Hamabe Masaaki , Tanimitsu Haruyuki
Published: September 2023

In this study, the influence of secondary air blowing on the main annulus flow field and performance of a transonic high-pressure turbine (HPT) was investigated experimentally and numerically.

The experimental setup was a single-stage, unshrouded turbine with a blading consistent with modern HPTs. The entire testing campaign was conducted in a full annular, rotating, continuous turbine test rig at the Japan Aerospace Exploration Agency (JAXA), which realized the most faithful matching unrivalled of both the primary and secondary stream similarity parameters to reality. An elaborate secondary air system implemented in the hardware enabled it to mimic all the dominant coolant/purge streams representative of advanced hot sections: the full coverage film-cooling on stator and rotor airfoils, disk wheelspace purge air blown forward and aft of the rotor, and coolant injection through the over-tip casing. Detailed three-dimensional flow field and efficiency measurements for various secondary air flowrates were performed by traversing a pneumatic thermometric combination probe downstream of the rotor.

A complete set of numerical simulations was run concurrently with the testing to determine how well they captured the flow physics, particularly the interaction of the ejected secondary streams with the primary flow. The JAXA in-house code, UPACS, and its best practice settings, based on past verification and validation efforts, were employed and not intentionally tuned to better fit the data. The investigation applied both steady and unsteady approaches. Given the study’s primary goal, important features such as coolant holes, internal plenums, and wheelspace cavities that affect the interactions were all directly resolved in the calculation rather than simplified by the boundary conditions and/or source-term modeling.

The rotor exit survey in the experiment suggested that the disk forward hub purge and the blowing from the over-tip casing both intensified the passage vortex in the cascade. In contrast, it was indicated that a positive effect also resulted from ejection from the tip casing, diminishing the tip leakage vortex. The stage performance evaluation implies that the resulting gain may offset or outweigh the negative effects of injection. Additionally, the data suggested that coolant blown off the airfoil has an impact also on the near-endwall zone in particular and can boost (by vane coolant) or weaken (by blade coolant) the secondary flow.
Experimental Investigation of Mode-Frequency Scattering at Fan Stages
Authors: Behn Maximilian , Tapken Ulf
Published: September 2023

For the development of low-noise fan designs the sound generation must be reduced at the source, but also sound transmission effects through the rotor can be exploited to reduce the noise emitted to the far-field. Rotor shielding has been identified as a means of noise abatement, where rotor counter-rotating modes are blocked by the rotor and transmit poorly to the inlet. An effect that is rarely considered in this context is mode-frequency scattering at the rotor, which can circumvent the blockage effect by shifting the sound energy in frequency and mode order, typically to a rotor co-rotating mode order that transmits efficiently to the inlet. An experimental investigation is presented, where the transmission, reflection and scattering of individually generated modes through a fan stage is measured by means of a loudspeaker array and microphone arrays, upstream and downstream. The highly resolved measured data comprise the variation of mode order, frequency, rotor speed and aerodynamic operating conditions. In this study the focus is on mode-frequency scattering, for which results are presented for high and low rotor speed.