bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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 &gt; 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.