bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Shock Boundary Layer Interaction in Transonic Compressor Blading
Authors: Hergt Alexander , Klose Björn , Klinner Joachim , Bergmann Michael , Munoz Lopez Edwin Joseph , Grund Sebastian , Morsbach Christian 
Published: September 2023

Abstract
Shock waves and their interaction with the boundary is a significant flow effect within transonic compressor blading. The main challenge here is the unsteady nature of this interaction effect because it imposes further requirements to maintain the structural integrity of the blading. Furthermore, it has been shown that the shock oscillations limit the working range of transonic blade profiles. Therefore, it is of great interest to mitigate these effects for the next generation of aero engine designs. In order to do this, it is mandatory to identify the mechanisms that originate the oscillation. Intensive experimental studies have already been carried out in the past using unsteady PIV, as well as Shadowgraphy, which have led to new insights into the nature behind the shock oscillation. However, the measurement insight into the flow is strongly limited and allows only an extract of the entire flow field. In order to get a deeper view, scale-resolving simulations have to be carried out. In addition to the experiments performed at DLR’s Transonic Cascade Wind Tunnel, the flow through a transonic compressor cascade was simulated using a high-order accurate discontinuous Galerkin spectral element method with a finite-volume (FV) subcell shock capturing. The implicit LES scheme is applied for subgrid-scale dissipation, i.e. the dissipation is provided by the intercell flux. The content of the paper includes first a validation of the LES results based on the steady measurement data from the experiment in order to ensure the datasets are comparable. The comparison shows that the experimental operating point is almost exactly reproduced by the LES with respect to the mean inflow conditions and the resulting profile Mach number distribution. A time-frequency analysis is also shown, which was based on the evaluation of local probe data and on spectral decomposition of the simulation snapshots taken. Dominant frequencies of the shock movement and the vortex shedding of the transonic flow are extracted and used to analyze the unsteady flow behavior in a direct comparison with the experimental results. These analyses give a unique insight into the self-exciting mechanism of the shock oscillation and form the basis for the applicability of combined experimental and LES data set for a deeper analysis of the mechanism in future studies.
Acoustic and Optical Flame Transfer Function Measurements in a High-Pressure Lean-Burn Aero-Engine Combustor Fueled With Jet A
Authors: Salazar Victor , Venkatesan Krisna , Han Fei , Wonfor Samuel , Passarelli Mitchell , Zheng Andy , Steinberg Adam 
Published: September 2023

Abstract
This paper reports flame transfer function (FTF) measurements obtained in a high-pressure lean-burn aero-engine combustor using acoustic and optical methods. A liquid fueled lean premixed pre-vaporized combustor was operated at various combustor fuel air ratios (FAR) relevant for supersonic transport. A high-pressure siren was employed to modulate the combustor inlet air flow at frequencies ranging from 30Hz up to 1050Hz. Acoustic FTFs were obtained via multi-microphone method using signals from multiple dynamic pressure sensors. Optical FTFs were obtained simultaneously with acoustic measurements by imaging OH*, CH* and C2* chemiluminescence from the combustor., Specifically, line-of-sight chemiluminescence signal for each species was collected with a fiber optic probe and imaged onto photomultiplier tubes with 10nm bandpass filters centered at 310nm, 430nm and 515nm, respectively. Complementary 2D high speed OH* chemiluminescence images were also acquired using a high-speed camera to gain insight into the flame dynamics and support the interpretation of the FTF findings. A comparison of FTFs using the acoustic and optical methods show good agreement in phases and magnitude trends. The measured FTFs show significant variations with varying fuel-air ratios at various frequency ranges confirming a strong dependency of FTFs with flame shapes.
Numerical Investigation of Steam Injection in a Premixed Swirl-Stabilized Methane-Air Flame Using the Flamelet-Generated-Manifold Method
Authors: Köhler Marius , Hiestermann Marian , Müller Hagen 
Published: September 2023

Abstract
A promising concept to further improve the efficiency of aircraft gas turbines while reducing pollutant emissions is the injection of water steam in the combustor. This approach, known as Water-Enhanced Turbofan (WET) concept, involves that water is recovered from the exhaust, compressed in a liquid state and finally fed to the combustion chamber after passing through a steam generator. In the present work, we investigate the suitability of the flamelet-generated-manifold method to model turbulent combustion under WET conditions, i.e., with high steam loads. As a test case, we use a premixed swirl-stabilized methane-air flame for which experimental reference data are available for dry conditions. The numerical results are in good agreement with both a finite-rate reference simulation as well as with experimental data for velocity and OH*-chemiluminescence. We also observe a significant impact of the steam content in the unburnt gas on the flame shape. In particular, increasing the water-gas-ratio leads to an elongation of the flame. At the same time, the reaction zone becomes wider, leading to reduced heat release maxima. As a consequence, a more homogeneous temperature distribution is observed, which leads to a reduction of NOx formation.
Numerical Investigation on Heat Transfer and Flow Characteristics of Combined Pin-Fin With Rib in a Rectangular Channel
Authors: Yan Shuangjie , Liu Jianjun , An Baitao , Li Chen 
Published: September 2023

Abstract
In this paper, numerical simulation has been conducted to investigate the heat transfer and flow characteristics for cooling schemes which combine pin-fins and ribs. A pin-fin internal cooling channel with an aspect ratio 4:1 was used as baseline, where the pin-fin height-to-diameter ratio was H/D = 2.5, and both streamwise and spanwise spacing were S/D = 2. The combined cooling schemes use partitioned strip ribs to replace part of pin-fins in the rectangular channel. The number of partitioned strip rib is 2, 3, 4 and 4 in Case A, Case B, Case C and Case D, respectively. Simulations were performed at five Reynolds numbers between 7300 and 36000. The results show that the combined cooling schemes bring higher heat transfer, but also produce higher pressure loss. The addition of ribs effectively extends the endwall heat transfer area. The higher blockage ratio of channel sharply increases the pressure loss while enhances heat transfer. Comparing to the baseline pin-fin channel, the overall thermal performance of Case A, Case B, Case C and Case D increases 6.2%, 12.2%, 21.9% and 39.2% respectively, at the Reynolds number of 22,000. The combined cooling scheme could be used in situations where higher cooling load is required and the pressure drop is not of much concern.
LES/Thickened Flame Model of Reheat Hydrogen Combustion With Water/Steam Injection
Authors: Kruljevic Boris , Cabello López Andrés , Langella Ivan , Ciani Andrea , Duesing Michael 
Published: September 2023

Abstract
In this study, the effects of water injection are analysed in a simplified geometry of a reheat combustor, which is based on a state of the art sequential reheat combustor from Ansaldo Energia. The inlet temperature of this burner and the chemical properties of hydrogen in terms of flame speed and autoignition imply that combustion occurs in an autoignition-assisted propagation regime. Large eddy simulations with an Artificial Thickened Flame modelling have been employed to analyse the dynamic behaviour of the hydrogen flame in lean premixed combustion mode. Results show that this approach can accurately predict the position of the flame front and the autoignition process as compared to a pre-existing DNS dataset. The flame front behaviour is further investigated, and observed to quickly move upstream and downstream, driven by the effect of pressure waves on the autoignition process. The study conducted here shows how the injection of water droplets can prevent the autoignition upstream and thus effectively help in achieving flame stability. Some light is also shed on the influence of the spray design parameters on the stability of the H2 flame and the NOx emissions.
Development and Testing of a Universal High Lift Power Turbine for the LM2500+ Engine
Authors: Guerrero David , Wadia Aspi , Bertini Francesco , Elorriaga Angel , Lopez Yonatan , Paredes Juan , Airaudo Massimiliano , Duckett Dion , Ruiz Alfredo 
Published: September 2023

Abstract
The LM2500 gas turbine was derived from General Electric TF39 and CF6 aircraft engines and has been a best-selling model for over 40 years. The fourth generation LM2500+G4 introduced in 2005 offers an output greater than 34.6 MW at ISO conditions with a thermal efficiency of more than 39%, supporting a wide range of power generation and mechanical drive Land and Marine applications. A fifth generation LM2500+G5 uprate of this successful product has achieved new levels of output shaft power and efficiency, enabled by a more efficient core and a new Universal Power Turbine (UPT) design.
The new power turbine module is briefly described in this document from the basic 1D parameters up to the design of the airfoils, which have high lift characteristics. In addition to the traditional goal of increasing performance, the design of the UPT also focused on achieving robustness and versatility. The UPT is now the best choice for a wide range of applications, with only minor hardware changes needed to adapt it to support the LM2500+, LM2500+G4 and the uprated LM2500+G5 gas generators for both 50Hz and 60Hz applications.
The compliance testing campaign for the LM2500+G5 UPT was conducted on ten engines, using development instrumentation to validate overall gas turbine performance in terms of power, efficiency, and emissions, as well as UPT module performance. The test objectives focused on different power ranges, combustor burner modes and mapping, compressor bleeds, and UPT speeds. The test exceeded expectations, demonstrating the overall engine and component performance of the UPT and, providing valuable data that will be used to further improve the design and performance of the gas turbine.
Numerical Assessment of a Rich-Quench-Lean Staging Strategy for Clean and Efficient Combustion of Partially Decomposed Ammonia in the Constant Pressure Sequential Combustion System
Authors: Heggset Tarjei , Meyer Ole , Gruber Andrea , Tay-Wo-Chong Luis , Ciani Andrea 
Published: September 2023

Abstract
In a future energy-system prospective, predictably dominated by (often) remote and (always) unsteady, non-dispatchable renewable power generation from solar and wind resources, hydrogen (H2) and ammonia (NH3) have emerged as logistically convenient, chemically-simple and carbon-free chemicals for energy transport and storage. Moreover, the reliability of supply of a specific fuel feedstock will remain unpredictable in the upcoming energy transition period. Therefore, the ability of gas turbines combustion systems to seamlessly switch between very disparate types of fuels must be ensured, aiming at intrinsically fuel-flexible combustion systems, i.e. capable of operating cleanly and efficiently with novel carbon-free energy vectors like H2 and NH3 as well as conventional fossil fuels, e.g. natural gas or fuel oils (back-up feedstock). In this context, a convenient feature of Ansaldo’s Constant Pressure Sequential Combustion (CPSC) system, resulting in a fundamental advantage compared to alternative approaches, is the possibility of controlling the amount of fuel independently fed to the two combustion stages, depending on the fuel reactivity and combustion characteristics. The fuel-staging strategy implemented in the CPSC system, due to the intrinsic characteristics of the auto-ignition stabilized reheat flame, has already been proven able of handling fuels with large hydrogen fractions without significant penalties in efficiency and emissions of pollutants. However, ammonia combustion is governed by widely different thermo-chemical processes compared to hydrogen, requiring a considerably different approach to mitigate crucial issues with extremely low flame reactivity (blowout) and formation of significant amounts of undesired pollutants and greenhouse gases (NOx and N2O). In this work, we present a fuel-flexible operational concept for the CPSC system and, based on unsteady Reynolds-Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) performed in conjunction with detailed chemical kinetics, we explore for the first time full-load operation of the CPSC architecture in a Rich-Quench-Lean (RQL) strategy applied to combustion of partially-decomposed ammonia. Results from the numerical simulations confirm the main features of ammonia-firing in RQL operation already observed from previous work on different combustion systems and suggests that the CPSC architecture has excellent potential to operate in RQL-mode with low NOx and N2O emissions and good combustion efficiency.
A Bayesian Data Driven Multi-Fidelity Modelling Approach for Experimental Under-Sampled Flow Reconstruction
Authors: Cruz Gonçalo G. , Babin Cedric , Ottavy Xavier , Fontaneto Fabrizio 
Published: September 2023

Abstract
This work showcases a multi-fidelity approach, which couples experimental techniques with numerical models within a Bayesian data-driven framework, thus enabling a direct uncertainty assessment. With such an approach, a substantial reduction of the instrumentation effort can be achieved, making it particularly interesting for high intrusiveness applications. A CFD model is employed to provide an initial belief of the flow, which is then updated based on random undersampled experimental observations in a multi-fidelity Gaussian Process framework. The approach is applied to a small aspect ratio axial compressor for which an experimental database is available. With a 70% random undersampling of a complete measurement test, the results exhibit a correct mean flow reconstruction with clear signatures of the typical flow features. The reconstructed flow error is comparable to the experimental measurement uncertainty. An assessment of the approach’s robustness shows an influence of the location of the measurements on the flow reconstruction that decreases with increased flow measurements.
A Combined Experimental and Turbulence-Resolved Modelling Approach for Aeroengine Turbine Rim Seals
Authors: Vella Simon , Darby Peter , Carnevale Mauro , Scobie James A. , Lock Gary D. , Jarrossay Clément , Salvatori Francesco , Bonneau Damien , Sangan Carl M. 
Published: September 2023

Abstract
Ingress is the penetration of hot mainstream gas into the rotor-stator wheel-space formed between adjacent discs; a rim seal is installed at the periphery of the wheel-space. Purge flow is bled from the compressor and re-introduced in the turbine to reduce, or in the limit prevent, ingress. This study presents a unique, concomitant experimental and turbulence-resolved numerical investigation of ingress in an aeroengine rim seal geometry, with leakage flow.
Experimental modelling is conducted in the University of Bath’s 1-stage turbine test facility. Measurements of gas concentration, pressure and swirl were used to assess the performance of the rim seal. A parallel study using Improved Delayed Detached Eddy Simulations (IDDES) was used to generate time-averaged and time-resolved flow-fields, enabling direct comparison with experimental data. The aeroengine architecture conformed to classical rim seal mechanics whereby the effectiveness level increased with purge flow. The inner wheel-space exhibited Batchelor-type flow; in the outer wheel-space, the effectiveness was nonaxisymmetric and synchronised in accordance with the local radial velocity field.
Utilisation of a DES TKE multiplier demonstrated regions where increased turbulence resolution was required to resolve the appropriate scale of turbulent eddies. IDDES computations were found to accurately capture the radial distributions of pressure, swirl and effectiveness, both in the absence and superposition of leakage flows. The IDDES approach exhibits significantly superior agreement with experiments when compared to previous studies employing an Unsteady Reynolds Averaged Navier-Stokes (URANS) methodology.
Effects of Water-to-Air Mass Ratio on Long-Term Washing Efficiency and Erosion Risk in an Axial Compressor Under Online Washing Conditions
Authors: Agati Giuliano , Gabriele Serena , Rispoli Franco , Venturini Paolo , Borello Domenico 
Published: September 2023

Abstract
One of the main reasons of gas turbines performance losses is the deposition of dirt on the compressor blades. Dirt deposit has to be periodically removed to keep the engine performance as high as possible. This is the reason motivating the presence of online water washing systems (WWS) in most of the compressor gas turbines. Such systems aim at cleaning the compressor blades to recover efficiency; thus, the larger the water flow the better it is assumed the compressor is cleaned (fixing all the other conditions). In the present work we simulate the long-term behaviour of a real axial compressor, from the inlet to the first-stage rotor, subject to online water washing with different water flow rates. The frozen rotor approach is adopted to solve the flow field in the rotor region. Simulations are performed by using the unsteady k-ε realizable model coupled with a Lagrangian tracking of the injected liquid phase. Water droplets erosion is handled by using a semi-empirical model developed by the authors. In each simulation 504000 parcels have been tracked, providing statistically reliable predictions. To simulate long-term evolution of the washing process, a discrete mesh morphing technique coupled with the use of specific scale factors is adopted. Each of the tested configuration is composed of three successive erosive steps up to the blade compressor end-of-life. Six different injection configurations are here assessed in terms of long-time average washing efficiency and erosion risk. Results predicted, show the dependence of the considered washing indices on water mass flow rate and set the stage for the development of a washing optimization tool, which helps the design and management processes. In the present simulations the optimal configurations are WAMF* = 0.250 in the case that a small weight is given to the washing indices, and WAMF* = 0.750 for high weights.
Heat Transfer Coefficient Dependence on Coolant Temperature For Supercritical CO2 Leading-Edge Jet Impingement
Authors: Olson Weston , Fernandez Erik , Vesely Ladislav , Kapat Jayanta 
Published: September 2023

Abstract
In this work a conjugate heat transfer analysis was performed on leading-edge jet impingement heat transfer with sCO2 as the working medium. The internal heat transfer coefficient distribution, as well as external metal temperature profiles, were evaluated for three different coolant temperatures. These coolant temperatures were 360K (pseudo-critical), 500K, and 650K. The heat transfer coefficient distribution was maximum when the coolant temperature was that of the pseudo-critical temperature (360K). A simulation with air as the working medium, with the highest coolant temperature (650K), was also included in the study. The air working medium case had the highest external metal temperature and the heat transfer coefficient was a whole order of magnitude less than that of the sCO2 working medium at the same coolant temperature. The results of the study conclude that convective effectiveness of jet impingement heat transfer is much more effective for sCO2, due to its thermal properties, than it is for air and impingement effectiveness is maximum for a coolant at the pseudo-critical temperature. The nondimensional parameters used to represent heat transfer effectiveness were also evaluated at the three coolant temperatures. The heat transfer coefficient can be characterized by the inertial heat capacitance scaled by the Stanton number.
Prospects for Low-Resolution NDIR Sensors to Discern Ignition Properties of Fuels
Authors: Sutar Ashish , Dalmiya Anandvinod , Sheyyab Manaf , Anahideh Hadis , Mayhew Eric K. , Brezinsky Kenneth , Lynch Patrick T. 
Published: September 2023

Abstract
The cetane number is an important fuel property to consider for compression ignition engines as it is a measure of a fuel’s ignition delay. Derived cetane number (DCN) already varies significantly within jet fuels. With the expected increasing prevalence of alternative jet fuels, additional variability is expected. DCN is usually assigned to fuels using ASTM methods that use large equipment like the Ignition Quality Tester (IQT), which consumes a lot of fuel and is cumbersome to operate. Over the last decade, there have been advances in the development of chemometric models, which use machine learning to correlate infrared spectra of fuels to fuel properties like DCN, density, and C/H ratio, amongst many others. These techniques have certain advantages over the ASTM methods, and previous studies performed on samples of diesel fuels have shown high accuracies in DCN prediction. However, this accuracy is generally a result of high resolution, making the equipment expensive, relatively large for handheld sensors, and power-hungry. On the other hand, nondispersive infrared (NDIR) sensors, despite having a low resolution, are attractive because they can be compact, inexpensive, and power efficient. These characteristics are important for handheld or onboard fuel sensors. However, one would anticipate a trade-off between these advantages and accuracy. This study investigates this trade-off and the feasibility of low-resolution NDIR sensors to discern fuel properties such as DCN by using Machine Learning models trained on real FTIR data, and DCNs obtained from IQT. DCN predictions were made for blends of ATJ/F-24, CN fuels, and neat Jet A1, A2, and JP 5, with an error limit of 10%. It was found that there seems to be sufficient variability in the near infrared range to discern DCN with a feasible number of channels, but the channels have to be narrow (e.g. FWHMs as narrow as 60nm). For the data set in the study, the performance of linear models was better than the non-linear model. Finally, NIR region beyond 1050 nm was found to be more important in DCN prediction, primarily the regions consisting of the first and second C-H overtones and the C-H combination band.