bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Impact of the Off-Design Conditions on the Entropy Wave Interaction With a High-Pressure Turbine Stage
Authors: Pinelli Lorenzo , Giannini Giovanni , Marconcini Michele , Pacciani Roberto , Notaristefano Andrea , Gaetani Paolo 
Published: September 2023

Abstract
The study of component interactions in aeronautical engines is a key aspect to improve the aerodynamic, aeromechanical and thermal performance and to reduce greenhouse gas and noise emissions. In this context, combustor systems (working with lean and premixed flames) generate pressure, velocity and temperature fluctuations that interact with the turbine module producing combustor instability, performance degradation and noise generation. A correct understanding of this interaction is thus required by the designers, especially with a view to introducing sustainable aviation fuel to achieve zero-emission aviation. The paper tackles this topic from a numerical and experimental point of view, focusing on off-design turbine conditions possibly encountered during an aeroengine mission. In detail, the effect of different stage loadings (obtained by keeping the stage pressure ratio and modifying the rotational speed) on engine-representative entropy waves evolving through the turbine stage is investigated. The combination of numerical and experimental results, that show a good agreement in terms of disturbance evolution within the stage, allows a deeper understanding of the flow field features that impact the stage aerodynamics and modify the secondary flow structures and the entropy wave transport, diffusion and decay through the rotor. Moreover, the most loaded operating condition reveals the appearance of a rotating instability at the rotor tip that also interacts with the injected disturbance. Finally, the numerical results (coming from full annulus URANS computation with incoming disturbances) are further post-processed to extract indirect noise emissions at the different load conditions and to assess the additional loading on the rotor blade caused by the presence of the disturbance.
Effects of Leading Edge Shape on Effusion Film Cooling
Authors: Chang Yu-Chuan , Huang Szu-Chi , Huang Chih-Yung , Liu Yao-Hsien 
Published: September 2023

Abstract
This study investigated effusion film cooling on turbine leading edge model using pressure sensitive paint (PSP) technique. Three leading edge profiles were tested, including a semi-cylinder and two elliptical leading edge models. Effusion cooling was implemented using a large number of holes with small hole-to-hole spacing, and Stereolithography was used to produce the perforated region. Effects of blowing ratio (0.4, 0.8, and 1.2) were tested and the density ratio was maintained at unity. Three rows of film cooling holes were employed on these leading edge models as a traditional film cooling scenario for benchmark testing. These film cooling rows exhibited 15 holes, located at the stagnation line (0°) and at ±30° away from the stagnation line. These test models were installed in a low-speed wind tunnel for testing. The Reynolds number was 100,000, which was estimated using the mainstream velocity and semi-cylinder diameter. Two streamwise spacings of the effusion holes were studied. The effusion cooling showed higher cooling effectiveness compared to the traditional film cooling. Increasing the streamwise spacing lowered the cooling effectiveness regardless of the leading edge profile. The variation of the blowing ratio had smaller effect on the effusion cooling effectiveness and coolant blow-off was not substantial.
Recursive Sequential Combustion Using Multiple Discrete Sectors
Authors: Giuliani Fabrice , Hofer Andrea , Paulitsch Nina , Akin Bugra 
Published: September 2023

Abstract
Recursive Sequential Combustion (RSC, introduced in paper GT2021-59592) is a new concept that maximises the interaction between burned gases and fresh reactants. The novelty compared to other concepts of flue gas recirculation in gas turbines is that this interaction is solely driven by the flow dynamics in the combustor. It consists of a novel inlet/outlet arrangement and an advanced flow design, which avoids complex extraction, reconditioning and re-injection of flue gases. The key feature is the burner arrangement which places the flames one after the other in a closed loop, maintaining a trapped circulation of constantly renewed hot gases flowing along annulus of the chamber. The aim is to achieve robust lean combustion supported by the high temperature of the flue gases, combined with the reburning effect of sequential combustion. The expected benefit of this technology is a steady lean operation with significantly lower NOx and soot formation than in conventional GT combustors.
This paper focuses on the flow design using a multiple discrete sector approach. A discrete sector has an inlet and an outlet accompanying the recursive hot gas flow, which is supplemented by fresh mixture injection, a flow mixer/conditioner, a flame tube and a flue gas separator. The N sectors are then arranged in a closed loop. Side feeds and outlets, as well as periodic boundaries along the annulus, allow circulation to occur.
An advanced discrete-sector concept designed for demonstration purposes is presented. The flow design is studied by CFD and supported by basic experiments. It is shown that the burnt gas circulation and interaction are effective, and that the closed loop recursive sequential combustion is within reach, demonstrating the plausibility of the concept.
A Data-Driven Approach for Generalizing the Laminar Kinetic Energy Model for Separation and Bypass Transition in Low- and High-Pressure Turbines
Authors: Fang Yuan , Zhao Yaomin , Akolekar Harshal D. , Ooi Andrew S. H. , Sandberg Richard D. , Pacciani Roberto , Marconcini Michele 
Published: September 2023

Abstract
The laminar kinetic energy (LKE) transition model recently has shown good predictions on separation-induced transition that frequently experienced by low pressure turbines (LPT). In contrast to LPTs, high-pressure turbines (HPT) often are subject to bypass transition which currently is not captured well with the LKE model. Because these two types are common transition modes for turbines, the current effort is focused on generalizing and improving the LKE model to be able to predict the different types of transition. In addition to modify the transition model to achieve better on-blade predictions, the turbulence model in the wake region is also revised for more accurately capturing the wake mixing. Hence, the main purpose of this study is to use a data-driven approach to simultaneously develop spatially separate transition and turbulence closures suitable for a range of different turbine configurations. To achieve this, two strategies are adopted. The first is to employ a multi-case multi-objective computational fluid dynamics (CFD) -driven model training framework. The training is performed on several LPT and HPT configurations, specifically the T108, T106A, and LS89 sections, that feature both separation-induced and bypass transition to ensure better generalizability of the models. The second strategy employed is the use of a newly derived set of local non-dimensionalized variables, that serves as the inputs for the LKE model corrections. Among the training cases, steady calculations are conducted for LPTs. The LS89 case is an HPT characterized by shocks, acoustic waves, and unsteady trailing edge vortex shedding. To capture these, for the first time an unsteady solver is utilized during the CFD-driven training, and the time-averaged results are used to calculate the cost function as part of the model development process. The model obtained from the new training process are tested on the a steady case - T108 with a higher Reynolds number and an unsteady case - PakB profile. Their performance are assessed in terms of pressure coefficient, wall shear stress and wake losses.
Mistuning Strategy on Long Blades to Mitigate Flutter
Authors: Pinelli Lorenzo , Arnone Andrea , Peruzzi Lorenzo , Bettini Claudio , Finzel Conrad , Kellerer Rudolf 
Published: September 2023

Abstract
Nowadays, the current favoured form for energy production is combined cycle, which allows efficient solutions through reduction of fuel consumption and hence a lower impact in terms of pollutant emissions. At the same time, the continuous request of more efficient solutions translates into large, higher flowing machines with slender and loaded blades.
The design of such blades now needs to include aeromechanical interactions, such as transonic conditions at the tip, leading to shock wave systems that impinge on and interact with the blade surfaces and high load conditions increasing the occurrence of flow induced vibrations as flutter.
Nowadays reliable CFD prediction models are used to estimate flutter stability based on the minimum of the logarithmic decrement curve to design robust configurations for the long rotor blades.
Currently, mistuning is one of the most used flutter mitigation techniques as it can be implemented in the field via, for instance, blade mass removal (e.g. Trailing Edge cutback), that also leads to a performance degradation. Methods are available for the application of mistuning to free standing blades. This paper provides an introduction to the physics of and methodology for determining mistuning solutions on mechanically coupled blade systems.
Preliminary Numerical Study of Methane-Hydrogen Co-Combustion Effects on Heavy-Duty Gas Turbines
Authors: Ancona Maria Alessandra , Bianchi Michele , Branchini Lisa , Catena Francesco , De Pascale Andrea , Ferrari Federico , Melino Francesco , Peretto Antonio 
Published: September 2023

Abstract
The use of hydrogen as a fuel for gas turbines is certainly an opportunity to limit greenhouse gas emissions, despite the still not-negligible limitations related to materials and the management of combustion processes.
This work aims at proposing a numerical model, developed by the Authors by means of the link between Matlab™ environment and Aspen HYSYS™ environment, able to evaluate the performance of commercial gas turbines with a set geometry in response to the co-combustion of CH4 and H2 for different fuel mixture compositions.
The purpose of this study is therefore to propose a modelling approach to assess the use of hydrogen injection in the combustion chamber of commercial gas turbines, already in operation, as a short-term strategy for reducing carbon emissions.
The preliminary results obtained by the simulation process show that the increase in the hydrogen content in the fuel mixture, up to a maximum of 62% by volume, corresponds to a slight decrease in the performance of the machine, in particular net electrical power and efficiency, of about 3%, but also to a reduction in CO2 emissions of more than 30%.
Automated Analysis of Stall Inception in Multistage Compressors Using 1D Methods
Authors: Conser Benjamin , Goldenberg Vlad 
Published: September 2023

Abstract
A compressor operating in stall can lead to large aerodynamic losses and potentially compressor surge. Understanding the operating point where stall first occurs is of importance to turbomachinery design engineers as they iterate between designs during the design process. A methodology has been developed which predicts the onset of stall using a 1D-solver approach. This methodology shows reasonable agreement in the stall inception point compared to both 3D CFD and experimental approaches. Utilizing this 1D approach allows for the prediction of the stall point, as well as the identification of the compressor stage where stall inception occurs, all in a matter of minutes. This allows for more rapid and targeted design changes earlier on in the engineering design process.
A New Empirical Correlation for Transition in Both Short and Long Separation Bubbles
Authors: Petronio Daniele , Dellacasagrande Matteo , Simoni Daniele , Lengani Davide 
Published: September 2023

Abstract
With the aim of improving the predicting capability of current correlation-based transition models, a new correlation for transition in separated flows is presented, which is based only on local quantities. The peak value of the vorticity-based Reynolds number at the detachment position has been chosen as a local indicator of the boundary layer state. As largely discussed in the literature [1], this facilitates the implementation of transition models into modern numerical schemes, characterized by parallel execution and unstructured grids.
The current experimental database consists of a total amount of almost 90 flow conditions concerning a flat plate boundary layer developing under variable Reynolds number, free-stream turbulence intensity and adverse pressure gradient. The typical operating conditions of low-pressure turbine profiles have been reproduced. Due to the wide range of Reynolds numbers tested, the bursting process of the laminar separation bubble has been observed. Using the present database, a proportionality coefficient between the momentum-thickness and the vorticity-based Reynolds numbers at the separation position has been computed, which is found to be the same for both short and long bubbles. This provides the link between local and integral quantities of the boundary layer. Then, the vorticity-based Reynolds number is adopted as main ingredient of a correlation for the prediction of the transition onset in separated boundary layers. The influence of other factors such as the free-stream turbulence and the streamwise pressure gradient has been also considered. The present work is thought to improve the code ability in predicting the profile losses and the blade loading distribution in case of separated flows, for both short and long bubble states.
On the Demonstration of a Humid Combustion System Performing Flexible Fuel-Switch From Pure Hydrogen to Natural Gas With Ultra-Low NOx Emissions
Authors: Dybe Simeon , Yasir Muhammad , Güthe Felix , Alemela Reddy , Bartlett Michael , Schuermans Bruno , Paschereit Christian Oliver 
Published: September 2023

Abstract
To fight global warming the European Union formulated the objective of completely decarbonising the energy sector, stimulating the advent of unconventional fuels and the adaption of the corresponding energy infrastructure. The decarbonisation strategy identified hydrogen to play a key role as an energy storage medium, making systems capable of pure hydrogen operation essential.
This requirement can be fulfilled with humid power cycles which offer additional advantages such as highly efficient and fuel-flexible operation with low emissions. As an integral part of such a cycle, a humid combustion system was presented previously showing promising results with respect to complete combustion with low emissions for a variety of fuels.
The current work introduces an upgraded version of that combustion system. The new Double Swirler system is capable of stable and safe combustion of low calorific value bio-syngas surrogate, hydrogen, and natural gas, from dry to steam-rich conditions within the required pressure drops. The inclusion of dry operation of the system can benefit the start-up procedure of the humid cycle.
The combustor’s fuel switching performance is demonstrated by a fast fuel switch at full load from pure hydrogen to pure natural gas and vice versa, while maintaining a stable performance with low NOx-emissions at otherwise constant operation parameters.
Role of the Inducer in Flow Instability of a High-Speed Centrifugal Compressor Impeller
Authors: Zhang Meijie , Wu Wangxia 
Published: September 2023

Abstract
The performance of a high-speed centrifugal compressor has been numerically studied in this paper. The flow instability of the centrifugal compressor impeller, in the inlet blade tip Mach number range of 0.57 to 0.92, is reviewed from the different perspectives of the inducer and centrifuge. The results show that the roles of the inducer and the centrifuge in the evolution of impeller flow instability are fickle. At the large mass flow rate far away from the onset of impeller flow instability, the inducer has been unstable, and the flow field analysis indicates that the leading-edge flow spillage can be used as the criterion for the onset of inducer flow instability. As the mass flow decreases further, the flow stability of the inducer worsens first and then becomes neutral. However, the flow stability of the centrifuge worsens continually and finally results in impeller flow instability. The back flow relates closely to the flow instability of the inducer and the centrifuge, and the detailed blade-to-blade flow field and the back flow loss are investigated. The results imply that the design of a new device to control the back flow in the centrifuge may obtain a wider stable flow range than the traditional recirculation casing treatment on the inducer casing.
Design of a Swirl-Stabilized Burner With Fluidically Variable Swirl Number
Authors: Eck Mattias Ettore Giulio , zur Nedden Philipp Maximilian , von Saldern Jakob Georg Raimund , Orchini Alessandro , Paschereit Christian Oliver 
Published: September 2023

Abstract
For flame stabilization, burner systems are usually equipped with swirlers which incite a defined air rotation, quantified by the swirl number. In consequence, the swirl number, which significantly influences the flame dynamics, is fixed. Applications exist in which the swirl number can be varied through mechanically adjustable swirler geometries. Such systems, however, comprise moving parts and actuators, the operation of which might be disadvantageous in a combustor environment. Hence, a swirler is developed that allows for continuous swirl number changes by means of fluidic flow control. The direction of a primary air flow is changed through the injection of an adjacent wall jet which follows a curved surface. This causes a directional change of the primary flow due to entrainment effects. The swirler consists of a cylindrical plenum into which a primary air flow is led through azimuthally distributed channels. Each channel comprises a slotted wall. A secondary air mass flow can be induced passing through the slots, hence creating an adjacent wall jet, which subsequently follows a curved surface. The resulting azimuthal direction change of the primary flow depends on the induced secondary air mass flow. The angular flow momentum and thus the swirl number can be therefore continuously changed. The development process of the proposed swirler is presented and the efficiency of swirl variation of different geometries is qualitatively assessed through computational flow simulations. The effects of stationary operation and unsteady swirl number variations are herein investigated and, moreover, the variation performance is assessed for a range of different air mass flows. The simulation results show the potential of a linear swirl number variation with respect to the induced secondary air mass flow. Moreover, the simulation results show that the achieved swirl numbers are comparable to those of state-of-the-art swirlers.
Quantifying Part-to-Part Flow Variations and Cooling Effectiveness in Engine-Run Blades
Authors: McCormack Kelsey E. , Gailey Nicholas L. , Berdanier Reid A. , Barringer Michael D. , Thole Karen A. 
Published: September 2023

Abstract
As turbine inlet temperatures continue to increase for modern gas turbine engines, the lifing of hot section components operating in a range of environments is becoming increasingly challenging. Engine operations in harsh environments can cause a reduction in cooling capability leading to reduced blade life relative to existing experience. This study analyzes the effects of harsh environments on the deterioration of blade flow and cooling effectiveness in turbine blades by comparing three commercially-operated engines with varied operational times referenced against a baseline blade. Spatially-resolved surface temperatures measured using infrared thermography at high-speed rotating conditions were evaluated to determine variations in cooling effectiveness as a function of engine operation and blade-to-blade variability from the different commercial applications. Engine-run blades were found to have reduced flow as well as greater part-to-part variation when compared to baseline blades. Blade surface temperature measurements on the deteriorated operational blades indicated film cooling traces dissipated closer to the hole exit relative to baseline blades. Furthermore, the cooling effectiveness varied significantly even between blades from the same engines. The reduction in cooling effectiveness in the engine-run blades led to higher blade temperatures and significantly shorter component life, with some exhibiting as much as an 18% reduction in life compared to baseline blades. This knowledge allows lifing models to be developed toward predicting blade operational effects in harsh environments.
An Optimized Chemical Kinetic Mechanism for the Accurate Modelling of Low Temperature Combustion of Syngas and Methane
Authors: Methling Torsten , Schmidt Marleen , Naumann Clemens , Köhler Markus 
Published: September 2023

Abstract
In the present study, the chemical kinetic mechanism DLR SynNG for the combustion of syngas and natural gas is optimized with various experimental data points with a focus on low temperature chemistry. For the optimization approach, the framework of the linear transformation model (linTM) is applied. The linTM was designed to optimize chemical kinetic model parameters with target quantities from a broad range of experimental facilities, like shock tubes, flow reactors, jet stirred reactors or various burner configurations. In this work, the optimization capabilities were extended for data from rapid compression machines (RCM), which are commonly used to investigate the ignition behavior under low temperature combustion conditions. RCM are typically simulated with homogeneous reactors with constrained pressure or volume profiles derived from the experiments. With the implementation of the RCM into the linTM framework, a novel parameterization approach for the simulation with constrained volume profiles is proposed. This new approach results in significantly reduced computational costs of RCM simulations and increased numerical stability for solving the underlying ordinary differential equation systems. Since several thousand RCM simulations throughout the optimization process are needed, this is highly beneficial for the applied optimization of the chemical kinetic mechanism.
In detail, the rate coefficients of sensitive reactions were optimized within their uncertainty boundaries. The optimized chemical kinetic model is capable of reproducing a broad range of experimental data for a large field of boundary conditions and fuel mixtures of hydrogen, carbon monoxide, methanol and methane. The experimental data include ignition delay times, laminar burning velocities as well as species profiles from flow reactors, jet stirred reactors and different laminar flame configurations.