bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gas Turbines Cantilever Nozzles Simplified Approach for Performance and Structural Optimization
Authors: Fardelli Andrea , Ragni Giacomo , Di Benedetto Daniele , De Luca Alessandro , Colantoni Simone 
Published: September 2023

Abstract
One of the most critical phases of designing a competitive product such as a Gas Turbine is the conceptual phase, in particular the definition of the flow path, which decides the performance of the engine. Therefore, the ability to optimize the aerodynamic performance of the flow path has significant benefits, but, due to constraints related to the reduction of the time to market of new products, the optimization process is extremely limited.
Typically, the definition of an acceptable flow path is an iterative process between the Aerodynamic and Structural teams, which requires a considerable amount of time leaving very little space for optimization.
Considering the common architecture of a turbine, only the first stage nozzle can be supported both at inner and outer diameter, while all the other stages can be only supported at the outer. This leads to an extraordinarily strong structural and life constraint for airfoils definition because they must be properly seized to comply with creep requirements.
According to the earlier design process, the aerodynamic optimization of the flow path was performed by means of a 1D tool, later on airfoils were built and analyzed from a structural standpoint to verify if they were complaint.
The proposed function is based on a newly developed transfer function between the geometry parameters available from the 1D aero tool and the bending stress on the airfoils. Function has been trained on legacy engines and later verified and applied in ongoing studies.
In this way the aerodynamic optimizer can obtain a preliminary mechanical assessment in real time on each configuration of the 1D flow path, allowing to generate only structurally verified configurations.
The article explains how the tool works along with a case study highlighting its application. The findings confirm that this innovative tool can simplify and speed up the optimization of a 1D flow path.
Axial Compressor Loss Sensitivity Analysis to Blade Row Design Parameters
Authors: Cruz Gonçalo G. , Babin Cedric , Fontaneto Fabrizio 
Published: September 2023

Abstract
In the preliminary design phase of an axial compressor stage, the selection of the most relevant design parameters within the shortest amount of time is paramount. An easier convergence toward the final design limits the use of costly optimization loops and extensive computational fluid dynamics simulations. By coupling a previously published physics-based loss decomposition tool, a mean line analysis, and radial equilibrium codes, the current study investigates the influence of design variables on blade row total pressure loss contributions. The core of the work presents a strategy to exploit the state-of-the-art design space. The compressor stage loss sensitivity to the design variables selected is evaluated using the probabilistic method of Sobol indices, quantifying parameters non-linear interactions inherent to the design process. As an example, the study synthesizes the relationship between loading, solidity, and row inlet boundary layer displacement thickness, to profile loss, end wall loss, and tip leakage loss. As a result, this work ranks the relative influence of the selected design parameters in the different loss sources, a process that may not be obvious from a term-to-term analysis of the loss models used.
Analysis of Single Blade Passage and Full Circumference Large-Eddy Simulations of Turbine Rim Seal Flows
Authors: Hösgen Thomas , Meinke Matthias , Schröder Wolfgang 
Published: September 2023

Abstract
The flow in a 1.5-stage axial flow turbine with 16 vanes and 32 blades is investigated by large-eddy simulations with special focus on the analysis of the hot gas ingress through the rim seal into the upstream wheel space. Two setups with different solution domains are used. In the first large-eddy simulation, the full circumference of the turbine is resolved on a mesh with approx. 1 billion mesh cells. The second setup includes only a single blade passage and is solved on a mesh with approx. 75 million cells. The analysis shows that the flow fields inside the upstream wheel space, i.e., between the disk of the upstream stator and the rotor disk strongly differ. In the 360° domain two large-scale rotating vortex structures are observed, which have a strong impact on the ingress of main annulus gas into the wheel space. These structures cannot be captured in the single blade passage domain. The instantaneous flow fields are further analyzed by Dynamic Mode Decomposition to determine similarities and differences in the two flow fields. The comparison of the modes from the two setups reveal that the hot gas ingress from modes at the blade passing frequency generate a reduced sealing efficiency only at the outer radius of the wheel space. The additional presence of large-scale modes, however, reduce the sealing efficiency also in the inner wheel space. These results suggest that a single blade passage simulation cannot be used for a reliable prediction of the hot gas ingress for the investigated turbine setup and operating condition.
Prediction of Gas Turbine Trip by Combining Gas Path Measurements and Vibration Signals
Authors: Losi Enzo , Venturini Mauro , Manservigi Lucrezia , Bechini Giovanni 
Published: September 2023

Abstract
As well-known, gas turbine (GT) trip causes a reduction of GT lifespan and makes costs increase, because of unscheduled stops. Thus, predicting GT trip in advance would allow saving costs and maintaining high operational efficiency and availability.
For these reasons, this paper presents the development of a model based on deep learning, i.e., a temporal convolutional neural network, aimed at GT trip prediction. The model exploits both vibration data collected from multiple sensors installed at different locations of the GT asset and gas path measurements. Its prediction capability is compared to that of the models fed only with vibration signals or gas path measurements. The simultaneous exploitation of vibration signals and gas path measurements, which is the main novel contribution of this paper, is aimed at enhancing the reliability of GT trip prediction, since trip causes are heterogeneous.
The paper also investigates different time frames for predicting GT trip, by considering training and testing time windows taken at different time points from trip occurrence.
The case study is represented by a collection of field measurements referring to real-world GT trips taken from multiple GTs during several years of operation. The field data used to validate the results cover multiple ambient and operating conditions.
The results demonstrate that the simultaneous exploitation of both gas path measurements and vibration signals actually enhances the reliability of GT trip prediction in the majority of the considered cases, with accuracy values up to 73%.
Experimental Nonlinear Analysis of Pre-Loaded Turbine Blades Dynamics With Frictional Shroud Contact
Authors: de Filippis Hugo , Thouverez Fabrice , Blanc Laurent , Girard Patrick , Chevillot Fabrice 
Published: September 2023

Abstract
The evaluation of damping, obtained as a consequence of the frictional contact between shrouded blades of a low-pressure turbine, is of major interest in the aeronautical industry. The main purpose of the shrouds is to keep the tightness of the primary air stream, but it also produces a nonlinear damping which makes it possible to limit the blades vibration amplitude during classical service conditions of a plane turbojet, like take-off or cruise. One of the possible technological choices to introduce this nonlinear damping consist of having a geometrical design of the low-pressure turbine blades which includes a pre-torsion angle, and will produce a static loading of the blades after the assembly, when the shrouds are brought into contact. In dynamic conditions, the contact between the shrouds can evolve to different statuses like bonding, sliding or even separation, which obviously leads to a strongly nonlinear behavior and depends on certain parameters like levels of excitation force, friction coefficient and static loading.
In order to reproduce as accurately as possible the static loading of the blades due to the pre-torsion angle, an experimental test bench has been designed and manufactured. The main goal is to evaluate the nonlinear damping through dynamic responses. The materials used and the manufacturing process are mentioned. The major novelties of the proposed test bench in comparison to the ones found in the literature are firstly the presence of three test blades, secondly the application of a static loading thanks to the blades assembly with the pre-torsion angle, and thirdly the realistic Z-shape shroud geometry.
Several experimental results are presented in this article: some modal analyses of the blades in free and embedded conditions to validate the numerical model and to estimate the blades disparity. Then each blade has been calibrated by means of strain gauges to estimate the applied torsion torque, to control precisely the blades position and the repeatability of the assembly process. Finally, the blades are tested under a dynamic excitation, using an electro-dynamic shaker and a laser Doppler vibrometer. The aim of this experiment is to observe the nonlinear damping on the blades frequency responses, and its dependence to different varying parameters like the excitation force, the static loading, etc.
Suppressing Energy Localizations in Rotating Machinery With Realistic Noise
Authors: DeBoer Jonathan , Breunung Thomas , Balachandran Balakumar 
Published: September 2023

Abstract
Vibrations in rotary machinery can increase wear, leading to a decreased lifetime. Especially harmful are localized vibrations, during which only a small region of the machine vibrates significantly. Apart from imperfections and non-homogeneities, such energy localizations can be induced by the structural nonlinearities of turbine blades. Through previous experiments and simulations conducted in the authors’ group, it has been shown that Gaussian white noise can effectively suppress these energy localizations. However, the Gaussian white noise model is unphysical, since the associated energy is infinite. Thus, the efficacy of suppressing localization with more realistic noise in rotating machinery remains to be studied.
Motivated by the beneficial employment of noise, the authors explore the utilization of omnipresent noise in turbomachinery applications as a low-cost control strategy to destroy undesired energy localizations. To this end, the authors present an experimental study to investigate the impact of different noise sources on the suppression of localization in rotating machinery applications. Building on prior efforts in the authors’ group, the authors utilize a test-rig consisting of a circular array of cantilever beams, which are representative of machinery blades, and magnets that are used to induce nonlinear restoring forces. Due to these nonlinearities, the system has multiple stable vibrational states and localized high-energy vibrations. The influence of different noise sources on such localized response states is investigated.
The Effect of Ignition Procedure on Flashback of Hydrogen-Enriched Flames
Authors: Yahou Tarik , Schuller Thierry , Dawson James R. 
Published: September 2023

Abstract
The impact of different ignition sequences on the ignition dynamics of CH4-H2 flames in a bluff body burner is investigated at atmospheric conditions. Experiments are performed over a wide range of operating conditions covering pure methane injection (PH0) to pure hydrogen injection (PH100). A perforated plate of total porosity σ = 0.17 is positioned at the outlet of the combustion chamber to increase the chamber back pressure and trigger transient flashback during ignition. Time-series of pressure, OH* chemiluminescence and OH-PLIF images of the propagating flame branch are recorded simultaneously to characterize the ignition process. Two ignition procedures are investigated. For ignition procedure A, designated as an early ignition procedure, the spark is initiated before fuel injection. For ignition procedure B, designated as a late ignition, the spark is only activated after the fuel injection. The impact of the fuel air mixing on the final stabilization state is investigated by changing the fuel delivery time (dt) before the initial spark. Three different time delays are considered dt = 1, 3 and 5 s. The final state of the flame is found to be highly sensitive to the selected ignition procedure and increasing dt favors the occurrence of flashback. At constant power, the magnitude of the pressure peak is driven by a competition between the fuel mass flow rate at the moment of ignition and the high reactivity of hydrogen which shifts the flammability limit towards lower equivalence ratios, hence generating a lower reaction rate. For procedure A, the peak of the chamber over pressure shows a non-monotonic growth for increasing levels of H2 in the fuel blend, while it linearly increases for procedure B. Experiments are then conducted at a fixed injection flow velocity Ub = 5 m.s−1 and fixed laminar burning velocity Sl0 = 0.25 m.s−1 by varying the level of hydrogen enrichment. For procedure A, the over pressure amplitude decreases with increasing the hydrogen enrichment leading to a soft ignition for all CH4-H2 blends. Under ignition procedure B, the amplitude of the over pressure reached during ignition is found to be relatively unaffected by the hydrogen concentration, but the flame stabilization mode shows a strong dependence to both the level of H2-enrichment and fuel delivery time dt. OH* as well as OH-PLIF images reveal that the trajectory of the flame leading point changes as dt increases. The different dynamics of the flame leading points is likely to be the cause the different types of stabilization modes observed.
Analytical, Numerical and Experimental Study of Flutter in a Realistic Labyrinth Seal
Authors: Bermejo Oscar , Gallardo Juan Manuel , Sotillo Adrian , Altuna Arnau , Alonso Roberto , Puente Andoni 
Published: September 2023

Abstract
Labyrinth seals are frequently used in modern turbomachinery in order to control leakage flows between static and rotating elements. Previous experiences have demonstrated that flutter is a potential risk for them and can lead to high cycle fatigue life reduction or even mechanical failure. This aeroelastic instability depends on the interaction between aerodynamics and structural dynamics and it is hard to predict accurately due to its sensitivity to the details during operation. In 2014, as part of the E-Break European Union research project, an experimental campaign aiming to study the phenomenon was conducted at Centro de Tecnologías Aeronáuticas. Three realistic seal geometries were tested at a comprehensive set of operating conditions and all of them exhibited flutter at some point. These seals will be the object of study of this work. This document is a continuation of a previous publication of the authors where the E-Break campaign was reproduced with a methodology based on Computational Fluid Dynamics simulations. The simulations showed a good agreement with experimental data and revealed the importance of accurately predicting the actual fin gaps during operation and the influence of external cavities. Here a new approach to study the stability of the seals is followed, consisting in the use of a simplified analytical model based on the works by Corral, Vega and Greco. The model is the result of solving a linearized version of the governing fluid equations under certain simplifying hypothesis. The stability results obtained are compared against both the available experimental data and the aforementioned high-fidelity simulations, showing a fairly good agreement at a vastly reduced computational cost. However, the main limitation of the model arises in those cases where the stability is dominated by the external cavities, as the simplified model is not able to account for their effect.
Coherent Turbulent Stresses in Unsteady Forced Transonic Nozzle With Shock-Induced Separation
Authors: Goffart Nicolas , Tartinville Benoît , Pirozzoli Sergio 
Published: September 2023

Abstract
The influence of rotor/stator interference on shockwave/boundary layer interaction is investigated by means of an implicit large-eddy simulation. To replicate actual turbomachinery conditions but at a lower cost, this work considers a transonic bump over which a shock-wave develops and interacts with the separated boundary layer. Moreover, the backpressure is set to fluctuate at a realistic reduced frequency. The analysis is focused on the coherent component of the flow and more particularly the turbulent stresses in the recirculation region. Phase-averaging is performed in order to highlight this component and the reference oscillator is based on the location of the separation point. Statistical convergence is assessed. Coherent turbulent stresses show a two-layers pattern, the upper layer being linked to the mixing layer and the inner layer developing below. The coherent component can reach up to 60% of the local mean value. Budgets show that only some production terms are significant and each of them is acting upon a specific layer of the associated coherent turbulent stress. Finally, pressure strain, responsible for the coupling between the transport equations, is also of importance.
A System Dynamics Approach to Assess the Impact of Policy Interventions on the Market Penetration of Micro Gas Turbines
Authors: Sharma Kirti , Al-Zaili Jafar , Sayma Abdulnaser 
Published: September 2023

Abstract
Decentralized power generating systems, such as micro-gas turbines (MGT) for micro combined heat and power (CHP), can contribute to achieving the global energy and emission targets thanks to features like low emissions, primary energy savings, and fuel flexibility. It can also help increase the share of renewables due to its ability to easily integrate with renewable energy systems. Micro gas turbines, despite being such a promising technology, have achieved very limited market success due to barriers like high investment costs and a lack of supporting policies. The large-scale market penetration of MGT requires clear and strong policy support to achieve widespread adoption.
This paper establishes a quantitative model to assess the impact of the policy measures on the long-term market penetration of MGT for the domestic micro-CHP to establish a relationship between policy parameters, economic factors, technological advancements, and the market share of MGT.
The work compares five different policy scenarios for the case study of the UK market. The results demonstrate that the usual economic forces are insufficient for MGT to achieve its long-term market growth. Several combinations of direct and indirect policies are to be implemented by the regulatory authorities to promote the commercial growth of the technology. Finally, some insight into policy and decision-making in the UK for micro-CHP is provided, indicating promising policies to pursue.
Efficient Pressure Mapping for the Calculation of the Dynamic Force on Reduced Order Models of Bladed Disks
Authors: Bouras Abdelhakim , Carassale Luigi 
Published: September 2023

Abstract
The design of bladed disks involves both fluid dynamic and structural calculations through numerical methods that involve the discretization of the domains. On the fluid side, computational fluid dynamics (CFD) software is used while on the structural side, models are formulated by the finite element (FE) method and are reduced using different model reduction techniques.
The fluid and the structural model are coupled as the aerodynamic pressure induces a load on the blades, while the blade deformation changes the boundary conditions for the flow field. In industrial applications, this fluid-structure interaction problem is usually implemented only partially, adopting a oneway coupling.
In forced-response calculation, the aerodynamic pressure is calculated using the geometry obtained, including the static blade deformation (mean pressure load, centrifugal force, temperature), disregarding the dynamic part of the response. The dynamic pressure field calculated in this way is then used as a dynamic load for the structural model. On the other hand, in flutter analyses, the blade motion is prescribed according to a selected mode shape, frequency and inter-blade phase angle and is used to define the boundary conditions for the CFD model. In both situations, it is necessary to transfer information (pressures or displacements) between the fluid and the structural model.
This paper describes a technique to transfer the pressure field calculated by a CFD analysis to a structural Reduced-Order Model (ROM) obtained from a high-fidelity FE model of the disk. The generalized forces acting on the ROM are obtained as a linear mapping of the pressure computed on the boundary of the CFD domain. This mapping depends only on geometry and mesh topologies, thus it can be calculated only once in a structural analysis, while for each time or frequency step, the generalized forces are obtained through a matrix multiplication.
Experimental and Numerical Investigations of Grain Size Changes in the Rim Zone During Turning of DA718
Authors: Gerhard Nicklas , Liu Hui , Splettstößer Antonia , Massanés Pedró Pere , Meurer Markus , Bergs Thomas 
Published: September 2023

Abstract
Safety critical engine components, whose functionality and longevity demands a high surface integrity, are widely made of the direct aged nickel-based alloy DA718. The high strength and low thermal conductivity of DA718 lead to high thermal loads, which causes modifications of the microstructure in the rim zone. Changes in grain size can result in cracking and thus detrimentally affect component functionality. According to the current state of the art, numerical simulation methods can be used to model the machining induced rim zone modification. For this purpose, experimental investigations of orthogonal cutting and friction tests were performed to determine the viscoplastic properties of the DA718 and frictional behavior between workpiece and tool. Based on this, a turning simulation was developed using the Coupled Eulerian-Lagrangian (CEL) method. This is followed by the implementation of a numerical model for the prediction of grain size changes in the workpiece rim zone. To validate this model, face turning tests of DA718 was performed with a ceramic tool, and the grain size alterations were compared with the simulation. The Comparison showed, that the model agreed well with the experimental measurements for different cutting conditions.