bluuebunny/crossref_metadata_2025_split huggingface dataset:
Study on Segment Fitting Method of Nusselt Number on the Turbine Vane
Authors: Zhang Fan , Liu Cunliang , Zhou Tianliang , Yan Haonan , Li Guodong 
Published: August 2024

Abstract
This study analyzes the distribution characteristics of the Nusselt number (NuC) on the turbine vane. Subsequently, the study proposes an original Nu segment fitting method applicable to the whole surface on the turbine vane. The flow near the leading edge can be approximated as flow around a semi-cylinder. The Nud in this region can be fitted using a power function of Red (the characteristic length is the diameter of the inner tangent circle of the leading edge) with phase correction. Due to transition is completed faster on the suction surface, Nu in the transition region is linearly related to Re (characteristic length is the arc length). In contrast, the flow in the region after the transition on the suction surface and in the region of the pressure surface is similar to the flow along a flat plate. The study proposes this segment fitting method using the experimental results on Vane A. This study also verified the feasibility of the method on Vane B and C. The error analysis presents the following conclusions: the fitting error is less than 10% for the vast majority of the regions on Vane A, while Vane B and C have an error greater than 20% only at the junction of the segments. The error is less than 10% in most regions of the vane surface.
Effects of Trench Structural Features on the Film Cooling Effectiveness and Particle Deposition Performances of a Fan-Shaped Hole
Authors: Chen Siyu , Li Haiwang , Xie Gang , Zhou Zhiyu , Meng Long 
Published: August 2024

Abstract
In the pursuit of designing a film cooling system that mitigates particle deposition and achieves high film cooling effectiveness, this paper investigates the combination of trenches with high-efficiency fan-shaped holes. Through numerical simulation methods, the current work focuses on the effect of trench depth and width on the film-cooling effectiveness and particle deposition distribution characteristics of fan-shaped holes with a trench. The RANS method with the Realizable k-ε turbulence model was used to obtain the details of the flow field. The critical velocity deposition model was used to calculate the adhesion/rebound and detachment process between the particles and the deposited wall surface. The study was performed at three different blowing ratios of 0.5, 1.0, and 2.0. Three trench heights (0.2D, 0.4D, and 0.8D) and three trench widths (0D, 0.75D, and 1.5D) were investigated. The numerical simulation results indicate that for trench depths exceeding 0.2D, there is a subsequent enhancement in film cooling effectiveness. The most significant improvement achieves an enhancement of 57% (H/D = 0.8, R/D = 0.75, M = 2.0) compared to the plate. The variation in deposition efficiency is influenced by the characteristics of the deposition target and the outflow of film-cooling air. While R/D = 0.75, The deposition efficiency for H/D = 0.8 decreases by 12% and 4.6% compared to H/D = 0.2 and H/D = 0.4 under M = 1.0. Additionally, widening trenches decreases deposition efficiency, the effects are especially pronounced with the variation in high blowing ratios.
LES and POD/DMD Analysis of Thermoacoustic Oscillation of a Hydrogen Micromix Flame Pair
Authors: Kroniger Daniel , Kamiya Hiromu , Horikawa Atsushi , Suzuki Ryuta , Munktell Erik , Braun René 
Published: August 2024

Abstract
The micromix combustion concept is a combustion technology for using high hydrogen content fuel in gas turbines. In September 2023, Kawasaki launched the world’s first DLE gas turbine for Hydrogen. Its combustor is a new design based on the micromix (MMX) combustion principle. The underlying gas turbine is the M1A-17 with a power output of 1.8 MWel. Natural gas co-firing of 50–100 vol.% H2 is possible for the entire load range. In the development of hydrogen gas turbine combustors, thermoacoustic oscillations become an important topic. The objective of this article is the investigation of dynamic effects of the micromix flames located inside a combustion chamber by unsteady Computational Fluid Dynamic (CFD) simulations. The computational domain comprises of a micromix flame pair with opposing injection direction and its location and properties of its boundaries are defined by means of an acoustic mode analysis. Large Eddy Simulation (LES) is applied and snapshots of the unsteady fields are captured and processed by Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD). The acoustic properties of the air inlet and hot gas outlet are varied to analyze their effect on the reproduction of thermoacoustic oscillations. It was found that a pressure reflecting boundary at the hot gas outlet has a dominant effect on the appearance of a longitudinal mode. Pressure reflecting boundaries in vertical direction did not stimulate acoustic resonance with a vertical mode.
Numerical Investigation of the Axial Thrust Load of a Prototype Radial Turbine for Supercritical CO2 Cycles
Authors: Lea Benedikt , di Mare Francesca , Franz Holger 
Published: August 2024

Abstract
Radial turbines enable flexible operation at high stage expansion ratios in supercritical CO2 based power cycles for waste heat recovery or thermal energy storage. However, due to the pressure difference between the front and back side of the wheel, they are exposed to high axial thrusts. The net axial thrust and the flow field of a recently developed radial turbine for the operation in energy storage systems using either dry air or supercritical CO2 as working fluid are investigated. The influence of the working fluid on the operating behavior of the stage is discussed by keeping the expansion ratio and the circumferential Mach number constant. To assess the performance of the covered impeller and to predict the static pressure distributions on the wheel surfaces, three-dimensional RANS simulations are conducted with an in-house density based CFD solver using a Spline-Based Table Look-Up Method (SBTL) for an efficient evaluation of the SpanWagner reference equation of state. In contrast to the majority of existing literature, a covered rotor design was chosen in order to minimize tip leakage losses and to yield an impeller, which is less susceptible to vibration-induced fatigue under flexible load conditions. Assessment of isentropic efficiency demonstrates reasonable performance over the desired operating range, even at part-load conditions. At the investigated design conditions, the compressibility factor ranges between 0.77 and 0.83. It was shown, that next to the labyrinth seals, the presence of the cover disc leads to a considerable reduction in net thrust.
Response Surface Analysis of the Backward-Diffusion Elliptical Hole
Authors: Wang Shanyou , Zhang Siyuan , Li Xueying , Ren Jing 
Published: August 2024

Abstract
The design of film cooling holes facing the higher thermal load in next-generation gas turbine vane should consider the overall performance of film cooling effectiveness and thermal stress properties. The previous study has shown that the elliptical hole is better than the cylinder hole in film cooling effectiveness, and it has a lower stress concentration factor. According to the traditional method for improving the film cooling performance further, the elliptical hole is modified into the backward-diffusion elliptical hole. This study investigates the overall performance of the backward-diffusion elliptical hole using the response surface method. Three independent variables parametrically represent the backward-diffusion elliptical hole: the ellipticity of the inlet ellipse x1 (x1 ∈ [1,4]), the ratio of the short axis between the exit ellipse and the entrance ellipse x2 (x2 ∈ [1,2]), the ratio of the long axis x3 (x3 ∈ [1,2]). The experimental design is carried out using a standard experimental design called a central composite design. Numerical tests are carried out by an experiment validated numerical method. The sensitivity of the film cooling effectiveness, and stress concentration factor to the three geometric parameters (x1, x2, x3) at different blowing ratios (M = 0.5, 1.0) is analyzed. The film effectiveness is positively correlated with x1 and x3 and negatively correlated with x2. The stress concentration factor is negatively correlated with x1 and x3 and positively correlated with x2. This suggests that increasing the ellipticity and lateral expansion is favorable to the film cooling effectiveness and the stress concentration factor.
Analysis of Thermo-Acoustic Instabilities Induced by Hydrogen Swirling Flames
Authors: Vaysse Nicolas , Durox Daniel , Vicquelin Ronan , Candel Sébastien , Renaud Antoine 
Published: August 2024

Abstract
A considerable research effort has concerned combustion dynamics of systems fed with hydrocarbon fuels. The case of pure hydrogen/air flames deserves to be specifically considered because hydrogen is highly reactive, has a tendency to develop thermo-diffusive instabilities, is envisaged in many future applications, most notably in gas turbines and is less well documented. Thermo-acoustic instabilities of pure hydrogen flames are here investigated in a configuration where hydrogen is injected in-crossflow in a swirling stream of air. The study is focused on operating conditions that lead to oscillatory regimes. Using Abel-transformed phase-averaged images of OH* emission and visible light emission in burnt gases, it is shown that the OH* signal evolves approximately in phase with the heat release rate. This signal is then used to determine the local Rayleigh source term that feeds acoustic energy in the oscillation. The contributions of this term are examined using a space-time analysis based on an integration of the source term in the transverse direction. This procedure allows a detailed analysis of the processes that contribute to the acoustic energy in the system, showing, in particular, that a strong positive addition of acoustic energy results from a roll-up of the flame tip and from the quick cyclic back propagation of the flame to the injector tip. A global integration of the Rayleigh source term is then used together with a volume-integrated acoustic energy to estimate the growth rate associated to these driving processes and estimate the damping rate. A special experimental method is then exploited to determine the effective growth rate of the instability. The system allowing a sweep in frequency, self-sustained instabilities obtained at different frequencies are used to extract the specific instability frequency band of the burner. Finally, the flame is externally forced in order to measure its flame describing function.
Flow Transition in the Wheel Side Space of a 1.5-Stage Test Turbine
Authors: Pehle Lukas , Dimidziev Nikita , Wirsum Manfred 
Published: August 2024

Abstract
Secondary air systems in gas turbines provide a pressurized purge for the protection of highly-stressed components. The selection of an appropriate purge air mass flow seeks to sufficiently reduce the ingestion of hot annulus gas into the side wheel space with minimal impact on gas turbine efficiency. This paper describes a computational study of the flow field in a wheel side space of a 1.5-stage test turbine under different operating conditions.
Measurement data for the investigated test turbine shows the formation of large flow structures (low pressure areas) in the wheel side space for sufficiently low dimensionless purge air mass flow rates CW when using an axial sealing geometry. These structures are mainly apparent through their influence on the unsteady pressure field within the wheel side space. Large pressure inhomogeneities increase the ingestion of hot annulus gas thus reducing sealing efficiency. Furthermore, the high angular momentum of the ingested gas causes an increase in fluid core rotation which in turn results in large radial pressure gradients in the time-averaged flow field. Depending on operating conditions the flow transition (breakdown of large flow structures) can be observed around a characteristic CW,trans. This flow transition has a profound impact on pressure distribution and sealing efficiency.
Contrary to the approach of high model complexity and large computational efforts for analysis of the highly intricate flow fields in wheel side spaces, this paper presents a methodology utilizing a highly simplified computational model with an (U)RANS approach.
Despite the low model complexity, the simulation results shown in this paper show good agreement with measuring data pertaining to the flow field in the rotor-stator cavities and more specifically the flow transition. Possible reasons for deviations from measurement data as well as possibilities for further feasible simplification in the modeling approach are discussed.
Furthermore, the presented simulation methodology is applied to a radial sealing geometry, which does not show a flow transition in experimental data. It is shown that the flow within the wheel side space can be modeled with comparatively small deviations from measurement data regarding pressure and sealing efficiency. To assert, whether a flow transition effect can be found outside of flow conditions measured in the experiment, simulations with very low purge air flow rates are conducted.
Unsteady Computational Fluid Dynamics Simulation of Inlet Fins in Centrifugal Compressor
Authors: Tokieda Katsunori , Ueno Takahiro , Unno Masaru , Morita Isao 
Published: August 2024

Abstract
In this paper, it will be shown that small inlet fins mounted in the compressor inlet pipe can improve the compressor stability limit by alleviating the impeller inlet recirculation flow. Performance tests on the hot gas test bench and unsteady Computational Fluid Dynamics (CFD) simulations were conducted to investigate the mechanisms for surge condition improvement. The stability limit was shifted to lower mass flow rates in the low Mach number region by inlet fins in performance test results. As the compressor rotational speed increased, the stability limit shifted to high mass flow rates (kink characteristic) at a certain pressure ratio. The stability limit was unaffected by inlet fins in the high Mach number region after the kink point. Therefore, it was considered that the factors responsible for triggering surge were different near the kink point. It is thought that the instability of the diffuser does not occur after impeller stall in the low speeds region, but that diffuser stall occurs in the high speeds region causing the kink characteristics. Flow patterns extracted from unsteady CFD at the near surge point determined from the performance tests are analyzed to investigate the difference of surge pattern between low and high Mach number region. In low Mach number region, inlet fins suppress the extension of high entropy flow upstream of the impeller. It is assumed that the high entropy region was recirculation flow attributable to impeller stall. In addition, there are differences in the behavior on compressor characteristics with and without inlet fins. The positive slopes of compressor’s pressure ratio to flow rate become gentle by suppressing the development of pre-swirl (better surge characteristic). In the high Mach number region, flow patterns and compressor characteristics are almost the same in both cases. It is considered that the diffuser stall occurred first, and the diffuser stall triggered surge before impeller stall developed toward upstream. Therefore, the inlet fins did not work sufficiently since there was no recirculation flow from impeller.
HYFLEXPOWER Project: Demonstration of an Industrial Power-to-H2-to-Power Advanced Plant Concept With Up to 100% H2 in an SGT-400 Gas Turbine
Authors: Parsania Nishant , Hermeth Sebastian , Witzel Benjamin , Yilmaz Ertan , Fourcade Stéphane , Garmadi Sami , Trump Harry , McCaig Peter 
Published: August 2024

Abstract
Hydrogen, when produced with renewable energy and used in a gas turbine can become a key enabler towards decarbonization. The HYFLEXPOWER project is the first such demonstration of a fully integrated industrial power-to-H2-to power pilot installation of an existing cogeneration plant with a dry low emissions (DLE) Siemens Energy SGT-400 gas turbine at a paper recycling factory in France.
This paper provides a comprehensive summary of successful development, installation, and operation of the power-to-H2-to-power application in this plant. In 2022 and 2023, test campaigns in the SGT-400 gas turbine with 100% H2 as well as with natural gas and blends in between were conducted successfully. Initial testing in 2022 with a modified combustor design enabled the industrial gas turbine to operate up to 30 vol% hydrogen. Additional development of H2 combustion technology, upgrades of gas turbine control methods and improvements in the hydrogen-natural gas mixing were done and implemented at site. In 2023, the team successfully demonstrated operation with 0–100% hydrogen blends in natural gas. The paper will present gas turbine testing conducted with natural gas at Siemens Energy factory in Lincoln (UK) and both test campaign results at the site in France including emissions and metal temperatures with hydrogen addition.
Modeling Stochastical Particle Rebound Based on High Velocity Experiments
Authors: Hartmann Jan , Koch Christian , Staudacher Stephan 
Published: August 2024

Abstract
Solid particle erosion is a major deterioration process which contributes to performance deterioration of modern axial compressors. The prediction of this deterioration process requires the correct computation of particle movement through the machine and their resulting impacts on the effected components. Especially for particles with high Stokes numbers the movement is determined mainly by the particle wall interaction, which is described by coefficients of restitution. Today, they are derived from experiments featuring high particle velocities and target materials, which are representative for turbomachinery applications. In this study, an already published rebound model is optimized for particle materials and velocities within high pressure compressors. The statistical spread of the rebound experiment is evaluated and the implementation into the rebound model is shown, which improves the prediction capability of the model. The model is implemented into a CFD software and numerical simulations are performed. The model is applied to a cylinder test specimen within a sand blast facility. The simulation shows the importance of the stochastics of the rebound, which is often neglected in particle wall models. Moreover, the numerical study shows requirements for the test specimen and its positioning in the experimental setup, which are prerequisites for the derivation of the coefficients of restitution using two dimensional particle evaluation equipment.
Fault Detection on Short-Haul or Highly Dynamic Flights Using Transient Flight Segments
Authors: Varchev Tihomir , Mathes Jürgen , Koch Christian , Staudacher Stephan 
Published: August 2024

Abstract
A machine learning based approach is presented which allows to detect persistent engine faults after a single flight. It utilizes transient in-flight measurements and a transient engine model. The time series of the residuals between the measured data and the data resulting from performance synthesis is evaluated using moving windows containing at least one transient segment. A continuous wavelet transformation and a pre-trained convolutional neural network are utilized on the residuals for feature extraction. The fault detection is carried out via a one-class support vector machine, trained exclusively on nominal engine operation data. Therefore, the approach requires no a-priory knowledge of the effects of engine faults on the in-flight measurements. Under the assumption of persistent faults, all windows of a single flight which contain at least one transient segment are considered in order to improve the reliability of the fault detection.
This approach is validated using measured data of a small helicopter engine that replicates the dynamic flight of the corresponding model helicopter on a ground test bed. Consequently, step changes as well as complex variations of the shaft power output are considered. Four standard gas path sensors are considered. The one-class support vector machine is used successfully to detect two types of total pressure sensor anomalies. Assuming a typical number of transient segments for an average short haul flight, it turns out that persistent faults can be detected within one flight with a probability of above 90%.
The Effect of Flight Speed and Altitude on Windmilling Restart Operation of Turbofan Engine System
Authors: Zhang Jingkai , Wang Zhitao , Li Shuying , Wei Pengfei 
Published: August 2024

Abstract
The unpredictable flame-out may occur due to various factors such as weather conditions and bird strikes. After flame-out, the engine should undergo a challenging and risky restart process to restore thrust. Simulation model is an economy and repeatable tool to conclude the effects of flight speed and altitude on this extreme process. In this paper, a thermodynamic model is constructed in a modular scheme, with respect to the analysis and prediction of the restart performance in different flight environments. The equations containing the temperature polynomial and the corrected torque are added to the fan and compressor model to ensure convergence of cycle analysis in the low rotation speed region. The similarity theory and backbone mapping approach are integrated to generate the full mode characteristics required for fan and compressor models. The shaft acceleration control loop, which has been used in many advanced aero-engine is applied to the fuel controller to tightly control the shaft acceleration. Based on developed model, the effects of flight speed and altitude on the start-up time and performance parameters are studied. The results indicate that higher altitude and Mach number shorten the start-up time. Besides, the results show that the turbine operates under more extreme conditions when the restart operation is conducted at high altitudes.
Thermodynamic Analysis and Optimization of a Supercritical CO2 Power Cycle Driven by a SOFC-GT Hybrid System
Authors: Cao Runqing , Wang Youna , Wu Zhongliang , Liu Wenhe , Cao Yue 
Published: August 2024

Abstract
Solid oxide fuel cell-gas turbine (SOFC-GT) hybrid systems are an advanced technology for power generation because of their high efficiency, stability and environmental friendliness. Because the exhaust from the gas turbine in the SOFC-GT system is still of high grade, a bottoming cycle is usually used to recover the exhaust’s waste heat. The supercritical CO2 power cycle is selected as the bottoming cycle for the SOFC-GT hybrid system to achieve cascaded utilization of this thermal energy. Here, a thermodynamic model is built for such a supercritical CO2 power cycle driven by an SOFC-GT hybrid system. Six key parameters, including the fuel flow rate, fuel utilization factor, SOFC operating temperature, combustion engine pressure ratio, CO2 turbine inlet pressure and cycle split ratio, are analysed to determine the effects on the thermodynamic performance of the system in terms of the output power, exergy loss and exergy efficiency of the system. Moreover, particle swarm optimization (PSO) is employed to perform multiobjective optimization of the hybrid system. The optimization results for the output power and efficiency of the system are presented at the Pareto front of the system. Further analyses are conducted for the distribution of the values of the key parameters corresponding to the Pareto solution. The optimal operating point of the hybrid system is finally determined by the linear programming decision method of multidimensional preference analysis.