bluuebunny/crossref_metadata_2025 huggingface dataset:
Unique High-Resolution Temperature Mapping of Stage 1 Turbine Vane in a Long-Term Engine Test
Authors: Hickey Jim , Lee Jaebin , Counte Joseph , Rai Kieron , Lee Kidon , Mun Younggi , Araguas Rodriguez Silvia , Karagiannopoulos Solon , Hong Giwon , Feist Jörg P.
Published: August 2024

In this study, surface temperature maps, resulting from a long-term engine test, were evaluated on a stage 1 turbine vane using Thermal History Coatings (THCs). THCs are ceramic-type sensor coatings doped with a lanthanide ion, giving the coating photoluminescent properties. The THC’s structure permanently changes when exposed to high temperatures, which in turn alters its photoluminescent properties. Therefore, historic maximum temperature maps are evaluated by optically probing the THC point-by-point across the vane’s surface.

The vane was exposed to a non-dedicated (multi-cycle, multi temperature-level) engine test lasting over 8 months. Two passes of THC measurements were taken, termed Low Resolution (LR) and High Resolution (HR), each respectively with point pitches of 5 mm and 1 mm. The latter provided a unique insight into the historic maximum temperature profile of the vane, particularly around high temperature gradient regions, such as those close to effusion cooling holes. The THC temperatures were compared to the engine manufacturer’s (Doosan Enerbility) heat-transfer code (DiTACS) for validation.

The THC temperature mapping was successful with good coverage across the vane. The leading edge and pressure side trailing edge regions were typically the hottest. The HR measurements clearly show sharp thermal gradients around the effusion cooling holes on the vane’s aerofoil and platforms. Critically, the THC measurements compared very well to the DiTACS measurements, validating THCs as a credible temperature measurement technique for long-term, non-dedicated engine-tests for components operating in some of the most extreme environments of an engine.
Noise Reduction by Lowering the Jet Mach Number and Using Inverted Velocity Profile at Fixed Thrust and Mass Flow
Authors: Liu Junhui
Published: August 2024

Noise reduction concepts of lowering the jet Mach number and using the inverted velocity profile at fixed thrust and mass flow have been assessed by large-eddy simulations. This assessment involves a baseline jet that has a relatively high jet Mach number near 1.5, and Low-Mj jets that have jet Mach numbers barely above 1.0. The Low-Mj jets have either a uniform or inverted inlet velocity profile. Both noise reduction concepts can reduce the noise in the downstream direction. The combination of these two methods can achieve a noise reduction up to 3.5dB near the peak radiation direction. In addition, because the Low-Mj jets generate very low shock-associated noise, they produce a substantial noise reduction in the upstream forward) direction. However, the inverted velocity profile elevates the noise level at both the upstream and small aft angles. This noise elevation gets worse as the velocity ratio increases. Lowering the jet Mach number at the fixed thrust and mass flow reduces the turbulent kinetic energy. The inverted velocity profile further reduces the turbulent kinetic energy, but it elevates the high-frequency noise source intensities near the nozzle exit. These two competing effects produce a double peak pattern in the far-field spectral sound pressure levels in the peak noise direction.
Criteria for the Occurrence of Tip Leakage Flow Induced Rotating Instability
Authors: Chen Xiangyi , Lange Martin , Koppe Björn , Jasmund Christoph , Chu Wuli , Mailach Ronald
Published: August 2024

In axial compressors, an unsteady flow phenomenon associated with fluctuating tip leakage flow can be observed at stable operating points with high aerodynamic loading close to stall, named rotating instability (RI). Within the frequency spectrum, e.g., from wall pressure measurements, RI is visualized as a hump lower than the blade passing frequency. Since RI indicates an increase in noise level and might cause blade vibration and other undesirable structural issues, it has been a hot-spot topic in the turbomachinery community over the last decades. In this paper, a study on RI is performed based on a single compressor rotor row of the Low Speed Research Compressor at Technische Universität Dresden. Firstly, setups with a solid casing and a casing groove mounted over the shroud are investigated based on the configuration with a blade tip clearance of 4.3% tip chord length. The results show that RI properties are dependent on the operating condition (flow coefficient) and the casing groove. By implementing dynamic mode decomposition on the transient simulation snapshots, the coherent flow structure corresponding to the dominant frequencies of RI is extracted and visualized as a wave-like flow feature located in the blade tip region. The RI is essentially equivalent to the superposition of periodic unsteady behaviors of the tip leakage vortex (TLV). Furthermore, RI is not detected in the configuration with a reduced blade tip clearance (1.3% of tip chord length), as the tip flow becomes less unsteady. Based on the comprehensive analysis, two criteria for the occurrence of RI are concluded as follows: The tip leakage flow from one blade tip gap can influence the formation of the TLV originating from the adjacent blade, and the inherent unsteadiness of the tip flow is intensive enough.
An Automatic Film Cooling Hole Mesh Generation System Based on Matrix Dividing Strategy
Authors: Fan Jiazheng , Jia Xiaotong , Han Chuang , Li Weihong , Duan Penghao
Published: August 2024

Film cooling is one of the essential measures to guarantee the turbine blade’s durability. In the film cooling system design process, it is inevitable for researchers to generate the cooling hole mesh in order to perform the CFD simulation of turbine blades. However, generating hundreds of cooling holes’ mesh is time-consuming and requires plenty of manual operations. In addition, to implement the optimal film cooling hole distribution, there is a need to develop a parametric design methodology to arrange the position of cooling holes reasonably. The present paper develops an automated film cooling hole mesh generation system, which adopts a matrix dividing strategy to parameterize the film cooling system. The geometrical representation of the cooling-hole distribution is parameterized by m × n matrices. The system first splits the existing block based on the matrix parameters, dividing the blade surface into m × n pieces. Then, it uses a parametric system to design the cooling hole geometry and automatically generates cooling hole blocking lines at the pieces of interest. The cylindrical and fan-shaped hole topology can be automatically generated in the parametric system. Finally, the transfinite interpolation method is used to automatically produce the structured mesh from the blocking lines. This system can also use the above technologies to generate the cooling hole mesh on the tip of rotor blades.

The film cooling hole mesh generation system has been integrated into our existing turbine blade design platform (NuFlux), which is designed to implement the fast changing of the 3D blade geometry and automated structured mesh generation. To verify the reliability of the cooling hole meshing system, the computational grids of NASA C3X film-cooled vane and transonic HPT rotor blade with tip cooling injection are produced using the system and examined in the mesh quality check system in NuFlux. The CFD simulation results using the grids are validated against the relevant experimental data. The integration of the cooling hole meshing system makes NuFlux a unique tool which is competent at turbine blade cooling system design optimization.
An Integrated Neural Network and Finite Element Method for Defect Characterization and Strength Prediction of Unidirectional Composites
Authors: Zhang Bo , Liu Changqi , Shi Duoqi , Yang Xiaoguang
Published: August 2024

This study proposes an integrated approach that combines neural networks and finite element analysis for robust defect recognition and accurate prediction of mechanical strength in unidirectional composite materials. ABAQUS is employed for simulating random distributions of fibers and pores, along with variations in mechanical properties. Numerical simulations, based on the Monte Carlo method, provide authentic mechanical performance data as output labels for the neural network. Two methods for recognizing geometric features are employed: 1) Image recognition using a two-point cross-correlation algorithm, refined through techniques like feature selection and principal component analysis for efficient extraction of essential geometric features. 2) Convolutional neural networks with attention mechanisms for improved capturing and recognition of features. Additional descriptors such as kurtosis, skewness, and eccentricity are incorporated for a comprehensive analysis of the influence of pore morphology on mechanical performance. Deep learning techniques reveal concealed patterns, leading to highly precise mechanical property models. This innovative approach for defect characterization in unidirectional composite materials yields rapid and accurate results, with predicted tensile strength errors consistently below 10%.
Compressor Blade Vibrations of Next Generation of Turbocharger With Focus on Damping: Simplified Prediction and AI-Based Evaluation
Authors: Weber Robby , Glatt Matthias
Published: August 2024

Recently [1], Accelleron announced the X300-L series, marking the beginning of a new concept in turbocharger technology. This innovative platform-based approach simplifies service procedures but also provides adaptability to respond to diverse demands caused by a certain variety of future fuels. The integration of enhanced power densities, standardized components, and a modular design offers fewer frame sizes and variants. Consequently, individual core components (i.e., compressor wheel or turbine impeller) are necessarily not only more compact and more powerful but also extend their utility across a wider range of applications.

Accurate blade vibration analysis is essential to identify potential performance issues, mitigate fatigue and wear, and prevent disastrous failures. The complete variety of numerical and experimental methods that are involved during the modern development process of new turbochargers will easily extend the scope of this contribution. To allow a more detailed insight, this paper presents a comprehensive study on compressor blade vibrations; with a particular focus on damping as one of the most important aspects of high-cycle fatigue.

First, a blade vibration measurement is carried out employing both strain gauges and blade tip timing, two cutting-edge methodologies that demonstrate strong mutual consistency. The dynamic stress of five chosen resonance crossings is investigated to primarily underline the robustness against high-cycle fatigue and show the agreement between strain gauge and tip timing measurements.

Second, a simplified method is adopted to predict critical damping ratios of specific blade vibration resonances. This approach incorporates inputs as modal parameters (like natural frequency and mode shape) and operational conditions (fluid density and speed of sound), all of which are conveniently accessible during the preliminary design phase.

Third, experimental data from several resonance crossings recorded with strain gauges are fed into an AI-driven methodology utilizing Deep Learning, enabling the assessment of genuine damping ratios for these resonances. Subsequently, a comparison is presented, contrasting the new damping evaluation (AI based on strain gauge measurement) with a state-of-the-art solution (SDOF-Fit of tip timing data) as well as the predicted damping ratios of the first part.

In conclusion, this paper not only highlights the good performance of the compressor in terms of HCF strength but also underscores its accelerated development through the use of reliable data from the early design phase. Modern measurement techniques offer remarkable precision, validate numerical predictions, and finally increase the trust in such methods. The proposed AI-based damping estimator validates damping predictions as a practical tool for engineers in the field of turbocharger development, facilitating the development of more reliable and efficient turbocharging systems for future applications.
On the Development of an Efficient Sliding Mesh Interface for the Harmonic Balance Method, Part II: Effects of Casing Treatments on the Aerodynamic Damping of a Compressor Blade
Authors: Hartmann Maximilian , Schlüß Daniel , Geiser Georg , Schwarzenthal Felix , Ashcroft Graham , Herbst Florian
Published: August 2024

In order to enable the Harmonic Balance (HB) method for efficiently capturing the non-linear effects of complicated configurations such as casing treatments, we introduce an algorithm for the coupling of non-conforming mesh topologies across domain boundaries in a series of two papers.

In this second paper, we demonstrate the novel sliding mesh method’s relevance for the design of modern transonic compressor rotors with casing treatments. In order to allow for a flutter assessment of the rotor with the flow solver TRACE a specific mesh topology for the frequency domain approach to connect stationary cavities with the moving rotor domain is introduced. It shows no significant impact on the flow characteristics of interest. HB results are successfully verified by means of time domain simulations (TD) with respect to average flow quantities and unsteady flow characteristics. Both methods clearly illustrate that a casing treatment not only affects the average flow field but also significantly changes the unsteady flow viz. the aerodynamic damping of the rotor. By providing the same prediction quality for more than one order of magnitude less computational resources than the TD approach the novel method enables an efficient industrial design process for such configurations with HB.
Prediction of the Flame Characteristics of an Industrial Gas Turbine Operated With CO2-Diluted Air Through an LES-Based CFD Analysis: A Comparison Between FGM and ATF
Authors: Lemmi Gianmarco , Castellani Simone , Galeotti Sofia , Picchi Alessio , Becchi Riccardo , Andreini Antonio , Babazzi Giulia , Meloni Roberto
Published: August 2024

In light of the global commitment to decarbonize industrial processes, Carbon Capture and Storage (CCS) plays a pivotal role in mitigating greenhouse gas emissions from Gas Turbine (GT) power generation processes. Achieving an efficient GT-CCS coupling requires the employment of high percentages of Exhaust Gas Recirculation (EGR) to maximize the CO2 content at the CCS inlet. Nevertheless, such operating conditions pose critical challenges for conventional combustion systems due to reduced oxygen levels associated with higher EGR, limiting engine operability. To address this challenge, the development of innovative technical solutions is essential to extend the combustor operational capabilities at high EGR rates. For this goal, a significant number of Computational Fluid Dynamics (CFD) simulations are required to identify the flame stability limits across various EGR levels and burner designs. It is imperative, in this context, to minimize computational costs while maintaining high accuracy. In this work, a comprehensive comparative study of an extended version of the Flamelet Generated Manifolds (FGM) and the Artificially Thickened Flame (ATF) model is performed through a Large Eddy Simulation (LES) based CFD analysis. The investigation is performed within the context of an industrial lean premixed burner manufactured by Baker Hughes, operating with Natural Gas and CO2-diluted air at atmospheric pressure. While the extended-FGM has been previously presented by the authors in a study on the same test rig under standard air conditions, the current work aims to extend its application to critical oxygen-depleted conditions, where near-blow-out phenomena such as flame lift-off and length elongation may become significantly pronounced. Numerical validation is carried out through a direct comparison of the computed averaged heat-release, representing the flame topology, with detailed OH* chemiluminescence images from a test campaign conducted by the THT Lab of the University of Florence. The experimental data will serve as the primary benchmark for assessing the models’ effectiveness in capturing the main dynamics of such critical operating conditions. Furthermore, potential disparities in both thermal and flow fields at the burner exit region between the two models will be discussed.
Effect of Dilution Hole Diameter on the Outlet Temperature Distribution in a Centrally Staged Combustor
Authors: Pang Liyao , Xu Honghao , Zhao Ningbo , Li Zongfu , Zheng Hongtao
Published: August 2024

Temperature distribution at combustor outlet is pivotal for lifetime and operational reliability of a turbine, wherein dilution hole diameter emerges as a significant design parameter influencing it. In the present work, numerical simulations of five schemes of a single-sector centrally staged combustor with different dilution hole diameters are conducted. The influence of dilution hole diameters ranging from 8 to 16 mm onflow characteristics inside combustors is explored, while the morphology and development of both high-temperature region and flame, as well as the formation process of hot streaks at outlet are analyzed. The results indicate that, with a constant inlet mass flow rate, the dilution hole diameter affects jet penetration depth and axial length of the primary recirculation zone (PRZ). As dilution hole diameter increases, equivalence ratio in the main combustion zone gradually approaches or even exceeds the stoichiometric ratio, resulting in a transition from lean to rich fuel therein, and an expansion of the high-temperature region. Under smaller dilution hole size, two obvious flame fronts form at the PRZ and the interface between the dilution hole jet and the shear layer. As the hole diameter increases to 16 mm, flame fronts are separated by the shear, leading to a reduction of obvious flame fronts to a single location in the PRZ after separation. As hole diameter increases from 8 to 16 mm, total pressure loss decreases from 3.5% to 2.6%, and combustion efficiency drops from 99.97% to 99.79%. Both pattern factor and radial pattern factor initially rise and subsequently reduce. The combustor exhibits optimal performance when dilution hole diameter is 14 mm.
Advanced Methods for Assessing Flow Physics of the TU Darmstadt Compressor Stage: Part 1 – Transitional Delayed Detached-Eddy Simulation
Authors: Möller Felix M. , Tucker Paul G. , Wang Zhong-Nan , Bode Christoph , Morsbach Christian , Matha Marcel , Sivel Pierre
Published: August 2024

In this first paper of the two-part series, we analyze the predictive quality of transitional Delayed Detached-Eddy Simulation (DDES) for the transonic TU Darmstadt (TUDa) compressor stage. Initially, we validate the DDES in a translational configuration of the compressor at reduced rotational speed. Here we compare DDES results with previously published Large-Eddy Simulation (LES), steady and unsteady Reynolds-averaged Navier-Stokes (RANS) simulations. As the application of the DDES shows noticeable improvements for the shock boundary layer interaction (SBLI) and resulting laminar-to-turbulent transition, we continue analyzing the fully 3D setup. For this configuration, two operating conditions (aerodynamic design point (ADP) and near stall) are considered. We show DDES results and compare them to steady and unsteady RANS simulations, and experiments where available. Although the DDES indicates some improvements at the ADP, RANS is also able of predicting integral turbomachinery performance quantities. However, steady and unsteady RANS fail to predict the flow field with satisfying accuracy at near stall conditions. Especially in separated regions, DDES proves its strength by resolving relevant turbulent structures, which yields noticeably improved results. We discuss reasons for that and highlight the potential of transitional DDES.
Study on Dynamic Characteristics of Single-Span Rotor Under Cross-Coupling Stiffness Control on Non-Drive End
Authors: Ma Yuhang , Li Qihang , Yang Bowen , Zhang Rui , Wang Weimin , Yao Jianfei
Published: August 2024

The sealing-induced cross-coupling stiffness (CCS) often decreases the rotordynamic stability of turbomachinery. In our previous study, an active negative CCS control strategy applied between two bearings in the middle of the rotor was validated to enhance the stability of the rotor system. In this paper, a different approach was taken by applying both positive and negative CCS control strategies to the non-drive end, aiming to investigate their effects on rotordynamic stability using a rotordynamic model. The model represented a single-span centrifugal compressor rotor with CCS at the seal node. The logarithmic decrements and unbalance response of the rotor system were compared under different CCS applications at the non-drive end and in the span. The results demonstrate that applying both positive and negative CCS at the non-drive end can improve system stability, but the positive CCS stragety has limitations, and its applicability is not as extensive as negative CCS. A “critical stiffness” phenomenon emerges when the rotor system is actively stabilized at the non-drive end, resembling critical resonance. Furthermore, when components like seals introduce cross-coupling stiffness out of the span, they contribute to system stabilization. These findings provide valuable insights into actively enhancing the stability of rotor systems.
Computationally Lightweight Method for Campbell Diagram Plotting in High-Speed Electric Machines
Authors: Kurvinen Emil , Khadim Qasim , Ikäheimo Eero , Choudhury Tuhin , Jastrzebski Rafal
Published: August 2024

Campbell diagram is plotted from calculation results to identify a rotating object’s critical speeds. The Campbell diagram is formed by calculating the supported natural frequencies in a defined operation speed range. It is an important step when designing rotating machines, e.g., an integrated high-speed electric motor that can be sensitive to the rotor’s dynamical behavior. Currently, minimizing unnecessary calculation points is important for rapid design iterations and utilization of physics-based models with artificial intelligence. In cases where large variants of rotor geometry or using high-fidelity models, the calculation burden becomes high. In the research, a methodology based on a minimum number of calculation points and a second-order fitting equation is proposed, i.e., instead of using a high number of fixed calculation intervals, a three-point calculation methodology is proposed. The proposed methodology can be applied with neural network-based methods or implemented with high-fidelity models such as solid element models where the physics-based models can be used to create sensitivity to model parameters and study their influence with the traditional rotordynamics Campbell diagram tool. In the results, a comparison of two case studies is shown, and the computational cost is compared.
Transient Shutdown Cooling Simulation of a Gas Turbine Test Rig Configuration Under Ventilated Natural Convection
Authors: Sun Zixiang , Amirante Dario , Barnes Chris , Hills Nick , Fahy Daniel
Published: August 2024

A transient simulation of shutdown cooling for a gas turbine test rig configuration under ventilated natural convection has been successfully demonstrated using a coupled aero-thermal approach. Large eddy simulation (LES) and finite element analysis (FEA) were employed for fluid domain computational fluid dynamics (CFD) and solid component thermal conduction simulation, respectively. Coupling between LES and FEA was achieved through a plugin communicator. The buoyancy-induced chimney effect under the axially ventilated natural convection is correctly reproduced. The hotter turbulent flow in the upper part of the annular path and the colder laminar-type air movement in the lower part of the annulus are appropriately captured. The heat transfer features in the annular passage are also faithfully replicated, with heat flux of the inner cylinder reaching its maximum and minimum at the bottom dead centre (BDC) and the top dead centre (TDC), respectively. Agreement with experimental measurements is good in terms of both temperature and heat flux, and the result of the transient simulation for the shutdown cooling is encouraging too. In addition, radiation is simulated in the FEA model based on the usual grey body assumptions and Lambert’s law for the coupled computation. It has been shown that at the high power (HP) condition, the radiation for the inner cylinder is approximately 11% of its convective heat flux counterpart. The importance of radiation is thus clearly revealed even for the present rig test case with a scaled-down temperature setup.
Optimisation of Geometric and Operational Conditions of a Flywheel Energy Storage System to Minimise Standby Losses
Authors: Eltaweel Mahmoud , Herfatmanesh Mohammad Reza
Published: August 2024

Flywheel energy storage systems (FESSs) have gained significant attention as a promising technology for effective harvesting, storage and redeployment of energy. This technology is used particularly in renewable energy applications where they help manage the intermittency and variability of energy output from renewable sources such as solar and wind by providing quick response, high power density, and cycling stability without the degradation issues associated with chemical batteries. This paper presents a comprehensive study on the optimisation of geometric and operational conditions of a FESS, with the view to reduce standby losses hence improving the overall efficiency of the system. The effects of the following parameters are investigated; the working fluid, operating pressure and geometrical configuration of the FESS casing, using Computational Fluid Dynamics (CFD) simulations to provide insights into the system performance characteristics. This study investigates the effects of concave and convex casing shapes compared to conventional uniform cylindrical casings. The use of these distinct shapes can lead to lower standby losses. In addition, the effects of the working fluid and the operating pressure are investigated. The effects of different working fluids including air, helium and carbon dioxide, on standby losses are studied at different operating pressures. The findings of this study highlight the significant potential for improving FESS efficiency through the optimisation of FESS casing design and the use of a suitable working fluid at optimal operating pressure. Windage losses can be reduced by 90% compared to the base model, allowing the FESS to function as a medium-duration storage solution rather than a short-duration, which is often a limiting factor when considering FESSs as an alternative solution to battery storage systems.
Sensitivity Analysis of Simplified Labyrinth Seals Model Stability to Flow Hypotheses
Authors: Foschi Giorgia , Thouverez Fabrice , Blanc Laurent , Fiore Giuseppe , Pampolini Giampiero , Girard Patrick
Published: August 2024

Labyrinth seals are a widely used non-contacting mechanical subsystem of space engines turbopumps. Thanks to a sequence of teeth and cavities, they provide to the working flow a tortuous path limiting leakage and recirculation phenomena through rotor/stator gap and they guarantee more efficient engine performances. The high fluctuations of pressure and velocity experienced by the flow running through labyrinth seals, together with the necessity for light structures, make them subject to aeroelastic instabilities. This problem is object of in-depth investigations in order to prevent failures caused by fatigue and provide safer turbopumps. In this work, the analysis of a straight-through one-cavity labyrinth gas seal stability is conducted through the development of a Navier-Stokes one-dimensional fluid model monolithically coupled to an elastic structure model. To this end, a sensitivity study to the variation of different parameters is presented, with a particular focus on the role of the energy equation, the leakage flow formulation and, for a viscous flow, the shear stress model. This study allows to characterize the role that different assumptions and working parameters have on the stable/unstable behaviour of a labyrinth gas seal, under the hypothesis of a strong fluid-structure coupling. The achieved results show how the characteristic of the fluid modelling can be crucial for the accurate representation of the aeroelastic problem and how the choice of the leakage flow and friction coefficient model, together with the sizing of some geometric parameters, can have a decisive impact on the system stability.
Numerical Investigation of the Combustion Process in a Lean Burn Gas Turbine Fuel Injector
Authors: Rajput Amit , Divyansh Ayush , K. P. Shanmugadas
Published: August 2024

The present work investigates the aerodynamics and combustion characteristics of a novel fuel flexible lean burn fuel injector. Methane and hydrogen are considered as the fuel with different mixing ratios. Flame stability, temperature distribution, and species concentration are assessed to obtain the operational characteristics of the fuel injector. The injector assembly consists of pilot and main mixer blocks and each of them includes a set of axial and radial swirler assemblies. Considering the mixture as partially premixed, steady-state RANS turbulent combustion modelling is performed with standard k-epsilon model and steady diffusion flamelet model. Hydrogen is blended with methane with different mixing ratios ranging from 0–100%. Four geometrical configurations with pilot and main mixer fuel-air combination are considered with representative flow conditions. The pilot and main mixers generate individual recirculation zones and stable flame anchoring is observed for all cases. A uniform and symmetric temperature distribution is observed with Two Temperature peaks corresponding to main and pilot flame fronts. The hardware anchors the flame till 50% hydrogen concentration and any further addition resulted in an unstable flame.
A Systematic Approach to Sensor Selection for Gas Turbine Exhaust Gas Temperature Prediction
Authors: Xu Jiasen , Lou Fangyuan
Published: August 2024

The performance of a gas turbine deteriorates over time due to various primary flow component degradations such as fouling, erosion, corrosion, and foreign object damage. Exhaust gas temperature, commonly used for engine control, condition monitoring, fault detection, and maintenance decisions, effectively indicates the severity of engine performance degradation. Although EGT can be directly measured by placing a few probes at the exit of the turbine, EGT sensors themselves are subject to frequent failures, providing a fairly inaccurate indication of the gas turbine hot-section status. This paper proposes an active-subspace-based approach to sensor selection for EGT prediction based on active subspace approach. Instead of selecting a subset of parameters, the active subspace approach identifies a few primary directions along with EGT changes fastest. The method’s effectiveness is examined using the Advanced Geared Turbofan (AGTF30) engine, representing a 30,000 lbf thrust-class turbofan engine for civil aviation. All the numerical simulations are performed using the open-source Toolbox for the Modeling and Analysis of Thermodynamic Systems (T-MATS) covering the operating conditions, including takeoff, climb, cruise, descent, and landing. Results show that the proposed method can effectively search for an optimal sensor suite for EGT prediction. The optimal suites yield reasonably good EGT predictions with majority predictions of 95% confidence interval and are less sensitive to input measurement uncertainties. Furthermore, intelligent selection of sensor suites is crucial for EGT prediction, and the inclusion of additional sensor counts can sometimes undermine the precision of the prediction.
A Roughness Prediction Method by Particle Deposition and its Effect on Flow and Heat Transfer in High-Pressure Turbine Cascade
Authors: Wang Zhenfei , Wang Zhiheng , Xi Guang
Published: August 2024

Particulate pollutants deposited on the blade surface alter the roughness and profile of the blade, leading to a decrease in the performance of the gas turbine. This paper proposes a method for predicting local roughness and integrates it with a critical velocity model to create a time-stepping calculation framework for particle deposition. This framework may be utilized to compute the alterations in flow and heat transfer caused by particle deposition. The framework was utilized to perform a steady-state numerical simulation on a high-pressure turbine cascade. The findings indicated that particles larger than 2 μm are primarily deposited on the pressure side, whereas smaller particles are mainly deposited on the suction side. As the diameter of the injected particles increases, the capture efficiency exhibits a trend of initially increasing and then decreasing, regardless of whether it is on the pressure or suction side. With the increase in operating time, particle deposition leads to a gradual rise in the surface roughness of the blade, although the extent of the increase gradually diminishes. Moreover, the roughness variations on the pressure side are more pronounced than those on the suction side. Changes in the blade surface roughness significantly impact the heat transfer coefficient on the blade surface. An increase in roughness at the blade’s leading edge results in a decrease in the heat transfer coefficient, while an increase in roughness elsewhere on the blade leads to an increase in the heat transfer coefficient. Furthermore, as operating time increases, the magnitude of the increase or decrease in the heat transfer coefficient gradually diminishes.
Mechanism Study of Stator Suction Slots to Inhibit the Boundary Layer Separation in a Single-Stage Axial Flow Compressor
Authors: Zhang Haoguang , Wang Hao , Feng Yiming , Xiao Jinhang , Chu Wuli
Published: August 2024

In addressing the flow phenomenon that the starting point of boundary layer separation is located at the stator leading edge, three suction slots with axial positions of 15% Ca, 50% Ca and 85% Ca were designed on NASA Stage35. Four schemes were developed to investigate the effect of different suction slots on the boundary layer separation. The results show that four schemes improve the compressor total performance under the small and medium mass flow rate conditions. Suction-AB scheme, with double slot located at 15% Ca and 50% Ca, improves the total pressure ratio and isentropic efficiency by 0.89% and 1.83% under the near-stall condition, respectively. The internal flow field analysis shows that the slot-B, located at the 50% Ca, plays a key role in inhibiting the boundary layer separation. The airflow inside the separation area only needs to make a minimal directional turn to flow into the slot-B, making it difficult for the boundary layer separation to continue downstream, which is also the reason why the slot-C, located at 85% Ca, is unable to bring more improvements. However, the airflow into the slot-A, located at 15% Ca, requires a bigger directional turn, resulting in a lack of ability in slot-A to inhibit the boundary layer separation.
Tracking of Bristle Tip Deflections to Demonstrate Blow-Down in Brush Seals
Authors: Bowen Joshua P. , Bowsher Aaron A. , Crudgington Peter F. , Bull Sam , Sangan Carl M. , Scobie James A.
Published: August 2024

Sealing in gas turbines is paramount to overall performance and efficiency. Brush seals offer superior performance compared to other sealing solutions commonplace in modern turbomachinery. When subjected to a pressure load, a ring of flexible fine wire bristles — fitted at a lay angle to the radial plane — compact to resist the oncoming flow and deflect towards the rotor in a process known as blow-down. This study employs Digital Image Correlation to track individual bristle tips in three spatial axes throughout a large-scale brush seal test facility. This is the first-time direct measurements of blow-down throughout the bristle pack have been presented, providing a unique insight into the mechanical behaviour of brush seals.

Increased magnitudes of blow-down and axial bristle deflection were demonstrated in upstream bristle rows and at larger clearances. Analysis of these results in conjunction with the interrogation of the inter-bristle pressure field proved that blow-down is more prevalent for pressure relieving brush seals in comparison to conventional configurations. The reduction in the through-flow clearance area resulted in a significant enhancement in sealing performance for a clearance seal, highlighting a key advantage of the pressure relieving back plate design.
Synchronous Response of Rotor Components by Rotated Wavelet Probing
Authors: Iaffaldano Davide , Guida Roberto , Carassale Luigi
Published: August 2024

The analysis of the synchronous response of the rotor components can be carried out efficiently using time-frequency methods based on the continuous wavelet transform. The wavelet transform provides a measure that may be regarded as weighted averaging of the signal amplitude with the support of the wavelet. This averaging area is referred to as Heisenberg box and, for Gabor wavelet, has an elliptical shape. In the case of wavelet probing, the estimation of the amplitude and phase needs to squeeze in frequency direction the Heisenberg box (HB) for increasing the resolution. The limit of this technique arise when, in proximity of the resonance crossing, the HB of the wavelet intersects both the synchronous and non-synchronous response components. This interaction is particularly important when the dynamical system is time-variant due to the variation of the rotor speed.

This paper proposes the estimation of the synchronous response with a time-frequency method based on a wavelet whose HB is an ellipse arbitrarily rotated to increase the capability of separating the signal components. After the analytical definition of the wavelet, the proposed method is applied both to simulated and experimental data.
Flow Reconstruction in a Transonic Turbine Cascade Using Physics-Informed Neural Networks (PINNs)
Authors: McNichols Ezra O. , Juangphanich Paht , Hawke Mallory S. , Shoemaker Ethan J. , Poulson Mackinnon J. , Brandt Meghan E. , Bons Jeffrey P.
Published: August 2024

This paper investigates the application of Physics-Informed Neural Networks (PINNs) for the analysis of turbine blades in a transonic cascade. The 2-D flow field in a transonic turbine cascade is reconstructed in three ways: the traditional forward approach (PINN not trained on experimental data), by training the PINN using discrete sets of experimentally measured pressure at midspan, and in the inverse sense where no inlet or outlet pressure boundary conditions are applied. Comparisons between the PINN solutions to measured data are made. This is repeated for three different turbine blades with distinct loading characteristics. Good agreement is shown between a CFD calculation of the CMC7 blade, and the PINN model trained with all data. The PINN is trained utilizing all available data, half the available data, data from only the leading edge region, and data from only the trailing edge region. The forward problem results deviate the most from experimental data but show promise. Solutions from the assisted training cases show that the PINN can reconstruct the flow field with acceptable accuracy when trained on measurements along the entire blade. In the inverse case, it is shown that to simultaneously achieve acceptable errors for inlet Mach number and outlet isentropic Mach number, the PINN must be trained on the static pressure data along the entire blade.
A Physics Informed Neural Network for Solving the Inverse Heat Transfer Problem in Gas Turbine Rotating Cavities
Authors: Puttock-Brown Mark R. , Mahesh Bindhu Goutham Krishna , Ashby Colin E.
Published: August 2024

Recently, Physics-Informed Neural Networks have displayed great potential in delivering swift and accurate solutions for inverse problems. Here, a Physics-Informed Neural Network (PINN) was used to solve the inverse heat conduction problem in the rotating cavities of a aeroengine high-pressure compressor internal air system. The neural network was designed to receive experimentally captured radially distributed temperature profiles as inputs and predict the associated surface heat fluxes. The correctness of these predicted heat fluxes are assessed by numerically solving the direct heat conduction equation using a 2D Finite-Element model, thereby recovering the original temperature profiles. A comparative analysis is conducted between the predicted temperature profiles and the initial inputs.

The physics informed neural network is trained using noise-free synthetic data, created from a range of radial temperature curve fit coefficients, and subsequently tested on noisy experimental data at engine representative conditions. The predicted temperature values exhibit some good agreement with their respective actual counterparts. Furthermore, the sensitivity of model hyperparameters are explored to showcase the capability of the proposed approach. The results show that Physics-Informed Neural Networks exhibit reduced susceptibility to experimental uncertainties when addressing inverse problems, in contrast to inverse solution methods, and offer a possible new approach for analysis of experimental data if trained on a sufficiently large dataset.
An Optimized and Reduced Chemical Kinetic Model for CFD Simulations of Hydrogen and Natural Gas Blends Combustion for Industrial Gas Turbines
Authors: Rahman Ramees K. , Kancherla Raghu , Vogel Gregory , Vasu Subith S.
Published: August 2024

Natural gas is one of the common fuels that is used in gas turbines for power generation. Due to its interest in power generation and other applications, there are several chemical kinetic models available in the literature for natural gas. The power generation sector is moving towards decarbonization and there has been increased interest in replacing conventional fuels with fuels that produce less/zero carbon emissions like hydrogen. Pure hydrogen has a very wide flammability range and poses risks related to flashback and high thermal NOx production. Blending hydrogen with natural gas helps in having better control over the fuel properties. However, the literature lacks well-validated chemical kinetic models for the combustion of hydrogen blended natural gas for undilute mixtures at gas turbine-relevant conditions (8–16 bar). Hence, in this work, we develop a detailed chemical kinetic model for hydrogen blended natural gas and validate it with a wide range of experimental data for both dilute and undilute mixtures relevant to gas turbine operating conditions. We outline the strengths and weaknesses of the current mechanism to aid future users of our chemical kinetic mechanism. The detailed chemical kinetic mechanism is then reduced to two smaller versions (60 species and 44 species mechanisms) without significant loss in accuracy using Directed Relation Graph with Error Propagation (DRGEP). To improve the prediction for pure hydrogen combustion, while retaining all other predictive capabilities, an optimization is carried out for the most sensitive reactions for hydrogen combustion. The resultant mechanism can predict a wide range of experimental results with the least cumulative error.
Advancing AI Modeling for Prediction of Safety Parameters for Combustion of Hydrogen/Syngas/Natural Gas Mixtures
Authors: Bounaceur Roda , Glaude Pierre-Alexandre , Fournet René , Sirjean Baptiste , Montagne Pierre , Auvray Alexandre , Impellizzeri Eric , Biehler Pierre , Molière Michel
Published: August 2024

One promising way supporting efforts to decarbonize energy production is to hybridize gas turbine fuels, and in particular to make increasing use of hydrogen. The use of alternative decarbonated or renewable fuels will significantly modify safety parameters. New simulation tools need to be developed that can rapidly assess and forecast the safety characteristics of different reactive fluids. This paper focuses on the development of a learning model to estimate Auto Ignition Temperature and Auto Ignition Delay Times (AIT and AID) during the combustion of several mixtures of dihydrogen, natural gas, and syngas. A numerical procedure has been developed, which generates automatically a dataset of AIT covering a wide range of operating conditions. The dataset contains 50,000 points and has been simulated using the comprehensive combustion model from the literature developed at National University of Ireland at Galway (NUIG). In order to fit optimally all the hyperparameters of a neural network model, several methods of optimization have been tested and are discussed. The model developed is capable of predicting AIT for pressures between 1 and 50 atm, temperatures between 200°C and 700°C and equivalence ratio between 0.2 and 5. For both the training and testing datasets, the average value of the correlation coefficient was above 99.95%, the Mean Absolute Error (MAE) and the Mean Square Error (MSE) around 0.003 and lower than 1e−4, respectively. The final machine learning model shows a high degree of robustness in reproducing the results of the detailed model over all the parameter domain studied. It was used eventually for the analysis of a typical case study of the risk of auto-ignition in pipes when gases are fed to a gas turbine.
Validation of a Methodology to Assess the Flutter Limit Cycle Oscillation Amplitude of Low-Pressure Turbine Bladed-Disks - Part I: Mach Number Effects
Authors: Escudero Alvaro , Rodríguez-Blanco Salvador , Corral Roque
Published: August 2024

This paper presents a methodology to estimate the vibration amplitude of fluttering low-pressure turbine blades saturated due to friction effects. The study utilizes an analytical model that balances aerodynamic work and dry-friction work. The analytical predictions are compared against experimental results to validate the model. The first part of this paper focuses on the influence of the Mach number on the work balance between aerodynamic and mechanical components. It is observed that the vibration amplitude of low-pressure turbine rotor blades notably increases with higher Mach numbers. In addition, numerical simulations are employed to assess the influence of the Mach number on the critical damping ratio. The results demonstrate that an appropriate scaling of the critical damping ratio with the exit Mach number collapses all the damping versus inter-blade phase angle curves into a single curve. This finding validates the scaling of the aerodynamic damping for different pressure ratios. Unsteady pressure measurements were acquired, carefully post-processed to extract their flutter-induced peak components and presented in a nodal diameter by nodal diameter basis. The post-processed data were then used to characterize the vibration amplitude observed in the experiments. The trends of the measured unsteady pressure on the casing of a rotating rig and the proposed model with the Mach number for different shaft speeds are in good agreement. The vibration amplitude and the mean unsteady pressure increase with the Mach number, and exhibit a maximum with the shaft speed.