bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact of Hydrogen Fuel Retrofits to Gas Turbine Performance and Hot Gas Path Components
Authors: Kapoor Riddhi , Bullard Timothy , Shoraka Amir , Hsia Kuo-Ting
Published: August 2024

Hydrogen is gaining prominence as a carbon reduction strategy for gas turbines by end users and equipment manufacturers within the power generation industry. The cost of new gas turbine units is restrictive, and many are already in service with remaining life. Therefore, there is a growing interest in retrofitting existing gas turbines that historically run on conventional fuels like natural gas and liquid oil. Though many gas turbine combustors currently run on small amounts of hydrogen, such older units have not been specifically designed to use high quantities of hydrogen as a fuel. Among the many technical challenges of implementing hydrogen on existing units is the potential impact on performance and on hot gas path components’ durability. The effects on performance can vary depending on the existing combustion system configuration, as some combustors utilize water or steam injection, and some operate in a dry mode. The current study provides insights into retrofitting dry combustors (i.e., without water or steam injection for emissions control), their influence on gas turbine performance, and potential implications to the hot section components. Two analytical models are employed. The first is a gas turbine performance code used to assess the effects of fuel composition changes on performance parameters such as output, heat rate, firing temperature, exhaust temperature, etc. The second is a thermal fatigue cycle model used to study the effects of the varied combustion products, including high amounts of H2O, on the turbine components.
From Early Development to Industry’s Successful Adoption, the Journey in Additive Manufacturing Cooling Technology for Improved Gas Turbine Capabilities
Authors: Vogel Gregory , Borja Michele , Zangara Mark , Hunt John
Published: August 2024

The power industry is a critical sector that fuels the global economy, heavily reliant on high-performance industrial gas turbines. Leading manufacturers of turbine hardware are continually investing in cutting-edge technologies to meet the industry’s growing demands. Among these technologies, additive manufacturing has emerged as a game changer.

In its early stages, additive manufacturing primarily focused on aspects such as powder morphology, process optimization and material properties characterizations. However, it quickly paved the way for the creation of innovative cooling designs for gas turbine components. Collaborations with prominent universities conducting fundamental experiments have been instrumental in gaining a deeper understanding of the advantages and challenges posed by these novel cooling design features and how they might perform in real engine conditions.

A significant milestone was reached in 2018 when Power Systems Mfg., LLC (PSM) successfully conducted a groundbreaking technology demonstration, featuring an additively manufactured advanced cooling design airfoil running in a heavy-duty industrial turbine. This demonstration provided valuable insights and experiences that marked a turning point in the gas turbine industry’s acceptance of this transformative technology.

Since that pivotal moment, numerous gas turbine units around the globe have been operating with this adopted technology, with some surpassing the impressive milestone of three years in continuous operations. This paper provides detailed technological information related to the journey and present the latest field experience of an additively manufactured F class row 1 turbine nozzle equipped with advanced cooling solutions, as well as valuable lessons learned from applying additive manufacturing technology to enhance cooling designs, ultimately leading to improved gas turbine efficiency.
Metallurgical Investigation and Failure Analysis in GTD-111 Stage 2 Buckets From an Industrial F-Class Gas Turbine
Authors: Bridges Alex , Shingledecker John , Wang Yongqing
Published: August 2024

A utility experienced cracking in multiple stage 2 buckets (S2Bs) in a large F-class power generation gas turbine after only 7,348 hours and 31 starts following a standard repair and rejuvenation heat treatment cycle. The blades were cast from a directionally solidified (DS) superalloy and the cracking was found in the shroud section of the blade in the Z-notch region. A detailed failure investigation was conducted to determine the failure mechanism and most likely contributing factors to root cause in terms of design, operation, fabrication, and metallurgy. Three blades, two with visible cracks and one without cracks, were subjected to non-destructive and destructive evaluation. Methods consisted of visual inspection, 3-D scanning, physical measurements, chemical analysis, optical metallography, LED surface topological evaluation, and scanning electron microscopy. The failure mechanism was determined to be due to creep with damage propagating along the grain boundaries in a high stress concentration area. Evaluation of precipitate structure and size also confirmed this area exhibited the highest temperature during operations. High temperature creep testing was also conducted in material from the two different casting houses to confirm metallurgical risk did not have a significant impact on creep performance. An evaluation of the operational profile of an entire fleet of GE 7FA units showed that the failed 7F.03 S2Bs were in the highest operating temperature base loaded units. The findings from this work will help better define key factors that influence the high temperature performance of nickel-base superalloys used in the hot section of industrial power generating turbines.
Development and Optimization of a Solid Oxide Fuel Cell Gas Turbine Hybrid System
Authors: Sprengel Michael , Echter Nick
Published: August 2024

Solid Oxide Fuel Cells (SOFC) are an advanced form of fuel cells which can convert hydrocarbon-based fuels into electricity at efficiencies reaching 60%. Fuel efficiency may be increased to 70% or higher by closely integrating a SOFC into the hot gas path of a Brayton cycle gas turbine. SOFCs, unlike more common low temperature fuel cell technologies such as PEM, operate at elevated temperatures between 500°C and 1,000°C, temperatures well suited for integration with turbomachinery.

Fuel efficiency is enhanced through several mechanisms including: (1) operating the SOFC at elevated pressure, (2) by tightly integrating the SOFC between the gas turbine’s compressor and expander, (3) by using the gas turbine’s combustor to oxidize dilute fuel in the anode tail gas further heating the already hot and pressurized cathode tail gas before expanding it through a turbine to create additional power, and (4) by eliminating much of the parasitic balance-of-plant (BOP) required to preheat and circulate air through the SOFC.

The authors are part of a multi-company collaboration to develop and demonstrate a SOFC/GT system with unique elements such as an integrated cathode recuperator and a fuel to AC electrical conversion efficiency exceeding 70%. This paper covers the system’s development with a specific focus on tradeoffs and optimizations throughout the system design.
Turbulence Measurements in Axial Turbines Using Fast Response Aerodynamic Pressure Probes
Authors: Notaristefano Andrea , Persico Giacomo , Gaetani Paolo
Published: August 2024

Improving the comprehension of turbomachinery fluid-dynamics is vital to increase their performance, and calls for the development or extension of advanced instrumentation. In this context, novel data acquisition and data reduction techniques have been recently developed at Politecnico di Milano for turbulence measurements performed with Fast-Response Aerodynamic Pressure Probes. These improvements address a gap in the capabilities of such probes, as turbulence data were among the few, yet very important, information they could provide only on a quality level. At first, the technique is validated against hot-wire measurements on a low-speed wind tunnel, where a combustor simulator is inserted with or without an upstream turbulence grid generator. Second, the developed methodology is applied downstream of both the stator and the rotor of a single-stage axial turbine, where the probe robustness and reliability are fully exploited to gain crucial flow information also in a harsh flow environment, where the use of hot wires might be critical. In this paper, the measured turbulence intensity using FRAPP is compared among three different operating conditions obtained by changing the rotor rotational speed. Furthermore, the paper explores the impact of non-uniform stage inlet conditions, that resemble the combustor outlet disturbances, on the stator and rotor flow features.

The regions with the highest turbulence levels are observed in areas characterized by secondary flows, wakes, end-walls, and the residual swirl profile. The stator-rotor interaction contributes to the turbulence generation both downstream of the stator and the rotor. Additionally, an increase in blade loading corresponds to higher intensity in secondary flows, leading to elevated turbulence levels at the rotor exit. The injection of combustor non-uniformities has a diminished impact as the rotor load increases, given that the flow field becomes predominantly influenced by strong secondary flows.
Investigation of Lean Blow Off Limits of a Spray Flame in a Laboratory-Scale RQL-Type Burner
Authors: Nagao Jun , Rajendram Soundararajan Preethi , Kurose Ryoichi , Mastorakos Epaminondas
Published: August 2024

This experimental study explores the stability of an ethanol spray flame under conditions close to lean blow-off (LBO) in a rich-quench-lean (RQL)-type combustor. The combustor has a primary inlet with a swirling air flow and four radially injected dilution air inlets. The split ratio (SR) of primary to dilution air was varied (10:0, 8:2, and 6:4) at different fuel mass flow rates to quantify the LBO conditions. Results showed that there was only a minor difference in the LBO conditions for SRs of 10:0 and 8:2 for all fuel mass flow rates. In contrast, the LBO equivalence ratio increased at SR of 6:4. This is attributed to the different blow-off mechanisms at SR of 6:4 compared to the case of lower dilution, as suggested by the analysis of the blow-off event obtained using high-speed OH* chemiluminescence imaging. Those revealed that the flame started to extinguish downstream and around the spray cone region for SR of 10:0 and 8:2, but the flame first lifted off and then extinguished close to the nozzle at SR of 6:4. The high-speed OH* images were analyzed with Proper Orthogonal Decomposition (POD), which demonstrated different modes of flame fluctuations between conditions far from and close to LBO. The results obtained from this study can be used for validating gas turbine combustor CFD models.
Investigation of Flow Mechanism for Solidity in Typical Modes of Variable Pitch Tandem Cascade
Authors: Sheng Xiaoying , Luo Qiaodan , Xu Huafeng , Yang Chengwu , Lu Xingen
Published: August 2024

Due to the influence of fan geometry and aerodynamic factors, aerospace propulsion systems have difficulty operating above Mach 3.5. Even with a hybrid power system equipped with a turbofan engine, there is an issue of insufficient intermediate thrust. This is attributed to the limited acceptable inflow range of traditional fan layouts. This paper proposes a novel variable pitch tandem fan (VPTF) configuration that has the potential to overcome this limitation and further expand the operating speed range of the fan. Subsequently, based on this scheme, three-dimensional Reynolds averaged Navier-Stokes simulations were conducted for VPTF in transonic mode (Ma1 = 1.5), supersonic mode (Ma1 = 2.5), and windmilling mode (Ma1 = 4). The comprehensive impact of solidity on the performance under these three typical modes was investigated. The results show that solidity primarily affects the shock intensity within the passage, as well as the location and number of interactions with the blade surface, thus influencing the aerodynamic performance and blade loading of VPTF. It was found that when the solidity is chosen around 4.5, VPTF can achieve relatively good performance. At this solidity, it exhibits lower losses and maximum pressure ratio in the transonic mode. The supersonic and windmilling modes also exhibit lower losses.
Investigating Power Augmentation of 1 MW Horizontal Axis Wind Turbine Using Auxiliary Turbines
Authors: M. R. Elbaz Ahmed , Shehab Ali
Published: August 2024

Researchers face challenges in enhancing wind energy efficiency to utilize a large amount of green energy at the lowest cost, as the global need for climate change mitigation increases. This paper presents a numerical study to improve the capture efficiency of a 1 MW horizontal axis wind turbine installation by making the best use of available space by employing two extra 100 kW auxiliary turbines. The proposed design concept is based on installing the auxiliary turbines below the primary turbine blade zone on both sides of the tower to catch intruding aerodynamic flow. To solve the Reynolds averaged Navier-Stokes (RANS) equations, the computational fluid dynamics (CFD) ANSYS-fluent software was utilized. Initially, a simple numerical model for a 1 MW horizontal axis wind turbine was created to simulate its performance characteristics. A steady-state solution was obtained using the Moving Reference Frame (MRF) approach for both single-rotor and multi-rotor turbines. The proposed design’s aerodynamic performance was then investigated using a transient model simulation with a sliding dynamic mesh approach. The numerical results of both steady and unsteady simulations revealed that the proposed design increased system power output by 12%.
Inverse Design of Compressor/Fan Blade Profiles Based on Conditional Invertible Neural Networks
Authors: Jia Xinkai , Huang Xiuquan , Jiang Shouyong , Wang Dingxi , Firrone Christian Maria
Published: August 2024

Compressors/fans are crucial components of modern aircraft engines, playing a key role in providing power and thrust, and ensuring combustion efficiency. The design of compressors and fans represents a paramount field of research and engineering necessity for which blade profile design serves as the fundamental aspect. A practical blade profile design often involves multiple constraints. Traditional design methods heavily rely on the expertise of designers, and typically require many iterations to achieve desired geometries which can be a daunting task. This paper proposes a blade profile inverse design approach based on a conditional Invertible Neural Networks to mitigate the drawbacks of the traditional methods. It can enable the direct generation of blade profiles that satisfy specified requirements, including aerodynamic performance and additional relevant constraints. This method encompasses two primary steps: forward process modeling and inverse process modeling. In the forward process, a surrogate model is established to map design parameters to blade profile performance metrics. Within a specified design space, a predetermined number of designs are sampled, and a dataset is produced through performing high-fidelity Computational Fluid Dynamics (CFD) analyses to obtain aerodynamic performance and other interested metrics. Subsequently, the dataset, after data preprocessing, is employed to train a Gaussian Process Regression model to replace costly CFD analyses. In the inverse modeling step, based on the substantial data generated by the trained Gaussian Process Regression model, a conditional Invertible Neural Network is trained, mapping design parameters to a latent space under the specified target conditions. This renders the learning of the inverse process feasible. Upon the completion of model training, the design parameters and blade geometry that meet the desired target could be directly derived. The proposed method is demonstrated using a subsonic blade profile inverse design case study.
Multi-Objective Aerodynamic Optimization of Gas Turbine Exhaust Diffuser: Experimental and Numerical Validations
Authors: Dong Yuxuan , Yang Rui , Wang Xidong , Li Zhigang , Li Jun , Song Liming
Published: August 2024

To improve the aerodynamic performance of a typical exhaust diffuser, a multi-objective optimization system for the shell profile of the exhaust diffuser is constructed under the condition of considering the inlet swirl. Exhaust diffuser performance is evaluated using two objectives: static pressure recovery coefficient and outlet velocity uniformity coefficient. The shell profile is defined by five control points, and the aerodynamic performance of the exhaust diffuser model is calculated using the realizable-k-ε turbulence model. The multi-objective optimization is carried out using the NSGA-II algorithm combined with the Kriging agent model, and two optimal design schemes, optimal design 1 with the maximum static pressure recovery coefficient and optimal design 2 with the best outlet velocity uniformity, are obtained. Numerical calculation and experimental measurement were carried out to evaluate the aerodynamic performance of the baseline and the optimized exhaust diffuser. The results show that the separation vortices in the two optimized exhaust diffusers are significantly weakened. The reverse pressure gradient and flow loss near the strut of optimal design 1 decrease significantly and the outflow uniformity of optimal design 2 is improved significantly. The static pressure recovery coefficient and the outlet velocity uniformity coefficient of the optimal design 1 exhaust diffuser are increased by 11.5% and 3.2%, respectively, and the static pressure recovery coefficient and the outlet velocity uniformity coefficient of the optimal design 2 are increased by 5.7% and 10.9%, respectively.
Numerical Investigation (H2/CH4) of an Industrial Gas Turbines for NOx Prediction and Validation
Authors: Arun A. K. , Rajesh M. , Cerutti M. , Pampaloni D.
Published: August 2024

Controlling the production of NOx for industrial gas turbine while maintaining a stable combustion operating regime for a wide variety of fuels must be addressed since the development phase. Well-established numerical practices are necessary for the development of gas turbine combustors, as they allow a significant reduction of the required testing. However, the validation of such models is crucial to the quality of the development. The first part of the paper presents the dataset available for the purpose of numerical practice validation: lab-scale experiments at atmosphere conditions had been collected for prototypal burners of an industrial gas turbine. Then the experiments have been carried out at gas turbine relevant pressure and temperatures. In both test campaign, NOx emissions have been collected as a function of burner main regulating parameters, as well as of fuel composition: in particular, data are available for either pure methane or hydrogen. The paper finally focuses on modeling guidelines for NOx prediction and the assessment of pressure losses, fuel air mixing and other combustion performance parameters.
Effects of the Shape Modification of the Leading Edge Impingement Cooling for Turbine Blade
Authors: Nita Kozo , Fujimoto Shu , Suzuki Masaya , Kazawa Junichi , Okita Yoji
Published: August 2024

In impingement cooling, it is important to consider eliminating the influence of crossflow to improve the heat transfer coefficient. Therefore, in this work, the effects of shape modification on the leading edge impingement cooling for the turbine blade with crossflow conditions have been investigated numerically and experimentally.

The heat transfer coefficient on the cooling side of the leading edge was calculated using CFD (RANS) in a static system. The CFD model was created using a shape that resembles a partial cut of the midspan position of the turbine blade leading edge, incorporating impingement cooling and film cooling. This was based on the effective heat transfer coefficient considering the area of impingement target surface. Shapes with installed pin-fins and varied impingement pitches were expected to have high cooling performance and be less affected by crossflow. Therefore, these shapes were selected as Opt-A and Opt-B configurations for rig testing.

In the experiment, the shape of the specimen was the same as the CFD model. The mainstream temperature and pressure were adjusted to achieve a Reynolds number equivalent to the actual operating conditions. And the cooling air for impingement and crossflow can be supplied separately. The impingement Reynolds number was varied from 9.0 × 103 to 3.0 × 104. Furthermore, to investigate the effect of crossflow, the flow rate was also varied at half, double, and zero flow rates compared to the base value.

Surface temperature was measured using calibrated Infrared thermal cameras and converted into cooling effectiveness.
Assessment of Rotordynamic Characteristics for the Hole-Pattern Damper Seal in a 150MW Steam Turbine
Authors: Zhao Weijun , Huang Biao , Zheng Chunbo , Zhang Zihan , Li Zhigang
Published: August 2024

Damper seals and swirl brakes have been commonly used for many years as a solution for the rotor vibration instability in multiple-stage centrifugal compressor. However, there are few literatures focusing on the application assessment of damper seals and swirl brakes in high-pressure steam turbines.

This paper presents two attempt schemes (swirl brake, damper seal) to resolve the strong subsynchronous vibration instability for a 150MW 3000rpm multistage single casing steam turbine. The rotor vibration instability has been demonstrated to be caused by the steam whirl forces generated at the balance piston seal location in combination with a long flexible rotor. The original balance piston seal scheme is a staggered labyrinth seal with both teeth on stator and rotor, yielding high cross-coupling stiffness and large negative effective damping at high inlet preswirl condition. To resolve the subsynchronous vibration instability and allow full load operation of the steam turbine, the hole-pattern damper seal schemes with/without inlet swirl brake were designed as the replacement of the original staggered labyrinth seal. A comprehensive assessment and comparison were conducted on the rotordynamic characteristics for the original staggered labyrinth seal and the new hole-pattern damper seals, using a proposed transient CFD-based perturbation method based on the multiple-frequency elliptical-orbit rotor whirling model. Results show that the present hole-pattern damper seal with inlet swirl brake produces the largest effective damping and the lowest crossover frequency, is a good balance piston seal scheme for the present steam turbine to increase the rotor net damping and eliminate the subsynchronous vibration.
Thermodynamic Analysis of a Solid-Oxide Fuel Cell Gas Turbine (SOFC-GT) Hybrid System for Marine Applications
Authors: Babaji Badamasi , Turner James W. G.
Published: August 2024

The maritime industry serves a pivotal role in global trade and transportation, yet its contribution to environmental pollution, notably emissions, poses a critical concern. Addressing and mitigating the carbon footprint of this industry has become imperative amidst the challenges posed by climate change. This study presents a thermodynamic analysis focused on a Solid Oxide Fuel Cell-Gas Turbine (SOFC-GT) hybrid system designed for marine applications. The integration of Solid Oxide Fuel Cells (SOFCs) with gas turbines holds significant promise for augmenting the efficiency and sustainability of marine propulsion systems. A steady-state thermodynamic model for the SOFC-GT was developed using ASPEN PLUS software, integrating built-in modules and functions along with a Fortran code specifically designed for SOFC electrochemistry. To ascertain the model’s accuracy, validation was performed against NASA’s SOFC model, established using the Numerical Propulsion System Simulator (NPSS), and publicly accessible data from a Westinghouse 120kW tubular SOFC. Both datasets exhibited a matching within a 1% error margin, validating the reliability of our model. Having established confidence in the model’s accuracy, this study investigates the intricate interactions between the SOFC and gas turbine components within the hybrid system. The incorporation of the gas turbine for heat recovery in the hybrid system utilizing the Westinghouse tubular SOFC showcased a notable increase in thermal efficiency, elevating it from 50% to 62%. The proposed hybrid system is compared to an existing marine gas turbine and has demonstrated improved thermal efficiency and reduced fuel consumption but fell short in terms of energy density.
Study on Integrated Through-Flow Method for Variable Cycle Compression System
Authors: Zhang Shuying , Fei Teng , Li Jiabin , Ji Lucheng
Published: August 2024

Variable cycle engine (VCE) is one of the ideal power units for advanced multipurpose aircraft. The addition of bypasses and adjustable mechanisms in the compression system enables the VCE to adjust the mass flow distribution according to the flight mission and expand the flight envelope. However, it also leads to strong aerodynamic coupling and complex matching relations between components. Therefore, it is necessary to develop an integrated design method for variable cycle compression system.

Through-flow design and analysis are important steps in aerodynamic design, which determine the meridional flow path and blade section parameters for compression system. An integrated through-flow design and analysis program for double bypass variable cycle compression system called SCAD was proposed. In the program, the whole computing domain was divided into three uninterrupted flow paths according to the position of the two splitters. Pairs of split streamlines and overlapped computing stations were set up to ensure the continuity of the flow parameters and the convergence of the iteration. It can achieve integrated coupling simulation of the front fan (FF), the rear fan (RF), and the high pressure compressor (HPC), and solve the matching problem of the variable cycle compression system in the preliminary design.

The errors of total pressure ratio and isentropic efficiency of most stages simulated by SCAD are no more than 2%, and the spanwise distributions of the key aerodynamic parameters at main flow field at each stage are consistent with the 3D CFD results, as shown in verification of a double bypass variable cycle compression system. SCAD has been applied in the design system of variable cycle compression system in China now.

Finally, the influence of the outer bypass ratio on the aerodynamic performance of the front/rear fan of the double bypass variable cycle compression system was studied by using SCAD. The results shows that the bypass ratio has little effect on the front fan, whereas the total pressure ratio and isentropic efficiency of the rear fan increase with it. When the bypass ratio is small, the increase of axial and radial velocities leads to blockage in the core flow path and decrease of rotor load. The forward blade of the tandem stator works at a large-negative-incidence condition, making the performance of the rear fan deteriorate sharply. It is reasonable to choose the design bypass ratio of the front/rear fan as 0.33.
Cylindrical Composite Structural Design for Underwater Compressed Air Energy Storage
Authors: Wang Tianqi , An Chen , Mao Yixuan
Published: August 2024

The utilization of renewable energy sources is pivotal for future energy sustainability. However, the effective utilization of this energy in marine environments necessitates the implementation of energy storage systems to compensate for energy losses induced by intermittent power usage. Underwater compressed air energy storage (UWCAES) is a cost-effective and emission-free method for storing energy underwater. This technology has proven to be effective and viable, and it offers significant benefits in terms of energy efficiency and sustainability. In this paper, a cylindrical composite structure UWCAES tank is designed. At first, the materials and shapes of the different forms of air containers were evaluated, and the relationship between container diameter, length, and number of air containers was analyzed on the basis of the range of energy storage densities for different kinds of systems. Subsequently, the materials to be applied in the tanks were investigated and selected according to the actual working conditions of the system. Eventually, finite element models and prediction formula were developed and the influence of changes in the thicknesses of the steel reinforcement were discussed. The results demonstrated that the storage tank possesses adequate environmental resistance and load-bearing capacity, which can provide a reference for its practical engineering implementation.
Application of Internal Heat Transfer Inverse Problem Solution Method to Jet Array Impingement Cooling System
Authors: Haslam Riess , Bacci Tommaso , Picchi Alessio , Facchini Bruno
Published: August 2024

Detailed thermal performance estimation of real-hardware internally cooled gas-turbine components is challenging due to the lack of optical and instrumentation access to the internal surfaces. In scaled, laboratory conditions, such estimates can be obtained by solving an inverse heat conduction problem that links the desired internal heat load distribution to a set of measured external temperatures through the solution of a partial differential equation. If sufficiently reliable, the results provide cooling system designers with valuable insights into the effects of the combinations of different cooling techniques, of secondary flows, and of manufacturing methods.

Without some form of regularization, however, such inverse problems are ill-posed in that the estimates are not uniquely defined by the temperature measurements and are highly sensitive to measurement noise. In this study, an adjoint-based deterministic optimization method is used to estimate high-dimensional internal heat transfer coefficient distributions produced by a jet-array impingement system with local extraction of post-impingement flow. A method for determining the optimum amount of regularization to apply is also adopted and validated using the experimental results.

Tests were performed by applying the impingement system in steady conditions to a heated metal plate and measuring the temperature response on the opposite side with a scientific grade infra-red camera. The particular cooling system was chosen because it produces high spatial gradients of heat transfer coefficients which are difficult to reconstruct from the external temperature measurements due to the three-dimensional conduction effects through the wall of the plate. Variations of plate thickness and Reynolds number were used to test the robustness of the method, and the resulting estimates for all conditions were compared to corresponding reference results obtained in a previous, dedicated test campaign.
CO2 Transcritical Turbines Stator Optimization for Refrigeration Applications
Authors: Renaud Saugnac , Egoï Ortego Sampedro , Chakib Bouallou
Published: August 2024

The main objective of this work presented in the paper is to perform an optimization of the stator nozzle. This is done using a 1D two-phase metastable model which includes a transitional interface area formulation, the Aleksandrov interface heat transfer coefficient and Schiller-Naumann interface drag model. The optimization is based on the research of an optimal pressure profile defined by Bezier curves leading to an optimal cross-sectional area profile. Various types of linear constrained optimization algorithms were explored. The results show that for inlet operating conditions close to critical point of CO2, the maximum efficiency that can be attained is always higher than at lower inlet temperature conditions. The obtained optimal nozzle profiles should be tested in subsequent experimental work in order to evaluate the performance of the method.
The Role of Operating Conditions on Flutter Instability of a Low-Pressure Turbine Rotor
Authors: Pinelli Lorenzo , Poli Francesco , Arnone Andrea , D’Ettole Antonio Giuseppe , Rosso Emanuele , Sartor Gianmaria , Kharyton Vsevolod
Published: August 2024

Modern trends in low pressure gas turbine design lead to lighter designs with fewer stages, thinner sections and highly loaded components. Blades are thus more prone to flutter induced vibrations that can compromise their structural integrity. Accurate predictions of flutter inception and evolution remains a challenging task. Several numerical methods have been developed for a long time and dedicated experimental campaigns have been carried out to have a better insight of flutter problems. The ARIAS EU project provided the opportunity to investigate flutter occurrences of turbine and compressor rotors with unique test benches and to test state of the art numerical techniques. In this context, the paper discusses the impact of the turbine operating conditions on flutter inception of an unstable low pressure turbine rotor extensively tested during the EU ARIAS project. The operating conditions were changed by modifying the rotor rotational speed, and the first bending and torsion mode families of a cantilever configuration have been analyzed. Numerical results reveal that an increase of the rotational speed leads to more unstable configurations for the bending mode-shape, while the torsional mode-shape moves from stable to unstable condition when lowering the rotational speed. Such numerical evidence has been confirmed by the blade tip timing acquisition technique also in terms of most unstable nodal diameter. Finally the limit cycle amplitudes measured with the tip timing are compared with the results of a vibration amplitude estimation method based on a combination of acoustic measurements and computational results.
Design for Sustainability of Gas Turbines: Accuracy on Carbon Footprint at Different Design Steps
Authors: Al Freijat Mosè , Orlandi Rachele , Pucciarelli Martina , Ragni Giacomo , Serra Angela , Fantozzi Francesco
Published: August 2024

In current scenario, industries and Governments are fighting against Global Warming and increasing the focus on environmental impact of products. Industries are taking commitment to reduce their GHGs emissions. Sustainable Product Development (SPD) is a methodology that can be used by companies to assess and therefore reduce environmental impact of new products. Since the design of the product will determine its performances, environmental performance must be considered as well in early design phase. Industries are so far experiencing an increasing attention in eco-design, which can be considered as a system of practices for designing a better performing product in terms of environmental impacts. In the design process, which foresees three distinct phases (conceptual, preliminary, detailed), uncertainties related to undefined features and information can affect the environmental impact estimation and a Life Cycle Assessment (LCA) could not be performed. This work aims to analyze this issue by a case study in the field of turbomachinery sector: the New Product Development (NPD) of a gas turbine is used as the opportunity to quantify the accuracy of an LCA performed in the early design, through the three steps, varying the defined information about the under-development product. The use case is a set of forged wheels of an aeroderivative gas turbine, which allows to analyze several scenarios of uncertainty: material, production process, production country, geometry. Focus is on Carbon Footprint (CF) assessment.
Computational Cost Optimization of Hydrogen-Air Combustion for NOx Prediction
Authors: Buisson Quentin , Leparoux Julien , Puggelli Stefano , Leroy Maxime , Mirat Clément
Published: August 2024

The switch from fossil fuels to hydrogen represents a break-through path towards the decarbonization of the aeronautical sector. However, compared to hydrocarbons, hydrogen has very different characteristics. This challenges the current state of the art of numerical methods that must be re-evaluated in terms of accuracy and computational cost for aeronautical applications. Large Eddy Simulations (LES) applied to hydrogen combustion can easily become too costly with respect to the industrial constraints.

In this work, a study to reduce the time-to-solution in LES is performed. The selected configuration is a two-staged swirled combustor. The reference LES setup includes a detailed chemical description by using a 21-species, 64-reactions chemical scheme (including NOx) and the thickened flame model to handle turbulent combustion. From this, different numerical combinations are investigated for each phase of the simulation (from non-reactive flow to flame stabilisation) as well in terms of chemistry description to minimise the LES return time. Ultimately, the switch towards a lighter 9-species, 12-reactions chemical scheme and the inclusion of NOx with a tabulated formalism is retained as optimized setup. This choice determines all in all a 50% reduction in terms of computational cost with respect to the reference setup, keeping the experimental flame topology fairly well retrieved. The general trend for NOx emissions at the burner outlet is as well correctly captured, even if the chosen methodologies differ on the absolute values.
Surrey Hydrogen Aircraft Performance Evaluator (SHAPE): Viability of Liquid Hydrogen-Fueled Wing/Fuselage/Gas-Turbine Aircraft
Authors: Tiwari Saurav , Pekris Michael J. , Doherty John
Published: August 2024

Liquid hydrogen has become a key focus in aviation as a potential energy vector for advancing towards 2050 Net Zero targets. This paper presents a new tool SHAPE (Surrey Hydrogen Aircraft Performance Evaluator) for system-level assessment of an adapted wing and tube aircraft configuration for liquid hydrogen fuel and the associated enabling technologies. SHAPE, a 0D steady-state solver, uses adapted empirical correlations with hydrogen-related technological assumptions and future projections for system sizing, mass, and performance predictions. The SHAPE predictions of conventional aircraft performance were validated against open-source information of A320neo and B737-800 aircraft along with results of widely used aircraft design tools SUAVE and TASOPT over a short haul mission. SHAPE’s results suggest that a liquid hydrogen-fueled aircraft with a gas turbine propulsion system could be demonstrated for an A320neo equivalent mission with competitive overall mass (+1%) and performance attributes (+2% energy consumption) compared to a kerosene aircraft. Certification for 2035 timescales would be challenging and requires considerable industry effort, collaboration, and early regulatory body engagement. Considering on-board technology uncertainties associated with hydrogen, a sensitivity analysis shows that the energy consumption prediction of the hydrogen aircraft could vary between +7.1% to −2.2% relative to equivalent kerosene aircraft, and overall aircraft mass could vary between +5.5% to −2.1% (with a 95% level of confidence). Fuel cell powered aircraft, even with optimistic assumptions, appear to be unfeasible for short/medium haul missions. The preliminary observations emphasize the opportunity for technology demonstration with tube-and-wing aircraft adapted for hydrogen combustion, given their higher weight and lower energy efficiency compared to kerosene aircraft. The findings of a large number of previous studies are benchmarked against the outputs of this work to provide further context and insight.
Ball Bearing Dynamic Stiffness Prediction Considering an Uncertain Position of Rolling Elements
Authors: Kochurov Roman , Martynenko Volodymyr , Moroz Leonid , Govorushchenko Yuriy
Published: August 2024

This paper considers the challenge of calculating accurate ball bearing stiffness, which is attributed to the uncertainty in the rolling element positions; and it solves that issue based on the simultaneous consideration of these positions and the physical effects of the rotating components. The novelty of the paper consists of the suggested methodology to resolve the uncertainty of the rolling element circumferential position when calculating bearing stiffness. The problem is solved through various formulations of dry and lubricated contact and validated based on the consideration of the finite-element model. The algorithms presented in the paper allow for the calculation of the resulting stiffness based on the stiffness values evaluated through different ball bearing positions. The approach presented in the paper is validated based on the experimental data. For this purpose, the model of the rotor in ball bearings is built, along with further calculation of the rotor dynamics. The comparison of the critical speeds calculated for the rotor in bearings, which have stiffness evaluated by the proposed approach with the measurements for the real machine, indicates a high accuracy of the suggested method in comparison with the methods that consider the single position of the rolling element when estimating their stiffness. In the paper, further recommendations for the use of the presented method are given, which will be useful for engineers in the field of turbomachinery dynamics.
Modeling of Frictional Inter-Bristle Contact in Brush Seals With Shaft Radial Movements
Authors: Phan Harry M. , Pekris Michael J. , Chew John W. , Greenslade Thomas J.
Published: August 2024

Brush seals are utilized in turbines to minimize leakage flows and enhance thermal efficiency. Their widespread use faces challenges like pressure-stiffening and hysteresis, leading to unpredictable performance. This work introduces an advanced numerical model to simulate inter-bristle frictional contact, shaft and backing ring interaction, and three-dimensional bristle bending. The model is adopted to investigate multi-bristle brush seal’s behavior under shaft radial movements and pressure loading. Backing ring friction emerges as a vital factor in hysteresis modeling, lessening the impact of shaft friction. When the shaft retracts, modeling the bristle tip clearance becomes important. The clearance greatly increases leakage flow rate and changes bristles’ aerodynamic loading distribution. With clearance, the normal force on upstream bristles rises markedly, opposing bristle hang-up, while the axial force decreases in downstream bristles, alleviating the bristle pack compression. Considering these factors, an improved model for pressurized seals in the shaft retraction phase is developed and compared to experimental data in the literature. Frictional inter-bristle contact significantly modifies the distribution of local tip force through the pack. These effects would influence localized wear and heat generation across the brush seal pack, shedding light on the uneven wear patterns often observed in experiments. The present high-fidelity model can capture these complex interactions, offering a means to deepen our understanding of the physical mechanisms underpinning novel brush seal designs.
Numerical Study on the Propagation Characteristics of Circumferential Temperature Distortion in a Combined Compressor
Authors: Wang Zhenfei , Wang Zhiheng , Li Tongxi , Xi Guang
Published: August 2024

It is normal practice to design aero compressors under the assumption of uniform inlet flow. However, the distortion of temperature or/and other parameters at compressor inlet frequently occurs during actual operation due to surrounding environment. The aerodynamic stability and efficiency of compressor are often decreased by the inlet distortion. The researches on total temperature distortion are currently primarily concerned with the impact on overall performance, and the related flow mechanisms are not fully understood yet. Therefore, in this paper, the unsteady three-dimensional numerical simulations are conducted to study the influence of total temperature distortion on the compressor flow and its propagation characteristics in an axial-centrifugal combined compressor. The inlet distortions considered in the paper are the total-temperature distortions covering a 60-deg sector (60deg distortion). The results indicate that the circumferential distortion lowers the efficiency and pressure ratio of compressor. By analyzing the variation trend of the distortion index along the flow direction and the influence of distortion on the flow structure of the end-wall zone, the propagation law of total temperature distortion in the axial centrifugal combination compressor was explained. The results show that the total temperature distortion index decreases along the flow direction, and shows the characteristics of decreasing in the rotor blade row and changing slightly in the stator blade row. The distortion causes the rolling position of the axial rotor leakage vortex to migrate downstream, and the direction of the leakage vortex trajectory changes. In addition, the distortion leads to an increase in turbulence kinetic energy and loss in the blade tip region of the centrifugal impeller.
Emission and Operational Characteristics Analysis of Axially Staged Combustors Based on Overall Parameters
Authors: Liang Enguang , Yu Zhijian , Zhang Chenjie , Zhu Min
Published: August 2024

Due to increasing requirements for gas turbine efficiency, it is necessary to effectively control thermal NOx emissions while elevating the combustor outlet temperature, in order to meet increasingly stringent environmental regulations. At the same time, the prospective demand for carbon reduction and capture requires gas turbines to improve fuel flexibility, capable of burning syngas or fuels enriched by higher proportions of hydrogen. Gas turbine manufacturers have been testing the axially staged combustion technology on H-class gas turbines, which helps to reduce NO emissions, improve fuel flexibility, and reduce the risk of combustion instability. Considering that the majority of previous literature separately studies the impact of individual parameters on emissions or stability, this paper will discuss the determination and optimization of axially staged combustors overall design parameters, namely the air, fuel, and residence time distribution ratios between the first and second stage burners, under the condition of specified thermal power and emission levels. The main work includes: 1) developing a mathematical model for predicting pollutants in axially staged combustors, while studying the impact of staged parameters on NO, and analyzing the parameter range for low emission operation of axially staged combustors; 2) verifying the model by conducting chemical reaction network calculations using detailed chemical reaction mechanisms; 3) by using NO emissions as the objective function to optimize the staged parameters, two ranges of parameters that meet the emission requirements were obtained, respectively characterizing the lean and rich burn conditions of the first staged burner; 4) discussing the impact of the hydro-carbon fuel components on the operating range. The results will provide guidance for expanding the operating range, improving fuel flexibility, and reducing emissions of axially staged combustors.