bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal and Structural-Mechanical Modeling and Optimization of a Transiently Operated Steam Turbine Using the FE Method
Authors: Lange Hendrik , Kostenko Yevgen , Veltmann David
Published: August 2024

Due to the growing share of renewable energy sources, there is increasing volatility in the energy fed into the grid. To cover the load when renewable energy is unavailable, steam turbines in conventional power plants must be operated more flexible and in line with the demand. The increased number of start-up processes after longer standstills results in high lifetime consumption of steam turbine. This mode of operation increases the utilization on components, which results in a reduction in service life.

The Hot Standby process has already been proven itself as a method of Siemens Energy Flex-Power Services for making steam turbine operating processes more flexible. Through targeted heat transfer to the steam turbine components using a trace heating system, a cold start can be avoided, and the operational flexibility of the turbine can be increased. Heat transfer occurs predominantly via thermal radiation, which is particularly difficult to simulate compared to other heat transfer mechanisms.

To simplify heat radiation exchange and still achieve realistic results, various methods and parameter settings are applied.

In this paper the heat transfer via thermal radiation and its influence on heating up of structural turbine components is investigated. At the beginning, different benchmark parameter settings and the associated result variations are presented. These findings are then implemented in the modeling of the SST-3000 turbo set of Siemens Energy and the results of the simulation are discussed. The simulation results are used to determine temperature gradients that are used to design hot standby features used for flexible power plant operations.
Impact of Diluents on Flame Stability With Blends of Natural Gas and Hydrogen
Authors: Rodriguez Camacho Javier , Le Dang , Blust James , O’Connor Jacqueline
Published: August 2024

Two potential decarbonization pathways for natural gas (NG) fueled gas turbine engines include blending hydrogen (H2) into NG and post-combustion carbon capture. H2 blending changes several combustion properties, including flame speed and stretch sensitivity. The use of post-combustion carbon capture systems is typically facilitated by the implementation of exhaust gas recirculation (EGR), where exhaust gases are injected into the inlet of the engine, increasing carbon dioxide (CO2) concentration at the outlet and, hence, increasing the efficiency of carbon capture technologies. In this work, we explore the impact of H2 blending and EGR on the stability of a swirl-stabilized, central-piloted flame. Mixtures of NG and H2 are tested at a range of different diluent compositions, with oxygen varied from 21% to 15% by volume in the oxidizer. In all cases, a constant adiabatic flame temperature is maintained to mimic the operation of a gas turbine at a given turbine inlet temperature. A variable-length combustor is used for testing, where combustor length is varied to understand the dynamic stability characteristics of the system. Results show that EGR and H2 work in opposition to each other, where higher levels of EGR result in poor flame holding and higher levels of H2 result in better flame holding. Increasing H2 generally increases the amplitude of thermoacoustic instability at each condition, a result of the change in flame position in this particular combustor. Importantly, H2 can be added to NG to improve flame holding without significantly decreasing CO2 levels in the products, showing that H2 blending can be a method for counteracting combustor operability issues that arise from high levels of EGR necessary to improve the efficiency of typical carbon capture systems.
Numerical Study on Combustion of a Novel Micromix Multi-Nozzles for Kerosene/Hydrogen Fuels
Authors: Fu Pengfei , Wang Yafen , Hou Lingyun
Published: August 2024

Hydrogen combustion is emerging as one of the most promising options for future commercial aircraft propulsion. Transition from fossil fuels to hydrogen is expected to take time, and drop-in technologies, such as blending hydrogen with hydrocarbon fuels for combustion, are of significant importance for meeting decarbonization goals in the short term. Liquid kerosene and gaseous hydrogen have significant differences in physical and combustion characteristics. It is a significant challenge to achieve stable combustion of both kerosene and hydrogen simultaneously.

A new micro-mixed coaxial nozzle for kerosene/hydrogen fuels was proposed. The kerosene spray flame is stabilized by a micro swirler, while hydrogen is mixed in a circular microchannel surrounding the swirler and coaxially arranged with the central axis of the spray nozzle. The numerical simulation including a skeletal reaction kinetics model with 54 species and 269 reactions was conducted and validated through comparisons with experimental data. The impact of hydrogen injection parameters, hydrogen blending ratio, swirling intensity, and nozzle distance on the combustion characteristics of the kerosene/hydrogen mixture were investigated. It is shown that the uniformity of hydrogen circumferential distribution in the annular mixing channel results in either individual multi-beam flames or a complete annular flame. Increasing the swirl number reduces the axial lengths of both the hydrogen and kerosene flames, resulting in more compact flame branches. NO emissions are minimized when the hydrogen blending ratio falls within the range of 10%–20%. The merged flame mode and free flame mode are observed for the adjacent hydrogen flames in different nozzle distances. It provides guidance for the design of low-carbon multi-fuel nozzle in gas turbine combustor.
Effects of Mainstream Incidence Angle on the Cooling Performance of the Rotational Turbine Blade Tip
Authors: Wang Xilai , Tao Zhi , Li Haiwang , Zhou Zhiyu , Xie Gang , Meng Long
Published: August 2024

The rotation fluctuation or the mainstream unsteadiness could cause the variation of the incoming incidence angle, affecting the cooling performance of the turbine blade. Most literature concentrates on the effects of incidence angle in the mid-pitch region, leaving the tip region less concerned. Considering that the complicated flow field in the tip region could sometimes worsen cooling effectiveness, this paper investigates the effects of mainstream incidence angle on the cooling performance of the rotational blade tip. The first stage of GE-E3 high pressure turbine blade with full composite cooling structure is used in this study and conjugate heat transfer numerical simulations are conducted on ANSYS CFX 2019R3 to calculate both the flow field and the solid temperature field. SST k-w turbulence model is adopted to enclose the RANS methods after multiple validations. Three rotational speeds, namely, 90%, 100% and 110% of the design point (13287 rpm), are simulated in three coolant mass flow rates (1.65%, 3.3% and 4.95% of the main flow rate) and three tip clearance ratios (0.5%, 1% and 1.5% of the total blade pitch). According to the results, the pressure side rim consistently gets cooler as the incidence angle changes from positive to negative because less leakage gets over the pressure rim. But in comparison, the trends of the suction side are complex. At the positive incidence angle, the large pressure difference forces nearly all coolant to exhaust over the suction rim, facilitating the coolant coverage there. At zero incidence angle, the leakage over the suction rim could raise the temperature in the thickest area. But as the incidence angle turns negative, the larger mainstream leakage over the suction rim could form an anti-rotating vortex. With large coolant flow rate or small tip clearance, the mainstream invasion would increase the temperature whereas with small coolant flow rate or large tip clearance, the vortex entrainment could decrease the temperature.
The Effect of Acoustic Boundary Conditions on the Oscillation Mode Transition of Combustion System
Authors: Lu Yudi , Jin Ming , Ge Bing , Zang Shusheng
Published: August 2024

The lean premixed combustion technology makes thermoacoustic oscillation possible to occur in gas turbine combustor. With the change of operating condition, the amplitude and frequency of thermoacoustic oscillation also change. The oscillation mode can even change suddenly. This mode transition is closely related to the acoustic boundary conditions of the system. This paper investigates the impact of the acoustic boundary conditions of the outlet of the combustion system on the oscillation modes. By varying the equivalence ratio, the system is made to oscillate in different modes. The acoustic reflection coefficient and impedance of the system outlet are measured through double-sound-transducer method, and numerical simulations are conducted to investigate their impact on the growth rates of the oscillation modes. The results indicate that under different equivalence ratios, the combustion system exhibits three distinct oscillation modes. As the equivalence ratio in the combustor increases, the low-frequency mode gradually disappears and even undergoes a sudden transition to a high-frequency mode. The phase of the outlet acoustic reflection coefficient and impedance of the three modes are significantly different, which can reach up to 180°. There are two different principles for the mode disappearance. One is due to the acoustic reflectivity exceeding the critical value, while the other is due to the gradual decrease of it. Numerical simulations of oscillation modes are conducted based on the acoustic impedance measured. The simulated modes with the highest growth rate agree well with the experimental results, with an error within 1.94%. This study provides experimental and numerical methods for accurately obtaining growth rates of oscillation modes. Accurate boundary acoustic impedance is crucial for predicting oscillations. The reflectivity and the phase of boundary acoustic impedance are the primary reasons for mode transitions.
Effect of Film Hole Configuration on the Impingement-Film Composite Cooling Performance of a Simulated Turbine Blade Leading Edge
Authors: Chen Xinnan , Bai Bo , Li Zhigang , Li Jun
Published: August 2024

Eight film hole configurations were implemented on a simulated turbine blade leading edge to serve as the showerhead. Both adiabatic and conjugate heat transfer analyses were conducted. The effect of film hole configuration on flow resistance, heat transfer characteristics, film coverage, and composite cooling performance of the leading edge were all investigated. Additionally, the influence of coolant mass flowrate across a wide range was also considered. The results indicate that all expansion holes effectively increased the discharge coefficient, especially at relatively higher coolant mass flowrate. The amplified hole and double-jet hole also reduced the flow resistance under high coolant mass flowrates, but caused severe gas ingestion at low mass flowrates. Furthermore, impingement cooling demonstrated continuous improvement in heat transfer intensity with increasing coolant mass flowrate, while the effect of expansion holes on it was nearly negligible. Moreover, the composite cooling performance of expansion holes was highly correlated with both forward and lateral expansion angles, which played a more critical role than hole shape designs in determining the cooling performance. In comparison to conventional showerhead designs, the two novel holes exhibited significantly improved composite cooling performance, especially the effusion hole. However, it should be noted that the incorporation of effusion hole also resulted in serious pressure loss of coolant.
Influence of SiC Fiber Dispersion on the Mechanical Strength of SiCf/SiC Composites
Authors: Kim Soo-Hyun , Kim Seyoung , Han In-Sub , Bang Hyung-Joon , Seong Young-Hoon , Lee Seulhee
Published: August 2024

The present study examines the influence of fiber dispersion on the internal structure and mechanical strength of SiCf/SiC composites fabricated utilizing spread SiC fibers. The fiber volume ratio of specimens incorporating spread SiC fibers decreased by 9 percentage points compared to those without spreading, resulting in smoother impregnation of resin slurry between fibers and, consequently, minimizing matrix porosity. To assess and compare the fiber dispersion in each specimen, a method was proposed for quantifying and evaluating the separation distance between fibers in composite materials. The results revealed a 2.23μm increase in the distance between fibers in the spread specimen relative to the non-spread specimen, corresponding to a notable 42.6% increase in the distance between fiber surfaces. Moreover, a 3-point flexural test showcased a 49.3% higher strength in the spread specimen, coupled with a more uniformly distributed deviation in test data. These findings underscore the substantial impact of SiC fiber dispersion on achieving uniform densification of the SiCf/SiC matrix and enhancing mechanical strength.
Thermal Performance Assessment of High-Temperature Sensible Solid Thermal Energy Storage (SSTES): Various Designs, Storage Materials and Heat Transfer Fluids
Authors: Bangalore Mohankumar Malini , Unger Sebastian , Guille Alexandre , Carro Andres , Chacartegui Ramírez Ricardo , Hampel Uwe
Published: August 2024

Integration of energy storage (ES) into an energy system with wind and solar power plants provides a solution to the problem of power balancing resulting from fluctuating power output. One promising approach are Thermal Energy Storage (TES) systems, particularly Power-to-Heat-to-Power (PHP) systems, which have a low environmental impact compared to, e.g. lithium-ion or lead acid battery storage systems. Solid sensible TES (SSTES) stores excess electricity in the form of sensible heat, the solid medium being heated either directly or indirectly using heat transfer fluids (HTF). The benefit of SSTES systems is their simplicity due to no phase change nor chemical reactions involved, making them cost-effective and easy to maintain. However, applications of SSTES at high temperatures remain relatively unexplored and have limited deployment globally. Nonetheless, the aforementioned advantages make them suitable for high-temperature applications, provided the solid material selected exhibits higher temperature stability.

The paper proposes a concept where an SSTES is charged indirectly using an electrically heated working fluid. In particular, an SSTES coupled with a sCO2 power cycle is considered in this work. Candidates for the storage medium are typical materials being used in high-temperature applications, such as high-temperature concrete, firebricks, as well as novel ceramic waste materials from aluminium production, like ALFERROCK™. As heat transfer fluids (HTF), we consider helium (He) and carbon dioxide (CO2) in this study. The thermal performance of an SSTES was investigated for a storage capacity of 50 MWhth at temperatures up to 800 °C. To conduct the numerical analysis we developed a one-dimensional MATLAB model. The impact of geometry, flow rate, solid material configuration in the storage container, and heat transfer surface area on the heat transfer characteristics and efficiency of the thermal energy storage (TES) system must be considered. Therefore, this research work also includes an assessment of different STES designs. The temperature of the storage material during charging and thermal efficiency are presented based on the results.

Overall, a comprehensive thermal performance assessment based on various factors that influence the STES system was done. The comparative analysis of various materials, heat transfer fluids, and geometries allows for determining their impact on the TES design and operation. These findings are being used to further investigate the system with finer 3D numerical methods.
Advanced Power Management Strategies for Complex Hybrid-Electric Aircraft
Authors: Bermperis Dimitrios , Kavvalos Mavroudis D. , Vouros Stavros , Kyprianidis Konstantinos
Published: August 2024

Aircraft electrification for propulsion is a promising way to alleviate the negative environmental impact of conventional carbon-powered aviation. Inclusion of the electrical powertrain aims to enhance design freedom allowing for more efficient power systems and operational schemes. In this work a design space exploration is performed aiming to derive power management guidelines based on aircraft environmental performance. A 19-passenger commuter aircraft employing the series/parallel partial hybrid-electric architecture is examined. Two underwing-mounted turboprop engines are combined with a boundary layer ingestion fan mounted in the aircraft aft and powered by an electrical drive. The primary electrical energy source is a battery system. A multi-disciplinary framework is utilized, comprising modelling approaches for multi-point thermal engine design, physics-based electrical component sizing and performance, aircraft sizing, mission design, and environmental assessment. The investigation revealed that the reference designed hybrid-electric configuration with entry-into-service 2035-assumed technologies yields roughly 18% improvement in block consumption and emissions, but an 8% increase in maximum take-off weight, compared to its 2014 conventional counterpart. The design space exploration for an optimal power management scheme indicated a minimum ratio of 1:1.35 between cruise and design point hybridization power. However, even the optimally operated hybrid aircraft showcases worse environmental performance compared to the conventional design of same entry-into-service date. The investigation has revealed that the complex powertrain and hybrid architecture selected may be more suitable for larger class aircraft, with the accumulated performance benefits reaching the order of 5% for the hybrid designs explored under relaxed top-level constraints.
Comprehensive Analysis of Adiabatic Compressed Air Energy Storage and Gas Turbine Hybrid System With Thermal Integrations
Authors: Kim Hyerim , Kim Tong Seop
Published: August 2024

Combining an adiabatic compressed air energy storage (A-CAES) with a gas turbine (GT) can address any sudden changes in demand, but a comprehensive analysis of the integration effects between A-CAES and GT is needed. This study introduced a regenerative A-CAES-GT hybrid system with two thermal integrations: preheating and regeneration. These integrations resulted in an 11% increase in electric power and a 3%p increase in round-trip efficiency for the hybrid system compared to A-CAES and GT stand-alone systems. In addition, the hybrid system generated thermal power through thermal integrations, leading to a combined heat and power (CHP) round-trip efficiency higher than 60%. Various load control strategies for part load operation of the hybrid system were used and investigated. With a stable control strategy, optimal dispatch for the regenerative A-CAES-GT hybrid system was obtained, considering the environmental and energy-autonomy indices. The hybrid system revealed a 41% lower equivalent carbon dioxide emission factor (CEF) than the optimal dispatch for the A-CAES and GT stand-alone systems. Furthermore, the hybrid system showed a 4%p higher self-sufficiency under a low CEF of the grid and high demand.
The Study of Unsteady Plasma Excitation to Control Vortex Shedding Appears in the Turbine Cascade
Authors: Jianyang Yu , Weixiao Xie , Yining Zhang , Qifan Guo , Jinsong Shen
Published: August 2024

In this work, the flow fields of a T106A turbine cascade under different unsteady excitation conditions are simulated based on large eddy simulation (LES). Moreover, the primary flow patterns and the interactions between induced and original flow structures are analyzed using proper orthogonal decomposition (POD) method and vortex identify method based on triple decomposition of the relative motion near a point (TDM). The numerical results reveal that plasma excitation amplifies large-scale turbulent pulsations, making it locked to the excitation frequency, and effectively suppressing the small-scale turbulence pulsation in other modes. This excitation substantially weakens the vortex structures in the trailing region, which is the primary source of aerodynamic losses, leading to a notable improvement in the spatiotemporal flow field structure. Based on the above study, the improvement of plasma excitation control effect is explored though the influence of excitation frequency (Stδ) and duty cycle (Dtc). When Stδ is set at 0.8, the induced flow field exhibits better coupling with the vortex structures near the trailing edge, resulting in a remarkable 20.96% reduction in the total pressure loss coefficient compared to the baseline. For Dtc greater than 0.5, it enhances the control effect by extending the excitation time. Conversely, for Dtc less than 0.5, a shorter excitation duration results in a lower peak total pressure loss coefficient and an extended recovery time, surpassing the control effect of Dtc = 0.5.
An Enhanced Predictive Method for Large Droplet Breakage Based on the Discrete Particle Model
Authors: Hongyu Ju , Jianqin Suo , Yue Li
Published: August 2024

In high-speed flows, a single droplet undergoes fragmentation, yielding numerous child droplets. Conventional breakup models usually group these droplets into a single parcel, neglecting the post-breakup spatial distribution. To address this limitation, detailed numerical simulations have been conducted focusing on the bag and bag-stamen breakup modes of 200 μm-diameter droplet at Weber numbers of 15 and 30. The result shows that the largest length of the child droplets cloud can reach up to 29 relative to the original diameter. Importantly, if the grid size is less than 29 times the droplet diameter, traditional models that use a single parcel for child droplets could produce inaccurate results. To overcome this limitation, a disk-like breakup (DLB) model was introduced. With this model, multiple parcels replace the original droplet and are initialized on a virtual disk. Additionally, partitioned breakup modeling was employed for both bag and bag-stamen breakups. Calculations using the DLB model were compared with the TAB, KH-RT and ETAB models. The result indicates that the DLB model is capable of simulating the spatial distribution of the droplet cloud post-breakup, achieving better agreement with the detailed numerical simulations using the VOF method in this paper and experiments in the literature.
Investigation of Viscor and Methanol Spray Dynamics Using Proper Orthogonal Decomposition in Siemens Energy Industrial Atomisers
Authors: Alshahrani Ali , Mohni Izwan , Ajisafe Adesile , Furi Marc , Houde Michel , Sadasivuni Suresh , Engelbrecht Geoffrey , Bulat Ghenadie , Talibi Midhat , Balachandran Ramanarayanan , Ducci Andrea
Published: August 2024

The demand to reduce carbon emissions has prompted research into alternative fuels that can replace conventional fuels like diesel in industrial gas turbines. Among different potential biofuels and e-fuels, methanol emerges as a sustainable and high-performance alternative to diesel for gas turbine applications. It is well established that the fuel physical properties, spray dynamics and degree of atomisation are strongly correlated and affect the engine performance. In this study, Proper Orthogonal Decomposition (POD) was applied on spatio-temporally resolved images to characterise Viscor, here used as diesel surrogate, and methanol sprays of pressure-swirl atomisers employed in Siemens Energy industrial gas turbine (SGT-400) combustors. The methanol experimental results were then compared against Viscor results at analogous operating conditions, including density adjusted atomiser pressure drop and ambient pressures. Results confirmed that the methanol spray cone angle is slightly wider than Viscor at corresponding operating conditions. The POD analysis allowed to identify dominant spatial oscillation modes and characterise them in terms of oscillation amplitude, wavelength and onset distance from the atomiser edge for both fuels. Oscillation wavelengths and maximum amplitudes were found to correlate with Weber number, average SMD and axial jet velocities.
Large Eddy Simulation of Turbulent Reacting Flow in a Pressurized Annular Combustor
Authors: Kamin Manu , Plewacki Nicholas , Koneru Rahul , Bravo Luis , Khare Prashant , Powers Russell , Miki Kenji , Ham Frank , Senga Masayoshi
Published: August 2024

Large eddy simulations (LES) are becoming increasingly popular in engineering to predict complex physical interactions governed by the temporal dynamics of the flow. In the context of propulsion systems with realistic combustors, LES is the ideal choice for modeling complex processes involving multiphase transport, vaporization, and reacting flow physics that span a wide range of scales. However, simulations of a full annular combustor have historically remained out of reach due to the steep cost associated with resolving the energetic scales in systems with such exceedingly complex geometries. Fortunately, with recent advances in supercomputing capabilities, such simulations are now possible and can be used to understand the underpinnings of combustion physics at scales that are often unavailable to experiments. Thus, the objective of this study is to investigate the ability of LES to predict turbulent combustion subject to system-level effects by considering a 360-degree annular combustor from the Energy Efficient Engine (EEE) program. In addition to showcasing LES calculations of the annular combustor, this study investigates the effects of incorporating a complex geometry on predicting self-sustaining oscillatory flows and its impact on combustion. To accomplish this, the massively parallel LES solver, CharLES, is employed, which utilizes a fully compressible Navier-Stokes Equation (NSE) solver and a flamelet progress variable approach on unstructured Voronoi-based cells. Due to the importance of estimating adequate grid size, the effect of mesh resolution is investigated by computing results on three grids and comparing results in terms of mean and fluctuating fields. A non-reacting analysis is first conducted to understand the unsteady fluid dynamics arising from the central recirculation zone, which plays an important role inflame stabilization. Next, the progress variable method is utilized to generate a combustion model coupled with Lagrangian particle tracking models for fuel spray breakup, vaporization, and ignition. The results, when compared to combustor exit temperature measurements from experiments, as well as previous LES simulations in the literature, show good agreement. Further analysis is conducted showing the onset of self-sustained oscillatory flow, owing to the azimuthal coupling, and proper orthogonal decomposition (POD) analysis shows the most energetic modes. Overall, the results are promising and present a novel tool for guiding the development of stable and reliable systems. This work is conducted in support of the DoD High Performance Computing Modernization Program (HPCMP) Frontier program at ARL and NAVAIR in collaboration with the University of Cincinnati, Cadence Design Systems, and Pratt & Whitney.
Design, Analysis, and Experimental Testing of Hydrogen Lean Direct Injection Nozzles at Elevated Pressure
Authors: Overbaugh Malcolm , McDonell Vincent , Buelow Philip , Ryon Jason , Williams Brandon , DeBeni Ottavio
Published: August 2024

There are many challenges of commissioning a hydrogen combustor into future gas turbine engines; especially regarding achieving emissions goals. Previously, Escudero et al. and Tran et al. conducted a study to adapt the liquid fuel Lean Direct Injection (LDI) concept from Jet-A to gaseous natural gas-hydrogen blends and pure hydrogen [1], [2]. Experimental data was collected at atmospheric conditions using a Box Behnken design of experiments. The design of experiments suggested that biasing the air split in favor of the inner air circuit and increasing the swirl strength of this inner air passage resulted in improved NOx emissions, while the inverse was true for stability, which was quantified by studying the lean blowoff point (LBO) [1], [2]. The trends revealed by the original experiment [1], [2] provided a design direction for further iterations of the experimental hardware. The study presented herein describes the further investigation of such LDI injectors through experimental methods and computational fluid dynamic (CFD) simulations at atmospheric conditions, which were used to identify potential flow behaviors driving enhanced emissions performance. Further evaluation of select injectors from both studies was then conducted at elevated pressures up to 6 atmospheres. The results from both experiments are presented in this study, which include flame observations, emissions measurements, and operational challenges. NOx emissions results are reported on a volume basis in ppmvd corrected to 15% O2 and corrected for fuel. A predictive model for relating NOx emissions to test conditions at atmospheric conditions show high significance to adiabatic flame temperature while little to no significance to fuel composition for the best performing configurations. The results illustrate the connection between atmospheric testing and testing elevated pressures. The design direction indicated by the initial tests and CFD results in promising configurations for implementation into a Multi-point LDI array.
DNS of Turbine Vanes Subjected to Inlet Temperature Variations and Robust Quantification of Aerothermal Flow Irreversibilities
Authors: Nardini Massimiliano , Kozul Melissa , Sandberg Richard D.
Published: August 2024

The aim of the present work is to investigate the aerothermal characteristics of high-pressure turbine (HPT) vanes subjected to burner-like mean inlet temperature and velocity variations. A systematic numerical investigation is carried out by means of Direct Numerical Simulation (DNS). A total of five cases are simulated: two non-uniform pitchwise inlet temperature distributions (hot streaks) with different clocking positions, one impinging on the blade leading edge and the other aligned with the mid-passage, two equivalent non-uniform pitchwise temperature and velocity distributions (hot jets), and a baseline with uniform inlet conditions. In all cases, large-scale turbulent fluctuations are superposed onto the mean inlet profiles. A robust methodology to correctly quantify viscous and thermal irreversibility production mechanisms based on an alternative formulation of the entropy transport equation is introduced. This ensures a correct representation of the turbulent dissipation and of the irreversible turbulent heat flux in the presence of incident fluctuations and thermal gradients. The critical role of turbulent dissipation and its sensitivity to the grid resolution due to small-scale turbulent fluctuations are discussed. The role of inlet conditions on the vanes’ aerothermal properties is investigated by analyzing the surface temperature distributions and the characteristics of the boundary layers. The temperature streak clocking positions are shown to directly affect the blade surface temperature distributions, and have an impact on the shock waves position and on the boundary layer transition characteristics via local modifications of the fluid viscosity and Mach number. The novel entropy framework is carefully validated and it is employed to investigate the role of viscous and thermal irreversibilities and their dependency on inlet conditions. Furthermore, an in-depth analysis of the mean and turbulent physical mechanisms of entropy generation associated with distinct regions of the flow such as boundary layers, wakes and passage is conducted and the results are discussed.
Generative Deep Learning on Images of Thermo-Mechanical Simulation Results
Authors: Nasti Adele , Voutchkov Ivan , Keane Andy
Published: August 2024

This paper presents a novel methodology that combines engineering simulation and machine learning for the thermomechanical design of a secondary air system double-sided seal in an aero engine turbine subassembly. Secondary air system seals are crucial in aero engine design as they have a direct impact on specific fuel consumption.

The study uses an automated analysis workflow to generate a large dataset of images embedding key design and performance attributes for the seals, such as running clearances at key operating conditions. These images are used to train a conditional Generative Adversarial Network (cGAN), which can then be used for design exploration or optimisation. The paper introduces a unique approach to encoding and decoding these images, enabling automatic quality monitoring of the generated images and training processes, as well as extraction of targeted results.

The predictability of the Deep Learning models is assessed, demonstrating how this methodology can generate designs in targeted categories and can support decision making both in the preliminary design phase, to enable classification of ‘good’ and ‘bad’ designs, and in the detailed design phase, to support optimisation and robust design. Beyond design, these methods can also be used to support the implementation of the Digital Twin.
An Optimal Design of Aircraft Hybrid Powertrain Based on a Coupled Method
Authors: Qiang Xuankai , Qian Yuping , Li Weifeng , Jiang Hongsheng , Zhuge Weilin , Zhang Yangjun
Published: August 2024

Hybrid aircraft can better meet the future needs of green aviation. The range and payload of battery electric aircraft are limited by the low energy density of the battery. Gas turbine hybrid systems can reduce the battery weight and increase the range and payload. In the engineering design aspect, how to select the optimal gas turbine power at design point and determine suitable off-design output power characteristics at different flight phases based on a specific mission profile is a worthy research topic.

This paper presents a coupled optimization method for hybrid powertrain. Firstly, a component model of the gas turbine generator system and a battery model based on test data are established. Secondly, A design point power optimization method based on the bisection method is proposed. Further, an off-design output power optimization method based on the particle swarm optimization algorithm is also established. Based on the maximum and minimum output power capability of the gas turbine, a general table of numerical results of the non-linear equations is generated to accelerate the calculation of the off-design points based on the flight mission. Finally, based on the mission profile of NASA-X57, this paper designs the corresponding hybrid power system and compares its performance with the battery electric system, and the results show that the aircraft with optimized hybrid powertrain could increase the efficient payload (people and cargo) by 25%, the specific transportation cost (RMB/kg/km) is increased by 19%. The method proposed in this paper could provide a fast optimal design and performance evaluation of the hybrid powertrain based on a certain flight mission profile, which could provide the aircraft and powertrain manufacturers an efficient design tool.
Vibrational Response Analysis of Rotating Mistuned Bladed-Disk Using a Deconvolution Method Based on Blade Tip Timing
Authors: Xiao Zhicheng , Xiao Jiaguangyi , Meng Yiming , Wang Shang , Chai Pengfei , Ouyang Hua
Published: August 2024

The blade tip timing measurement of rotating mistuned bladed-disk vibration is modeled and analyzed by a newly proposed method. The motion of the blades is simplified by a 2-degree-of-freedom lumped mass model responding to traveling wave excitations. A deconvolution algorithm is established to recognize the amplitudes and natural frequencies of system modes based on the undersampled tip displacement data collected by several circumferentially distributed probes. Theoretical analysis shows that the algorithm could obtain accurate amplitudes given a sufficient candidate vector that includes the orders of dominant vibrational components. The robustness is demonstrated by a numerical study which reveals that the uncertainty of the magnitude caused by normally distributed random noise with 0.1 standard deviation is within ±5% as long as the leakage effect is insignificant. The proposed method is applied to analyze a 2F/4EO vibration of a fan in a real aero-engine test. The response curves generated by the present method successfully reconstruct the feature of multiple peaks observed in the measurements. More importantly, the maximum amplitude obtained by the present method agrees with that measured by the strain gauge, while the traditional SDOF method underestimates the value by 38.2% on average.
Numerical Analysis of a Two-Phase Turbine: a Comparative Study Between Barotropic and Mixture Models
Authors: Kumar Amit , Parisi Simone , Agromayor Roberto , Walther Jens Honore , Haglind Fredrik
Published: August 2024

Two-phase turbines offer the potential to significantly enhance the performance of power generation and refrigeration systems. However, their development has been hindered by comparatively lower efficiencies resulting from additional loss mechanisms absent in single-phase turbines. In this context, Computational Fluid Dynamics (CFD) emerges as a crucial tool to predict the performance of two-phase turbines and guide the design process towards higher efficiency. To date, most multiphase CFD studies on turbomachinery have focused on condensation in the final stages of steam turbines, and on cavitation in hydraulic pumps and turbines. These applications, however, are not representative of the conditions in two-phase turbines, where a liquid-dominated mixture undergoes a large expansion ratio, leading to a significant increase in the gas phase volume fraction throughout the entire flow. Recognizing the lack of an established modeling approach, this paper aims to identify a suitable modeling methodology for two-phase turbines. Our evaluation is centered around two models: the mixture model and the barotropic model. The validity and accuracy of these two modeling approaches is assessed using existing experimental data from a single-stage impulse turbine operating with several mixtures of water and nitrogen as working fluid. The results indicate that both the mixture and barotropic models are consistent and accurately predict the nozzle mass flow rate, yet, both models systematically overpredict the nozzle exit velocity and rotor torque. Adding correction terms for windage and unsteady pumping losses significantly improves the torque predictions, bringing them within the uncertainty range of the experimental data. In addition, refining the models to account for the effect of slip presents a promising avenue to enhance the prediction of nozzle exit velocity and overall performance of two-phase turbines.
Multi-Point Aerodynamic Optimization of a Backward-Curved Impeller Fan
Authors: Motamedi Zokae Hamid , Tabor Gavin , Moxey David , Page Martin , Stokes Martin
Published: August 2024

Centrifugal fans find widespread application in building ventilation and air-conditioning systems. Nonetheless, they face challenges in meeting the growing need for energy efficiency, better performance, and reduced noise levels. These limitations stem from the inherent constraints imposed by the circular arc blade design. In this paper, aerodynamic optimization of a backward-curved centrifugal fan was carried out. For this purpose, 3D computational fluid dynamics (CFD) simulations of the initial fan were first validated against test data. Then, using five geometric design parameters, the blade flow angle distribution, from leading edge (LE) to trailing edge (TE), was optimized within its operating range by means of a surrogate-based optimization technique. Efficiencies at different operating points of the fan were selected as objectives while the constraints of the optimization practice include flowrates as well as blade thicknesses of the initial geometry. The suggested optimum geometry generated from this process was independently simulated by CFD to assess the meta-model predictions. The computed results demonstrated up to a 1.7% increase in efficiency in its operating range compared to the initial model. Moreover, studying the features of the flow passing through the blades indicated an improved aerodynamic behavior with reduced separation zones for the optimized geometry compared with the initial one. Geometric comparison of initial and optimized geometries also revealed a curvature redistribution in the fan blades.
Numerical Study on the Console Hole Film Cooling Performance With Varied Hole Inlet Shape
Authors: Luo Yiming , Li Haiwang , Zhou Zhiyu , Xie Gang , Meng Long
Published: August 2024

The shaped holes are widely used to improve the film cooling performance in gas turbine thermal protection. Among them, the converging slot-hole (console) is a well-performed shaped hole, but its cooling effectiveness can be severely deteriorated near the centerline at a small incident degree. In this paper, the geometry of the console, particularly the inlet shape, was adjusted using numerical simulation methods to improve the cooling performance of the console. Different consoles with varying inlet widths but the same inlet area were tested on a flat plate with an injection angle of 30 degrees, and the blowing ratios ranged from 0.5 to 2.0. The mainstream Reynolds number was set to 10000 based on the film hole inlet diameter, and the density ratio was 1.5. The RANS equations were closed by the RNG k-ε model and the structured grid consisting of 7.64 million cells was adopted to provide a relatively accurate predictive result. It is found that kidney vortices near the centerline of the typical console are responsible for the severe deterioration in cooling performance, resulting in the loss of coolant protection in the downstream centerline region and exhibiting trace bifurcation. These kidney vortices mainly originate from flow separation generated when coolant flows from the plenum into the hole. Widening the inlet width of the console increases the spacing between kidney vortices within the hole. This reduces the mutual induction between the vortices and suppresses their development within the hole, ultimately eliminating the kidney vortices along the downstream centerline. In the flow field of the console with a larger inlet width, the predominant structures are anti-kidney vortices. Although this leads to a slightly shorter length of coolant trace, an appropriate increase in the console inlet width can increase the area-averaged cooling effectiveness by up to 117.3% within the downstream range of 40D.
Effect of Swirling Number and Direction on Flame Morphology and Combustion Performance in a Centrally Staged Swirl Combustor
Authors: Xu Honghao , Li Zongfu , Pang Liyao , Zhao Ningbo , Zheng Hongtao
Published: August 2024

Swirl flow is a prominent technology for effectively controlling combustion stability, combustion intensity, and various other aspects in a gas turbine combustor, while the interaction between the two stages of the swirler affects the flame morphology within the recirculation zone, subsequently influencing the combustion performance. In the present work, focusing on the interaction between the main and pilot stages of the swirler, as well as the regularity that influences the combustion flow field, experimental research and numerical simulations are conducted in the single-sector centrally staged model combustors with different swirling numbers and directions of the pilot stage, while the swirling parameters of the primary stage remain constant. Under constant operating conditions, the flow characteristics of the combustion flow field, the development of high-temperature zones, the evolution of flame morphology, and variations in combustor performance are analyzed. The above analysis is carried out with the swirling numbers of the pilot stage respectively maintained at 0.44, 0.55, and 0.68, as well as the swirling direction of the two stages set as either identical or opposite. Simultaneously, the flame cooperation mechanism between the main and pilot stages is explored. Flame within the combustors exhibit stratified structure. Under a constant swirling direction, changing swirling number causes a variation in opening angle between inner shear layers, then altering fuel distribution, opening angles of flames, as well as confluence between inner and outer main flames. In co-swirl condition, as swirling number of pilot stage increases, total pressure losses rise while PF decreases. Effect of swirling direction combination on PF varies across different swirling numbers of pilot stage. At a swirling number of 0.44, counter-swirl results in a slightly lower PF than co-swirl. Nevertheless, at swirling numbers of 0.55 and 0.68, co-swirl proves more effective in achieving lower PF.
Flashback Prevention in a Hydrogen-Fueled Reheat Combustor by Water Injection Optimized With Global Sensitivity Analysis
Authors: Rouco Pousada Pablo , Doan Nguyen Anh Khoa , Aditya Konduri , Düsing Michael , Ciani Andrea , Langella Ivan
Published: August 2024

This paper presents an investigation of the effects of water injection within a simplified version of the Ansaldo GT36 reheat system. The investigation is carried out under realistic operating conditions of 20 atm and using large eddy simulation (LES) coupled with the thickened flame model (TFM) and an adaptive mesh refinement. The water injection conditions are optimized by performing a parametric study based on global sensitivity analysis and a surrogate model based on Gaussian process is employed as a way to reduce computational cost. In particular, the influence on the system performance of four design parameters, namely Sauter mean diameter, water mass flow and the angles of the spray’s hollow cone, is tested to achieve an optimized solution. In the ‘dry’ case, the LES simulations show several flashback events, which are a defining aspect of the considered conditions, and attributed to compressive pressure waves resulting from autoignition in the core flow near the crossover temperature. The use of water injection is found to be effective in suppressing the flashback occurrence. In particular, the global sensitivity analysis shows that the external angle of the spray cone and the mass flow of water are the most important design parameters for flashback prevention. Moreover, NOx was shown to be reduced by about 17% by the use of the water injection at the tested conditions. Once an optimised condition with water injection is found, a recently proposed method to downscale the combustor to lower pressures is applied and tested. Additional LES are performed for this purpose at the ‘dry’, unstable condition and the ‘wet’, stable condition. Results show that similar dynamics, respectively unstable and stable, is predicted at 1 atm, suggesting the robustness of the method. This provides avenues for experimentally testing combustion dynamics at simplified conditions which are still representative of high-pressure practical configurations.