bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear Normal Modes-Related Isolated Branches of Subharmonic Solutions for Forced Response Blade-Tip/Casing Contact Problems
Authors: Vadcard Thibaut , Thouverez Fabrice , Batailly Alain
Published: August 2024

This article investigates the emergence of isolated branches of solutions for blade-tip/casing structural contact configurations by means of a numerical procedure relying on Melnikov’s energy principle. This study is carried out on the open fan blade model NASA rotor 67 in order to promote the reproducibility of the results. The blade is subjected to an harmonic forcing so as to initiate rubbing interactions. Contact is modeled in the frequency domain by the dynamic Lagrangian frequency-time harmonic balance method (DLFT-HBM) that accounts for vibro-impact as well as dry friction. This paper employs an isola detection procedure that was shown to give accurate results on such highly nonlinear applications [1]. Several types of harmonic forcing are applied to the blade in order to observe subharmonic (i.e. with a fundamental frequency expressed as a fraction of the excitation frequency) isolated solutions. The existence of these solutions is shown to be related to nonlinear normal modes that feature lower periodicities than the excitation. The periodicity of the solutions is assumed to be linked to the periodicity of the nonlinear normal modes from which these solutions emerge. In some configurations, it is shown that nonlinear periodic solutions exist in the form of isolated branches while the main predicted response remains within the linear domain. This behavior is particularly detrimental since numerical strategies tackling nonlinear problems are usually not put to use when the response of the system is expected to be linear. The existence of such solutions is cross-checked by means of reference time integration simulations. Finally, an excitation of random shape is applied to show that this complex phenomenon persists for non-simplified excitation shapes.
Techno-Economic Analysis and Optimal sCO2 Power Cycle Configuration for Novel CSP Plants Adopting Tubular Fluidized Particles Central Receivers
Authors: Alfani Dario , Sobic Filip , Astolfi Marco , Binotti Marco , Silva Paolo
Published: August 2024

Concentrating Solar Power (CSP) plants, thanks to the use of cost-competitive Thermal Energy Storage (TES), can provide back-up power guaranteeing a zero-emission alternative to conventional power plants and offer of balancing services on the electrical grid. Current state-of-the-art solar tower plants are based on conventional steam Rankine cycles and adopt solar salts both as heat transfer and storage fluid in a direct 2-tanks TES system. However, the 2022 average CSP levelized cost of electricity, equal to 0.118 $/kWh, is still remarkably higher than other renewable technologies. Next generation CSP solar towers are expected to employ novel high-temperature receivers able to reach temperatures above 700°C, leading to improved efficiency of the power block and thus to more competitive technoeconomic performances. In this context, the Horizon Europe Powder2Power project aims at demonstrating at the MW-scale the operation of an innovative tubular solar receiver adopting fluidized particles that will allow to reach temperature as high as 750°C while ensuring intra-week storage capacities at reduced cost, thereby increasing the flexibility and the competitiveness of CSP generation and its value for the grid.

For such a high temperature and high flexibility application, the adoption of sCO2 Brayton cycles as power conversion systems is the most recommended option thanks to their high efficiency, compactness of turbomachinery, simple plant arrangement, no water consumption, and fast transients in operation. This work aims to confirm the potential advantages of this power block technology for next generation CSP plants based on tubular fluidized particles solar receivers. A MATLAB+REFPROP V10 numerical model is developed to calculate the system overall efficiency and the capital cost for different cycle configurations, and it is employed to identify the optimal techno-economic solutions which can minimize the specific cost of the overall CSP plant. The model implements ad-hoc routines for the component sizing and uses referenced cost correlations for each component of the power block (compressor, heat rejection unit, recuperators, and turbine) and of the solar field (heliostat, tower, and receiver).

Results allow selecting the optimal sCO2 power cycle configuration and nominal design parameters, also considering the tradeoff on the solar-to-electricity efficiency and the total investment cost of the system.
Effect of Piston Ring Grooves on the Radial and Tangential Forces of a Squeeze Film Damper
Authors: Giampaolo Emanuele , Arghir Mihai , Festjens Hugo
Published: August 2024

Squeeze film dampers (SFDs) are components of rotating machinery used to reduce vibration amplitudes and improve the rotor dynamic stability. Piston rings (PRs) are often employed as end seals for SFDs. They enhance the damping forces while remaining limited to a small axial length. Piston rings are installed in grooves whose dimensions (width and depth) are generally one order of magnitude larger than the radial clearance of the SFD. The radial and axial clearances after the PR is mounted may impact the forces generated by the SFD to the point that they have to be considered as design parameters. CFD and bulk flow (BF) approaches were used to determine the impact of the axial and radial clearances introduced by the presence of the PRs. CFD is an accurate, direct approach to the problem but it requires intensive computational resources. Therefore, BF-based methods are considered as an appropriate option for a wide range of SFD operating conditions. The BF approach developed previously is now extended to include the PR clearances. The results are validated using CFD simulations for a simplified SFD geometry. This comparison underlines the strengths and limits of the BF approach. The impact of the PR clearances on the radial and tangential forces is then evaluated on a realistic SFD by using the BF model. A parametric study is conducted to explore the impact of varying the axial and radial PR clearances. Overall, a procedure for correctly considering PR clearances in a BF framework is proposed and validated, while complementary elements for understanding the role of PR clearances are described.
Study on Segment Fitting Method of Nusselt Number on the Turbine Vane
Authors: Zhang Fan , Liu Cunliang , Zhou Tianliang , Yan Haonan , Li Guodong
Published: August 2024

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

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

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

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

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

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

Secondary air systems in gas turbines provide a pressurized purge for the protection of highly-stressed components. The selection of an appropriate purge air mass flow seeks to sufficiently reduce the ingestion of hot annulus gas into the side wheel space with minimal impact on gas turbine efficiency. This paper describes a computational study of the flow field in a wheel side space of a 1.5-stage test turbine under different operating conditions.

Measurement data for the investigated test turbine shows the formation of large flow structures (low pressure areas) in the wheel side space for sufficiently low dimensionless purge air mass flow rates CW when using an axial sealing geometry. These structures are mainly apparent through their influence on the unsteady pressure field within the wheel side space. Large pressure inhomogeneities increase the ingestion of hot annulus gas thus reducing sealing efficiency. Furthermore, the high angular momentum of the ingested gas causes an increase in fluid core rotation which in turn results in large radial pressure gradients in the time-averaged flow field. Depending on operating conditions the flow transition (breakdown of large flow structures) can be observed around a characteristic CW,trans. This flow transition has a profound impact on pressure distribution and sealing efficiency.

Contrary to the approach of high model complexity and large computational efforts for analysis of the highly intricate flow fields in wheel side spaces, this paper presents a methodology utilizing a highly simplified computational model with an (U)RANS approach.

Despite the low model complexity, the simulation results shown in this paper show good agreement with measuring data pertaining to the flow field in the rotor-stator cavities and more specifically the flow transition. Possible reasons for deviations from measurement data as well as possibilities for further feasible simplification in the modeling approach are discussed.

Furthermore, the presented simulation methodology is applied to a radial sealing geometry, which does not show a flow transition in experimental data. It is shown that the flow within the wheel side space can be modeled with comparatively small deviations from measurement data regarding pressure and sealing efficiency. To assert, whether a flow transition effect can be found outside of flow conditions measured in the experiment, simulations with very low purge air flow rates are conducted.
Unsteady Computational Fluid Dynamics Simulation of Inlet Fins in Centrifugal Compressor
Authors: Tokieda Katsunori , Ueno Takahiro , Unno Masaru , Morita Isao
Published: August 2024

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

Hydrogen, when produced with renewable energy and used in a gas turbine can become a key enabler towards decarbonization. The HYFLEXPOWER project is the first such demonstration of a fully integrated industrial power-to-H2-to power pilot installation of an existing cogeneration plant with a dry low emissions (DLE) Siemens Energy SGT-400 gas turbine at a paper recycling factory in France.

This paper provides a comprehensive summary of successful development, installation, and operation of the power-to-H2-to-power application in this plant. In 2022 and 2023, test campaigns in the SGT-400 gas turbine with 100% H2 as well as with natural gas and blends in between were conducted successfully. Initial testing in 2022 with a modified combustor design enabled the industrial gas turbine to operate up to 30 vol% hydrogen. Additional development of H2 combustion technology, upgrades of gas turbine control methods and improvements in the hydrogen-natural gas mixing were done and implemented at site. In 2023, the team successfully demonstrated operation with 0–100% hydrogen blends in natural gas. The paper will present gas turbine testing conducted with natural gas at Siemens Energy factory in Lincoln (UK) and both test campaign results at the site in France including emissions and metal temperatures with hydrogen addition.
Modeling Stochastical Particle Rebound Based on High Velocity Experiments
Authors: Hartmann Jan , Koch Christian , Staudacher Stephan
Published: August 2024

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

A machine learning based approach is presented which allows to detect persistent engine faults after a single flight. It utilizes transient in-flight measurements and a transient engine model. The time series of the residuals between the measured data and the data resulting from performance synthesis is evaluated using moving windows containing at least one transient segment. A continuous wavelet transformation and a pre-trained convolutional neural network are utilized on the residuals for feature extraction. The fault detection is carried out via a one-class support vector machine, trained exclusively on nominal engine operation data. Therefore, the approach requires no a-priory knowledge of the effects of engine faults on the in-flight measurements. Under the assumption of persistent faults, all windows of a single flight which contain at least one transient segment are considered in order to improve the reliability of the fault detection.

This approach is validated using measured data of a small helicopter engine that replicates the dynamic flight of the corresponding model helicopter on a ground test bed. Consequently, step changes as well as complex variations of the shaft power output are considered. Four standard gas path sensors are considered. The one-class support vector machine is used successfully to detect two types of total pressure sensor anomalies. Assuming a typical number of transient segments for an average short haul flight, it turns out that persistent faults can be detected within one flight with a probability of above 90%.
The Effect of Flight Speed and Altitude on Windmilling Restart Operation of Turbofan Engine System
Authors: Zhang Jingkai , Wang Zhitao , Li Shuying , Wei Pengfei
Published: August 2024

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

Solid oxide fuel cell-gas turbine (SOFC-GT) hybrid systems are an advanced technology for power generation because of their high efficiency, stability and environmental friendliness. Because the exhaust from the gas turbine in the SOFC-GT system is still of high grade, a bottoming cycle is usually used to recover the exhaust’s waste heat. The supercritical CO2 power cycle is selected as the bottoming cycle for the SOFC-GT hybrid system to achieve cascaded utilization of this thermal energy. Here, a thermodynamic model is built for such a supercritical CO2 power cycle driven by an SOFC-GT hybrid system. Six key parameters, including the fuel flow rate, fuel utilization factor, SOFC operating temperature, combustion engine pressure ratio, CO2 turbine inlet pressure and cycle split ratio, are analysed to determine the effects on the thermodynamic performance of the system in terms of the output power, exergy loss and exergy efficiency of the system. Moreover, particle swarm optimization (PSO) is employed to perform multiobjective optimization of the hybrid system. The optimization results for the output power and efficiency of the system are presented at the Pareto front of the system. Further analyses are conducted for the distribution of the values of the key parameters corresponding to the Pareto solution. The optimal operating point of the hybrid system is finally determined by the linear programming decision method of multidimensional preference analysis.
Predicting Exhaust Gas Recirculation Impacts on Instability and Emissions of an Industrial Gas Turbine Combustor Using Large Eddy Simulations
Authors: Xu Chao , Sung Yonduck , Johnson Daniel , Steele Chris
Published: August 2024

Carbon capture at engine exhaust is a promising technology to reduce carbon footprint for industrial gas turbines. Exhaust gas recirculation (EGR) has been proposed as a potential solution to increase the exhaust CO2 concentration for reducing the cost of carbon capture. A key challenge of applying EGR to practical gas turbines is the enhanced combustion instability as the level of EGR increases. Hence, identifying the upper limit of EGR that maximizes the exhaust CO2 concentration while still allowing for stable combustion is critical to demonstrating the technology feasibility and reducing the number of expensive experimental tests. In this study, a large eddy simulation (LES) model is developed to predict the combustion instability and NOx emissions in an industrial gas turbine combustor under EGR conditions. Adaptive mesh refinement (AMR) is used to resolve complex local flow and flame structures. The finite rate chemistry based combustion model is used to predict the highly transient combustion and emissions behaviors. To accelerate the finite rate chemistry calculation, a 39-species skeletal chemical kinetics mechanism accounting for NOx chemistry is developed for methane/air mixture under EGR conditions for realistic gas turbine operations. The LES model is validated against experimental temperature profile at the combustor exit and good agreement is achieved between LES and experiment. The model is then employed to conduct a parametric study comprising of various levels of EGR and piloting. As EGR level increases, the instability amplitude, defined by the pressure fluctuation inside the combustor, is shown to increase monotonically attributed to the decreased flame speed. The flame jumps from a stable mode to an unstable mode at a threshold EGR level. Piloting is shown to promote or inhibit the instability amplitude depending on the level of EGR. Analysis of adiabatic flame temperatures for both main and pilot flames shows that piloting may not be effective in suppressing combustion instability when the corresponding pilot flame temperature is lower than the main flame temperature. Instead, the instability amplitude is found to be strongly correlated to the laminar flame speed of the main flame alone. On the other hand, when increasing EGR level, the NOx emissions first decrease in the stable regime, then increases abruptly as flame transitions from the stable to unstable mode, and finally decreases again within the unstable regime. Such complex response of NOx is found to be associated with the availability of excess O2 as well as the change of flame size and flame surface area.
A Reduced-Order Model for Predicting Flow and Temperature in a Rotating Tapered Duct Under Constant Thermal Loading
Authors: Kim Wanjae , Shih Tom I-. P. , Bryden Kenneth Mark , Dalton Richard P.
Published: August 2024

Blades in gas turbines have cross sections at the root that are larger than those at the tip so that internal cooling passages in blades are tapered. In this study, a reduced-order model (ROM) — based on the integral continuity, momentum, and energy equations for a thermally and calorically perfect gas was developed to enable rapid assessments of radially outward flow in a tapered duct subjected to constant heat flux with and without rotation. The following parameters were investigated by using the ROM developed: taper angle (α = 0°, 1.5°, 3.0°), ratio of mean radius to hydraulic diameter (Rm/Dh = 45, 150), rotation number (Ro = 0, 0.025, 0.25), Reynolds number (Re = 37,000, 154,000), and thermal loading (q” = 5 × 104, 105 W/m2). Results obtained show the density and pressure variation along the duct to be most affected by rotation number; velocity to be more affected by duct’s taper angle; and temperature by rotation number and taper angle. Results obtained also show the temperature along the duct could decrease if the taper is sufficiently large even with high heat flux into the duct because taper increases velocity, which converts thermal energy to mechanical energy. Within the range of parameters studied, the mass flow of the cooling flow could be reduced by as much as 44% for a tapered duct to achieve bulk temperature variation similar to that of a duct without a taper. The ROM developed was validated by comparing its predictions with grid-converged CFD results obtained by steady RANS with the SST turbulence model. The maximum relative errors for density, velocity, temperature, and pressure distributions along the duct were found to be 0.6%, 3.3%, 0.4%, 0.3% for the smooth section of the duct and 3.2%, 5.6%, 0.9%, 3.0% for the ribbed section of the duct. Thus, the ROM developed performs nearly as well as CFD based on RANS but orders of magnitude more efficient computationally.
Experimental Study of the Effect of Swirling Inflow on Full-Film Cooling of Turbine Guide Vane
Authors: Yan Hao-nan , Liu Cun-liang , Zhou Tian-liang , Zhang Fan , Ren Ming
Published: August 2024

The use of compact engines reduces the distance between the combustor and the turbine, leading to the interaction of the remaining inhomogeneous swirling flow at the combustor outlet with the mainstream of the turbine vane cascade. Consequently, previous turbine vane cooling designs may struggle to meet the cooling requirements for swirling inflow conditions. This study aims to investigate the impact of swirling inflow on the full-film cooling of turbine guide vanes. The film cooling effectiveness (η) of the turbine vanes under two inflow conditions and three mass flow ratios was measured using the pressure-sensitive paint technique. The cylindrical film holes on the suction and pressure surfaces of the vane were replaced with different types of laid-back fan-shaped holes (LBFS), and the cylindrical holes at the leading edge were replaced with droplet holes. The results revealed that swirling flow alters the coolant outlet flow from the film holes on the vane surface, causing deflection of the film. Droplet holes at the leading edge were found to reduce the coolant outlet momentum and improve η, in comparison to cylindrical holes. Furthermore, LBFS demonstrated a significant advantage in mitigating the negative effects of swirling flow. Specifically, LBFS with wider outlet width were found to be more suitable for the pressure side, while no additional outlet width of the air film holes was required for the suction side.
The Use of Artificial Neural Networks With a Systems Engineering Approach for Data Enhancement in Humidified Micro-Gas Turbine Application
Authors: Jamil Ahmad , Dinh Tina , De Paepe Ward , Nikpey Somehsaraei Homam
Published: August 2024

Globally the energy sector is being transformed by innovations based on decarbonization, decentralization, and digitalization. These encompass transitioning towards a future with distributed generation systems having an increased share of renewables, artificial intelligence, and digital solutions. Micro-gas turbines are a competitive enabling technology in distributed power generation owing to benefits like fuel flexibility, reduced operation and maintenance costs, and emissions. However, its economic performance stumbles when not running in combined heat and power mode, requiring cycle modifications to increase electrical efficiency.

The humidified micro-gas turbine is one such modification that shows great potential. For its viability in digitalized future energy systems with ever-growing amounts of data, there needs to be reliable and deployable advanced tools for performance and health management. This requires access to sufficient quality data, making data quality management an essential need. Therefore, the study presented in this paper investigates the use of a special type of artificial neural network called an autoencoder for data enhancement of a humidified micro-gas turbine. Data from 15 sensors has been enhanced by denoising for use in any subsequent data-driven insight and decision. To achieve this, different neural network models have been developed and compared to predict the denoised values. The auto-encoder network model that can best produce satisfactory denoised results has been identified as having 3 bottleneck and 6 mapping layer nodes. Furthermore, a systems engineering framework has been adopted for effective information and complexity management amongst all stakeholders. The framework sets a foundation for employing model-based systems engineering concepts in developing digital solutions.

The results demonstrate the functionality of deploying denoising autoencoders with a systems engineering approach for data quality management of the humidified micro-gas turbine. The outcomes from this work can be used for data-driven performance and health management of the humidified micro-gas turbine. This will improve the system’s reliability and promote its use in energy systems of the future.
Transitional Flows Within Cooled HP Turbines
Authors: Clark Christopher J. , Atkins Nicholas R. , Stokes Mark , Vazquez-Diaz Raul
Published: August 2024

All modern gas turbines, from a small business jet to a large civil engine, make use of film cooling within the HP turbine. Transition on the blade surfaces has a large impact on blade heat transfer and profile loss. Many studies have considered the role of freestream turbulence and surface roughness on transition, yet no systematic study of the role of film cooling on transition has been reported.

This paper shows that film cooling is as potent at causing transition as roughness typically found on the suction surface of end-of-life engines, and more so than freestream turbulence. For the blades tested, film cooling induced transition begins at the rear of the suction surface, the transition point moving forward to the film cooling hole with a doubling in Reynolds number. Averaging the acceleration parameter over a fixed distance downstream of the cooling hole collapses the transitional behaviour for varied film ejection locations. A model is proposed to capture the Reynolds sensitivity of film cooling induced transition.

The simultaneous presence of freestream turbulence and roughness as well as film cooling, are shown to enhance transition compared to any mechanism in isolation, despite the localised nature of the film cooling holes. It is likely that the combined effect of the mechanisms is maximised when each mechanism in isolation would result in transition at a similar Reynolds number. Therefore a method of mapping each transition mechanism in isolation is demonstrated to identify which mechanism is dominant, the proximity of other mechanisms and hence their likely enhancement of transition.

By testing combinations of film cooling, roughness and freestream turbulence typical of a cooled HP rotor the transitional region is found to cover the range 300,000 < Rex < 1,000,000, where transition will be primarily dependent on surface roughness and film cooling. Below Rex = 300,000 transition is likely via a laminar separation bubble and above Rex = 1,000,000 the suction surface boundary layers will be fully turbulent. Large civil engines sit within the top of the transitional range at cruise and smaller engines span the entire range between cruise and take-off conditions.
Steam Turbine Diaphragms Re-Design and Manufacturing Challenges
Authors: Alamoudi Abdullah M. , Khan Raja S. , Shaik Javeed , Alqahtani Mohammed M.
Published: August 2024

This paper illustrates a recent project to resolve the issue of unavailable major spare parts for one of the heavy duty steam turbines utilizing reverse engineering principles in order to re-manufacture the critical components.

Steam Turbines are critical prime movers within the company’s various hydrocarbon and refinery plants. Single stage turbines are used for light duty applications while multi stage steam turbines are used to run large gas compressors or pumps. Many of the steam turbines have been running for more than 40 years with well-established designs and technology. For the large multistage special purpose steam turbines, the spare parts such as casing, rotor, shaft and diaphragms are not shelf items and usually will take over 12 months to manufacture and supply by out of kingdom manufacturers which compromises the plant productivity and reliable operations, not to mention the high costs involved.

Mechanical Services Shops Department, a machinery services organization within the company, was approached by one of the operating plants to overhaul a 6-stage steam turbine due to low performance and as part of a planned plant T&I shutdown. Upon dismantling, excessive pitting, erosion and micro-cracking was found on all 5 stages diaphragms, nozzle ring and bucketing diaphragm which led to the decision of replacing all diaphragms. Due to the unavailability of spare parts and long lead time, it was decided to reverse engineer these critical spare parts locally.

Material of construction analysis were performed in order to understand how the original parts were manufactured. FEA study was conducted on various designs alternatives and materials to investigate how different types of materials are affecting the diaphragm ability to handle thermal and mechanical stresses and deformation. Accordingly, materials and design were selected based on the study outcome which showed 48% Improvement in stress load capability and 27% greater resistance to deformation due to thermal expansion compared to the original design.

3D scanning of the old parts was performed in order to create 3D models which are a digital replica of the existing parts. These models have been modified in order to compensate for the material lost due to the excessive erosion. Detailed manufacturing drawings were developed and manufacturing method of the new parts was changed from fabrication and welding of different components to a more modern method of 5 axis CNC machining from one single billet of forged metal.
Effect of Film Cooling Hole Geometry on Thermal Stress Based on Thermo-Solid Coupled Analysis
Authors: Yan Xiao , Huang Tong , Su Xinrong , Yuan Xin
Published: August 2024

This article examines the impact of various cooling hole shapes on the surface cooling effect and thermal stress distribution of flat utilizing the thermal-fluid structure coupling method. A thermo-solid coupling model was adopted, which accounted for the influence of solid thermal conductivity on the results. Five shape parameters were selected to analyze 46 samples, comparing them with the standard 7-7-7 hole. Among the 46 samples, the highest average effectiveness of the main wall reaches 0.294, while the lowest von Mises stress is 479.55 MPa. They correspond to different geometries. Further analysis revealed a negative correlation between the surface average effectiveness and the outlet velocity of the coolant gas in the z-direction. By further comparing the cooling and mechanical properties of all samples, the optimal geometric shape was identified. This geometric design can serve as a reference for further optimization, which is significant for achieving high cooling efficiency while ensuring structural strength in turbine blade design.
On the Development of an Efficient Sliding Mesh Interface for the Harmonic Balance Method, Part I: Implementation and Verification
Authors: Geiser Georg , Schwarzenthal Felix , Ashcroft Graham , Hartmann Maximilian , Schlüß Daniel
Published: August 2024

In recent years the Harmonic Balance method has become a popular tool in the field of turbomachinery design. While it can efficiently capture nonlinear effects in time-periodic flows, its application to complex configurations such as cavities or casing treatments requires sophisticated domain coupling methods. To address this topic, in a series of two papers, we present and validate an algorithm for the coupling of non-conforming mesh topologies across domain boundaries. In this first paper the basic algorithm and its verification are presented in detail. In the second paper the method is applied to analyze the impact of a casing treatment on blade flutter in a compressor stage. It is shown in this paper that memory layout can have a strong impact on memory usage and CPU time. To handle indexed modes, i.e., modes with the same frequency but different inter-blade phase angles, we introduce virtual passage segments on which the required spatial Discrete Fourier Transform (DFT) is performed. Using Almost Periodic Fourier Transforms (APFT) to transfer the temporal solution harmonics we show that the computational overhead can be significantly reduced when compared to a standard temporal DFT ansatz. In this context a simple, but robust algorithm is proposed to determine the temporal sampling interval and distribution of the sampling points such that a bound on the condition number of the resulting APFT matrix is satisfied. The method is verified and analyzed using three academic test cases: the propagation of an entropy wave across moving interfaces in an empty duct with a rotating mean flow; the aerodynamic excitation of a simple rotor blade exposed to a time-periodic gust disturbance; and the flow in a duct with an attached cavity.