bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Rear Engine Concept Distortion on the Aerodynamic Performance of a Fan Rotor
Authors: Xue Yifan , Deng Hefang , Qiang Xiaoqing
Published: August 2024

The civil aviation industry is facing serious environmental and energy issues, and boundary layer ingestion technology (BLI) is a viable solution. However, how to ensure that the engine can work continuously under the condition of BLI inlet distortion has become the focus of research. In this paper, Unsteady Reynolds-averaged Navier-Stokes (URANS) and RANS simulation methods are used to simulate a full-annular fan, and the aerodynamic performance of NASA rotor 67 under different BLI inlet distortion is studied. The focus of analysis is on swirl distortion, which has been neglected in previous studies. The loss source in non-uniform flow field is studied by using the loss analysis method based on entropy dissipation. Results show that under side-slip conditions, the intensity of swirl distortion on windward side and leeward side is different, and swirl distortion greatly affects swirl angle distribution, which has a significant impact on fan performance. The loss is mainly located near part of the blade tip and part of the wheel hub, which is related to the structure of the BLI inlet distortion. The relative Mach number and shock wave structure change significantly in the tip region, and dramatically in the region directly affected by the distortion. The interaction between shock wave, boundary layer and tip leakage flow can cause a lot of losses. When the total dissipation decreases, the viscous dissipation caused by swirl distortion decreases and the proportion of thermal dissipation increases. The BLI distortion increases the loss mainly through the swirl distortion. In the region with weak swirl distortion, the total pressure distortion still affects the flow in the tip region.
Stability and Robustness Analysis and Optimization for Gain-Scheduled Control of Aero-Engines
Authors: Jiang Jincen , Yang Jiali , Wang Xiting , Yang Xiao , Hu Zhongzhi
Published: August 2024

Gain-scheduled control has found extensive applications for aero-engines, yet the selection of design points for gain-scheduling controllers to ensure stability and robustness throughout the range of scheduling variables remains theoretically unguided. To address this issue, this paper introduces an analysis and optimization method for the stability and robustness of gain-scheduled control, aimed at providing a systematic theoretical framework for design points selection. Initially, the optimization method characterizes the gain-scheduled control system as a polytopic Linear Parameter Varying (LPV) system, wherein the design points of the gain-scheduled control system correspond to the vertices of the polytopic LPV system. Subsequently, the method utilizes Linear Matrix Inequality (LMI) techniques to demonstrate the stability of a polytopic LPV system with a corresponding number of vertices, and by assessing the approximation degree between the polytopic LPV system and the gain-scheduled control system with an identical number of design points, it evaluates and ensures the stability of the latter, thereby establishing the minimal requirements for the number of design points. Upon ensuring system stability, the optimization method further refines the number of design points within the gain-scheduled control system to meet additional robustness and performance considerations. Through a case study on turbofan engine controls, the proposed optimization method has been validated, exhibiting improved system stability and robustness, as well as accurate high-pressure rotor speed tracking performance. This optimization method offers a novel perspective and methodology, assisting engineers in more effectively balancing the interplay between stability, robustness, and the number of design points during the design of gain-scheduled controllers.
Numerical Modelling of a Primary Heat Exchanger in sCO2 Power Cycles for Thermal Energy Storage Systems
Authors: Guille Alexandre , Bangalore Mohankumar Malini , Unger Sebastian , Hampel Uwe
Published: August 2024

Renewable energy sources are the key for long-term decarbonization of energy. However, the intermittent nature of renewables does not always meet the energy demand in the electrical grid. Thus, electrical heated Thermal Energy Storage systems (TES) coupled with sCO2 power cycles are investigated at Helmholtz-Zentrum Dresden-Rossendorf as a possible solution to balance this mismatch. In this study, a Printed Circuit Heat Exchanger (PCHE) is considered as candidate for the 1 MW primary heat exchanger, given the mechanical challenge induced by drastic pressure difference between the hot fluid of the TES and the cold fluid of the power cycle. The present work consists of two parts, one elaborates a 1D model in order to optimize the PCHE regarding the pump power required to compensate the pressure loss. It was found that the hot fluid coming from the TES accounts for 80 % of the total pump power after optimization because of its low density and its high mass flow rate. Furthermore, 3D simulations by Computational Fluid Dynamics (CFD) were done and compared to the results from the 1D model to ensure its validity. It was observed that the results from the 1D model and the CFD simulations are consistent, with a slight potential deviation in the calculation of the pressure profile.
Numerical Investigation of Two-Phase Shock Waves in CO2 Flows Using a Modified Hertz-Knudsen Model
Authors: Petruccelli Giuseppe , Dolatabadi Amir Momeni , Grönman Aki , Turunen-Saaresti Teemu , Guardone Alberto
Published: August 2024

Understanding the complex behavior of two-phase shocks in CO2 flows is essential for a variety of applications, including carbon capture and storage (CCS) and transcritical refrigeration cycles. This study presents a comprehensive numerical investigation of two-phase shock waves using the multispecies User-Defined Real Gas Model in Ansys Fluent. The simulations are performed for de Laval nozzles, exploring the two-phase shock features for three-dimensional (3D), two-dimensional (2D), and two-dimensional axisymmetric geometries. The non-equilibrium condensation, subsequent evaporation and denucleation occurring across the shock are modeled through a set of User-Defined Scalar transport equations implemented within Ansys Fluent. The two-phase CFD simulations are carried out in proximity to the critical point where real gas effects are relevant. The CO2 real gas properties are computed using an in-house Python code and integrated into the solver via User-Defined Functions as external look-up tables. This study provides valuable insights into the physical processes underlying two-phase shocks in CO2 flows and their sensitivity to geometric variations and thermodynamic conditions. The findings contribute to the development and modification of predictive models and optimized designs for systems involving two-phase CO2 flows. The results highlight the influence of geometry configurations and thermodynamic conditions on shock location and intensity, providing comparisons for shock waves occurring in two-phase flows and supercritical single-phase flows.
Understanding Entropy Wave Evolution in High-Pressure Turbines: the Role of Hot Spot Position and Features
Authors: Pinelli Lorenzo , Giannini Giovanni , Marconcini Michele , Pacciani Roberto , Notaristefano Andrea , Gaetani Paolo
Published: August 2024

Mutual interaction of turbomachinery components plays a key role for a comprehensive optimization of the machine. Among these interactions, the aerodynamic coupling between combustor systems and high-pressure turbine (HPT) stages may lead to aerodynamic performance degradation, cooling issues, combustion instability and noise generation. This interaction is mainly caused by steady and pulsating temperature distortions (hot streaks and entropy waves, respectively) generated by combustion systems: such flow non-uniformities are convected downstream in a swirling flow field and interact with HPT stage. New trends of introducing alternative fuels (sustainable aviation fuel, hydrogen, ...) may also require an even more accurate understanding of such interactions. In this context, the paper reports an extensive CFD investigation examining how circumferential and radial injection positions affect the migration and interaction of swirling entropy waves (EWs) with an uncooled aeronautical HPT stage. The numerical method, based on full-annulus URANS analyses, has been already intensively validated against experimental acquisitions in previous works exploring the effect of different EW-vane tangential alignments, swirling flow rotational directions and turbine operating conditions. Results reveal a complex interaction among the EW spots and secondary flows of both stator and rotor. Moreover, a simplified analytical model proposed by the authors for fast prediction of combustor non-uniformities evolution has been applied to all the presented cases to prove its ability to reproduce the main features of EW evolution. The combination of model and CFD results can provide important insights for turbomachinery designers both during the preliminary design and for the final evaluation.
Effects of Secondary Jet Angle Variation on Flow, Flame Structure and Emission in the Reburning Zone Under Axial Fuel Staging Combustion of CH4/NH3/H2 Fuel
Authors: Li Yuze , Li Yuansen , Xiao Yunlai , Jia Yuliang , Zhu Xutong , Ge Bing , Zang Shusheng
Published: August 2024

Axial Fuel Staging (AFS) combustion technology is an advanced low-pollution combustion technology for heavy-duty gas turbines. In order to investigate the impact of jet angle in the reburning zone on flow field, flame structure, and emission in the secondary zone during axial fractional combustion of methane/hydrogen/ammonia fuel, we employed high-frequency PIV and OH-based self-luminescence techniques. Under atmospheric pressure conditions with a momentum flux ratio of 6, we examined the effects of jet angle variations (45°, 90°, and 135°) on axial fractional flow field, reburning flame morphology, and pollutant emission for different fuel types. It is found that when CH4 fuel is used and the jet Angle is 90°, the flame in the reburning zone has three different forms, namely, self-ignition detached flame, transition state flame, and premix continuous combustion plume flame. At this Angle, there is a good mixing effect and the ignition position is controllable, so NOx emission is significantly lower than the other two jet angles; When the jet Angle is 45°, the secondary fuel is mixed with hydrogen, the reburning flame changes from a detached flame to a short continuous flame. The reburning flame during flame form conversion exhibits minimal flame area and chemical residence time, thus reducing NO emissions. When the jet angle is 135°, the methane reburning flame shifts upstream, exhibiting a circular flame shape and an extended high temperature chemical residence time, resulting in reduced CO emissions but increased NO emissions. During the initial stage of ammonium-doped combustion, as the ammonium-doped ratio increases, the jet flame transitions from a continuous flame to a debulk flame.
An Additively Manufactured Two-Fluid Heat Exchanger Designed With Topology Optimization Tools
Authors: Caruso Claudio , Morante Francesco , Pampaloni Giacomo , Rossin Stefano , Canova Alessandro , Casari Nicola , Rees Thomas
Published: August 2024

Heat exchangers are widely used in gas turbine plants for several purposes, with traditional designs including shell and tube or plate-fin coolers. Recent developments in additive manufacturing techniques such as laser powder bed fusion have led to interest in the use of alternative heat exchanger designs, such as those generated with topology optimization techniques. These design techniques can result in more efficient heat exchangers with complex internal structures which can only be manufactured using additive techniques. Nevertheless, manufacturing heat exchangers for gas turbine applications with additive techniques is not straightforward. Two of the primary difficulties in the use of laser powder bed fusion are the printing of materials with high thermal conductivity such as copper alloys as well as powder cleaning from any complex internal channels such as those which may be generated by topology optimization tools.

To investigate the feasibility of combining topology optimization techniques with additive manufacturing to design novel heat exchangers a proprietary topology optimization software is used to design an oil/air cooler with significantly reduced size and pressure drop compared to an equivalent one based on a conventional design. In a potential future application on oil circuits, this could consequently result in an optimization of the lubricant oil circuit components, for example pumps, piping, console dimensions and weight. The design was also optimized to consider manufacturability constraints such as overhang angles and minimum thickness as well as to correct in line with feedback from initial trial prints. The cooler was manufactured using additive manufacturing techniques.
Numerical Investigation of the Effect of Diffusion Factor Variation on the Performance of Single-Row and Tandem Bladings in Low-Speed Axial Compressor Stages
Authors: von Jeinsen Philipp , Giannini Samuele , Gümmer Volker
Published: August 2024

The use of tandem blade configurations in axial compressor stages offers designers the opportunity to achieve higher work coefficients, which in turn allows for the creation of smaller compressors. However, tandem airfoils introduce a more complex flow field compared to their single airfoil counterparts, often resulting in a decrease in stage efficiency.

This paper aims to investigate the aerodynamic performance of single and tandem airfoils across a wide design space represented by the “Smith Chart” (work coefficient vs. flow coefficient). A prior study indicated that tandem stages exhibit superior efficiency when DeHaller numbers are low. However, this comparison was conducted under strict design conditions, leading to suboptimal diffusion factors for various designs and impairing the comparison of their off-design performance. The current study seeks to address this limitation by examining the effects of varying the diffusion factor and ensuring comparability in off-design behavior.

The 3.5-stage low-speed axial research compressor at the Institute of Turbomachinery and Flight Propulsion at the TUM sets this study’s geometrical and aerodynamic baseline. The first 1.5 stages of this compressor will be redesigned, either considering a set-up of IGV, single rotor, and single stator or a set-up of IGV, tandem rotor, and tandem stator. The numerical analyses are based on the throughflow – B2B coupled quasi-3D design process.

The first part of the paper presents a brief overview of the methodological approach and highlights the necessary changes to the design procedure compared to the prior investigation. The second part explores the effect of diffusion number variation on the midspan airfoils across the entire design space. These findings lead to the final part of the paper, where the efficiency maps of single and tandem stage configurations are compared.

The present paper confirms that the potential efficiency gain of tandem airfoil geometries over single ones largely depends on the DeHaller number of each row. Single airfoil configurations demonstrate superior performance at high DeHaller values, while tandem airfoils excel at low DeHaller numbers, potentially unlocking a design space with increased work coefficients.
Water-Based Yttrium Additive for Hot Corrosion Inhibition in a Gas Turbine
Authors: Selim Hatem , Suleiman Baha , Dawood Alaaeldin , Montagne Pierre , Amancherla Sundar , Khalidi Abdurrahman
Published: August 2024

Hot corrosion is a major problem for operating gas turbines running on vanadium-laden liquid fuels. Upon combustion, vanadium combines with oxygen forming vanadium pentoxide (V2O5) which is highly corrosive and has a melting point below the hot gas path (HGP) operating temperature. This causes V2O5 to melt down and attack the HGP parts in what is known as hot corrosion. To mitigate the potential for hot corrosion of vanadium on gas turbine parts, a corrosion inhibitor is typically injected with the fuel. The role of the corrosion inhibitor is to chemically react with V2O5 to form non-corrosive chemical molecules, which appear as “ash”. Magnesium-based inhibitors are commonly used in gas turbine applications. However, a high volume of ash accumulates on turbine blades causing degradation of the turbine performance. A promising alterative, which is a yttrium-based inhibitor, was tested and compared with magnesium-based inhibitor in this investigation. Laboratory-scale testing of ash formation and corrosion inhibition were conducted for both inhibitors. The results proved that yttrium inhibitor achieved superior performance in comparison to magnesium inhibitor in terms of less ash formation and higher hot corrosion resistance. Furthermore, both inhibitors were tested in an E-class gas turbine pilot test. The acquired performance data confirmed the superiority of yttrium as an inhibitor in comparison to magnesium.
Experimental Evaluation of Combustor Configuration’s Impact on a Swirl-Assisted Jet-Stabilized Combustor Performance
Authors: Izadi Saeed , Zanger Jan , Seliger-Ost Hannah , Kutne Peter , Aigner Manfred
Published: August 2024

A major challenge for gas turbine combustor technology is the emission of NOx and CO. Achieving an optimal premixed, prevaporized, dry low-NOx condition is a critical issue for liquid fuel combustors. To accomplish this, the relationship between combustor configuration and the performance of a newly developed swirl-assisted jet-stabilized combustor is investigated in an atmospheric combustion facility. The combustor consists of a pressure-swirl fuel atomizer, a prefilmer/mixing channel, an axial moderate swirler (swirl number = 0.6), and a jet nozzle. The jet nozzle allowed for bulk velocities of 50–130 m/s. The influence of each combustor component on combustion performance and fuel evaporation behavior is evaluated independently using optical combustion diagnostics. In addition, the effect of air and liquid fuel temperature on fuel evaporation is characterized. Jet A-1 was injected coaxially into the air stream under both spray and superheated conditions. During the experiments, five critical combustor components were varied to understand their individual effect on fuel vaporization and thus combustion performance. Exhaust gas emissions of NOx, CO and UHC as well as OH* chemiluminescence images were used to evaluate combustor performance. Mie scattering technique was used to analyze the degree of liquid fuel evaporation for different test cases. It was found that the combustion performance indicators CO, height above burner and flame length were well controlled by the degree of fuel evaporation, while NOx emissions showed little change with different combustor configurations. While the main factor influencing the level of NOx emissions was the adiabatic flame temperature, the quality of fuel evaporation played a minor role. It was found that the operating range of the combustor and the geometric shape of the flame are significantly influenced by the components of the combustor.
Efficient Quantification of Aerodynamic Performance Uncertainty due to Geometric Variability Using an Adjoint Method
Authors: Zhang Qian , Xu Shenren , Meng Dejun , Wang Dingxi , Huang Xiuquan
Published: August 2024

Manufactured compressor blades deviate from their intended design, leading to a shift in the mean and scattering of aerodynamic performance. To mitigate performance deterioration without escalating manufacturing costs, accurate and efficient evaluation of aerodynamic uncertainty, known as uncertainty quantification (UQ), is crucial. The computational cost of three-dimensional computational fluid dynamics (CFD) simulations has prompted UQ studies to predominantly target two-dimensional cases or extend to three dimensions with a limited number of geometric variables. Since geometric deviations exist at various positions on three-dimensional blades, accurately describing them would necessitate a geometric deviation space with a large number of dimensions. To investigate high-dimensional uncertainty problems, an efficient adjoint-based UQ method is proposed and demonstrated using the three-dimensional transonic fan, NASA Rotor 67. The method proves to be not only hundreds of times faster than full-fidelity CFD but also yields results with satisfactory accuracy. The investigation into the underlying mechanism reveals that geometric uncertainties significantly influence shock waves, tip clearance vortices, corner vortices, and the radial distribution of three-dimensional flows, ultimately resulting in deviations in aerodynamic performance.
Enhancing Diagnostic Capability by Utilization of Twin-Engine Aircraft Configuration Aspects
Authors: Stenfelt Mikael , Desalegn Fentaye Amare , Kyprianidis Konstantinos
Published: August 2024

Depending on the data available, gas turbine diagnostics may be performed in various ways. For model based diagnostics methods, the most common data to use is from steady state operation. Regarding the amount of data, the smallest dataset comprise of a single operating condition for a specific gas turbine. The other end of the scale considers a fleet of engines, where data can be utilized for cross comparisons and identification of deviations in engine operation. In-between these two extremes, twin-engine airplanes can be utilized to obtain additional diagnostic information.

In this paper, a multi-point diagnostic method for a twin-engine airplane is developed and evaluated. It is based on the assumption that one engine can be operated individually for data collection, by varying the bleed flow extraction, while the other engine supply the airplane subsystems with the required bleed flow during the data collection time. The collected data then goes into a multi-point optimization which minimizes the difference between the health parameter estimations. From the health parameters, measurements corresponding to a reference operating condition are obtained and used by a data-driven classifier for fault identification and isolation. The method has proven to be able to detect both single and double component faults with high accuracy for the evaluated dataset.
Metal Fuel Combustion Tests Using NRCan’s 0.3 MWth Vertical Combustor Research Facility
Authors: Ilinich Margarita , Zanganeh Kourosh , Shafeen Ahmed , Staneva Katrin
Published: August 2024

Reactive metals, such as iron (Fe) and aluminum (Al), have high energy density, making them a potentially suitable candidate for partial replacement of hydrocarbon fuels. These materials, herein referred to as metal fuels (MeFs), have the potential to simultaneously produce heat and power, zero-carbon hydrogen (H2), and other value-added products. To this end, the role of MeFs for producing clean hydrogen is becoming increasingly important for achieving 2050 net-zero emission targets and industrial decarbonization.

To date, limited work has been done to demonstrate MeF combustion at pilot scale. In this paper, the preliminary results of MeF combustion using the 0.3 MWth Vertical Combustor Research Facility (VCRF) of Natural Resources Canada (NRCan) are presented. This facility was originally designed for advanced research on combustion of fossil fuels, including air- and oxy-combustion of solid, liquid, and gaseous fuels with CO2 capture, but has been recently retrofitted to be utilized for combustion of MeFs. The VCRF is equipped with a full range of instruments to monitor and record combustion process parameters in real time. These include combustion air flow, combustor pressure and temperature profile, as well as the flame shape and size (with the aid of a camera probe). This paper presents the results of co-firing of natural gas with two Fe powders (90 μm and 40 μm). The feedstock MeF powders were analyzed through particle size distribution (PSD) and scanning electron microscopy (SEM), to study the size, shape, and morphology of the particles. The preliminary tests with low MeFs firing rate showed promising results and further testing is ongoing with increased firing rate up to 0.3 MWth. The gaseous combustion products were measured by continuous emission monitoring (CEMs) analyzers during the tests, and solid particles were collected and characterized using SEM, energy dispersive spectroscopy (EDS), and x-ray diffraction (XRD).
Combustion Instability Detection Based on Multi-Signal Information Fusion for an Industrial Gas Turbine Combustor
Authors: Fu Yanni , Zhang Yuming , Zang Peng , Sui Yongfeng , Zheng Yao , Xia Yifan
Published: August 2024

Combustion instability is a major challenge for low emission combustors. It is caused by the coupling between the combustor acoustic modes and heat release fluctuations. Early detection of combustion instability is very important for the safety and reliability of gas turbines. In this work, high-pressure and high-temperature experiments were conducted to investigate the thermoacoustic features of an industrial-scale combustor. The combustor contains a pilot burner and a main burner, which adopt diffusion and premixed combustion, respectively. The transition processes of thermoacoustic state from stable to unstable are experimentally studied for different operating pressures. Recurrence quantification analysis (RQA) is used to study the nonlinear dynamics of the dynamic pressure (DP) and acceleration (ACC) signals obtained during the experiments. Based on multi-signal information fusion of DP and ACC, an early detection method of combustion instability is proposed via a machine learning method. The proposed method combines the dynamic behaviors of DP and ACC signals into a two-dimensional map. A support vector machine (SVM) model is used to classify the thermoacoustic states of the combustor. Four cases are used to train the SVM model, while two additional cases are applied to assess the robustness of the SVM-based precursor. Compared to the conventional method based on the root-mean-square (RMS) of the DP signals, the SVM-based precursor achieves an overall accuracy of the early detection of combustion instability in the combustor.
A Method to Develop Radial Inflow Turbine Performance Maps for Off-Design and Dynamic Simulation Studies of sCO2 Cycles
Authors: du Sart Colin , Rousseau Pieter , Laubscher Ryno
Published: August 2024

There is a growing interest in the use of supercritical carbon dioxide (sCO2) Brayton cycles for power generation applications. Consequently, many researchers have developed cycle-only models, or plant models at various levels of detail to study the feasibility of such technologies. In these studies, the turbine model used has a significant effect on the results obtained. Despite this, researchers typically specify a constant isentropic efficiency, or adopt one of the efficiency correlations presented by Dyreby. The former approach is only suitable for steady state design point studies, and the use of Dyreby’s efficiency correlations are limiting. Furthermore, Dyreby’s correlations may be employed without considering the velocities of the fluid, which is critical for the determination of fluid properties throughout the turbomachine. Therefore, neither approach is suitable for off-design or dynamic studies but are applied regardless because of the limited public data available on sCO2 turbomachinery. In this paper, a method is presented that may be used to size a single stage radial inflow turbine for given nominal boundary conditions, and to develop performance maps for the same turbine at off-design conditions. These maps may then be employed to perform off-design and dynamic studies. The method employs a one-dimensional mean-line analysis approach with enthalpy loss correlations and is verified using the performance map of an existing turbine at Sandia National Laboratories. Additionally, case studies are presented where the method is used to produce conceptual designs for turbines for a proposed 50 MWe concentrated solar power plant.
On the Application of Background Oriented Schlieren to a Transonic Low-Reynolds Turbine Cascade
Authors: Halby Alexandre , Cakir Bora Orcun , Da Valle Lorenzo , Lopes Gustavo , Okada Mizuki , Lavagnoli Sergio
Published: August 2024

Qualitative and quantitative visualizations of transonic turbomachinery flows provide essential information on compressibility and Mach number effects on boundary layer development, shock-boundary layer interactions (SBLI) and trailing edge flows. Background Oriented Schlieren (BOS) is a relatively new optical technique that allows capturing unsteady density gradient fields through turbomachinery cascades and thus, quantitative experimental data to validate transonic and supersonic blade designs. However, only very few experimental works in the open literature have successfully applied Background Oriented Schlieren (BOS) to transonic turbine or compressor flows. The current study presents the application of BOS to a transonic low pressure turbine cascade, the VKI SPLEEN C1 cascade for a range of Reynolds numbers (70,000 to 140,000) and transonic Mach numbers (0.90 to 1.00). The linear turbine cascade is tested at the von Karman Institute in the S-1/C high-speed wind tunnel. The test section is instrumented with different BOS optical setups to visualize the time-resolved density gradients through the turbine passage and at the trailing edge plane with dedicated field of views. The BOS images are processed using the classical cross-correlation algorithm, and the optical flow approach, recently introduced in BOS applications to gain spatial resolution and increased sensitivity. Steady-state density gradients of the cascade flow characterize the airfoil boundary layers, wakes and shock waves. The results from the two data reduction methods are assessed and compared against available RANS CFD predictions. Time-resolved measurements reveals the low-frequency motion of weak shock waves generated in the blade passage using POD and spectra analysis.
Optimization of a Novel Design-For-Additive-Manufacturing Film Cooling Hole
Authors: Castelli Niccolò , Picchi Alessio , Facchini Bruno , Winchler Lorenzo , Morante Francesco
Published: August 2024

Additive Manufacturing has been proving a very interesting potential to produce objects having both tiny dimensions and complex and twisted shapes. For this reason, in the last years, many efforts have been done to employ AM techniques to film cooling technique in the turbine blade cooling field. The aim of the present work is to present a methodology aimed to develop a novel diffusive film cooling hole within the framework of Design-for-Additive-Manufacturing. First, starting from a set of fundamental parameters, the hole has been designed as a result of a numerical optimization in order to find out the best trade-off between different needs. Both the discharge coefficient and the adiabatic effectiveness have been evaluated and compared with the well-established 7-7-7 fan-shaped hole in order to quantify the potential of the novel geometry.

Once the numerical procedure ended, one candidate point was selected as the output to be printed by means of a Laser Powder Bed Fusion (LPBF) technique. Flow checks tests were performed on a row of 11 holes per shape and the measured discharge coefficient was found to be far lower than expected. A Computed Tomography analysis showed that the hole internal surfaces and entry/exit section collapsed in some areas. Hence, on the one hand, the numerical procedure and the outcoming shape were validated over an up-scaled flat plate housing the novel holes. Pressure Sensitive Paints measurements were performed in an open-loop wind tunnel for a blowing ratio ranging between 0.25 and 2.00. The adiabatic effectiveness showed a good agreement with CFD data, with the novel hole outperforming the 7-7-7 one. On the other hand, a compensation strategy was developed for the optimized geometries in order to overcome the difficulties encountered by the AM process due to the very tiny dimensions of the hole. After the critical features were identified and fixed by a re-design of the optimized shape, a CFD validation showed a very similar performance compared to first optimization geometry. In the end, the re-designed hole was printed. Flow check tests confirmed a higher discharge coefficient than the original one, while PSP measurements showed an improved effectiveness than the fan-shaped hole.
Techno-Economic Assessment of Hydrogen-Natural Gas Blends for Open Cycle Gas Turbines
Authors: Mogorosi Thuso Booth , Monaghan Rory F. D.
Published: August 2024

Hydrogen’s use at large scale for electricity generation in the current fleet of gas turbines (GTs) could present several technical, economic and environmental challenges, including high flame temperature and flame propagation velocity, potential to produce high levels of nitrogen oxides (NOx), the change in volumetric and mass flow rate, which could affect the overall power output, and the high cost of H2, which will affect the price of generated electricity. The objective of this study was to carry out a techno-economic assessment (TEA) of the use of hydrogen/natural gas (H2/NG) blends in open cycle gas turbines (OCGTs). Two NG-fuelled aero-derivative OCGTs are used as case studies, a 41-MW GE LM6000PA and a 50-MW Mitsubishi FT8 SWIFTPAC, both of which were selected based on survey of the power generation industry in Ireland. The presented method entails two steps: (1) thermodynamic modelling and (2) economic assessment. Thermodynamic modelling is performed using Thermoflex 30.0, with the purpose of evaluating the effects of H2/NG blending on the GT’s electrical efficiency, power output, and CO2 emission intensity. Variables considered for the two OCGTs in this stage are H2 blend volume fractions and GT loads. Economic assessment is then performed in an Excel-based cash flow model, with the purpose of determining the levelized cost of electricity (LCOE) of the GTs operating under different commercial conditions, including H2 and NG prices, CO2 tax, and annual OCGT capacity factor. The results shows that H2 improve the efficiency and power output of the gas turbines. Moreover, H2 blending reduces electricity generation CO2 emissions intensity. However, high LCOE are observed as the H2 blending percentage volume increases because of the current price H2, the LOCE are even higher at lower capacity factor.
CO2-Based Power Cycles: What Effect Does Additive Molecular Complexity Have on the Cycle Layout?
Authors: Aqel Omar , White Martin , Sayma Abdulnaser
Published: August 2024

Since their inception, CO2 power cycles have gained prominence for their superior performance and compactness. However, the efficiency of the simple supercritical CO2 cycle is hindered by relatively large temperature differences in the recuperator, leading to increased exergy destruction. Although complex cycles like the recompression or precompression cycles can reduce recuperator irreversibility, their higher complexity and additional equipment requirements raise the cost of the power plant.

This paper aims to demonstrate that recuperator irreversibility in a simple recuperated transcritical cycle can be alleviated using CO2-based mixtures, without resorting to complex cycles. This is achieved by comparing the efficiencies of simple and recompression cycles using CO2-based mixtures with nine additives of various molecular complexities: H2S, SO2, C3H8, C4H10, C5H12, C6H6, C4H4S, TiCl4, and C6F6. The effect of additive molar fraction (ranging from 0.05 to 0.5) on the efficiency of both cycles is examined.

Thermal efficiency optimisation reveals a correlation between the efficiency difference of the simple and recompression cycles and the molecular complexity of the working fluid. The reduction in recuperator irreversibility is attributed to the decrease in the difference in the isobaric specific heat capacities between the streams in the recuperator with the use of complex additives. Consequently, the advantage of a recompression cycle diminishes as the aggregate molecular complexity of the working fluid increases. Simple additives like H2S, SO2, and C3H8 result in recompression cycles outperforming simple recuperated cycles by 4% to 8% in terms of absolute thermal efficiency, depending on the additive and its molar fraction. Conversely, more complex additives like C4H4S, TiCl4, and C6F6, exhibit thermal efficiencies in simple recuperated cycles comparable to those of recompression cycles. The additive molar fraction at which both cycles achieve similar performances depends on the molecular complexity of the additive; the more complex the additive, the lower the additive molar fraction required to create a complex working fluid. Moreover, the split fraction in recompression cycles exhibits a similar correlation with molecular complexity as observed in the efficiency difference, suggesting that recompression cycles will morph into simple recuperated cycles as molecular complexity increases.

In conclusion, the use of additives provides an additional dimension through which the efficiency of CO2 cycles can be optimised, enabling improved performance without the need for complex cycles.
Development of Thermo-Mechanical Service-Like Testing for Supercritical CO2 Expanders
Authors: Bucciarelli Federico , Checcacci Damaso , Macoretta Giuseppe , Disma Monelli Bernardo , Bertini Leonardo
Published: August 2024

The detailed prediction of the actual life expenditure of expanders operating in power plants has become a common topic of investigation. In the current energy market axial expanders are subjected to frequent load change and to the exposure to higher temperatures. The proper prediction of their life expenditure determines operability and availability improvements through faster start-ups and longer maintenance intervals. A common strategy to achieve this objective has led in the last years towards the development of progressively more and more detailed “service-like” tests aimed at recreating the actual loading conditions in terms of strain and temperature profiles. Recently the need to face the challenge of energy transition through the introduction of advanced cycle employing supercritical carbon dioxide is requiring to further improve this kind of tests by including the effect of environmental attack through corrosion and carburization. This work addresses this topic by presenting the development of customized specimens and of a testing campaign able to evaluate the degradation of creep and fatigue capabilities when high temperature carbon dioxide exposure occurs. After a short introduction on the state of the art, the specimen design will be detailed with FE simulation evaluating stress and temperature distribution in specimens and key insights will be given regarding the design of a proper test matrix and the essential theoretical framework for the interpretation of the results of a testing campaign.
GPU-Accelerated Full-Wheel Large-Eddy Simulations of a Transonic Fan Stage
Authors: Wang Kan , Bose Sanjeeb , Ivey Christopher
Published: August 2024

A single-stage transonic axial-flow fan is simulated using GPU-accelerated wall-modeled large-eddy simulations. The computational meshes are generated using Voronoi-diagram based approach. Two types of mesh are employed for grid sensitivity study. The first type uses isotropic hexagonal close-packed (HCP) seeding whereas the second combines the background HCP mesh with anisotropic boundary-layer type of mesh around the blade surfaces. The effect of the rotor tip clearance is examined using a rotor-only configuration. Sweep of the performance curve at full rotation speed is carried out for both the rotor and the stage. The computational results are compared against the experimental measurement and excellent agreement is observed when adequate near-wall resolution is employed. The code performance of the GPU-accelerated solver is compared to the CPU-based version. The high throughput of the GPU solver significantly reduces the computational cost. On a mesh with 84 million control volumes, 10 rotor revolutions can be computed within one day using 20 GPUs.
LES Analysis of Loss Anomaly of a Turbine Blade With Large Trailing Edge Radius
Authors: Miki Kenji , Ameri Ali , Giel Paul
Published: August 2024

There is great interest in the usage of Ceramic Matrix Composites (CMC) as a turbine blade material. However, depending on the manufacturing process of the CMC, blades may have a thicker trailing edge. The design space therefore needs to be updated due to the resulting flow physics. Recently, experimental results acquired at NASA Glenn Transonic Turbine Blade Cascade Rig showed that a loss measure generally increased with increasing trailing edge thickness. For some cases however, the general downward trend of the loss with increasing Reynolds number was interrupted by a local loss peak around Re ∼1.24 × 106, and then subsequently dropped to the original pre-peak trend. A possible cause of this intriguing phenomenon was speculated to be transonic vortex shedding, which is the mechanism of vortex shedding promoted by reflected shed pressure waves at the trailing edge at relatively high Reynolds numbers and transonic Mach numbers. A Reynolds-averaged Navier-Stokes (RANS) analysis or an under-resolved large eddy simulation (LES) does not reproduce this apparent anomaly and thus a highly-resolved LES (the total mesh count of ∼290 million cells) was performed to investigate the aerodynamics of the CMC blade. The numerical results at Re = 1,246,350 show that the pressure waves generated by the vortex shedding in the wake travel upstream and significantly influence the transition and separation on the suction side thus enhancing the vortex shedding in the wake. This feedback does not hold under a low-Re condition (Re = 621,900). The Reynolds number dependence was also examined by numerical perturbation of the pressure waves in the wake and by examining how such perturbation attenuates or endures. It is confirmed that the perturbation of the pressure waves is quickly damped below a set Reynolds number.
Effect of Variable Stator Vanes With Penny Cavities on the Performance and Secondary Flow of a Single-Stage Axial Compressor
Authors: Chen Shuaitong , Chen Shaowen , Zhang Yimin , Yang Pengcheng
Published: August 2024

The present study focuses on the first stage of the E3 which is a typical variable compressor, comparing its performance with and without pennies. The changes in overall performance from the penny structures are investigated. Furthermore, a detailed analysis is carried out to investigate how the two kinds of gap influences the three-dimensional flow field at the blade tip and the corner separation zone. Using unsteady calculation methods, the flow characteristics and unsteady behavior of two kinds of gap leakage flow caused by the penny structures in the shroud and hub are discussed. The results show that the pennies on the endwalls significantly diminishes overall performance at the design speed, leading to a decline in isentropic efficiency and total pressure ratio by 1.79% and 1.8%, respectively. The secondary flow losses caused by the variable stator vanes structures accounts for 68.6% of the stator losses. Compared with the hub, the momentum rate distribution of penny cavity leakage flow at the casing is stronger and more concentrated, resulting in larger losses and wider influence range. At the same time, the counter-rotating leakage vortex pairs are found in the flow field near the shroud and hub, in which the radial gap leakage vortices have a relatively stable vortex structure in the flow field, while the penny cavity leakage vortices are generated in the form of shedding vortices and then broken into smaller three-dimensional vortices, and dissipate while rotating around the radial gap leakage vortices.
Characteristics of Premixed Ammonia/Methane/Air Blends As an Alternative Fuel in a Swirl-Stabilized Gas Turbine Combustor Under Varying Pilot Percentage
Authors: Das Chaudhury Meghna , Sahoo Abinash , Nonavinakere Vinod Kaushik , Fisher Wesley , Ekkad Srinath V. , Naranaswamy Venkateswaran , Fang Tiegang
Published: August 2024

Alternative low carbon fuel blends are a promising way towards clean energy transition in the transportation and power generation sectors. In this work, the objective was to study the combustion characteristics of one such low carbon fuel blend (premixed Ammonia, Methane and Air) in a swirl stabilized Gas Turbine Can Combustor under varying % of pilot fuel flow (= 8 % to 10 % of the main fuel flow rate) at atmospheric pressure conditions. Pure Methane was used as the pilot flame which helped in the ignition and stabilization of the main flame and was kept on throughout the experiment. Different volume % of Ammonia and Methane blends were analyzed (starting from 10 to 50 % Ammonia in the fuel blend and the rest being Methane) at Reynolds number of the incoming air ∼ 50000, and at equivalence ratio = 0.6 and 0.7. Characteristics such as Combustor liner wall heat load and flame stability were studied using the Infrared Thermography technique and High-Speed flame imaging respectively. Additionally, both carbon and NOx emission trends were estimated for selected cases using the CONVERGE CFD software under steady state conditions incorporating the RANS RNG k-ϵ and SAGE modeling techniques. Among all cases, wall heat load was observed to be the least for the 50 % Ammonia-50 % Methane case and for cases under reduced pilot %. Also, under reduced pilot %, flames were mostly unstable wherein the manifestation of instabilities at equivalence ratio = 0.6 and 0.7 were markedly different from one another.
Performance and Flexibility of the DLN 2.6e Combustion System on the 7HA.03 Gas Turbine
Authors: York William D. , Cai Jun , Stoia Lucas J.
Published: August 2024

At GE Vernova, the newest advanced dry-low NOx (DLN) combustion system for HA gas turbines is the DLN 2.6e. After describing the key enabling features of the DLN 2.6e, this paper focuses on the emissions performance and operational flexibility of the combustion system on the 7HA.03, currently GE Vernova’s most efficient gas turbine in the 60 Hz electric power generation segment. While some full-scale, single-can lab results are presented, the primary focus of this manuscript is the performance on natural gas fuel from the testing of three 7HA.03 gas turbines, one at the GE Vernova full-load test stand and two at a commercial generating facility.

The DLN 2.6e is a can-annular, lean premixed combustion system. The advanced premixer at the head end efficiently mixes fuel and air in straight tubes, which are arranged in three fueling circuits. Additionally, the DLN 2.6e system has four axial fuel staging injectors located in the downstream half of the combustion liner, split into two fueling circuits. At high load, the axial fuel stage creates a secondary combustion zone with a substantial fraction of the total energy release and with a low residence time to the combustor exit plane. These features, along with the efficient premixing at the head end, enable the system to achieve below 25 ppm NOx at 15% O2 at the high firing temperatures of the 7HA.03. From full load, the combustor exit temperature may be lowered to attain 5 ppm NOx at 15% O2 before lean blow out occurs. At low loads, the fuel flow to one of the two axial fuel stage circuits may be eliminated, enabling the system to achieve less than 25 ppm NOx at 15% O2 and 9 ppm CO emissions down to near 15 percent of gas turbine full load.

7HA.03 engine data is presented showing low combustion dynamics and little change to emissions when running with cold fuel, representing a 22 percent increase in modified Wobbe index compared to the heated fuel design point. The combustion and control systems support accelerated load ramping. A 7HA.03 gas turbine was demonstrated to progress from ignition to full load in around ten minutes. Finally, the DLN 2.6e has been demonstrated in lab testing to be operable with up to 50% hydrogen by volume in the fuel, and an associated increase in NOx emissions was observed.