bluuebunny/crossref_metadata_2025_split huggingface dataset:
Windage Torque Reduction in Low-Pressure Turbine Cavities Part 2: Experimental and Numerical Results
Authors: Jackson Richard , Lock Gary D. , Sangan Carl M. , Scobie James A. , Li Zhihui , Christodoulou Loizos , Jefferson-Loveday Richard , Ambrose Stephen 
Published: September 2023

Abstract
Minimizing the losses within a low-pressure turbine (LPT) system is critical for the design of next-generation ultra-high bypass ratio aero-engines. The stator-well cavity windage torque can be a significant source of loss within the system, influenced by the ingestion of mainstream annulus air with a tangential velocity opposite to that of the rotor.
This paper presents experimental and numerical results of three carefully designed Flow Control Concepts (FCCs) — additional geometric features on the stator surfaces, which were optimized to minimize the windage torque within a scaled, engine-representative stator-well cavity. FCC1 and FCC2 featured rows of guide vanes at the inlet to the downstream and upstream wheel-spaces, respectively. FCC3 combined FCC1 and FCC2. Superposed flows were introduced to the upstream section of the cavity, which modelled the low radius coolant and higher radius leakage between the rotor blades. In addition to torque measurements, total and static pressures were collected, from which the cavity swirl ratio was derived. Additional swirl measurements were collected using a five-hole aerodynamic probe, which traversed radially at the entrance and exit of the cavity.
A cavity windage torque reduction of 55% on the baseline (which has no flow control) was measured for FCC3, at the design condition with superposed flow. For this concept, an increase in the cavity swirl in both the upstream and downstream wheel-spaces was demonstrated experimentally and numerically. With increasing superposed flow, the contribution of FCC1 surpassed FCC2, due to more mass flow entering the downstream wheel-space across the rotor fins (passing FCC1), and less ingestion from the annulus into the upstream wheel-space (passing FCC2). The torque changes from the concepts are explained using the fluid dynamic evidence from experimental swirl measurements and computational simulations. The simulations allow translation to engine-operating conditions and practical information to the engine designer.
Hysteresis Effect of Volute on Compressor Performance Under Pulsating Flow Condition
Authors: Hayashi Yoshihiro , Parikh Aakeen , Barrera-Medrano Maria Esperanza , Martinez-Botas Ricardo 
Published: September 2023

Abstract
Centrifugal compressors for turbochargers are affected by pressure pulsations, generated by the engine valvetrain. It results in a hysteresis loop on a compressor performance map, and the time-averaged performance deviates from the one in constant pressure condition. Since regulations of greenhouse gas emissions are tightening, achieving higher turbocharger efficiency in real-operating conditions is essential. Therefore, understanding of loss mechanisms in pulsating pressure conditions is crucial.
A high number of studies far have contributed to revealing the effects of pulsation on compressor performance. However, numerical investigations of unsteady flow structure in a volute are still lacking, and there are only some validated examples by measurement.
This paper presents a comprehensive experimental and numerical study that sheds light on the pulsating flow field in the volute. An instantaneous and time-averaged pressure signal inside a volute has been captured by measurement. A numerical simulation with Unsteady Reynolds Averaged Navier-Stokes equations has been carried out. Pressure distributions from the simulated results has shown good consistency with experimental results.
Leading off from the validated simulation results, the instantaneous velocity distribution and energy loss profile have been obtained. It can be seen that the flow direction is switched around the volute tongue when the volume flow rate reaches the maximum value. This phenomenon leads to different flow patterns depending on whether the flow rate increases or decreases. When the volume flow rate turns to decrease from the maximum value, the switched flow direction leads a leak flow from the tongue to the volute exit. The total pressure of this flow significantly decreases when it passes the tongue, and it finally appears as the low-energy fluid at the volute exit. It causes a notable blockage, and consequently leads to an additional friction loss. Due to these effects, the energy loss of volute increases from the steady flow condition.
Influence of Variable Swirl on Emissions in a Non-Premixed Fuel-Flexible Burner at Elevated Ambient Conditions
Authors: Pugh Daniel , Bowen Philip , Navaratne Rukshan , Goktepe Burak , Giles Anthony , Valera Medina Agustin , Morris Steven , Vivoli Robin 
Published: September 2023

Abstract
As alternative fuels are designated for future energy applications, flexible combustor designs require considerable development to ensure stable operation with reduced NOx emissions. A non-premixed variable swirl burner was used to experimentally appraise changes in NO production pathways, with CH4 NH3, and H2 flames, alongside intermediate fuel blends. Maintaining an equivalent thermal power and flame temperature between fuels, preheated reactants (500 K) were supplied to the burner, with parametric changes made to pressure (1–6 bara) and swirl number (0.8–2.0). NO production was characterized, alongside variations in flame structure and topology, with a correlation demonstrated for exhaust emissions. NO production was shown to be sensitive to combustor pressure, providing an expected increase for CH4 and H2 flames. Emission profiles from both NH3 and H2 flames are shown to be significantly augmented by a change in swirl number. As NH3 fractions were increased in the H2 blend, a decaying trend in NO emissions was observed with an increase in pressure, and as a function of mixture ratio. However, this behaviour was markedly augmented by a change in swirl number and suggests that further reductions may be possible at increased pressure. At the low swirl/high pressure condition the NH3/H2 blend outperformed pure H2, providing lower NO concentrations. Emissions data were normalised using the traditional dry/O2 correction, alongside mass scaled by thermal power, with a comparison provided. The corresponding differences in emission formation pathways were investigated, alongside high-speed OH* chemiluminescence to further elucidate findings.
Experimental Measurements of Flow-Averaged Toroidal Vortices in Buoyancy-Dominated Rotating Cavities
Authors: Fox Emma C. , Puttock-Brown Mark R. 
Published: September 2023

Abstract
The flow structures and heat transfer within rotating cavities of aero-engine axial compressors influences the thermal expansion of the rotor discs, and consequently the blade-tip clearances. To investigate the flow field at the bore and lower cavity region, experimental measurements have been acquired in an engine representative test facility. Axial, tangential and radial velocities were measured using a miniature five-hole probe at a range of axial and radial positions. Time-averaged results from 28 tests carried out at non-dimensional parameters comparable to engine conditions: 1.3 × 104 ≤ Rez ≤ 8.2 × 104, 3.0 × 105 ≤ Reθ ≤ 3.2 × 106, 0.11 ≤ Ro ≤ 3.24, 0.14 ≤ βΔT ≤ 0.37 are presented in this paper.
The axial and tangential velocity measurements conform to previous work, while the radial velocity component provides quantitative evidence of an asymmetric toroidal vortex in the cavity gap, biased towards the downstream disc. The vortex is characterised by the local vorticity and grows in strength and size as Rossby number increases above Ro = 0.34 to 1.63. The effect of βΔT on the vortex formation is negligible compared to the influence of the tangential Reynolds number as the local circulation is suppressed by the Coriolis forces at high rotational speeds. Both the tangential and radial velocity results suggest that as Ro is increased, the proportion of air that is radially ingested and expelled from a cavity decreases.
Heat Transfer Coefficient and Adiabatic Effectiveness Measurements on a Nozzle Guide Vane With a Single Row of Cylindrical Holes
Authors: Galeotti Sofia , Bacci Tommaso , Picchi Alessio , Facchini Bruno , Cubeda Simone 
Published: September 2023

Abstract
Film cooling injection significantly affects the thermal behaviour of turbine vane surfaces. In addition to the beneficial effect of the film shielding the vane from the hot gas flow, alteration of the thermal boundary layer should also be taken into account. The aim of the present work is to detail the film cooling performance in terms of adiabatic effectiveness and external heat transfer coefficient on a 2D nozzle guide vane.
A single row of cylindrical holes was tested on both pressure and suction side of a literature vane, the VKI LS89, in a linear cascade. The employed measurement technique is a transient thermal method based on IR thermography, which was thoroughly described and validated in a previous work. The influence of inlet free stream turbulence and blowing ratio was evaluated, and two different injection angles were considered for both pressure and suction side. Spatially resolved distributions of adiabatic effectiveness and heat transfer coefficient on the vane surface allow to precisely quantify the above mentioned aspects and highlight qualitative differences between pressure and suction side behaviour. Details regarding the generated non-uniformities in the measured parameters could be also provided, to emphasize how average quantities are not always sufficient to characterize such complex phenomena. The impact of different reference conditions to scale HTC results was also investigated. Such effect was found not negligible on the overall performance of the film cooling system, especially on the suction side where transition plays a critial role.
Ultimately, the collected results constitutes a wide and detailed experimental database for numerical modeling validation in a well-studied environment as the LS89 configuration.
Thermoacoustic Characterization of a Swirl Premixed Flame Using Doak’s Momentum Potential Theory
Authors: D’Aniello Raffaele , Gövert Simon , Janus Bertram , Knobloch Karsten 
Published: September 2023

Abstract
This study proposes a novel approach, based on Doak’s Momentum Potential Theory, for the characterization of the thermoacoustic behavior of turbulent premixed flames. The novel approach has the following two advantages: firstly, an unambiguously separation of acoustic, thermal and turbulent dynamics is achieved by means of a Helmholtz decomposition of the momentum fluctuations density; secondly, the development as well as the interaction between the different dynamics are related to the fluxes of turbulent, acoustic, and thermal mean energies, which can be identified in the fluctuating stagnation enthalpy. The Momentum Potential Theory is applied here for the first time to describe the thermoacoustic behaviour of a confined turbulent flame, represented by large-eddy simulation data of a premixed CH4/Air model combustor. Interaction and energy exchange mechanisms between the fluctuations are analyzed in order to show the potential of the theory as a general framework for the characterization of thermoacoustic problems.
Best Practices for Electricity Generators and Energy Storage Optimal Dispatch Problems
Authors: Vasylyev Andriy , Vannoni Alberto , Sorce Alessandro 
Published: September 2023

Abstract
The growing share of renewable energy sources in the energy mix and the liberalization of electricity markets has drastically affected the operation of electricity generators. Especially, in the last decade, fossil fuel-based generators have shifted their role from providing continuous base load to covering the peak demand and providing backup capacity to stabilize the grid. At the same time, a large amount of storage capacity is foreseen to be integrated into electricity grids in the coming years to shave demand peaks, mitigate price volatility and provide services to the grid. In such a situation, in order to properly manage these crucial technologies, and thus guarantee the economic viability of the operation, it is essential to properly optimize the dispatch and define the best scheduling. This paper considers a Gas Turbine Combined Cycle and Battery Energy Storage to study the problem of dispatch optimization of both generators and storage technologies. Different optimization algorithms have been considered and Mixed Integer Linear Programming is selected for its ability to identify the global optimum and the reduced optimization time. The impact of optimization windows (i.e., the forecast horizon of electricity prices) is also investigated. It is highlighted that an increase in forecasting ability, at least up to 36h, guarantees more effective scheduling; on the other hand, it may require a significantly longer time. Subsequently, different approaches to account for the operation and maintenance costs at the optimization stage are assessed, and, finally, a sensitivity analysis is carried out with respect to market parameters (price average and variability) and technology features (conversion efficiency, cycle cost, etc.).
Study on Secondary Flow Phenomena With Variable Leading Edge Fillet and Endwall Contouring on the Low-Pressure Turbine Vane Linear Cascade
Authors: Darji Anand P. , Baloni Beena D. , Mistry Chetan S. 
Published: September 2023

Abstract
Detailed understanding of the secondary flow field is crucial for reducing low-pressure turbine losses. With the aid of numerical tools, it is possible to investigate, understand and develop triggering methodologies that reduce endwall losses. The present study explores passive control techniques to examine their impact on endwall losses.
The two-section paper discusses the effect of three different fillet configurations on endwall secondary flows in the first part. The second section explores the impact of the optimized non-axisymmetric endwall (NAEW) profile and fillet structures on the secondary flow field. The study is performed for design incidence where steady-state RANS-equations are solved using an SST γ-θ turbulence model with low turbulence intensity for linear low-pressure turbine vane cascade at chord exit Reynolds number of 1.6 × 105. A successful attempt was made to reduce the passage vortex (PV) effect within the passage region. According to the study, among all three fillet alone configurations, fillet-2 was found to be the most suitable design. Furthermore, the comparative study found that optimized NAEW with fillet-3 reduced the loss coefficient by 8%, while optimized NAEW alone reduced the loss coefficient by 11.64%.
The Structure and Stability of Premixed CH4, H2, and NH3/H2 Flames in an Axially Staged Can Combustor
Authors: Ånestad Aksel , Sampath Ramgopal , Moeck Jonas , Gruber Andrea , Worth Nicholas A. 
Published: September 2023

Abstract
An experimental investigation of flame structure, stability, and emissions performance was conducted in a two-stage lab-scale generic combustor design operated with CH4, H2, and NH3/H2 fuel blends. The main flame zone features a premixed bluff body stabilized flame, with a secondary flame zone initiated downstream by injecting premixed air and fuel using two opposing radial jets. The total power and air flow rate are kept constant between the different fuelling cases, while the air split between stages and equivalence ratios are varied to explore conditions relevant to gas turbine operation. Given the relative novelty of the configuration, special emphasis is given to analysing the structure of the opposing jet flames in the secondary stage. In contrast to previous literature on reacting jets in cross flow, these interact significantly due to their proximity, leading to a merged flame zone at the impingement location in the centre of the combustion chamber, and some flame propagation upstream of the jet location. As the jet-to-crossflow momentum ratio increases, the merged flame zone changes shape, reaching close to the walls for the methane cases, but remaining very compact when operating with almost pure hydrogen. For the hydrogen flames, diverting more air to the second stage allows higher total thermal power conditions to be reached, while avoiding flashback, and eliminates thermoacoustic instabilities. For ammonia-hydrogen flames, air is diverted to the second stage, while a constant fuel flow is sent to the primary stage, resulting in some locally rich conditions in the primary flame. A local minima in terms of NOx occurs when the primary flame is operated at an equivalence ratio of 1.15. Analysis of the flame structure suggests that this state corresponds to almost complete combustion or pyrolysis of NH3 in the main flame, with the remaining hydrogen burned in an inverse diffusion flame in the secondary zone.
Numerical Investigation of Friction Induced Interaction of Flutter Modes in a Realistic LPT Rotor
Authors: Rodríguez-Blanco Salvador , González-Monge Javier , Martel Carlos 
Published: September 2023

Abstract
Flutter response of bladed disks is a quite important problem in modern designs of low pressure turbines, but, even for tuned configurations, it is not fully understood yet. Some research work suggests that, in a tuned rotor, the flutter induced vibration state that sets in consists of just a single traveling wave mode, while others show flutter states composed of several traveling waves active at the same time. Many of these studies were performed using conceptual models, such as mass-spring systems or asymptotically reduced models. In this work, a high fidelity bladed disk model is integrated in the time domain for the case of a realistic aerodynamically unstable low pressure turbine. In this configuration, the only nonlinear effect is the friction present at the blade disk attachment, which is responsible for the saturation of the flutter growth, and it is also the only mechanism that allows the interaction among the different unstable traveling wave modes. A case with multiple unstable modes of the same modal family is studied first. After that, the study is extended to a case where modes of different modal families are unstable and have similar aerodynamic instability levels. The interaction of unstable modes from different modal families is studied, we believe, for the first time, as previous flutter analyses were restricted to the interaction of unstable modes from the same family.
Hydrogen-Enriched Natural Gas Co-Firing: A Comparison of FGM and EDC Models
Authors: Zhao Rang , Igie Uyioghosa , Abbott David 
Published: September 2023

Abstract
To facilitate the transition from natural gas to a future hydrogen economy, the combustion of natural gas/hydrogen blends in gas turbines will play an important role in power generation. The influence of hydrogen content on technically premixed swirl-stabilized flame using large eddy simulation has proven to be powerful but with high computational costs. Hence, RANS-based models are useful for preliminary investigations and sensitivity studies. Flamelet Generated Manifold (FGM) and Eddy-Dissipation Concept (EDC) are two widely used RANS-based combustion models. EDC, in particular, accounts for the interaction between chemistry and turbulence using detailed chemical mechanisms, but at the cost of higher computational resources. FGM preprocesses the flamelet as a function of mixture fraction and progress variable and pre-integrates the chemistry-turbulence interaction into a Probability Density Functions (PDF) table, which makes FGM computationally inexpensive. This study aims to compare the predictions of these models with experimental data of a methane-fueled technically premixed swirl-stabilized low-pressure burner. The better-performing model is used to evaluate the influence of methane and hydrogen blends (up 40% by volume) in a higher-pressure burner also validated with experiments. The study has shown that EDC produces better agreement with the experimental data than FGM in estimating the flame temperature, flow velocity, and carbon dioxide profiles. FGM did not correctly capture the flame pattern and overestimated the reaction rate. This is possibly due to its simplified preprocessed chemistry mechanism, which could not evaluate the local thermal properties of the gas mixture properly. For the higher pressure evaluation at 5 bar, the EDC model captured the influence of hydrogen content addition on flame behaviour. As the hydrogen content increased, the chemical reaction rate increased, and the flame length indicated by OH decreased. This reduction in flame length is consistent with the experimental results. The CFD showed that at 20% H2, the change in NOx emission compared to 100% methane is negligible using the mass of NOx per unit of heat release calculation. A slight increase in NOx is shown for the same case using the concentration by volume corrected to 15% O2 approach. Nevertheless, both approaches showed NOx reductions at 40% H2. This study has shown that the behaviour of a technically premixed swirl-stabilized flame-firing methane/hydrogen blend is well represented by a non-adiabatic RANS-EDC model with low computation cost. This confirms its applicability in evaluating acceptable lean premixed burners characteristics for gas turbines.
Techno-Economic Analysis of the Solid Oxide Semi-Closed CO2 Cycle and Comparison With Other Power Generation Cycles With CO2 Capture
Authors: Martinelli Matteo , Scaccabarozzi Roberto , Gatti Manuele , Campanari Stefano , Martelli Emanuele 
Published: September 2023

Abstract
This work presents the techno-economic analysis of the Solid oxide semi-closed CO2 cycle (SOS-CO2), a hybrid sem-iclosed cycle with solid oxide fuel cells (SOFC) recently de-veloped by Politecnico di Milano for power generation from natural gas with high efficiency and near-zero CO2 emis-sions. All the cycles components, including the fuel cell and the turbine, have been designed and sized with the aim of assessing the performance and the capital cost. The performance and the economic key performance indicators are compared with those of two benchmark technologies for power generation with CO2 capture: the Allam cycle and a combined cycle equipped with ammines for post-combustion capture. Moreover, a sensitivity analysis is performed on the cost of the natural gas and the SOFC stacks. The results indicate that the specific total capital requirement of the SOS-CO2 cycle (2500 €/kWel) is higher than the Allam cycle (1930 €/kWel) and combined cycle with post-combustion capture (1980 €/kWel). On the other hand, the SOS-CO2 cycle benefits from its higher efficiency (74.0% vs. 53.9% of the Allam cycle and 52.8% of the combined cycle) which makes the cycle less sensitive to the fuel cost and CO2 tax. In terms of cost of electricity, the SOS-CO2 cycle turns out to be the best technology for natural gas prices above 8 €/GJ, while the Allam cycle appears to be the preferred option at lower fuel prices. For a fuel cost of 12 €/GJ, the SOS-CO2 features a cost of electricity of 106.2 €/MWh, lower than the Allam cycle (119.1 €/MWh) and the NGCC (126.9 €/MWh).