bluuebunny/crossref_metadata_2025 huggingface dataset:
Scaling of Lean Aeronautical Gas Turbine Combustors
Authors: Gövert Simon , Gruhlke Pascal , Behrendt Thomas , Janus Bertram
Published: September 2023

A numerical procedure is presented for the scaling of lean aeronautical gas turbine combustors to different thrust classes. The procedure considers multiple operating points and aims for a self-similar flow field with respect to a reference configuration. The developed scaling approach relies on an optimization-based workflow which involves automated geometry and numerical grid generation, unsteady Reynolds-averaged Navier-Stokes (URANS) simulations and post-processing of the reacting flow field. Kriging is applied as a meta model to identify new sets of parameters for combustor geometry generation. A generic lean-burn high pressure aeronautical combustor has been designed to serve as a first verification test case with reactive flow characteristics comparable to real combustion chambers. The burner geometry is parameterized by 23 free parameters which are altered within the scaling process. The definition of a suitable scaling function is essential for the success of the scaling approach. A scaling function based on pressure loss, axial location of heat release, pilot air split and the temperature profile at the combustor exit is proposed. The developed procedure is tested and applied for the scaling of an internally-staged lean combustor to a lower thrust class considering multiple operating points simultaneously. In total, 65 different combustor variants have been evaluated by the scaling procedure. Simulations were performed for each of these configurations at take-off, approach and idle operating conditions. The final combustor configuration, scaled to a lower thrust class, shows good agreement to the reference configuration in terms of the scaling targets and reasonably resembles the emission indices. Integrating the scaling procedure into the design process of future combustion systems could reduce the required design iterations and thereby contribute to significantly reduced development times and costs.
Numerical Modelling of Swirl Stabilised Lean-Premixed H2-CH4 Flames With the Artificially Thickened Flame Model
Authors: Castellani Simone , Nassini Pier Carlo , Andreini Antonio , Meloni Roberto , Pucci Egidio , Valera-Medina Agustin , Morris Steven , Goktepe Burak , Mashruk Syed
Published: September 2023

The lean premixed technology is a very convenient combustion strategy to progressively move from natural gas to high hydrogen content fuels in gas turbines limiting the pollutants emissions at the same time. The enabling process that will allow the combustor to manage a full H2 operation requires relevant design modifications, and in this framework, the numerical modelling will be a pivotal tool that will support this transition. In this work, high-fidelity simulations of perfectly premixed swirl stabilized flames have been performed varying the H2 content in the fuel from 0 to 100% to investigate the effect of the hydrogen addition on the methane flame. The artificially thickened flame model (ATFM) has been used to treat the turbulent chemistry interaction. The numerical results have been compared with the detailed experimental data performed at Cardiff University’s Gas Turbine Research Centre. After the numerical model validation against experimental OH* chemiluminescence maps has been presented, a deep numerical investigation of the effect of the H2 addition on the flame has been performed. In this way, the work aims to highlight the good prediction capability of the ATFM, and, at the same time, highlight the change in the different contributions that govern the flame reactivity moving from 100% CH4 to 100% H2 in very lean conditions.
Multidisciplinary Optimization of a High-Speed Low Pressure Turbine Rotor Using 3D Inverse Design Method
Authors: Zhang Luying , Zangeneh Mehrdad
Published: September 2023

The design of high-speed low-pressure turbine (LPT) is challenging due to the mechanical constraints and the increased Mach number. A tradeoff has to be made between the aerodynamic performance and structural integrity. This was previously done through iterations with computational fluid dynamics (CFD) simulations and Finite Element Analysis (FEA). In this paper, a fast automated optimization workflow using a 3D inverse design method coupled with a multi-objective genetic algorithm is presented. The inverse design method generates the blade geometry for a given specification of blade loading parameters and spanwise work distribution. It can explore a large design space with fewer design parameters compared to direct design methods where the blade geometries are parameterized by geometrical variables. The maximum thickness and stacking can also be varied during the optimization. Both the blade geometry and the 3D inviscid flow field are provided by the inverse design solver. The aerodynamic performance can be related to the loss factors (such as profile loss, leakage loss and endwall loss) calculated from the blade surface velocities. The centrifugal and bending stresses are related to the blade geometry features. These can be optimized in the automated workflow without running time consuming CFD and FEA. This fast design optimization process is applied to a high-speed LP turbine for aeroengine applications. CFD and FEA are only used to validate the output from the fast optimization process and the results show improvement in efficiency without any increase in stresses.
Temperature Effect on Solid Deposit Formation in Turbine Lubricants
Authors: Juárez Raquel , Gutierrez Noble , Petersen Eric L.
Published: September 2023

When exposed to extremely high temperatures, oils in turbomachinery applications can degrade until they form solid, carbonaceous coke deposits that can cause serious operational issues. Three of the main factors that affect the coke formation process are temperature, residence time, and oil composition (basestock and additives). This study explored the effect of surface temperature on the coking induction time of four turbine oils. The induction time is defined as the amount of time required for deposits to start forming and accumulating under specific test conditions. Experiments were conducted at maximum measured surface temperatures that ranged between approximately 430°C to 540°C. It was confirmed that increasing the surface temperature results in an exponential increase of the oil degradation rate (or an exponential decrease in induction time). Using the Arrhenius relation, the ratio of apparent activation energy to ideal gas constant, Ea/Ru, was calculated for two different definitions of test temperature. These activation energies ranged from 12,900 to 46,800 K. These values, which are related to the oils’ resistance to thermal breakdown, may be used to predict how an oil will perform under specific operating conditions. It was found that three of the four oils performed similarly, while the remaining one had an inferior performance. Future studies should explore the effect of more factors, such as residence time, exposure to oxygen, and heated-surface geometry, on the induction time.
On the Influence of Bearing Modeling Details on the Dynamical System Effects of a Mid-Size Turbocharger Rotor
Authors: Zobel Arthur , Fuhrer Christopher , Vogt Damian M. , Nakos Alex , Beirow Bernd , Blessing Alexander , Zippack Carolin
Published: September 2023

The investigation of the excitation of turbocharger rotors to quantify the High-Cycle-Fatigue (HCF) risk is still a demanding task nowadays. The common way to investigate such phenomena is to look either at the turbine or the compressor rotor in an isolated manner. This approach gives mostly reliable results, if the investigated excitation pattern is stemming from the up- or downstream parts in the machine. However, there is a lack of studies on the existence of responses, which may exist due to the coupling between compressor and turbine. With the increase of computational capabilities and the improvement of FE tools, it is possible to create a full rotor model featuring the compressor and the turbine wheel as well as the bearings to investigate the dynamical behavior of the full rotor at different resonances.

To carry out such an investigation, both wheels and the shaft are modeled. The axial, as well as the radial bearings, are modelled realistically by suitable elements and values. Due to the asymmetry of damping and stiffness properties, the resulting system matrices are asymmetrical as well. The eigenfrequencies and mode shapes of such a system can be obtained in a reasonable time by carrying out a modal analysis using the QR damp eigensolver in Ansys APDL.

The present paper will show the differences in dynamical system effects of a mid-size turbocharger with different shaft support conditions. For this purpose, the FE simulation with the full rotor and fixed support at the radial bearing position, which is comparable to the isolated rotor consideration, will be compared to the model featuring the detailed bearing modeling with stiffness and damping values originating from the OEM. Besides the detailed process of modeling the bearings, the mutual influence of both rotor wheels at certain eigenfrequencies is analyzed. This allows to conclude on the level of detailing needed to ensure that dynamical system effects are properly accounted.
Pressure Actuated Leaf Seal Design and Test for sCO2 Applications
Authors: Grondahl Clayton , Armstrong Rich
Published: September 2023

Interstage shaft leakage in sCO2 turbomachinery is challenged by high differential pressure, high speed and relatively small shaft diameters where secondary seal leakage flow of conventional seals can adversely impact performance. With several programs now focused on sCO2 power conversion cycles, sealing solutions need to be advanced in their TRL to facilitate commercial applications. To this end, Sandia National Laboratories is working with industry partners to identify and test solutions. Pressure actuated leaf seals is one of the technologies identified with significant application potential. They are well suited to meet these challenges with designs capable of high differential pressure, high speed and favorable rotor dynamics owing to their short axial length without cross-coupled stiffness hazard. Thin sheet metal seal leaves passively close with system differential pressure after transition through shaft modes that can damage fixed seals. These seals have been applied in one sCO2 development application to date. To evaluate their use in sCO2 power conversion cycles with advanced nuclear reactors now under development two seal configurations were designed and fabricated for test in the Sandia Brayton Energy Laboratory at differential pressure of up to 3,000 psid (207bar) and maximum shaft speed of 40,000 RPM. Features of both configurations are discussed. Prior to dynamic testing at Sandia National Laboratories, a static test of each seal configuration was conducted at CMG Tech using high pressure water to confirm pressure actuated seal closure and assess interleaf seal leakage. Test results of measured seal leakage is discussed. Successful demonstration of pressure actuated leaf seal function and low leakage flow in static testing provides a confident starting point for dynamic testing in the Sandia sCO2 test facility. Demonstration of Pressure Actuated Leaf Seals technology readiness for extreme sCO2 conditions advances their consideration for use in a broad range of turbomachinery including gas and steam turbine shaft sealing, compressor interstage sealing, and pump wear rings.
The Effect of Trailing Edge Grid Resolution in Large-Eddy Simulations
Authors: Miki Kenji , Ameri Ali
Published: September 2023

Ceramic Matrix Composite (CMC) with environmental barrier coating can tolerate significantly higher temperatures compared with the conventional metal alloy blades and thus can help achieve higher thermal efficiency in gas turbine engines. Due to the complex fabrication process of CMC blades, larger blade trailing edge thicknesses and larger leading-edge radii of curvature are expected. These features significantly alter aerodynamic performance especially near the trailing edge and thus the loss profile. In previous studies, the authors used large eddy simulation (LES) as well as the Reynolds Averaged Navier-Stokes (RANS) coupled with an intermittency function-based transition model to simulate aerodynamic performance of three different CMC blades and compared the predictions against the data acquired at NASA Glenn Transonic Turbine Blade Cascade Rig. Although these were able to successfully predict different characteristics of aerodynamic performance among three different blades (e.g., pressure loading and integrated losses), LES consistently predicted a small recirculation bubble at the end of the suction side. This was not inconsistent with the physics of the flow, but the pressure loading, locally, near the trailing edge, and as a result, the measured wake profiles did not match the experimental data. To delve further into these issues, a new LES grid with a much finer mesh near the trailing edge was generated. The spanwise extent of the grid was increased by 50% at the same time to accommodate large vortices which might not have been captured by the original domain due to size limitations. An LES simulation for the CMC blade with the largest trailing edge thicknesses at the high-freestream turbulence (Tu = 13%) condition showed that using such a mesh is necessary for LES to accurately capture the transition phenomena on the suction side. The resulting total pressure coefficient profile and the shift of the wake profile were greatly improved. The increase in the span was found to be inconsequential.
Techno-Economic Analysis of a Physisorption-Based Hydrogen Storage System
Authors: Schueler Yannik , Otto Marcel , Kapat Jayanta , Schmitt Joshua
Published: September 2023

Alternative long-term storage of energy is becoming increasingly important due to climate change. Hydrogen-based storage technologies have long been considered promising alternatives to batteries. However, the different forms of hydrogen storage have various disadvantages and are still comparatively expensive. As an alternative, this paper deals with a new concept for hydrogen storage, the Cryogenic Flux Capacitor (CFC). It is intended as an intermediate between high-pressure and liquid storage to exploit the advantages and reduce the disadvantages. This paper ranks the CFC technology against the others. For this purpose, it investigates the economic viability and the specific application as a grid-connected system. A complete system from hydrogen production and storage to conversion into electrical energy is considered. In detail, the costs for storage and storage time are compared, and the size scaling of a CFC-based system as a grid-connected system is examined. The Levelized Costs of Energy (LCOE) is calculated and compared as a benchmark. It turns out that a CFC-based storage system also requires a tremendous amount of energy in the form of liquid nitrogen and the associated operational costs for cooling down the hydrogen. Nevertheless, the overall operating costs are between high-pressure and liquid hydrogen storage. Most surprising is the LCOE, which at 0.192 $/kWh-0.234 $/kWh, is well within the range of the other storage technologies. As a grid-connected storage system, CFC technology can be used as a small to a medium-scale energy storage system, e.g., to serve smaller neighborhoods.
Numerical and Experimental Evaluation of Noise and Performance in UAV Propellers
Authors: Serrano José R. , García-Tíscar Jorge , Quintero Pedro , Ramírez Federico N.
Published: September 2023

Due to the increasing use of unmanned air vehicles (UAVs) for civil and military purposes, accurate evaluation of this kind of aircraft is becoming a fundamental aim during their development. Particularly, propellers are often the most critical elements influencing a UAV’s performance and noise emission. Therefore, selecting the appropriate tools for modeling the behavior of this element becomes crucial, especially at the design stages, evaluating both their accuracy and cost. In this paper, we will test the suitability of different tools for numerical modeling and perform an experimental campaign to validate the numerical results.

Particularly, from the computational point of view, the performance of a typical propeller will be evaluated for various values of the advance ratio and various rotational speeds at hover, paying special attention to the thrust and thrust coefficient. Various modeling approaches will be analyzed in this sense, including low-order Blade Element Momentum Theory (BEMT) evaluation, Reynolds Averaged Navier-Stokes (RANS) methodologies (both stationary using a moving reference frame and transient), and transient Detached Eddy Simulations (DES), to analyze the turbulent structures arising in these devices. Noise emission will be evaluated at the most significant working conditions by applying a Ffowcs-William & Hawkings approach to the computed unsteady results and a simplified Farassat formulation to the BEMT results. These numerical calculations will be carried out using open-source software such as OpenFOAM and libAcoustics in the case of CFD modeling or in-house codes for low-order models.

Regarding experimental validation measurements, the hovering propeller’s thrust and far-field acoustic measurements will be performed in an anechoic chamber. The experimental setup will also be mounted in a wind tunnel for forward flight tests and to validate the performance results at different advance ratios. Furthermore, rapid prototyping is a necessary part of the development process for small propellers; thanks to progress in additive manufacturing (AM), this could even become the preferred way to manufacture in-house spares. In this paper, we will also assess the suitability of Fused Deposition Modeling — one of the most popular AM techniques — for manufacturing research propeller prototypes by comparing the propulsive and acoustic performance of a commercial propeller against its 3D-printed version.
Numerical Investigations of Transitional SBLI on a Highly Loaded Transonic Compressor Passage
Authors: Kahraman Selin , Bourgeois Jason A. , Janke Christian , Swoboda Marius
Published: September 2023

The present paper focuses on the adverse effects caused by transitional shock wave boundary layer interaction (SBLI) on a highly loaded variable stator vane (VSV) at altitude. The VSV section under investigation is representative of business jet applications. A new design solution is proposed, which mitigates the limiting effects of transonic speeds. An optimization study has been carried out at multiple mission points. Reynolds numbers (Re) of 750k and 200k (respectively sea-level and altitude conditions) have been investigated numerically at multiple operating speeds. At higher Mach numbers, due to strong transitional SBLI effects, the vane passage is choked by the shock wave moving rearward at Re 200k. This phenomenon, which is only observed at altitude conditions, results in significantly increased losses and a reduced working range. The new section design alleviates these detrimental effects by decreasing the acceleration in the front portion of the suction surface, controlling the shock location. The losses are significantly reduced, and the choking limit is increased to M = 0.903 at over-speed. In this condition, amultiple-shock structure is introduced with high loading observed in the passage. This shock structure may strengthen oscillations and instability, which will be investigated via high fidelity methods in the future.
Impact of Liquid Properties on Flame Behavior for Sustainable Aviation Fuels in Gas Turbine Combustors
Authors: Dasgupta Debolina , Bhattacharya Chandrachur , Som Sibendu
Published: September 2023

Sustainable Aviation Fuels provide a means for decarbonization of the aviation sector. The properties of these fuels can be different from that of conventional jet fuels. To assess the impact of changes in fuel properties on the flame behavior, Large-Eddy Simulations of the Referee Rig are performed for a stable condition. The average jet fuel, A-2 is used as the reference fuel and density, viscosity and heat of combustion are perturbed to understand their individual impact on the flame behavior. Additionally, combined changes of two and all three properties are also assessed. Individual changes in density and viscosity have limited changes to the flame shape and flame stabilization. A decrease in viscosity leads to a more symmetric flame. Additionally, less larger droplets are seen due to increased secondary break-up. Heat of combustion shows a more pronounced impact with larger regions of higher temperature observed for a higher heat of combustion. A combined decrease of density and viscosity is shown to lead to a more symmetric flame with a more uniform distribution of higher temperature and OH regions. A combined decrease of these two quantities with a higher heat of combustion is shown to increase the local temperatures within the flame. These impacts on the flame shape are expected to have consequential changes to the off-stable performance of these fuels such as lean blow out.
Impacts of Superalloys on the Surface Quality of Additively Manufactured Channels
Authors: Corbett Thomas M. , Thole Karen A. , Ryan Daniel , Bollapragada Sudhakar , Kirka Michael , Ledford Christopher
Published: September 2023

Gas turbines feature many components that require superalloys capable of handling extreme thermal environments. Increasing the selection of materials available for these components is important to their use in these extremely high temperature environments. This study investigated two recently developed materials intended to be used for additive manufacturing (AM) with one superalloy based on Cobalt and the other on Nickel. Sets of four test coupons were built using the materials, in addition to the commonly used Inconel-718, on multiple laser powder bed fusion (L-PBF) machines. Several build conditions were varied between coupon sets including coupon orientation, contour settings, and upskin and downskin treatment. Each set of test coupons featured four unique cooling designs to explore how different cooling technologies would be impacted by the variations in build conditions. After being built, coupons were CT scanned to determine accuracy to design intent and quantify the surface roughness. The CT scans indicated that horizontally built test coupons had significantly higher deviation from design intent and higher surface roughness than those built vertically. Results also indicated that the Cobalt-based alloy consistently had a smoother surface quality with lower surface roughness compared to the nickel-based alloy. After geometric characterization, the cooling performance of the test coupons was measured experimentally. Pressure losses were found to correlate with increases in surface roughness; however, in some cases the convective heat transfer did not increase proportionally to the pressure loss as a result of surface features significantly blocking the flow without proportionally increasing convective heat transfer.
Evaluation of Minimum NOx Emission From Ammonia Combustion
Authors: Gubbi Srujan , Cole Renee , Emerson Ben , Noble David , Steele Robert , Sun Wenting , Lieuwen Tim
Published: September 2023

Ammonia (NH3) is being explored as a hydrogen carrier with no carbon emissions. However, if burned directly as NH3, rather than being completely decomposed back to N2/H2, the fuel-bound nitrogen comes with a potentially significant NOx emissions penalty. Indeed, several existing studies are showing ammonia combustion NOx emissions that exceed current natural gas fueled, DLN technologies by one to two orders of magnitude. Therefore, it is important to establish the theoretical minimum NOx emissions for an ammonia combustor, to determine how much NOx levels can be reduced via further technology development. This work determines this minimum NOx level for a two-stage combustor system for a given combustor exit temperature and residence time, with a constraint on unburned fuel levels. As expected, the optimum configuration is an RQL combustor with a rich front end to burn and crack ammonia with significant H2 production, followed by a lean second stage that consumes the remaining H2. The optimum residence time and stoichiometry of each zone is determined in the fast mixing limit. These results show minimum NOx levels are in the 195–400 ppm range at 1 bar, but drop to levels of ∼25 ppm at 20 bar. These NOx emissions are dominated by NOx production in the primary stage which relaxes to equilibrium levels quite slowly. As processes controlling NOx relaxation to equilibrium in the primary stage dominate overall NO emission levels, combustor NOx sensitivities are essentially opposite that of natural gas fired, DLN systems. Specifically, NOx values drop with increased combustor residence time, increased pressure, and increased combustor exit temperature. These results also suggest that promising routes for research are kinetic means to accelerate primary zone NOx relaxation rate to equilibrium. They also show that combustors specifically designed for ammonia will have residence times that are one to two orders of magnitude larger than current natural gas systems. By doing so, NOx levels below 10 ppm may be achievable.
Numerical Investigations of Near Surge Operating Conditions in a Two-Stage Radial Compressor With Refrigerant Gas
Authors: Cravero Carlo , Marsano Davide , Sishtla Vishnu , Halbe Chaitanya , Cousins William T.
Published: September 2023

Modern compressor design targets require high performance and a wide operating range in order to reduce the environmental impact. To understand the fluid dynamics mechanisms that trigger instability, studying the system at the stability limit is required. In this work, a two-stage back-to-back centrifugal compressor for refrigerant applications has been simulated with CFD techniques using unsteady calculations in different operating points close to surge. These models have been validated by comparing numerical performance with experimental data. An in-depth fluid dynamics analysis combined with the monitoring of several pressure signals, post-processed with FFT, identified different flow phenomena in the two stages towards the surge limit. The key role of the volute that induces a stronger upstream counter-pressure in the first stage has been highlighted. This effect causes the formation of high entropy (low momentum) rotating cells in the diffuser that involve a higher channel portion with respect to the flow structure in the second diffuser. This phenomenon affects the upstream flow conditions at the impeller. In addition, the interaction between the IGV and the inducer has been analysed, observing that in the second stage, due to the flow non-uniformity after the ICP, non-negligible separations occur. Starting from the peaks detected in the FFT analysis of the pressure signals all the above flow mechanisms have been detected and discussed.
Desktop-DNS: An Open Toolkit for Turbomachinery Aerodynamics
Authors: Wheeler Andrew P. S.
Published: September 2023

The prevailing view is that high fidelity simulation, particularly DNS (direct numerical simulation), is not something for the practical turbomachinery aerodynamicist — requiring too much computational and personal effort to make it worth it. The aim of the ‘Desktop-DNS’ toolkit described in this paper is to change this by greatly lowering the barrier to entry for running DNS. The paper shows how, using an efficient high-order Navier-Stokes computer code, it is becoming increasingly possible to solve testcases of industry relevance with high fidelity LES and DNS, making use of the latest advances in single compute node performance. This is achievable using both efficient algorithms and GPU acceleration. The paper will use a compressor blade testcase to illustrate how, in some cases, high-fidelity simulations can be performed at relatively low costs on a small number of computer nodes. This raises the possibility of a much more widespread use of DNS to inform early design choices, enhance or benchmark current models, and to potentially reveal new physical mechanisms. An increasing uptake of DNS into mainstream CFD use has profound consequences in terms of data-processing and the training needs for practitioners. The paper therefore provides guidance on some practical ways in which high fidelity data can be exploited for turbomachinery design, as well as a step-by-step guide and set of codes to enable a turbomachinery aerodynamicist to explore DNS.
Assessment of Flamelet Generated Manifold Approach With Inclusion of Stretch Effects of Pure Hydrogen Flames
Authors: Amerighi Matteo , Nassini Pier Carlo , Andreini Antonio , Orsino Stefano , Verma Ishan , Yadav Rakesh , Patil Sunil
Published: September 2023

Hydrogen provides the most significant potential to meet the net-zero carbon target for the power generation and aviation propulsion, since it can be directly used in gas turbines. Its high energy density, higher auto-ignition temperatures, and ability to lean-burn are well suited for consumption in gas turbines. On the other hand, the high adiabatic flame temperature and reactivity need special attention for limiting the NOx emissions and the flashback risks. Therefore, the development of numerical models capable of predicting its behavior is essential to speed up the design phase of a new aero-engines combustor operating with pure hydrogen fuel. The present work aims to study through high-fidelity simulations a laboratory-scale rig investigated at the University of Berlin (TUB) featuring a swirl stabilized, premixed hydrogen flame. A tabulated chemistry approach based on the Flamelet Generated Manifold (FGM) is adopted for all the simulations, implementing key improvements to the canonic formulation. Specifically, a cost-efficient strategy to include the stretch and heat loss effects on flame reactivity is developed and tested to capture the peculiar behavior of hydrogen flames. Additionally, a hybrid approach based on FGM is proposed in which turbulence chemistry interaction is modeled through flame thickening. The model predictions are then analyzed in detail to highlight their differences, and a comparison with the available experimental data was performed to assess the most accurate model.
Auto-Ignition Test Results of Hydrogen and Natural Gas Fuels at Atmospheric And Elevated Pressures for Gas Turbine Safety
Authors: Loving Christopher , Mastantuono Garrett , Terracciano Anthony C. , Vasu Subith S. , Pigon Travis , Hernandez Angel , Cloyd Scott
Published: September 2023

The success of the global Energy Transition hinges on meeting the world’s growing demand for power, while at the same time reducing greenhouse gas (GHG) emissions. Achieving this will require significant growth in electricity generation from clean and carbon-free energy sources. Several energy providers [1,2] have already begun the transition from traditional carbon-based fuels to cleaner alternatives, such as hydrogen (H2) and hydrogen enriched natural gas (HENG). However, there are still many technical questions/challenges that must be addressed when applying these fuels in gas turbines.

The application of H2 or H2/natural gas (NG) blends to advanced class gas turbines, which have higher operating pressures and temperatures, has raised concerns about the potential for leakages or fuel sequencing operations where flammable mixtures of fuel and air could auto-ignite. Public information on the auto-ignition of H2 in air at atmospheric pressure is well documented. Such data shows auto-ignition temperature (AIT) of H2 is ∼100°C lower than that of methane (CH4). Studies also show that as pressure increases, methane’s AIT decreases. However, there was insufficient information in the published literature to characterize the influence of pressure on auto-ignition for hydrogen fuel applications.

This study describes the test methodology used to evaluate conditions where auto-ignition occurs for various fuel-air mixtures operating at different pressures (1–30 atm) and temperatures. Testing was completed with 100% H2 and multiple H2/NG blends at various equivalence ratios (φ). Testing was similarly performed for 100% NG to validate the test and data collection methods cited in prior published literature. Results indicate that, at atmospheric pressures, an increase in H2 concentration results in a reduced AIT. However, at 30 atm, the AIT of H2 increased. Variations of auto-ignition delay times (AIDT) were also observed during the testing and are compared to modeling predictions, providing insight into auto-ignition characteristics.
A Systematic Probe Into the Starting Torque Characteristics of a Bio-Inspired Orange Sea-Pen Bladed Savonius Wind Rotor
Authors: Rathod Umang H. , Nalavade Chetan S. , Saha Ujjwal K. , Kulkarni Vinayak
Published: September 2023

In the pursuit of exploiting wind energy, the drag-based Savonius wind rotors have been extensively used in the low wind velocity regions. These type of rotors, as small-scale stand-alone systems, are characterized by their direction independency, ease of fabrication and the absence of yaw-mechanism. Over the past few decades, various blade profiles/shapes and augmentation techniques have been developed to improve the performance of the Savonius rotors. In recent times, in the quest of further improvement, the nature-inspired (such as golden spiral) and the biomorphic (such as fish-ridge) blades have also been evolved. Some researchers have also studied bio-inspired blade shapes (such as sea-pen) to utilize the organism’s strategy of optimized vortex induced feeding. In the present paper, the starting torque characteristics of a sea-pen bladed Savonius rotor is explored experimentally. The rotor blades are derived from the reported data of the Orange sea-pen (Ptilosarcus gurneyi). Wind tunnel experiments are conducted in the range of 5 m/s to 8 m/s. In order to have a direct comparison, the starting torque characteristics of a conventional semicircular bladed rotor is also obtained in the same range of velocities. The present investigation demonstrates the enhancement of starting torque characteristics of the sea-pen bladed wind rotor at specific rotor angles.
ECAT+: A Second-Generation High-Temperature Engine Component Aerothermal Facility at the University of Oxford
Authors: Messenger Andrew , Cartlidge James , Chowdhury Nafiz , Goenaga Frédéric , Povey Thomas
Published: September 2023

This paper describes the extension in capability of the Engine Component AeroThermal (ECAT) facility at the University of Oxford. The ECAT facility is an established, high technology readiness level facility for research and development of aeroengine components, particularly high-pressure turbine nozzle guide vanes (NGVs). The original facility is capable of matching Mach number, Reynolds number and coolant-to-mainstream pressure ratio to engine conditions. It is also possible to use a combustor simulator module to match combustor exit temperature and swirl profiles.

It was desired to further increase the capability of the facility to match engine mainstream-to-coolant temperature ratio (TR), achieved by increasing the mainstream inlet temperature to 600 K. This required: a new high temperature air feed and exhaust system with all the associated compressor plant and air heating systems; a new test section capable of high temperature operation; a new control system; and new high-temperature-rated instrumentation. The facility operates in a semi-transient mode, with air stored at 50 bar (g) and 600 K in three large air receivers. The air is released in a controlled manner through the test section, allowing test times over 100s in duration. This presents a particular challenge for the thermomechanical design of the test section, due to rapid heating of components leading to high transient thermal stress.

The extended facility (referred to as ECAT+) has been successfully commissioned and an initial test campaign undertaken. The facility design, results from the commissioning tests and operating envelope are described within the paper. These results demonstrate the new facility meets all of the operating requirements for high TRL research and product development. The results showed very good agreement with a low order transient system model which was used throughout the design process. It is anticipated that details of the design, and the design process itself, will be of interest to other developers of high TRL facilities.
Improvements in the Prediction of Steady and Unsteady Transition and Mixing in Low Pressure Turbines by Means of Machine-Learnt Closures
Authors: Pacciani Roberto , Marconcini Michele , Arnone Andrea , Bertini Francesco , Spano Ennio , Rosa Taddei Simone , Sandberg Richard D.
Published: September 2023

In this paper novel machine-learnt transition and turbulence models are applied to the prediction of boundary-layer transition and wake-mixing in a Low-Pressure Turbine (LPT) cascade, including unsteady inflow cases with incoming wakes. A Laminar Kinetic Energy (LKE) transport approach is employed as baseline transition framework. The application of the machine learnt EARSMs takes advantage of a zonal strategy based on a newly developed sensing function that allows automated wake demarcation. This work compares the performance of several approaches that are based on the application of improved transition models without machine learnt EARSMs, baseline transition model with EARSMs trained for improved wake mixing, and new transition and turbulence closures that are simultaneously developed in a fully coupled way and aimed at improving both transition and wake mixing predictions in LPTs. The investigation is carried out on a cascade of industrial footprint, representative of modern LPT bladings. First of all, the various modelling frameworks are evaluated, without bar wakes (steady conditions), over a wide range of Reynolds number values. URANS analyses have also been carried out to investigate the predictive capabilities of machine-learnt closures in the presence of incoming bar wakes. RANS/URANS results are scrutinized against LES calculations and experimental data. It will be demonstrated that machine learnt EARSMs are capable of producing realistic wake mixing when simply applied on top of the baseline transition models. However, the most accurate predictions will be shown to be provided by fully integrated machine-learnt transition/turbulence closures.
Effect of Rim Seal Geometry on Rotationally-Driven Ingestion
Authors: Burden Shaun , Chew John W. , Gao Feng , Marxen Olaf
Published: September 2023

This study investigates turbine rim seal geometry effects within the rotationally-driven ingestion regime. Computations were performed with a wall-resolved unsteady Reynolds-averaged Navier-Stokes (URANS) model and a large-eddy simulation (LES) model including near-wall boundary layer modelling, that is wall-modelled LES (WMLES). Use of simplified rim sealing models is proposed as an efficient method of ranking seal designs and investigating sensitivity to seal geometry. Four rim seal configurations, two chute seals, an axial seal and a radial seal which are representative of those used in gas turbines and in previous research were investigated. Furthermore, hybrid seals combining geometric characteristics from both the chute and radial seal were considered. Significant sensitivities of sealing performance to turbulence modelling are identified, but URANS and WMLES show similar trends in ranking of seal performance, and these are consistent with previous experimental work. The addition of an outer radial clearance section to a chute seal is effective in reducing ingestion levels.
Application of Numerical Bifurcation Tracking Strategy to Blade-Tip/Casing Interactions in Aircraft Engines
Authors: Delbé Clément , Colaïtis Yann , Batailly Alain
Published: September 2023

Building on the regularized-Lanczos harmonic balance method, a previously developed frequency method, this paper presents a numerical bifurcation tracking strategy dedicated to high-dimensional nonlinear mechanical systems. In order to demonstrate its applicability to industrial applications, it is here used to obtain original results in the context of blade-tip/casing interactions in aircraft engines. The emphasis is put specifically on the tracking of predicted limit point bifurcations as key parameters — such as the amplitude of the aerodynamic forcing applied on the blade, the friction coefficient or the operating clearances — vary. Overall, presented results underline that the employed frequency method is well-suited to tackle the numerical challenges inherent to such computations on high-dimensional systems. For the mechanical system of interest, the industrial fan blade NASA rotor 67, it is shown that the application of the presented strategy yields an efficient way to identify isolated branches of solutions, which may be of critical importance from a design standpoint.
Working Fluid Selection and Thermodynamic Optimization of the Novel Renewable-Energy Based RESTORE Seasonal Storage Technology
Authors: Alfani Dario , Giostri Andrea , Astolfi Marco
Published: September 2023

Seasonal based energy storage aimed at increasing the dispatchability of renewable energies is expected to be one of the main options for the decarbonization of the space heating sector. Technologies available today can only partially fulfill the requirements of efficiency, energy density and affordability, being based on the use of hot water. This work focuses on the analysis of a non-conventional system based on the adoption of pumped thermal energy storage concept to maximize the usage of renewable energies and waste heat excess during summer season and make them available during winter months. Organic fluid-based cycles are adopted for both the heat upgrade during hot season (heat pump) and to produce electricity and hot water during cold season (power unit). Upgraded thermal energy is used for supporting an endothermic reaction producing dehydrated solid salts that can be stored for months using inexpensive, high efficiency and high energy density (up to 2 GJ/m3) solutions. This paper focuses on the design of the thermodynamic cycles, comparing the performance attainable with several different working fluids. Two different systems are investigated: coupled systems sharing the same heat exchangers and the same fluid in both operating modes and decoupled systems. Analysis is completed with a preliminary economic assessment of the system, including a sensitivity analysis on electricity and heat cost. Cyclopentane resulted to be one of the most promising working fluids for coupled systems, reaching a competitive round-trip efficiency of around 35%, maximizing the ratio between performance and total heat transfer surface, without showing excessive turbomachinery volume ratios and volumetric flow rates. Economic analysis also highlighted that in this cogenerative application the use of working fluids with lower efficiency, but also low system capital cost, can achieve competitive payback times. On the contrary, decoupled cycles systems result to be less attractive, being able to reach only slightly higher thermodynamic performance, but requiring a higher capital cost and thus possibly being of interest only in specific applications.
Experimental and Numerical Results of a Non-DLE Aeroderivative GT Combustion System Burning Methane-Ammonia Blends at Intermediate Pressures
Authors: Ditaranto Mario , Füri Marc , Solvang Sindre , Saanum Inge
Published: September 2023

Ammonia is considered as a practical hydrogen carrier, as it can be stored in liquid form at moderate pressures and temperatures and is commonly produced and transported today. Ammonia could be used directly as a Gas Turbine fuel to replace current hydrocarbon-based fuels, but its low reactivity and propensity to produce high NOx will require major combustor design changes. Alternatively, ammonia can be fully or partially converted back into hydrogen and nitrogen before using it as a fuel with additional equipment and penalty on cycle performance. Another option is to replace only part of the natural gas with ammonia to minimize the changes of combustion properties and hence combustor design. Although this only partially decarbonizes the fuel, it may be a viable intermediate step to reduce the gas turbine footprint in the short term and with minimum hardware changes to the GT. This experimental and numerical study investigates combustion of methane-ammonia blends with a simplified version of the non-DLE Siemens Energy SGT-A35 turbine combustion system (Rich-Quench-Lean system, RQL) at pressures up to 8 [bar] and powers up to 100 [kW]. The effect of ammonia/methane ratios and Primary Zone Equivalence Ratio (PZER) on emissions of NOx, CO and N2O has been investigated for different pressures and power. A pressure exponent has been extracted based on this experimental data to provide an order of magnitude of NOx emissions at engine conditions. To complement these experimental results, a simple Chemical Reactor Network (CRN) has been used to support the experimental results further. The experimental results showed that even small amounts of ammonia in methane result in unacceptably high NOx emissions for all Primary Zone temperatures and pressures investigated. Although increasing pressure reduces NOx emissions (as previously reported), extrapolation to engine conditions showed that the order of magnitude of NOx emissions will remain unacceptably high. It is also shown that flame stability becomes insufficient for fuels containing more than 40–50 [% by vol.] of NH3 as blow out occurred for these fuels. Furthermore, the results showed that N2O emissions are very low for rich Primary Zone Equivalence Ratios and increase approximately exponentially with decreasing equivalence ratios, but remained below 10 [ppm] for cases at higher pressures. Finally, the CRN results reproduced the experimental trends qualitatively well for %NH3 variations but PZ ER variations and absolute values could not be matched for all cases simultaneously without re-tuning of the CRN.
On the Design of Integrated Thermal Management Systems for eVTOL Aircraft
Authors: Kang Sangkeun , Saias Chana , Roumeliotis Ioannis , Broca Olivier
Published: September 2023

Vertical take-off and landing aircraft equipped with hybrid or fully electric propulsion systems have gained interest for urban air mobility applications. Besides the low energy density of state of art electric systems, their strict operating temperature requirement and low-grade heat highlight the importance of effective thermal management system design. This paper aims to establish a design process for the thermal management system for a parallel hybrid electric tiltrotor and showcase it for a system consisting of direct ram-air cooling cold plate and phase change materials. The cold plate is designed for cruise conditions and used as heat acquisition and cooling system, whereas the phase change materials is used as a heat storage system when ram air is limited. Three sizing conditions are considered comprising the baseline design mission, a certification condition for One Engine Inoperative (OEI) and an off-design mission. The effects of thermal management system integration on overall performance are quantified and discussed. The results indicate that designing the system for the baseline sizing mission results in a 5% increase in fuel burn per payload relative to the equivalent counterpart without thermal management consideration. This penalty increases to 14% when certification requirements are accounted. It is highlighted that tor shorter mission thermal management is the limiting factor for battery utilization, hence the expected benefits are significantly reduced. As electric components technology increases thermal management becomes less sensitive to the sizing conditions.