bluuebunny/crossref_metadata_2025 huggingface dataset:
An Innovative Concept for the Complete and Low-NOx Combustion of Non-Carbon Eco-Fuels Using a Thermo-Acoustically-Driven, Hydrogen-Powered Pilot Stage
Authors: Paulitsch Nina , Giuliani Fabrice , Hofer Andrea , Hofer Johannes , Andracher Lukas
Published: October 2022

The problem of climate change, triggered by a high concentration of pollutants in the atmosphere, and the scarcity of fossil resources, increases the need of low emission thermal utilisation of novel, non-carbon eco-fuels such as hydrogen, ammonia (both for energy and propulsion) or hydrogen sulphide (sulphuric acid production). While all of these listed eco-fuels have the potential to decarbonise industry and the energy sector, they also pose demanding challenges regarding combustion. To address these challenges the idea is to combine the advantages of current low-NOx technologies in terms of ultra-lean combustion with a precisely controlled, forced flame turbulence generated by a pulsation actuator. The aim is to develop a safe and highly digitalised combustion technology, including a two-staged burner design for application in the megawatt range with multi eco-fuel capacities and a fully automated control loop for the combustion process.

To achieve effective thermo-acoustic modulation an actuator type siren is used. Further improvements towards the demanding application in industry were done leading to the latest siren model, Siren E. A siren is a robust pulsation apparatus that generates powerful noise levels and effective flow pulsations under elevated pressure and temperature conditions [1–3]. By scanning through a certain frequency range during combustion, one is able to detect eigenfrequencies of the flame which increases flame turbulence when excited. The effective flow control of the siren can guarantee a complete burnout of the partially toxic eco-fuels. In addition, gaseous pollutants such as NOx can be reduced to a minimum, since the flame pulsation process provides the opportunity to run reliably a mixture with an otherwise unstable combustion process. The Siren E with its new features is introduced in this paper in detail. To verify the method for eigenfrequency detection, initial combustion tests are first carried out with propane on the so-called MethaNull test rig. There, the main aspect is to meet the same eigenfrequencies as in a previous work. Then, initial combustion tests with premixed hydrogen are performed up to a thermal power of 10 kW. First, different methods for the injection of hydrogen are tested resulting in a prioritised premixed variant. Using this premixing method in the test setup the response to thermo-acoustic excitation via loudspeaker and siren is investigated. Prior to the experiments, a numerical study was performed on a model representing a simplified pilot stage. All numerical and experimental results are presented in detail in this paper.
Design and Development of a Five-Hole Probe Calibrator and Traverse to Investigate Ingestion in Rotating Cavities of HP Compressors
Authors: Fox Emma C. , Puttock-Brown Mark R. , Davies Simon J.
Published: October 2022

The internal air system is essential within aero-engine HP compressors for cooling and controlling blade tip clearances. Reducing the amount of air diverted from the main flow to the internal system improves the overall thermal efficiency, and so there is a need to understand the interactions of the flow within the compressor cavities. This paper describes the implementation and use of miniature five-hole probes to investigate the ingress and egress of the bore flow in an established engine representative test rig.

The development of an inexpensive but accurate automated calibration device to calibrate different shaped probes over a wide range of pitch and yaw angles is described. The Reynolds number of the calibration flow was matched to the operating conditions of the pressurised test rig. A bespoke traversing mechanism was designed and installed within the shaft of the rig. The traverse enables the probe to move axially across one cavity, radially from the shaft to low cavity region and rotate to align with the local flow direction. Velocity data from a single commissioning test case at Ro = 0.65, Rez = 5.5 × 104, Reθ = 1.6 × 106, βΔT = 0.37 is presented. A Monte Carlo uncertainty analysis of the calibration and data collection procedure was conducted to validate the use of a five-hole probe for axial, tangential and radial velocity measurements in rotating cavities.
Mesh Refinement and Inlet Turbulence Intensity in the Numerical Evaluation of Cooling Effectiveness: A Systematic Study on an Industrial Gas Turbine
Authors: Lo Presti Federico , Winhart Benjamin , Post Pascal , di Mare Francesca , Wiedermann Alexander , Greving Johannes , Krewinkel Robert
Published: October 2022

In this study, the influence of grid resolution and inflow turbulence on the prediction of gas temperature distribution around HP-turbine blades and the effectiveness of cooling flows are assessed by means of a comparative, systematic study with increasing grid resolution, starting from a typical RANS-mesh with progressive refinement, by means of scale-resolving simulations. The investigation is focused on a three-stage industrial gas turbine in the mid-range output class, whereby we restrict our analysis to the first stage, where most of the external cooling flow is injected, this regions being characterized by the highest temperature fluctuations. The extent of these variations and their unsteady characteristics need to be determined to verify if they have a measurable influence on the material temperature. As the interaction of turbulence with cooling flows is a key element in the prediction of cooling effectiveness, turbulence levels play a major role in addition to the grid resolution. Therefore, special attention is paid to the accurate description of turbulence scaling laws and correlations at the turbine inflow. The results of the investigation provide insight in a viable modelling and simulation tool which can be adopted during design cycles and reveals valuable details of the unsteady aerothermal stresses on the HP turbine blades.
Circumferentially Grooved Seal Flow Field Analysis Based on Effective Film Thickness to Improve Bulk Flow Models
Authors: Gibbons Nathaniel , Watson-Kassa Cori , Goyne Christopher , He Minhui
Published: October 2022

Bulk flow modeling of circumferentially grooved seals uses simplified physics models to predict leakage and rotordynamic coefficients more efficiently than full computational fluid dynamics (CFD) simulations, but at the expense of accuracy. Reducing bulk flow modeling inaccuracies, mainly a result of uncertainties in empirical quantities like friction factors and loss coefficients, requires a more fundamental and physical understanding of the flow features and their dependencies. This study utilizes CFD and an effective film thickness, a physical boundary between the jet and recirculating flows, to investigate Reynolds number effects on grooved seal flow fields and shear stresses. Simulations were run using ANSYS CFX for a single groove seal model assuming fully developed flow for a range of pressure differentials and rotor speeds. The effective film thickness boundary was defined by generating streamlines in the jet flow region that traversed the entire axial length of the model. Radial averaging across the local film thickness yielded bulk flow quantities used in processing and analysis. Flow structures, film thicknesses, shear stresses, and net flow expansion into the groove are found to be described completely by the ratio of circumferential to axial Reynolds number and the total resultant Reynolds number. Decreases in leakage with rotor speed are found to be dictated by increased land shear stresses and a decreased role of the groove at inducing pressure drop. An optimal groove aspect ratio between 0.07 and 0.19 is presented based on maximizing expanded film area while retaining a main groove recirculation region. This is the first paper to analyze circumferentially grooved seal flow from the standpoint of the effective film thickness, and by doing so, provides physical insight needed for a full description of the flow behavior. The results presented highlight bulk flow analysis areas where an effective film thickness approach could lead to new, physics motivated model development and the elimination of particular empirical coefficients. The effective film thickness approach thus provides a strong foundation on which substantial improvements in bulk flow modeling accuracy can be achieved.
Attributes of Bi-Directional Turbomachinery for Pumped Thermal Energy Storage
Authors: Chiapperi J. D. , Greitzer E. M. , Tan C. S.
Published: October 2022

In this paper we (i) present a methodology for determining the aerodynamic performance of bi-directional turbomachines for pumped thermal energy storage, i.e., turbomachines designed to operate as a compressor in one direction, and then as a turbine in the opposite direction, (ii) carry out performance computations for such turbomachines, and (iii) propose principles for conceptual design of these devices. Focus is placed on using the energy storage cycle not only to identify the novel requirements placed on bi-directional turbomachines, but also to estimate the effect of these requirements on the efficiency of the energy storage process. In particular, the difference between aerodynamic loading in forward and in backward operation causes the blading to work at incidences leading to performance below maximum efficiency, resulting in a lower round-trip efficiency. The description of the design principles includes determination of the number of stages, definition of non-dimensional parameters for blading selection, and optimization of two-dimensional blading for bi-directional operation. The assessment of stage count shows the relationship between relative Mach number, pressure ratio, and round-trip efficiency. The non-dimensional parameters are assessed through a bi-directional analogue to existing “Smith charts”, for the efficiency of single direction turbomachines, as a function of camber and stagger. The blade shape evaluation and optimization shows how the blade profile can be modified to address the requirements of a bi-directional turbomachine, enabling an increase in round-trip efficiency of 2 percentage points compared to a baseline double circular arc configuration.
Vibration-Based Diagnostic of Aircraft Bearings Operating Under Strong Speed Variations
Authors: Abboud Dany , Griffaton Julien , Marnissi Yosra , Gomez Chirinos Jose Luis , Elbadaoui Mohammed
Published: October 2022

This paper proposes a vibration-based diagnostic methodology for aircraft bearings based on a joint first- and second-order cyclostationary analysis. The idea is to track the first- and second-order content over a predefined operating speed range, instead of ignoring the later or performing the diagnosis on an arbitrary stationary speed. The methodology applies to relatively long vibration signals recorded under strong speed variations, using a sliding window over which fluctuations are low. First, we obtain the time-evolution of the spectral statistics by computing the so-called instantaneous power and coherence spectra reflecting the first and second order content, respectively. Then, we design a time-to-speed transform based on fuzzy logic to transform the previously obtained time-cyclic maps into speed-cyclic maps, expressing the spectral statistics as functions of a predefined operating speed grid of interest. Last, we demonstrate the proposed methodology on a real vibration signal captured from an accessory gearbox of a CFM56 aircraft engine, with multiple bearing faults.
High-Frequency Mode Shape Dependent Flame-Acoustic Interactions in Reheat Flames
Authors: McClure Jonathan , Bothien Mirko , Sattelmayer Thomas
Published: October 2022

Gas turbines featuring sequentially staged combustion systems offer excellent performance in terms of fuel flexibility, part load performance and combined-cycle efficiency. These reheat combustion systems are therefore a key technology for meeting fluctuating power demand in energy infrastructures with increasing proportions of volatile renewable energy sources. To allow the high operational flexibility required to operate in this role, it is essential that the impact of thermoacoustic instabilities is minimised at all engine load conditions. In this case, high-frequency thermoacoustic instabilities in the second “reheat” combustion stage are investigated. Reheat flames are stabilised by both autoignition and propagation and, as a result, additional thermoacoustic driving mechanisms are present compared with more conventional swirl-stabilised combustors. Two self-excited thermoacoustic modes have been observed in a 1MW reheat test rig at atmospheric pressure, one which exhibits limit-cycle behaviour while the other is only intermittently unstable. The underlying driving mechanisms for each individual mode have been investigated previously and, in this paper, the two modes are directly compared to understand why these instabilities are each associated with different driving phenomena. It is shown that, due to the different flame regimes present in the reheat combustor, the potential for flame-acoustic coupling is highly dependent on the thermoacoustic mode shape. Different interactions between the flame and acoustics are possible depending on the orientation of the acoustic pressure nodes and antinodes relative to the autoignition- and propagation-stabilised flame regions, with the strongest coupling occurring when an antinode is located close to the autoignition zone. This provides insight into the significance of the different driving mechanisms and contributes to the ongoing development of models to allow prediction and mitigation of thermoacoustic instabilities in reheat combustion systems, which are crucial for reliable combustor designs in the future.
Analysis of the NOx Emissions Deriving From Hydrogen/Air Combustion in a Swirling Non-Premixed Annular Micro-Combustor
Authors: Mazzotta Luca , Di Gruttola Francesca , Palone Orlando , Gagliardi Gabriele Guglielmo , Borello Domenico
Published: October 2022

The objective of this paper is to analyse the thermal performances and emission levels of a swirling non-premixed annular micro-combustor. A three-dimensional simulation of the internal flow in an annular combustion chamber fuelled by hydrogen/air in non-premixed conditions was carried out through Ansys Fluent 2020 R2. A detailed mechanism involving many species and reactions was required to represent the complexity of the combustion process. A 19-reactions and 9 species mechanism was deemed to be appropriate to predict the combustion characteristics with great accuracy and limited processing resources. The reaction mechanism was implemented in Fluent through Chemkin. This model was then compared with the built-in model of the chemical kinetics, which involves just one reaction. The results showed that the 19-reactions model is more accurate to reproduce the centerline temperature distribution than the default simpler model: the 1-reaction model differs by 230 K compared to the experimental data, while the 19-reactions one only by 80 K. The comparison between the velocity of the mixture inside the combustor with and without combustion was also carried out, providing an estimate of the influence of temperature on the flow field. Finally, to meet the emission limits established by the European Commission in 2015, the thermal NOx and NOx derived by NNH were examined on both the outlet and the centerline of the combustor. The study reveals great potential of hydrogen mixtures in reducing emissions and provides insights on the cooling requirements to guarantee wall materials reliability.
Multilayered Fibre-Matrix Interphases Derived From the Electrophoretic Deposition of Ceramic Nano-Powders
Authors: Robertson Taylor , Huang Xiao , Kearsey Rick
Published: October 2022

A significant challenge within the manufacturing of Ceramic Matrix Composites (CMCs) is the creation of the fibre-matrix interphase which enables the damage tolerant behavior of CMCs. Chemical vapour deposition (CVD) has been a highly successful approach for fabricating fibre-matrix interphases; however, CVD requires capital intensive facilities and hazardous precursors. This work examines electrophoretic deposition (EPD) as an alternative route for the production of fibre-matrix interphases. Four multilayered fibre-matrix interphases (SiC/Al2O3, BN/ZrO2, ZrC/85wt%Al2O3-15wt%ZrO2, and SiC/Si3N4/SiC) were produced through multi-staged electrophoretic deposition of ceramic nano-powders upon SiC fibre bundles. A 25-2 factorial design of experiments is utilized to explore the effect of different levels of the following variables: electric field strength, duration, surfactant, solids loading and binder. Following deposition of the fibre-matrix interphase the fibre bundles are thinly coated with a SiC matrix through a reactive melt infiltration technique. The resultant microcomposites are then subjected to tensile loading until failure to determine which coating and deposition combination are the most likely to yield favorable tensile properties. Additional microscopy is performed to determine the uniformity and thickness of the coatings. The results are then examined to evaluate the suitability of electrophoretic deposition as a production technique for fibre-matrix interphase coatings in CMCs.
High-Pressure Laminar Flame Speeds and Markstein Lengths of Syngas Flames Diluted in Carbon Dioxide and Helium
Authors: Turner Mattias A. , Petersen Eric L.
Published: October 2022

New laminar flame speed and burned-gas Markstein length data for H2-CO-O2-CO2-He mixtures have been measured from spherically expanding flames. Experiments were conducted at 10 atm and room temperature for H2:CO ratios ranging from 2:1 to 1:4 and for overall CO2 mole fractions from 0 to 30%. CO2 dilution had little effect on Markstein length, but CO2 dilutions of 10%, 20%, and 30% caused average reductions in flame speed of 47%, 73%, and 89% respectively, regardless of H2:CO ratio. The study was designed to isolate the dilution effect of CO2 on flame speed, and a detailed analysis using the FCO2 method was used to show that the chemical-kinetic participation of CO2 was responsible for up to 20% of the reduction in flame speed. Hence, the majority (80% or more) of the reduction in flame speed due to CO2 is from the thermal effect. Accurate flame speed predictions were produced by five different chemical kinetics mechanisms for most conditions, with the slight exception of high-CO, high-CO2 mixtures. A thorough sensitivity analysis highlighted the larger effect of CO2 dilution on the important kinetics reactions than the effect of changing H2:CO. Sensitivity analysis also showed that the chain branching reaction H2O+O⇌OH+OH could be modified (albeit beyond its uncertainty) to achieve more accurate flame speed predictions, but also indicated that further improvement of flame speed modeling would require changes to many lesser reactions.
Integrated Aerodynamic and Structural Blade Shape Optimisation of Axial Turbines Operating With Supercritical Carbon Dioxide Blended With Dopants
Authors: Abdeldayem Abdelrahman S. , White Martin T. , Paggini Andrea , Ruggiero Marco , Sayma Abdulnaser I.
Published: October 2022

Within this study, the blade shape of a large-scale axial turbine operating with sCO2 blended with dopants is optimised using an integrated aerodynamic-structural 3D numerical model, whereby the optimisation aims at maximising the aerodynamic efficiency whilst meeting a set of stress constraints to ensure safe operation. Specifically, three candidate mixtures are considered, namely CO2 blended with titaniumtetrachloride (TiCl4), hexafluorobenzene (C6F6) or sulfur dioxide (SO2), where the selected blends and boundary conditions are defined by the EU project, SCARABEUS. A single passage axial turbine numerical model is setup and applied to the first stage of a large-scale multi-stage axial turbine design. The aerodynamic performance is simulated using a 3D steady-state viscous computational fluid dynamic (CFD) model while the blade stress distribution is obtained from a static structural finite element analysis (FEA). A genetic algorithm is used to optimise parameters defining the blade angle and thickness distributions along the chord line while a surrogate model is used to provide fast and reliable model predictions during optimisation using genetic aggregation response surface. The uncertainty of the surrogate model represented by the difference between the surrogate model results and the CFD/FEA model results is evaluated using a set of verification points and found to be less than 0.3% for aerodynamic efficiency and 1% for both the mass flow rate and the maximum equivalent stresses. The comparison between the final optimised blade cross-sections have shown some common trends in optimising the blade design by decreasing stator and rotor trailing edge thickness, increasing stator thickness near the trailing edge, decreasing rotor thickness near the trailing edge and decreasing the rotor outlet angle. Further investigations of the loss breakdown of the optimised and reference blade designs are presented to highlight the role of the optimisation process in reducing aerodynamic losses. It has been noted that the performance improvement achieved through shape optimisation is mainly due to decreasing the endwall losses of both stator and rotor blades.
Dynamic Modelling and Simulation of a 100 kW Micro Gas Turbine Running With Blended Methane/Hydrogen Fuel
Authors: Banihabib Reyhaneh , Assadi Mohsen
Published: October 2022

The current shift from centralized to decentralized power generation with renewables as prime movers necessitates the integration of reliable small-scale power supply units to compensate for the intermittency of renewables. Micro gas turbines’ (MGTs) characteristics such as high reliability and low maintenance, along with flexible operation and quick load-following capabilities have made them a dependable source for the modern power generation industry and for households. MGTs are small-scale gas turbine units with a power range lower than 500 kW that can operate with low-calorific fuels such as biofuels and syngas as well as conventional fossil fuels and zero-carbon fuels.

The utilization of MGTs in innovative cycle layouts or varying types of feeding fuels is increasing, which requires the evaluation of system dynamics to ensure the safe operation of the engine and its components. Moreover, the role of MGTs as a backup for the intermittent renewable inputs means that they operate under more transient conditions rather than constant power production mode. Therefore, a reliable dynamic model of an MGT is required to investigate the dynamic response of the engine under various transient modes to ensure safe operation. Moreover, utilizing a dynamic model is vital in the designing process of MGT-based cycles in order to evaluate the behaviour of coupled components in off-design conditions and to optimize the controller parameters. To that end, developing a dynamic model of the MGT cycle that is accurate enough to predict the dynamic response of the engine and its components and fast enough to be utilized in design iterations is necessary.

In this paper, a high-fidelity model for real-time simulation of an MGT, based on a lumped and nonlinear representation of gas turbine components is presented. The model for a recuperated T100 MGT was constructed in Simscape, the object-oriented environment of MATLAB for modelling physical systems. MGT components were modelled as lumped volumes with dynamic equations of mass, momentum, and energy balance along with component-characteristic maps describing the evolution of the flow passing through them. Results from simulations were validated by experimental data collected from a real engine operating under different load conditions. Experimental tests and numerical simulations were conducted for pure methane as well as for blended methane/hydrogen as feeding fuels.
Transient Analysis of a Micro Gas Turbine With Fuel Composition Change
Authors: Raggio Martina , Bellotti Daria , Ferrari Mario Luigi
Published: October 2022

The aim of this study is to analyze the effect of fuel composition change on the performance and dynamic behavior of a T100 micro gas turbine. Fuel flexibility is a key asset of micro gas turbines and can support the energy transition when alternative fuels obtained from renewable energy sources are used. While the current research is mainly focusing on improving combustor performance, it is also required to investigate the effects of different fuel blends on the overall system. During transient operation, the use of fuels with a low LHV requires an increased fuel mass flow that can potentially reduce the compressor surge margin. Conversely, sudden composition changes of high LHV fuel can cause temperature peaks, detrimental for the turbine and recuperator life.

In this paper, a validated transient model for the T100 machine has been used to simulate the injection of different fuels in the natural gas line (feeding the burner). Injection of hydrogen and ammonia, two promising carbon-free fuels, have been tested. A transient analysis was performed with this tool to monitor the main performance parameters with the aim to (i) verify compressor safe operations during different working conditions and (ii) to identify appropriate fuel composition change schedules to ensure Turbine Outlet Temperature values within an acceptable range, while keeping the original fuel control system.
Assessment of a Conjugate Heat Transfer Method on an Effusion Cooled Combustor Operated With a Swirl Stabilized Partially Premixed Flame
Authors: Amerini A. , Paccati S. , Mazzei L. , Andreini A.
Published: October 2022

Computational fluid dynamics play a crucial role in the design of cooling systems in gas turbine combustors due to the difficulties and costs related to experimental measurements performed in pressurized reactive environments. Despite the massive advances in computational resources in the last years, reactive unsteady and multi-scale simulations of combustor real operating conditions are still computationally expensive.

Modern combustors often employ cooling schemes based on effusion technique, which provides uniform protection of the liner from hot gases, combining the heat removal by means of heat sink effect with liner coverage and protection by film cooling. However, a large number of effusion holes results in a relevant increase of computational resources required to perform a CFD simulation capable of correctly predicting the thermal load on the metal walls within the combustor. Moreover, a multi-physics and multi-scale approach is mandatory to properly consider the different characteristic scales of the several heat transfer modes within combustion chambers to achieve a reliable prediction of aero-thermal fields within the combustor and wall heat fluxes and temperatures. From this point of view, loosely-coupled approaches permit a strong reduction of the calculation time, since each physics is solved through a dedicated solver optimized according to the considered heat transfer mechanism. The object of this work is to highlight the capabilities of a loosely-coupled unsteady multi-physics tool (U-THERM3D) developed at the University of Florence within ANSYS Fluent.

The coupling strategy will be employed for the numerical analysis of the TECFLAM effusion cooled swirl burner, an academic test rig well representative of the working conditions of a partially premixed combustion chamber equipped with an effusion cooling system, developed by the collaboration of the Universities of Darmstadt, Heidelberg, Karlsruhe, and the DLR. The highly detailed numerical results obtained from the unsteady multi-physics and multi-scale simulation will be compared with experimental data to validate the numerical procedure.
Validation of Steady-State Aerodynamics in a Transonic Linear Cascade at Near Stall Conditions
Authors: Tavera Guerrero Carlos , Glodic Nenad , Groth Pieter
Published: October 2022

A new set of steady-state aerodynamics data from the recently build KTH transonic linear cascade (TLC) is presented. The operational point is representative of an open source virtual compressor (VINK) operating near stall at 70% speed line. The inlet Mach number (M = 0.81) is above its airfoil critical value with high incidence angle, producing a leading edge separation bubble. The test object in the TLC has a 2% tip gap, and the reference measurement plane is at 85% span. Results show repeatability, and periodicity. Upstream flow field was mapped by a non-intrusive, Laser-2-Focus (L2F) method. The blade loading was recovered by a set of pressure taps. Flow field properties downstream the test section were recovered by a five-hole probe. A flow structures comparison was performed between numerical and experimental data. Numerical results were obtained from the commercial software Ansys CFX, where different turbulence models were tested: SST, SST with reattachment method (RM) and SST with turbulent transition (γ – θ). The closest match to the experimental data was recovered by SST-γ – θ RM. Separation onset and flow properties downstream are strongly affected by the selected turbulence transition model. The results are aimed to work as step towards validation for CFD in separated regions. These data is the first of a series of test campaigns for experimental validation for aerodynamic damping in separated flows.
Recrystallization of René N4 and N5
Authors: van Esch Hans , Pietersen Stijn , Bridges Alex , Scheibel John , Zuber Robert , Greaves Wayne
Published: October 2022

Recrystallization of equiaxed, directionally solidified and single crystal cast nickel base superalloys can occur during some of the manufacturing and repair processes. While equiaxed, and to a lesser extent, directionally solidified cast nickel-based superalloys have grain boundary strengthening this is nonexistent for single crystal superalloys. Therefore, it is especially important to avoid or limit recrystallization during manufacture and repair of these nickel base single crystal gas turbine components.

This study performed by TEServices, EPRI, MD&A and Sulzer concerns the effect of recrystallization when compressive stresses are introduced during manufacturing and repair processes (grit cleaning and shot peening) when followed by (full solution, partial solution and stress relieve) heat treatments. The objective of this paper is to obtain a better understanding the recrystallization behavior of two single crystal superalloys, René N4 and N5, during the repair processes (grit cleaning, shot peening and heat treatments) and determine how to minimize the depth of recrystallization. The impact of recrystallization on mechanical strength (stress rupture and fatigue) on René N4 material was limitedly tested.

This study concludes that for both single crystal alloys, René N4 and N5, the less compressive stresses that are introduced during manufacturing and repair, and the lower temperature of exposure during follow up heat treatments, results in a lower recrystallization layer depth.
Experimental and Numerical Study on Effusion Cooling Configuration for the Swirl CMC Combustor Platform
Authors: Du Kun , Chen Qihao , Liang Tingrui , Jia Yihao , Liu Cunliang
Published: October 2022

With advantageous thermal, strength, and weight properties at high temperatures, Ceramic Matrix Composite (CMC) is regarded as the potential structural material for modern aeroengines with the extreme increase of operating temperature. However, the anisotropic thermal conductivities caused by the weaving type call for a novel cooling structure design since it brings a completely different thermal conduction performance inside the hot components compared to the superalloy. The infrared thermographic experiment was carried out based on the SiC/SiC composite platform prepared by a 2-D plain weave braid structure with the CVI process with three staggered effusion hole configurations in this paper to explore the cooling characteristic of the CMC. The surface overall cooling effectiveness (ϕ) of the platform was measured under a temperature ratio of 1.5 (Tg/Tc = 1.5) and seven mass flow ratios. And a separate numerical simulation with different swirl effects was conducted as a supplement for the combustor operation condition. The results indicate that the thermal conductivity along the thickness direction is of great importance for the platform cooling. The overall cooling effectiveness of the CMC platform was smaller in comparison with the superalloy platform because of its smaller through-thickness thermal conductivity. Moreover, the concentrated coolant outflow is beneficial for the CMC cooling performance given that the area-averaged overall cooling effectiveness disparity of the two materials was narrowed with the smaller hole spacing. The swirling flow strongly inhibits the outflow of coolant near the swirling core but expands the lateral coverage of the film simultaneously. Such behavior alters the film cooling potential as well as the cooling pattern. The difference between CMC and superalloy was increased with the low swirl situation and decreased with the high swirl situation.
Clearance Sensitivity Mitigation in Small Core Compressors
Authors: Evans Simon , Nolan Sean , Botros Barbara , Port Bianca , Chin Peter , Kulkarni Sameer , Stephens Julia
Published: October 2022

As future aircraft become lighter and more aerodynamically efficient, thrust requirements will decrease, reducing the core size of the engine. Furthermore, in the pursuit of improved fuel burn, engine overall pressure ratio and bypass ratio will increase, further driving down engine core size. These drivers together mean that the core size, or corrected mass flow rate at the compressor exit, for future single-aisle aircraft applications will shrink below 3.0 lbm/s. Traditionally, this small core compressor size is in the domain of axi-centrifugal designs, machines that are typically less efficient and limited to pressure ratios of ∼25 due to stress and thermomechanical fatigue in the centrifugal impeller. In this light, NASA, Pratt & Whitney and the Raytheon Technologies Research Center embarked upon a program to develop technologies to enable an all-axial high-pressure compressor with a core size below 3.0 lbm/s and an overall pressure ratio greater than 50.

One of the challenges with an all-axial high-pressure compressor at this core size is the small span at the rear of the compressor. As core size is scaled down, the rotor tip clearances do not scale with span, leading to significant efficiency penalties. This paper documents a numerical and experimental effort to mitigate this penalty through design optimization and technology insertion, enabling an estimated 5 to 10% fuel burn reduction relative to 2020 best-in-class. The experimental program consisted of two builds of a high-speed rig: a baseline build and a second build to insert technology to manage large rotor tip gap/span ratios. The results demonstrated a reduction in the sensitivity of the compressor to large clearance ratios, which would be likely at the end-of-life of a small core application. The test campaign demonstrated that, with the insertion of technology, small core compressors can maintain a similar efficiency to current best-in-class large core size compressors.

In addition to advancing the state-of-the-art of technology, the program also advanced the modeling standards for multistage compressors with large clearance-to-span ratios. The validation of this approach is described in the paper.
Approximating Gas Turbine Combustor Exit Temperature Distribution Factors Using Spatially Under-Sampled Measurements
Authors: Lou Fangyuan
Published: October 2022

In gas turbine engines, the temperature field at the exit plane of the combustor is highly unsteady and complex, with large radial and circumferential variations. The circumferential temperature variations (hot-streaks) are caused by the discrete nature of fuel and dilution air jets, and combustor lining coolant flow results in a strong radial temperature gradient. Two widely adopted parameters include the radial temperature distribution factor (RTDF) and the overall temperature distribution factor (OTDF) to quantify combustor exit temperature nonuniformity. The state-of-the-art approach of characterizing the combustor exit temperature nonuniformity is to carry out an extensive traverse along the circumferential direction at a spatial resolution of two to three degrees. With hundreds of measurements in place, the combustor OTDF and RTDF can be obtained. Though the approach is practical, this involves the design of complex traverse mechanisms and can be costly. To address this challenge, this paper presents a novel method for predicting combustor exit TDFs using much sparser measurements. The approach’s effectiveness was examined using three engine representative combustor exit temperature measurements covering a single-burner, double-burner, and entire annulus. In all cases, the hot-streaks-related features are well resolved in the reconstructed temperature field, and the multi-wavelet approximation method yields almost identical RTDF to experiment with majority variations of less than 1.0% using sparse measurements. In addition, the method’s robustness was examined, and considerations for the implementation of the method were provided.
Gas Turbine Transition Duct Design Considerations
Authors: Satheesh Aparna , Manoharan S. , Soundiramourty Sendil , Babu S.
Published: October 2022

The gas turbine twin shaft variant requires an aerodynamic coupling between its high-pressure gas generator module and low-pressure power module. These two modules are spaced apart for aerodynamic and mechanical reasons. Typically, this is achieved by having a transition duct (TD) in between these two modules which smoothly allows the gas flow from HP turbine to LP turbine. To fulfill this purpose, it includes a radial inner shell and a radial outer shell defining a flow passage and radial struts which connects inner shell and outer shell. Cross-section of these struts are airfoil shaped to facilitate smooth flow of flue gas through TD. In addition, TD allows flow passage for cooling medium, support seals to prevent leakage at various interface locations and holds thermo-well for temperature measurement. Considering thermal and mechanical loads on the TD for standard operating conditions, Low cycle fatigue, creep and oxidation calculations are performed to ensure durability of TD design and necessary design changes are made to fulfill product requirement. Suitable material is selected, and manufacturing method finalized based on the design analysis. While standard offerings of gas turbine fulfill majority of requirements, there are some off-design or customized requirements which require detailed study. To fulfill these types of customized requirements, standard offerings of gas turbine are further analyzed for changed thermal boundary condition. These types of customizations facilitate running gas turbine with different options with a clear understanding of how it impacts durability. Through these studies, necessary maintenance factors are established to arrive at revised maintenance intervals based on severity of change. Low cycle fatigue, creep and oxidation calculations are performed with changed boundary condition also and maintenance factor is determined. This paper is intended to describe the steps followed in determining durability, establish maintenance factor and provide service recommendations.
Influence From Nozzle Guide Vane Wakes and Inlet End-Wall Boundary Layers on Turbine Rear Structure Aerodynamics
Authors: Nylander Pär , Deshpande Srikanth , Larsson Jonas
Published: October 2022

CFD results can be improved by imposing accurate inlet boundary conditions. A previous paper presented extensive measurements from an engine realistic Turbine Rear Structure (TRS), complemented with CFD results using normal radial profiles (1D) at the inlet [10]. This paper extends stat study with two separate studies, investigating the effect of the upstream Nozzle Guide Vane (NGV) wakes and the inlet end-wall boundary layers. In the first study, simulations are done using full 2D inlet boundary condition, imposing the NGV wakes on the inlet. The second study investigates different inlet end-wall boundary layers. Comparisons with measurements show for some aspects that the upstream Nozzle Guide Vane (NGV) wakes and the inlet end-wall boundary layers are important.

Predicting upstream forcing from the TRS on the LPT rotor requires a 2D inlet boundary condition. Also, a strong interaction between the incoming NGV wakes and the secondary flow loss-regions at the outlet is found. However, flow quantities like blade loading, outlet swirl, and OGV wakes are well predicted using regular 1D radial inlet profiles.

How the inlet end-wall boundary layers are modelled have significant impact on secondary flows and outlet swirl. If the full boundary layers are prescribed, the secondary flows are over-predicted. This gives under turning and premature separations. With no inlet boundary layers, secondary flows are well captured and gives better separations, improved outlet swirl and wake predictions. The recommendation is therefore to remove the inlet boundary layers when using the Transition SST k-ω γ-Reθ model in TRS CFD simulations.
Design Methodology and Concept Demonstration of Preassembled Additively Manufactured Turbomachinery Systems: Case Study of Turbocharger Based Medical Ventilators
Authors: Çelik Acar , Linsky David , Miezner Ron , Kleiman Alex , Leizeronok Boris , Palman Michael , Acarer Sercan , Cukurel Beni
Published: October 2022

The present research focuses on analyzing the feasibility of manufacturing complex turbomachinery geometries in a pre-assembled manner through an uninterrupted additive manufacturing process, absent of internal support structures or post-processing. In the context of the present COVID-19 pandemic, the concept is illustrated by a 3D-printable turbine-driven blower-type medical ventilator, which solely relies on availability of high-pressure oxygen supply and a conventional plastic-printer. Forming a fully pre-assembled turbomachine in its final form, the architecture consists of two concentric parts, a static casing with an embedded hydrostatic bearing surrounding a rotating monolithic shell structure that includes a radial turbine mechanically driving a centrifugal blower, which in turn supplies the oxygen enriched air to the lungs of the patient. Although the component level turbomachinery design of the described architecture relies on well-established guidelines and computational fluid dynamics methods, this approach has the capability to shift the focus of additive manufacturing methods to design for preassembled turbomachinery systems. Upon finalizing the topology, the geometry is manufactured from PETG plastic using a simple tabletop extrusion-based machine and its performance is evaluated in a test facility. The findings of the experimental campaign are reported in terms of flow and loading coefficients and are compared with simulation results. A good agreement is observed between the two data sets, thereby fully corroborating the applied design approach and the viability of additively manufactured pre-assembled turbomachines. Eliminating long and costly processes due to presence of numerous parts, different manufacturing methods, logistics of various subcontractors and complex assembly procedures, the proposed concept has the potential to reduce the cost of a turbomachine to capital equipment depreciation and raw material.
Design of a 1MW Direct-Fired Oxy Combustor for sCO2 Power Cycles
Authors: White Steve , Berry Grey , Connolly Brian
Published: October 2022

Direct-fired super-critical carbon dioxide (sCO2) power cycles are a potential method for efficiently capturing nearly all of the CO2 emissions from burning fossil fuels. Direct-fired sCO2 cycles require a very high degree of recuperation, which in turn means that the inlet temperature to the combustor is significantly higher than would typically be seen in a similar gas turbine combustor. Previous efforts have shown that combustor inlet temperatures of around 700°C at 200 bar are to be expected for a cycle with around 1200°C combustor exit temperatures.

The project team led by Southwest Research Institute is in the process of building and commissioning a 1MW scale direct-fired sCO2 oxy combustor. The test rig at SwRI uses laser ignition and advanced optical access to monitor combustion and characterize behavior. This paper will detail some of the challenges associated with the design and fabrication of the combustor and sCO2 power loop. These obstacles include thermal management, water generation, and constituent monitoring. The first ever unsteady simulations of this type of combustor were conducted as part of the design process. A presentation of the test rig layout, design considerations, and integration challenges will be covered.
Optimization Under Uncertainties of a Biogas-Fueled SOFC-GT Hybrid System
Authors: Finocchi Paolo , Zaccaria Valentina , Ferrari Mario L. , Tucker David
Published: October 2022

SOFC-GT hybrid systems can be a good solution for small-medium size applications of distributed generation thanks to their high efficiency and their high fuel flexibility. Fueling these systems with raw biogas coming from biomass gasification makes them also completely renewable, but it introduces a high variability of performance due to the syngas composition fluctuations. For this reason, this work pursues the aim of realizing a robust system optimization, necessary to obtain the best design and ensure high efficiency combined with low variability. To do this, a co-flow, planar, anode supported SOFC Simulink model was used. Moreover, a related surrogate model was created to decrease the computational time and increase exponentially the number of simulations. To calculate the robust optimum design, the Monte Carlo method was used, simulating the syngas composition distribution with 2000 points and to the operating envelope with 5000 input combinations. Mean value and standard deviation in system efficiency were used to select a Pareto front. The robust points turned out to be those with low electric load, small-medium pressure, and high temperature, while maximum efficiency points were characterized by higher pressure levels. The smaller standard deviation at lower pressure was shown to be linked to the bottoming cycle operation and in particular to the gas turbine off-design condition. This difference between the two design conditions (robust optimum and efficiency optimum) confirmed the importance of this optimization process and the influence of fuel composition on system performance.
Restitution of Impacting Projectiles in Ceramic Matrix Composites (CMCs) Subject to Foreign Object Damage
Authors: Faucett David C. , Mattison Jacob , Choi Sung
Published: October 2022

Accurate assessments of rebound velocity of a projectile in impact events for ceramic matrix composites (CMCs) are important since the rebound velocity affects the degree of resultant impact damage in both CMC targets and projectiles. A series of in-depth characterizations of coefficients of restitution (COR), which is defined as rebound velocity divided by impact velocity of a projectile, was made using various types of gas-turbine grade ceramic matrix composites (CMCs) in conjunction with dynamic imaging and data-acquisition systems. Both the impact aspects and the coefficients of restitution were characterized as a function of impact velocities ranging from 150 m/s to Mach 1 and were analyzed with respect to materials’ key properties. An important experimental observation was that regardless of types of CMCs employed, the corresponding CORs at an impact velocity of 350 m/s (i.e., Mach 1) yielded consistently the same value close to 0.1–0.2. The temperature effect in COR was found to be minor to 1100°C as assessed with the specialty SiC/SiCs, also independent of environmental barrier coatings. The coefficients of restitution were also determined in other materials systems such as advanced monolithic ceramics and some metallic materials in an attempt to construct an overall COR map in response to related foreign object damage (FOD) events.