bluuebunny/crossref_metadata_2025 huggingface dataset:
Response of Autoignition-Stabilized Flames to One-Dimensional Disturbances: Intrinsic Response
Authors: Gopalakrishnan Harish S. , Gruber Andrea , Moeck Jonas
Published: September 2021

Burning carbon-free fuels such as hydrogen in gas turbines promises power generation with strongly reduced greenhouse gas emissions. A two-stage combustor architecture with a propagation-stabilized flame in the first stage and an autoignition-stabilized flame in the second stage allows for efficient combustion of hydrogen fuels. However, interactions between the autoignition-stabilized flame and the acoustic field of the combustor may result in self-sustained oscillations of the flame front position and heat release rate, which severely affect the stable operation of the combustor. We study one such ‘intrinsic’ mode of interaction wherein acoustic waves generated by the unsteady flame front travel upstream and modulate the incoming mixture resulting in flame front oscillations. In particular, we study the response of an autoignition-stabilized flame to upstream traveling acoustic disturbances in a simplified one-dimensional configuration. We first present a numerical framework to calculate the response of autoignition-stabilized flames to acoustic and entropy disturbances in a one-dimensional combustor. The flame response is computed by solving the energy and species mass balance equations, coupled with detailed chemistry. We validate the framework with compressible direct numerical simulations. Lastly, we present results for the flame response to upstream traveling acoustic perturbations. The results show that autoignition-stabilized flames are highly sensitive to acoustic temperature fluctuations and exhibit a characteristic frequency-dependent response. Acoustic pressure and velocity fluctuations can either constructively or destructively superpose with temperature fluctuations, depending on the mean pressure and relative phase between the fluctuations. The findings of the present work are essential for understanding and modeling the intrinsic feedback mechanism in combustors with autoignition-stabilized flames.
Wet Gas Formation and Carryover in Compressor Suction Equipment
Authors: Beck Griffin , Andrews Nathan , Berry A. Grey , McCleney Amy
Published: September 2021

In gas processing, boosting, and gathering applications, gas-liquid separator equipment (typically referred to as a scrubber) is placed upstream of each reciprocating compressor stage to remove water and hydrocarbon condensates. However, field experience indicates that liquids are often still present downstream of the separation equipment. When liquids are ingested into the reciprocating compressor, machinery failures, some of which are severe, can result. While it is generally understood that liquid carryover and condensation can occur, it is less clear how the multiphase fluid moves through equipment downstream of the scrubber.

In this paper, mechanisms responsible for liquid formation and carryover into reciprocating compressors are explored. First, the effects of liquid ingestion on reciprocating compressors reported in the open literature are reviewed. Then, the role of heat and pressure loss along the gas flow path is investigated to determine whether liquid formation (i.e., condensation) is likely to occur for two identical compressors with different pulsation bottle configurations. For this investigation, conjugate heat transfer (CHT) models of the suction pulsation bottles are used to identify regions where liquid dropout is likely to occur. Results of these investigations are presented. Next, liquid carryover from the upstream scrubber is considered. Multiphase models are developed to determine how the multiphase fluid flows through the complex flow path within the pulsation bottle. Two liquid droplet size distributions are employed in these models. Descriptions of the modeling techniques, assumptions, and boundary conditions are provided.
A Novel Hybrid Seal: Design and Experimental Validation on a High Pressure Rotordynamic Test Rig
Authors: Vannini Giuseppe , Defoy Benjamin , Ganiger Manjush , Mazzali Carlo
Published: September 2021

The design and experimental activity presented in this paper is related to a novel hybrid seal which is intended to work as a balance piston seal in an AMBs levitated high-pressure (about 300 bar delivery pressure) motor-compressor. The typical solution adopted for balance piston application is a damper seal (e.g. honeycomb seal), as the rotordynamic stability is a primary focus. However, due to interactions between the AMB controller and seal high stiffness level, the aforementioned selection is not so straightforward.

After a review of the state of the art it was found that a combination of some conventional geometries (e.g. labyrinth and honeycomb) can be adopted to achieve the desired target. The design was done using a novel tool combining the validated bulk flow codes for each geometry. Moreover, a CFD analysis, based on some literature references, was carried out as a final verification of the design.

The experimental activity was then performed at the Authors’ internal seal test rig. As in typical rotordynamic seal testing activity, the operating parameters leveraged to explore performance sensitivity are rotational speed, inlet pressure, pressure ratio and inlet swirl level. The outcome was satisfactory both in terms of leakage and rotordynamic coefficients.
Investigation of a Novel Turbine Housing to Produce a Non-Uniform Spanwise Flow Field at the Inlet to a Mixed Flow Turbine and Provide Variable Geometry Capabilities
Authors: Morrison Richard , Stuart Charles , Kim Sung In , Spence Stephen , Starke Andre , Leonard Thomas
Published: September 2021

Automotive engine downsizing has placed an increased focus on the ability of the turbocharger to provide adequate boost levels across the full engine operating rage. To achieve the desired levels of turbocharger performance the turbine must be capable of operating effectively at the intended design point and also at off-design conditions. Mixed flow turbines (MFTs) provide a potential method to improve performance at off-design conditions and during transient engine operation. A unique feature of a MFT is the spanwise variation of incidence angle at the rotor leading edge. This results in additional flow separation from the blade suction surface near the hub under a wide range of operating conditions. The flow separation generates additional loss and has a detrimental impact on turbine performance.

A novel design of turbine volute similar to a conventional twin-entry turbine volute was examined. The novel turbine volutes were designed to produce a spanwise variation in flow conditions at the rotor inlet. The primary objective was to reduce the incidence angle and increase the mass flow rate at the hub side of the passage relative to the shroud side, as it has previously been identified that this can be beneficial for MFT performance. A number of different volute geometries were examined by numerical analysis to determine the impact of key parameters on turbine performance. The results indicated that generating a suitable spanwise flow distribution could produce a moderate improvement in turbine efficiency at off-design operating conditions. The novel volute design also provided a means of achieving a degree of variable geometry operation to further improve off-design performance. Turbine performance was examined under the variable geometry operation and an improvement in turbine power output at low speed, off-design conditions was achieved. This was analogous to operating with a conventional pivoting vane variable geometry system and had the potential to benefit performance during transient engine operation.
Scale Resolving CFD Investigations of Aerothermal Field and Emissions of a Lean Burn Aeroengine Combustor
Authors: Paccati S. , Mazzei L. , Andreini A. , Patil S. , Shrivastava S. , Bessette D. , Arguinzoni C. , Yadav R.
Published: September 2021

Due to the increasingly stringent international limitations in terms of NOx emissions, the development of new combustor concepts has become extremely important in order for aircraft engines to comply with these regulations. In this framework, lean-burn technology represents a promising solution and several studies and emission data from production engines have proven that it is more promising in reducing NOx emissions than rich-burn technology.

Considering the drawbacks of this combustion strategy (flame stabilization, flashback or blowout or the occurrence of large pressure fluctuations causing thermo-acoustics phenomena) as well as the difficulties and the high costs related to experimental campaigns at relevant operating conditions, Computational Fluid Dynamics (CFD) plays a key role in deepening understanding of the complex phenomena that are involved in such reactive conditions.

During last years, large research efforts have been devoted to develop new advanced numerical strategies for high-fidelity predictions in simulating reactive flows that feature strong unsteadiness and high levels of turbulence intensity with affordable computational resources. In this sense, hybrid RANS-LES models represent a good compromise between accurate prediction of flame behaviour and computational cost with respect to fully-LES approaches. Stress-Blended Eddy Simulation (SBES) is a new global hybrid RANS-LES methodology which ensures an improved shielding of RANS boundary layers and a more rapid RANS-LES “transition” compared to other hybrid RANS-LES formulations.

In the present work, a full annular aeronautical lean-burn combustor operated at real conditions is investigated from a numerical point of view employing the new SBES approach using poly-hexcore mesh topology, which allows to adopt an isotropic grid for more accurate scale-resolving calculations by means of fully regular hexahedral elements in the main stream. The results are compared to experimental data and to previous reference numerical results obtained with Scale Adaptive Simulation formulation on a tetrahedral mesh grid in order to underline the improvements achieved with the new advanced numerical setup.
Impact of Boundary Condition and Kinetic Parameter Uncertainties on NOx Predictions in Methane-Air Stagnation Flame Experiments
Authors: Durocher Antoine , Wang Jiayi , Bourque Gilles , Bergthorson Jeffrey M.
Published: September 2021

A comprehensive understanding of uncertainty sources in experimental measurements is required to develop robust thermochemical models for use in industrial applications. Due to the complexity of the combustion process in gas turbine engines, simpler flames are generally used to study fundamental combustion properties and measure concentrations of important species to validate and improve modelling. Stable, laminar flames have increasingly been used to study nitrogen oxide (NOx) formation in lean-to-rich compositions in low-to-high pressures to assess model predictions and improve accuracy to help develop future low-emissions systems. They allow for non-intrusive diagnostics to measure sub-ppm concentrations of pollutant molecules, as well as important precursors, and provide well-defined boundary conditions to directly compare experiments with simulations. The uncertainties of experimentally-measured boundary conditions and the inherent kinetic uncertainties in the nitrogen chemistry are propagated through one-dimensional stagnation flame simulations to quantify the relative importance of the two sources and estimate their impact on predictions. Measurements in lean, stoichiometric, and rich methane-air flames are used to investigate the production pathways active in those conditions. Various spectral expansions are used to develop surrogate models with different levels of accuracy to perform the uncertainty analysis for 15 important reactions in the nitrogen chemistry and the 6 boundary conditions (ϕ, Tin, uin, du/dzin, Tsurf, P) simultaneously. After estimating the individual parametric contributions, the uncertainty of the boundary conditions are shown to have a relatively small impact on the prediction of NOx compared to kinetic uncertainties in these laboratory experiments. These results show that properly calibrated laminar flame experiments can, not only provide validation targets for modelling, but also accurate indirect measurements that can later be used to infer individual kinetic rates to improve thermochemical models.
Effect of Shock Wave Behavior on Unsteady Aerodynamic Characteristics of Oscillating Transonic Compressor Cascade
Authors: Gan Jiuliang , Watanabe Toshinori , Himeno Takehiro
Published: September 2021

The unsteady behavior of the shock wave was studied in an oscillating transonic compressor cascade. The experimental measurement and corresponding numerical simulation were conducted on the cascade with different shock patterns based on influence coefficient method. The unsteady pressure distribution on blade surface was measured with fast-response pressure-sensitive paint (PSP) to capture the unsteady aerodynamic force as well as the shock wave movement. It was found that the movement of shock waves in the neighboring flow passages of the oscillating blade was almost anti-phase between the two shock patterns, namely, the double shocks pattern and the merged shock pattern. It was also found that the amplitude of the unsteady pressure caused by the passage shock wave was very large under the merged shock pattern compared with the double shocks pattern. The stability of blade vibration was also analyzed for both shock patterns including 3-D flow effect. These findings were thought to shed light on the fundamental understanding of the unsteady aerodynamic characteristics of oscillating cascade caused by the shock wave behavior.
A Method of Solving Three Temperature Problem of Turbine With Adiabatic Wall Temperature
Authors: Wu Zeyu , Luo Xiang , Zhu Jianqin , Zhang Zhe , Liu Jiahua
Published: September 2021

The aeroengine turbine cavity with pre-swirl structure makes the turbine component obtain better cooling effect, but the complex design of inlet and outlet makes it difficult to determine the heat transfer reference temperature of turbine disk. For the pre-swirl structure with two air intakes, the driving temperature difference of heat transfer between disk and cooling air cannot be determined either in theory or in test, which is usually called three-temperature problem. In this paper, the three-temperature problem of a rotating cavity with two cross inlets are studied by means of experiment and numerical simulation. By substituting the adiabatic wall temperature for the inlet temperature and summarizing its variation law, the problem of selecting the reference temperature of the multi-inlet cavity can be solved. The results show that the distribution of the adiabatic wall temperature is divided into the high jet area and the low inflow area, which are mainly affected by the turbulence parameters λT, the rotating Reynolds number Reω, the high inlet temperature Tf,H* and the low radius inlet temperature Tf,L* of the inflow, while the partition position rd can be considered only related to the turbulence parameters λT and the rotating Reynolds number Reω of the inflow. In this paper, based on the analysis of the numerical simulation results, the calculation formulas of the partition position rd and the adiabatic wall temperature distribution are obtained. The results show that the method of experiment combined with adiabatic wall temperature zone simulation can effectively solve the three-temperature problem of rotating cavity.
Exploring Use of Hydrogen for Extending Operability of a Full-Scale Annular Combustor
Authors: Hernandez Candy , McDonell Vincent , Delimont Jacob , Oskam Gareth , Ramotowski Michael
Published: September 2021

In anticipation of increased use of hydrogen as a means of decarbonizing future power generation used widely in combined heat and power plants, studies are underway to understand how hydrogen impacts operability and emissions from existing low emission gas turbines. In the current study, a full-scale annular combustor is used to study how added hydrogen to methane (as a proxy for natural gas) impacts lean blow-off limits. Of particular interest is understanding if hydrogen can be used strategically to extend low emissions operation at lower load. This would facilitate use of gas turbines to offset intermittent renewable power which is becoming increasing integrated into microgrid environments where combined heat and power system are prevalent. A combined experimental and numerical approach is taken. Tests were carried out at Southwest Research Institute using a full-scale annular combustor test rig at elevated temperatures and atmospheric pressure. The individual fuel injectors used were piloted injectors based on natural gas injectors used in practice. Various blends of hydrogen and methane were tested for different scaled load conditions and different pilot to main fuel splits. Besides identifying the overall equivalence ratio at blow-off, measurements also included temperature uniformity at the exit plane and imaging of the reaction. To complement and extend the study a chemical reactor network approach was also applied. The reactor network was initially validated on a prior study involving use of a piloted model combustor. The reactor network was applied to the current configuration and further tuned to align with the measured data. The agreement between the reactor network blow-off and measured blow-off was reasonable. The validated reactor network was then used in combination with a statistically designed simulation matrix to derive a design tool. The tool is then used to estimate other performance features including CO emissions near LBO and the impacts of ambient humidity and the presence of higher hydrocarbons typically found in natural gas. The design tool quantifies the extent to which hydrogen content and pilot percentage can extended part load operability for the full annular combustor system.
Aerodynamic Mitigation of Mechanical Constraints in Small Compressor Blade Profiles
Authors: Dickens Tony , Taylor James , Hall Chris , Miller Rob
Published: September 2021

The drive for ever higher aircraft efficiency inevitably leads to a reduction in core compressor size; over the past 30 years the height of the rear stages of a typical aeroengine has reduced by 40%. This trend will continue; a further reduction of almost 50% is expected by 2050.

It is shown in this paper that the two greatest sources of increased profile loss as core size is reduced comes from the mechanical and manufacturing constraints placed on the maximum and trailing edge thickness. Furthermore, mitigation strategies are presented which successfully minimized or eliminated these loss sources.

An experimental study showed that local modification to the trailing edge shape from a semi-circle to a more elliptical shape almost entirely eliminated the increase in trailing edge loss associated with a reduction in compressor size. Elliptical trailing edges improved loss by both narrowing the wake and increasing the base pressure. Despite the local nature of the modification, the elliptical trailing edges had a powerful effect on flow turning. This was accounted for by redesigning each design to achieve the specified exit flow angle.

A set of “as manufactured” small core blades was created by combining measured data from existing manufacture methods with airfoils scaled to ensure minimum thicknesses necessary for mechanical integrity along the blade were not breached. Core sizes down to 40% of current designs were run in CFD. It is often assumed that the loss in efficiency as core size is reduced is unavoidable. However, it was shown that approximately half of this is directly due to the increase in thickness to satisfy tolerancing. Part to part deviation has negligible effect at all but the smallest compressor size tested (at 40% of current values).
Washing Effectiveness Assessment of Different Cleaners on a Small-Scale Multistage Compressor
Authors: Vulpio Alessandro , Suman Alessio , Casari Nicola , Pinelli Michele , Appleby Craig , Kyte Simon
Published: September 2021

Suspended micrometric particles are always present in the air swallowed by gas turbines. These solid particles can overpass the filters of heavy-duty gas turbines and deposit onto the internal surfaces of the compressor, leading to the overtime reduction of the machine performances, and, as a result, to the fuel consumption augmentation. A widely employed method to slow down the engine degradation is to wash the engine frequently. Over the years, the washing techniques have been continuously improved in order to reach the best compromise between low fluid consumption and high washing capabilities. In this work, an experimental campaign has been carried out to estimate the washing effectiveness on a multistage axial-flow compressor fouled with micrometric soot particles. The cleaning fluids tested in the present work were demineralized water and two cleaners provided by ZOK International Group ltd: a commercial cleaner available on the market (ZOK 27), and a new, under development, environmentally-sensitive formula. The fluids have been tested employing three droplet size distributions (with mean diameters of 20 μm, 50 μm, and 100 μm). The washing effectiveness has been assessed through image post-processing techniques by analyzing the pictures of the stator vanes and rotor blades taken in fouled and washed conditions. From the present investigation, two results arise. The finest droplets show a greater capability to remove soot deposits showing how, when the washing operation takes place during quasi-idle operating condition, the turbulent-driven motion spread smaller particles on a wider blade region. The second results is the demonstration how a environmentally-sensitive chemical formula allows the obtainment of good results in terms removal capability for the same amount of product. This finding could help the plant manager to operate the gas turbine with less constraints in terms of cost and rules.
Overview of the Best 2020 Axial-Flow Fan Data and Inclusion in Similarity Charts for the Search of the Best Design
Authors: Masi Massimo , Danieli Piero , Lazzaretto Andrea
Published: September 2021

The paper deals with the aerodynamic performance of ducted axial-flow fans available in the 2020 market and aims to create a general picture of the best designs and design trends, as a tool for fan designers. To this end, the paper first presents the general formulation of the similarity approach to the fan performance analysis, including the effects of rotational speed (which affects the validity of the Reynolds similarity) and turbomachine size (which can hinder the perfect geometrical similarity of some shape details). The second part reports a statistical survey of the axial-flow fan performance based on data from catalogues of major manufacturers, and compares the resulting Cordier-lines with optimum fan designs from empirical or CFD-based models available in the literature. In addition to the global performance at maximum aeraulic and total-to-static efficiencies, this survey uses the form of dimensionless Balje-Cordier charts to identify the trends and values of other design parameters, such as hub-to-tip ratio, blade count, and blade positioning angle. As a result, a summary of the aerodynamic performance of year 2020 best designs, the improvements achieved during the last forty years, and the present design trends in contra-rotating, vane-axial, and tube-axial fan types are made available to fan designers.
The Influence of Purge Flow Parameters on Heat Transfer and Film Cooling in Turbine Center Frames
Authors: Jagerhofer Patrick R. , Patinios Marios , Glasenapp Tobias , Göttlich Emil , Farisco Federica
Published: September 2021

Due to stringent environmental legislation and increasing fuel costs, the efficiencies of modern turbofan engines have to be further improved. Commonly, this is facilitated by increasing the turbine inlet temperatures in excess of the melting point of the turbine components. This trend has reached a point where not only the high-pressure turbine has to be adequately cooled, but also components further downstream in the engine. Such a component is the turbine center frame (TCF), having a complex aerodynamic flow field that is also highly influenced by purge-mainstream interactions. The purge air, being injected through the wheelspace cavities of the upstream high-pressure turbine, bears a significant cooling potential for the TCF. Despite this, fundamental knowledge of the influencing parameters on heat transfer and film cooling in the TCF is still missing.

This paper examines the influence of purge-to-mainstream blowing ratio, purge-to-mainstream density ratio and purge flow swirl angle on the convective heat transfer coefficient and the film cooling effectiveness in the TCF. The experiments are conducted in a sector-cascade test rig specifically designed for such heat transfer studies using infrared thermography and tailor-made flexible heating foils with constant heat flux. The inlet flow is characterized by radially traversing a five-hole-probe. Three purge-to-mainstream blowing ratios and an additional no purge case are investigated. The purge flow is injected without swirl and also with engine-similar swirl angles. The purge swirl and blowing ratio significantly impact the magnitude and the spread of film cooling in the TCF. Increasing blowing ratios lead to an intensification of heat transfer. By cooling the purge flow, a moderate variation in purge-to-mainstream density ratio is investigated, and the influence is found to be negligible.
On the Shaft Speed Selection of Parallel Hybrid Aero Engines
Authors: Sielemann Michael , Gohl Jesse , Zhao Xin , Kyprianidis Konstantinos , Valente Giorgio , Sumsurooah Sharmila
Published: September 2021

The boosted turbo fan or parallel hybrid is a promising means to reduce fuel consumption of gas turbines on aircraft. With an electric drive on the low-pressure spool of the gas turbine, it requires a trade-off between the characteristics of the gas turbine and the electric power sub-systems. Reducing specific thrust at a given thrust requirement results in a larger fan with a lower pressure ratio. This leads to improved propulsive efficiency but at the expense of increased weight and nacelle drag. At a given design relative tip Mach number, increasing fan size and hence tip diameter means the fan shaft speed will need to be reduced. This will, according to occasionally quoted ‘rules of thumb’, make the directly coupled electrical drive more efficient but heavier. The objective of this paper is to expose some key aspects of this trade-off in terms of efficiency and weight, and relate them to these guidelines. The paper applies sophisticated methodology in both addressed domains. For the gas turbine, multi-point design is used. Here, established synthesis matching schemes focusing on gas turbine performance parameters are extended with parameters from the sizing and weight estimation such as diameters and tip speeds. For the electrical machine, fully analytical sizing capturing the impact of cooling supply is used. The paper reports estimated gas path and machine geometries. It gives an understanding of the interactions between both sub-systems and allows concluding which low pressure spool speed gives the best instantaneous performance. It largely confirms the quoted rules of thumb but exposes that the factors affecting machine efficiency are more involved than implied for an integrated design.
Stability and Unbalance Analysis of Rigid Rotors Supported by Spiral Groove Bearings: Comparison of Different Approaches
Authors: Iseli Elia , Schiffmann Jürg
Published: September 2021

The dynamic behavior of spiral-grooved gas bearing supported 4DoF rotors is investigated by means of linearized bearing force coefficients and full time-integrated transient analysis. The transient method consists of a state-space representation, which couples the equations of motion with the compressible thin film fluid equation. The linearized method is based on the perturbation analysis around a given eccentric shaft position ε, allowing to compute the static and linear dynamic bearing force coefficients at different excitation frequencies.

The two methods are compared for a variation of test rotors and bearing geometries in a given compressibility number interval of Λ = [0,40]. The limitations and weaknesses of the linearized model are presented. It is shown that shafts with two symmetric herringbone-groove journal bearings have their maximum stability and load capacity if the center of gravity lays in the middle of the two bearings. For symmetric rotors (la/lb = 1) the two rigid modes, cylindrical and conical, are present and are influenced by the mass and transverse moment of inertia independently. For asymmetric rotors (la/lb < 1) the stability region decreases and the modes have a mixed shape. It is no longer possible to clearly distinguish between pure cylindrical and pure conical mode shapes. The two methods predict the critical mass and critical transverse moment of inertias within a difference of < 7%.

A quasi-linear unbalance module for rigid gas bearing supported rotors is presented, which considers eccentricity dependent bearing force coefficients, allowing to speed up the unbalance response analysis by four orders of magnitude. The unbalance module is compared with the full transient orbital analysis, suggesting that the quasi-linear module predicts the non-linear unbalance response with < 6 % deviation for amplitudes up to ε < 0.5 within the complete compressibility number range.
The Effects of Forcing Direction on the Flame Transfer Function of a Lean-Burn Spray Flame
Authors: Treleaven Nicholas C. W. , Fischer André , Lahiri Claus , Staufer Max , Garmory Andrew , Page Gary J.
Published: September 2021

The flame transfer function (FTF) of an industrial lean-burn fuel injector has been computed using large eddy simulation (LES) and compared to experimental measurements using the multi-microphone technique and OH* measurements. The flame transfer function relates the fluctuations of heat release in the combustion chamber to fluctuations of airflow through the fuel injector and is a critical part of thermoacoustic analysis of combustion systems. The multi-microphone method derives the FTF by forcing the flame acoustically, alternating from the upstream and downstream side. Simulations emulating this methodology have been completed using compressible large eddy simulations (LES). These simulations are also used to derive an FTF by measuring the fluctuations of mass flow rate and heat release rate directly which reduces the number of simulations per frequency to one, significantly reducing the simulation cost. Simulations acoustically forced from downstream are shown to result in a lower value of the FTF gain than simulations forced from upstream with a small change in phase, this is shown to be consistent with theory. Through using a slightly different definition of the FTF, this is also shown to be consistent with measurements of the heat release rate using OH* chemiluminescence however these results are inconsistent with the multi-microphone method result. The discrepancy comes from not having an accurate measurement of the acoustic impedance at the exit plane of the injector and from certain convective phenomena that alter the downstream velocity and pressure field with respect to the purely acoustic signal. All simulations show a lower gain in the FTF than the experiments but with good reproduction of phase. Previous work suggests this error is likely due to fluctuations of the fuel spray atomisation process due to the acoustic forcing which is not modelled in this study.
Adjoint-Based Optimisation of Rocket Engine Turbine Blades
Authors: Sanghera Bhupinder Singh , Anand Nitish , Souverein Louis , Penin Loïc , Pini Matteo
Published: September 2021

Axial turbine stages for gas generator cycle type rocket engines typically employ highly-loaded supersonic stator vanes. Consequently, the flow pattern downstream of the vanes is characterized by shock waves which induce high-frequency excitation on the subsequent rotor. For this reason, the optimal design of the stator is crucial in the context of development of the next generation of high-performance rocket engines, where reusability is a principal design criterion. A thorough comprehension of the loss mechanisms combined with the adoption of automated optimisation techniques can therefore enable new stator designs that may provide large benefits in terms of overall turbine performance and lifespan.

The scope of this study stems from these considerations and its objective is twofold, namely i) the shape optimisation of a supersonic stator for rocket engines and ii) the investigation of the loss mechanisms in supersonic axial turbine stator vanes at on- and off-design conditions. The investigation is performed on stator vanes that are under development for the first turbine stage of a gas generator cycle type rocket engine. The stator vanes are therefore optimised in order to reduce the profile losses by exploiting a novel adjoint optimisation framework for turbomachinery implemented in the open-source code SU2. The effect on the resulting flow field and loss sources is finally investigated.

Results show that entropy based loss coefficient gains of 6% can be achieved via shape optimisation and that the fluid-dynamic performance of these vanes is less sensitive to changes in pressure ratio compared to the performance provided by the baseline configuration. Eventually, shock-waves remain the primary loss source.
Ancillary Services Potential for Flexible Combined Cycles
Authors: Vannoni Alberto , Garcia Jose Angel , Mantilla Weimar , Guedez Rafael , Sorce Alessandro
Published: September 2021

Combined Cycle Gas Turbines, CCGTs, are often considered as the bridging technology to a decarbonized energy system thanks to their high exploitation rate of the fuel energetic potential. At present time in most European countries, however, revenues from the electricity market on their own are insufficient to operate existing CCGTs profitably, also discouraging new investments and compromising the future of the technology. In addition to their high efficiency, CCGTs offer ancillary services in support of the operation of the grid such as spinning reserve and frequency control, thus any potential risk of plant decommissioning or reduced investments could translate into a risk for the well-functioning of the network. To ensure the reliability of the electricity system in a transition towards a higher share of renewables, the economic sustainability of CCGTs must be preserved, for which it becomes relevant to monetize properly the ancillary services provided. In this paper, an accurate statistical analysis was performed on the day-ahead, intra-day, ancillary service, and balancing markets for the whole Italian power-oriented CCGT fleet. The profitability of 45 real production units, spread among 6 market zones, was assessed on an hourly basis considering local temperature, specific plant layouts, and off-design performance. The assessment revealed that net income from the ancillary service market doubled, on average, the one from the day-ahead energy market. It was observed that to be competitive in the ancillary services market CCGTs are required to be more flexible in terms of ramp rates, minimum environmental loads, and partial load efficiencies. This paper explores how integrating a Heat Pump and a Thermal Energy Storage within a CCGT could allow improving its competitiveness in the ancillary services market, and thus its profitability, by means of implementing a model of optimal dispatch operating on the ancillary services market.
HCF Optimization of a High Speed Variable Geometry Turbine
Authors: Simpson Alister , Kim Sung in , Park Jongyoon , Kwon Seong , Yoo Sejong
Published: September 2021

This paper describes the structural optimization of a high speed, 35mm tip diameter radial turbine wheel in a Variable Geometry Turbine (VGT) system, subjected to the wide range of aerodynamic loads experienced during the full operating cycle. VGTs exhibit a wide range of unsteady flow features, which vary as the nozzle vanes rotate through different positions during operation, as do the magnitudes and frequencies of the resulting pressure fluctuations experienced by the downstream turbine blades. The turbine wheel typically passes through a number of blade natural frequencies over their operating cycle, and there are a number of potential conditions where these unsteady aerodynamic loads can lead to resonant blade vibration. The focus of this work is on the development of a pragmatic design approach to improve the structural characteristics of a radial turbine blade with respect to High Cycle Fatigue (HCF), informed by detailed time-accurate Computational Fluid Dynamics (CFD) prediction of the unsteady pressure loads, coupled with FE vibration analysis to quantify the resulting blade vibration magnitudes. Unsteady CFD simulations are performed to determine the time-accurate pressure loads on the blades, and the results are used as input to forced response analysis to determine the peak alternating stress amplitudes. The detailed analysis results are then used to guide a subsequent parametric study in order to investigate the influence of key geometric parameters on the structural performance of the blade, with the optimum design identified through the use of a Goodman Diagram. The results quantify the influence of both blade thickness distribution and hub fillet details on the vibration characteristics of radial turbines.
Two Phase Flow CFD Modeling of a Steam Turbine Low Pressure Section: Comparison With Data and Correlations
Authors: Maceli Nicola , Arcangeli Lorenzo , Arnone Andrea
Published: September 2021

Testing a sub-component or testing a scaled model are the approaches currently used to reduce the development cost of the new low-pressure (LP) section of a steam turbine. In any case, testing campaigns are run at a limited number of operating conditions. Therefore, some correlations are used to build a performance model of the LP module and expand the usage of a limited set of experimental data to cover the application range encountered in the steam turbine market. Another approach, which has become feasible during the last decade, is the usage of CFD calculations.

These two approaches include a certain amount of uncertainty in the performance of the LP section, mainly related to the losses caused by the moisture content in the flow.

In the present paper, the results of the analysis of a cutting-edge low-pressure section for small steam turbines are presented. The results are obtained by using a CFD commercial code with a set of user defined subroutines to model the effects of droplets nucleation and growth. Different operating conditions are considered, with different wetness at the exit and different pressure ratios, in order to clearly show the loss trend for different levels of exit moisture. The numerical results are compared with the experimental data, showing a significant improvement in the performance predictability for the considered case and demonstrating the benefit of using a CFD approach instead of using existing correlations.
Synchrotron X-Ray Diffraction to Quantify In-Situ Strain on Rare-Earth Doped Yttria-Stabilized Zirconia Thermal Barrier Coatings
Authors: Fouliard Quentin , Hernandez Johnathan , Ebrahimi Hossein , Vo Khanh , Ghosh Ranajay , Raghavan Seetha , Accornero Frank , McCay Mary , Park Jun-Sang , Almer Jonathan
Published: September 2021

The recent advancement in multifunctional thermal barrier coatings (TBCs) for temperature sensing or defect monitoring has gained interest over the past decade as they have shown great potential for optimized engine operation with higher efficiency, reduced fuel consumption and maintenance costs. Specifically, sensor coatings containing luminescent ions enable materials monitoring using integrated spectral characteristics. While facilitating sensing capabilities, luminescent rare-earth dopants ideally present minimal intrusiveness for the thermal barrier coating. However, the effects of rare-earth dopant addition on thermomechanical and thermochemical properties remain unclear. Our study intends to fill this knowledge gap by characterizing coatings’ internal thermomechnical properties under realistic gas turbine engine operating temperatures. In this work, TBC configurations including industry standard coatings and sensor coatings were compared to quantify dopant intrusiveness. The TBC configurations have been characterized using high-energy synchrotron X-ray diffraction while being heated up to gas turbine engine temperatures. The TBC samples have been subjected to a single cycle thermal load with multiple ramps and holds during XRD data collection. Depth-resolved XRD was used to obtain the 2D diffraction patterns corresponding to each depth location for the determination of strain distributions along the TBCs. Internal strains and stresses acting through the coatings were quantified mostly highlighting that there is negligible variation between the standard and novel sensor coatings. Thus, the thermal response at high temperature remains unaffected with addition of luminescent dopants. This evaluation of novel coating configurations provides valuable insight for future safe implementation of these temperature sensing coatings without performance reductions.
A Supercritical CO2 Brayton Cycle Micro Turbine for Waste Heat Conversion: Optimization Layout in Cogenerative Applications
Authors: Reale Fabrizio , Sannino Raniero , Tuccillo Raffaele
Published: September 2021

Waste heat recovery (WHR) can represent a good solution to increase overall performance of energy systems, even more in case of small systems. The exhaust gas at the outlet of micro gas turbines (MGTs) has still a large amount of thermal energy that can be converted into mechanical energy, because of its satisfactory temperature levels, even though the typical MGT layouts perform a recuperated cycle. In recent studies, supercritical CO2 Brayton Cycle (sCO2 GT) turbines were studied as WHR systems whose thermal source was the exhausts from gas turbines. In particular, subject of this study is the 100 kW MGT Turbec T100.

In this paper, the authors analyze innovative layouts, with comparison in terms of performance variations and cogenerative indices. The study was carried out through the adoption of a commercial software, Thermoflex, for the thermodynamic analysis of the layouts. The MGT model was validated in previous papers while the characteristic parameters of the bottoming sCO2 GT were taken from the literature. The combined cycle layouts include simple and recompression sCO2 bottoming cycles and different fuel energy sources like conventional natural gas and syngases derived by biomasses gasification. A further option of bottoming cycle was also considered, namely an organic Rankine cycle (ORC) system for the final conversion of waste heat from sCO2 cycle into additional mechanical energy. Finally, the proposed plants have been compared, and the improvement in terms of flexibility and operating range have been highlighted.
Combustor Development and Engine Demonstration of Micro-Mix Hydrogen Combustion Applied to M1A-17 Gas Turbine
Authors: Horikawa Atsushi , Okada Kunio , Yamaguchi Masato , Aoki Shigeki , Wirsum Manfred , Funke Harald H.-W. , Kusterer Karsten
Published: September 2021

Kawasaki Heavy Industries, LTD. (KHI) has research and development projects for a future hydrogen society. These projects comprise the complete hydrogen cycle, including the production of hydrogen gas, the refinement and liquefaction for transportation and storage, and finally the utilization in a gas turbine for electricity and heat supply. Within the development of the hydrogen gas turbine, the key technology is stable and low NOx hydrogen combustion, namely the Dry Low NOx (DLN) hydrogen combustion.

KHI, Aachen University of Applied Science, and B&B-AGEMA have investigated the possibility of low NOx micro-mix hydrogen combustion and its application to an industrial gas turbine combustor. From 2014 to 2018, KHI developed a DLN hydrogen combustor for a 2MW class industrial gas turbine with the micro-mix technology. Thereby, the ignition performance, the flame stability for equivalent rotational speed, and higher load conditions were investigated. NOx emission values were kept about half of the Air Pollution Control Law in Japan: 84ppm (O2-15%). Hereby, the elementary combustor development was completed.

From May 2020, KHI started the engine demonstration operation by using an M1A-17 gas turbine with a co-generation system located in the hydrogen-fueled power generation plant in Kobe City, Japan. During the first engine demonstration tests, adjustments of engine starting and load control with fuel staging were investigated. On 21st May, the electrical power output reached 1,635 kW, which corresponds to 100% load (ambient temperature 20 °C), and thereby NOx emissions of 65 ppm (O2-15, 60 RH%) were verified. Here, for the first time, a DLN hydrogen-fueled gas turbine successfully generated power and heat.
Turboprop Engine Loading During High and Low Maneuver Intensity Flight Mode
Authors: Templalexis Ioannis , Giachalis Lambros , Lionis Ioannis
Published: September 2021

The life consumption rate of the aircraft engine is a vital input for aircraft operators who aim to an efficient fleet management. T6 aircraft, propelled by the PT6 turboprop engine, is operated by the Hellenic Air Force, both for training and aerobatic purposes. The current study focuses on quantifying and comparatively assessing the engine life consumption rate for the following missions: i) An “aerobatic” mission which is a typical high intensity maneuver flight and ii) a “training for patrol” mission, representing a typical low intensity maneuver flight. Missions were selected with the criterion of setting the lowest and the highest possible engine loading during a certain mission. In other words, the goal of the study is to define the extent of the loading the engine can encounter as a propulsion system of the T-6 aircraft during a certain mission. This is the first step before proceeding in setting up a methodology for continuously monitoring the engine life consumption rate in support of the squadron flight management plan. The study was based on real time data recorded during the respective flights. An engine model built using “GasTurb” gas turbine simulation software was used to fill in engine operating data at stations where recordings have not been taken. Engine life consumption was based on creep and low cycle fatigue failure mechanisms of the first gas generator turbine stage. Creep life fractions were calculated based on the Larson-Miller parameter curves and the fatigue cycles were counted using the rainflow method. The study showed that the life consumption is about 10 times lower when the aircraft is operated at a low loading mode as opposed to a high loading mode.