bluuebunny/crossref_metadata_2025_split huggingface dataset:
Impact of Central Piloting on the Static and Dynamic Stability of Swirl-Stabilized Flames
Authors: Doleiden Daniel , Karmarkar Ashwini , O’Connor Jacqueline , Blust James 
Published: October 2022

Abstract
One of the key challenges of lean, low-emissions combustor operation is flame stabilization, including both static and dynamic stabilization. Static flame stability encompasses a range of issues like flame holding, flashback, and blow-off. Dynamic flame stability refers to thermoacoustic combustion oscillations, which are driven by a coupling between combustor acoustics and flame heat release rate oscillations. Pilot flames are used as a passive means of achieving both static and dynamic stability in a number of gas turbine combustor technologies, likely by acting as a source of heat and radical species at the base of the main flame. Previous work used high-speed CH* chemiluminescence imaging to characterize the effect of a central pilot flame on the macrostructure and dynamic stability of a swirled lean-premixed natural gas-air main flame. In this study, the static and dynamic stability of the main flame are controlled by modifying the equivalence ratios of the main and pilot flames to better understand the mechanisms by which pilot flames enhance both static and dynamic stability. High-speed OH planar laser-induced fluorescence (OH-PLIF) is used to capture local instantaneous dynamics of the main and pilot flames across a range of operating conditions and stability outcomes, building upon the line-of-sight chemiluminescence analysis of the previous work. We find that the presence of the pilot flame controls anchoring of a relatively lean main flame. When the pilot flame is added to an unpiloted main flame, the main flame can rapidly change stabilization location, anchoring to the centerbody of the fuel injector. When a piloted main flame has the pilot removed, the flame lingers on the centerbody for a longer duration, likely due to the high-temperature boundary condition at the centerbody anchoring point. Further, the pilot flame mitigates combustion instability for a relatively broad range of operating conditions. Analysis of high-speed OH-PLIF shows that the main and pilot flames do not directly interact, and therefore the stabilizing mechanism of the pilot flame is indirect, as previously suggested.
Prediction of Rotating Instabilities in Low Pressure Steam Turbines Operating at Low Load
Authors: Pütz Oliver 
Published: October 2022

Abstract
Due to the increasing need for operational flexibility nowadays, the low-pressure (LP) steam turbine might face widely variable operation conditions up to extreme low volume flow situations. Hereby, rotating instabilities (RIS), well known from compressor aerodynamics, can initiate non-synchronous blade excitations which can lead to increased vibrations of the last stage moving blade (L-0R). This paper describes a numerical method able to be used in an applicable way for blade designing.
To judge the onset and the shape of RIS, a numerical approach based on a transient 3D URANS flow computation of the single passage L-1 stage, a full row L-0 stage, and an axis-symmetric diffuser was established. Mesh size, solver settings and other parameters were optimized to reduce the computational effort without losing prediction accuracy.
The dominant harmonic compound of a spatial Fourier transform of all monitored L-0R blade forces over the blade row’s circumference reveals the stall cell count and excitation amplitude for each timestep. The transient change of the corresponding phase lag provides the stall cell speed; and multiplied with the stall cell count the excitation frequency. Their distribution over decreasing flow rates finally displays the likely onset of RIS.
The approach is capable to run the analyses of several load conditions within a couple of days and was successfully validated using measured blade tip deflections and unsteady pressure probes in multistage test turbines. Furthermore, it is shown that the approach can be used to find LP blade designs where the effects of RIS can be significantly suppressed.
Optimal Strategy of the Energy Management Within the Microgrid Using the Hydrogen Fueled Gas Turbine
Authors: Ancona Maria Alessandra , Bianchi Michele , Branchini Lisa , Catena Francesco , De Pascale Andrea , Melino Francesco , Ottaviano Saverio , Peretto Antonio 
Published: October 2022

Abstract
The hydrogen production by means of renewable energy exploitation has the potential to address issues that arise when an increasing share of power is generated from sources that have a highly variable output. Although these systems have been widely studied, one of the key aspects to be considered is the choice of the energy management strategy.
The aim of this paper is to define and present an optimal strategy for the energy flow management of a pilot plant consisting of a turbine gas facility making use of power produced during turbine tests — along with solar — for hydrogen production integrated with batteries storage.
Key results from the analyses are: i) increasing the hydrogen production target, the hydrogen production ratio increases up to a maximum value equal to about 100%; ii) optimizing the management strategy, the system is always able to meet the demand of hydrogen; iii) with a larger hydrogen storage capacity, the microgrid is able to exploit a higher amount of renewable production, achieving the total renewable energy exploitation.
A Probabilistic Method for Predicting Particle-Blade Impact Kinematics in Turbomachinery
Authors: Klaoudatos D. , Bojdo N. , Filippone A. , Covey-Crump S. , Jones M. , Pawley A. 
Published: October 2022

Abstract
The trajectories of dust particles ingested into gas turbine engines are dictated by their inertial properties, which influence the likelihood of collision with solid surfaces along the gas path, including compressor blades and casing. If a particle impacts a surface, it will either bounce, stick, or shatter. The fate is dependent on the kinematics of the interaction, which vary widely across the blade span and chord, and across the range of particle size and composition that a gas engine may typically ingest. This makes the prediction of compressor fouling or erosion using traditional deterministic methods computationally expensive. In this contribution, a new reduced-order model is proposed that can rapidly predict the probability of particle interaction with the blade and casing, and the probability of particle escape from the rotor outlet as a function of a dimensionless parameter, the generalized centrifugal Stokes number. Numerical simulations of particle-laden flow through a single-stage axial compressor rotor, the NASA Rotor 37, are performed to generate a dataset of particle-surface interaction kinematics for three minerals, each with a wide size distribution (0.3–135 μm), at three different blade rotation speeds. We also introduce a new dimensionless parameter, the particle kinetic energy ratio, to enable a non-dimensional particle impact kinematic analysis. Our results show that particle impact kinetic energy may be estimated on the basis of Stokes number alone.
Spray Characterization of a Preheated Bio-Oil Surrogate at Elevated Pressures
Authors: Broumand Mohsen , Thomson Murray J. , Yun Sean , Hong Zekai 
Published: October 2022

Abstract
Atomization plays an important role in the gasification or combustion of bio-oils, where the atomizer parameters need to be properly controlled to efficiently atomize a highly viscous liquid at elevated pressures with imparting the least amount of kinetic energy to the discharged droplets because of evaporation and chemical reaction constraints. With a focus on bio-oil deployments in micro gas turbines (MGTs), an aqueous surrogate of a preheated bio-oil, injected from an original equipment manufacturer (OEM) twin-fluid atomizer, is used in the present study for spray size and velocity measurements at elevated pressures. The experiments were conducted in High Pressure Spray Facility of the National Research Council of Canada (NRC) using various optical diagnostics including laser sheet imaging (LSI), phase Doppler anemometry (PDA), and laser diffraction (LD). A scaling strategy was adopted to conserve the ranges of gas-to-liquid momentum flux ratio, M, at different working pressures, P. Over the range of conditions studied, it is found out that the cone angle of sprays is insensitive to P, but they decrease with increasing M. For a constant value of M, droplet mean diameters increase and their corresponding velocities decrease with increasing P, attributed to the effect of gas-to-liquid density ratio on the primary breakup of a liquid jet in a coaxial gas stream. Therefore, to predict the Sauter mean diameter of spray droplets, D32, a correlation previously reported in the literature is modified by including the effect of system air density at elevated pressures, and a novel correlation is proposed based on four dimensionless groups, namely gas Weber number and gas-to-liquid momentum flux ratio, density ratio, and viscosity ratio. The detailed results obtained in the present study could be used to define the optimal parameters required for twin-fluid atomization of high viscosity liquids with various atomization gases under realistic operating conditions and to enhance the capabilities of their numerical simulations.
Performance Assessment of a Recuperated Turboshaft Engine: A Multifuel Case
Authors: Anfossi Jody , Al-Zaili Jafar , El Samad Tala , Sayma Abdulnaser 
Published: October 2022

Abstract
The low cycle efficiency of simple cycle micro gas turbines is typically raised by the use of recuperators. The recuperated cycle allows for improved efficiency at low power-to-weight ratio, mainly due to the weight of the added heat exchanger. As weight is considered to be a key parameter for aeroengines, an analysis that addresses benefits and drawbacks of a more efficient, but heavier propulsion system design is required to be carried out. This paper assesses propulsion systems based on simple and recuperated cycle small gas turbine configurations, unusual in aviation, running with conventional jet fuel or hydrogen. An analytical model capable of modelling a turboshaft engine steady state design and off-design operation is developed. The specific fuel consumption of different engine arrangements is therefore calculated to evaluate the performance trade-off between the improved power plant fuel economy and its larger weight under a generic reference mission for a light helicopter. To enable a consistent mission analysis study of the hydrogen fueled rotorcraft, the weight of the tanks for liquid hydrogen storage is estimated according to a preliminary design model. The results obtained suggest that a hydrogen-fueled recuperated powerplant can shorten the flight time to reach the breakeven point, compared to a recuperated jet fuel powerplant of the same power rating.
Modeling and Cycle Parameter Matching of a High-Speed Variable Cycle Turbofan-Ramjet Engine
Authors: Yao Yao , Zhang Xiaobo , Zhang Mingyang , Wang Zhanxue 
Published: October 2022

Abstract
Variable cycle turbofan-ramjet (VCTR) engine is a promising propulsion system candidate for future Mach 4+ vehicles. Compared with conventional turbine engines, the VCTR engine has a higher thrust-to-weight ratio, a smaller diameter and a more compact structure. A component-based simulation model is developed to explore the operating characteristics of a high-speed VCTR concept. Modeling methods of variable-geometry components are characterized in this paper, and then the way to build the VCTR model solver is described. The VCTR engine simulation model is validated by the numerical and experimental results of double bypass variable cycle engines from NASA technical reports. Performance and control law of the VCTR engine along the flight trajectory with flight Mach number varying from 0.5 to 4.0 are obtained to maximize net thrust and compared with that of a conventional two-spool afterburning mixed-flow turbofan (MFTF). Results show that the VCTR’s performance is highly dependent on the fan characteristics and limited by various operating constraints, such as fan surge margin, turbine inlet temperature, and compressor discharge temperature. In addition, the thrust level of the MFTF with the variable-area low-pressure turbine is close to the VCTR engine.
Acoustic Optimization Approach for Annular Diffusers in Turbomachinery Applications Using Plane Wave Modelling
Authors: Fischer Felix , Seume Jörg 
Published: October 2022

Abstract
The experimental investigation of unsteady aerodynamic effects in turbomachinery test rigs requires the establishment of anechoic boundary conditions in order to acquire data unaffected by acoustic reflections outside the test section. In this manner, controlled measurement environments can be achieved that allow for the acquisition of high-quality aeroacoustic and -elastic measurement data in turbomachinery test rigs. In the case of the initial design of the Aeroacoustic Wind Tunnel (AWT) at the Institute of Turbomachinery and Fluid Dynamics, acoustic reflections were observed in the diffuser section of the test rig, which interfered with the sound transmission measurements of low-pressure turbine airfoils.
The present paper describes a one-dimensional semi-analytical modelling and optimization approach of sound propagation in the AWTs diffuser section for plane waves based on Webster’s horn equation. With this approach, a new hub diffuser was designed for defined geometric and aerodynamic boundary conditions, which compared to the original geometry, reduce acoustic reflections due to continuous impedance matching. The design of a new supporting strut configuration further reduces reflections due to scattering from installations in the flow path. Validation of the modelling and solution approaches are carried out based on a comparison with experimental data of the initial (reference) design, as well as numerical simulations of both designs. According to analytical and numerical models the optimized design reduces acoustic reflections by up to 21.2 dB compared to the initial design.
Analysis of Turbulent Effects in a Low-Pressure Model Steam Turbine Operating Under Various Operating Conditions Using Detached Eddy Simulation
Authors: Ercan Ilgit , Vogt Damian M. 
Published: October 2022

Abstract
Steam turbines are sometimes operated at extreme part-load conditions, specifically if the energy balance in power grids featuring a high share of fluctuating energy sources necessitates such operation. At such extreme operating conditions, the last stages of the low-pressure turbine are subject to highly unsteady flow. As the flow is heavily separated, Rotating Instabilities (RI) may establish, among other turbulent effects. These highly unsteady flow structures result in fluctuations of the flow field over a wide range of low frequencies.
The simulation of the flow at such extreme operating conditions using CFD is challenging due to its highly turbulent and separated nature. On one hand, the employed flow model must be able to handle turbulent structures with varying size in a computationally efficient manner. On the other hand, the extent of the computational domain must be relevant with respect to the unsteady flow phenomena. The analyzed domain in this study consists of a three-stage low-pressure model steam turbine. To capture the asymmetry, the model spans the full annulus and comprises the non-axisymmetric inlet section, all three stages, the axial-radial diffuser as well as the exhaust hood.
Based on the findings of a previous study in which the Improved Delayed Detached Eddy Simulation (iDDES) has been applied to low-volume flow operating conditions [1], the focus of this paper is drawn towards the turbulent structures that establish at extreme flow conditions, and whether they can also be found at increased volume flows. Time-averaged and FFT results of the unsteady pressure signals at different span heights measured during experimental and numerical radial probe traverses indicate a higher unsteadiness during the lowest volume flow condition when compared to higher volume flows. Various turbulent structures have been identified at the hub region, the midspan section and the tip region of the last stage rotor blade that could be linked to the higher flow unsteadiness.
Furthermore, the possibility of using URANS simulations for the prediction of such extreme flows has been investigated, leading to the finding that the choice of flow model has an impact on the results. Additionally, it was investigated if the extent of the computational domain could be reduced to save computational costs. It was found that a reduced domain did not yield the low frequencies that are of relevance at such operating conditions.
Large Eddy Simulation of an Open Rotor Fan Blade
Authors: Priebe Stephan , Wood Trevor , Yi Junsok , Mousavi Arash 
Published: October 2022

Abstract
Open rotor fan blades, when exercised across a range of operating conditions and design options, present a variety of complex flow physics including leading-edge flow separation, wake evolution and interaction effects, and laminar-to-turbulent transition. In this paper, we present a large-eddy-simulation (LES) study of a three-dimensional open rotor fan blade at realistic conditions. Specifically, we focus in this paper on takeoff conditions, run at a Reynolds number representative of a subscale rig typically used for aeroacoustic technology maturation testing, to explore the flow behavior and its effects on takeoff aerodynamic performance and aeroacoustics that contribute to community noise. The simulations were performed using GENESIS, a high-order unstructured LES solver. The convergence of the solution is assessed by varying the polynomial order of the solution from low to high order. The analysis presented in the paper focuses on the evolution of the flow near the blade surface and the subsequent mixing downstream in the wake for a realistic blade design that exhibits the full three-dimensionality of these flow physics. A detailed understanding of these flow features is most useful for the aerodynamic and acoustic design of open rotor propulsors and the related implications of the LES results relative to conventional RANS-based CFD/CAA predictions is discussed.
A Novel 100% Hydrogen Gas Turbine Combustor Development for Industrial Use
Authors: Cho Eun-Seong , Jeong Hanjin , Hwang Jeongjae , Kim Minkuk 
Published: October 2022

Abstract
Doosan is developing a 5 MW 100% hydrogen gas turbine combustor based on the existing NG (natural gas) firing combustor through a national project. This engine consists of 8 (eight) cans of the combustor and our plan is to develop a hydrogen burner to replace the existing NG burner, if possible, without any change of other combustor components such as liner & transition piece, etc. We developed various concept nozzles for 100% hydrogen combustion without flash back during the operating condition and low NOx emission using dry low NOx premixed combustion methods. Among the various concept nozzles several candidates conducted experiment test in ambient pressure condition which they showed low NOx emission and larger operating conditions through lean blow off and flame holding flash back test. The best nozzle will be selected and tested at ambient & high pressure can test for evaluating 100% hydrogen combustor development targets.
Innovative Cycles for Industrial Combined Heat and Power Generation With Carbon Capture and Storage
Authors: Kapoor Riddhi R. , Klein Sikke 
Published: October 2022

Abstract
Industry is a major contributor to the rise in global CO2 emissions, constituting one fifth of the global energy consumption, of which a significant amount is provided by fossil fuel combustion. Following the Paris agreement, emphasis has been made on the decarbonization of the industrial sector. This study focuses on industrial decarbonization by employing Carbon Capture and Storage for Combined Heat and Power (CHP) gas turbine plants. The scope of this study includes conceptual modelling and thermodynamic analysis of potential decarbonization options for zero carbon CHP plants. The studied options include post-combustion capture, exhaust gas recirculation, pre-combustion capture and oxyfuel combustion. As conventional air Brayton cycles are not applicable for oxy-fuel combustion in gas turbines, different working fluids and cycle configurations are proposed and thermodynamic performance is evaluated. Selected cycles were then compared based on thermodynamics, economics and off-design performance at a typical constant power to heat ratio of 0.78. It was observed that oxyfuel CHP cycle with CO2 working fluid is a promising solution for zero carbon CHP with relatively low costs and 100% CO2 capture. However, this solution requires new turbomachinery design.
Experimental Investigation of Interactions Between Two Closely Spaced Azimuthal Modes in a Multi-Nozzle Can Combustor
Authors: Kim Jeong-Won , John Tony , Adhikari Subodh , Wu David , Emerson Benjamin , Acharya Vishal , Lieuwen Timothy , Isono Mitsunori , Saito Toshihiko 
Published: October 2022

Abstract
Thermoacoustic instabilities in annular or circular combustors are often coupled with azimuthal modes. These modes can be characterized by a spin ratio, which quantifies the dominant mode between two counter-rotating waves, and a phase difference between them, which is directly related to the orientation of the anti-nodal line. This study investigates the instability amplitudes, spin ratio, and phase difference of two closely spaced (3% frequency difference), yet distinct azimuthal modes; one is the first azimuthal (1A) mode, and the other is a combination of first azimuthal and first longitudinal (1A1L) mode. Each mode itself consists of two peaks that are spaced even more closely in frequency (0.8% difference). Furthermore, distinct harmonics at 2X and 3X of these frequencies, presumably associated with nonlinearities, are also evident in the spectra. Each mode is band-pass filtered in spectrum to analyze them separately. For the 1A mode, the spin ratio and phase difference exhibit a variety of behaviors — including quasi-periodic standing waves, spinning waves, and intermittency — depending on operating conditions such as thermal power and azimuthal fuel staging. Similar trends are observed for the 1A1L mode. Moreover, there is clear coupling between the 1A and 1A1L modes, as their spin ratios are almost synchronized during the quasi-periodic standing wave. This synchronization is observed in phase differences as well, but not in the instability amplitude. For spinning dominant wave conditions, the spin ratio and phase difference of the two modes fluctuate in a seemingly random fashion, but the instability amplitudes are correlated, with modulation of the 1A mode leading that of the 1A1L mode. These results clearly indicate that complex coupling occurs across closely spaced and harmonically space frequencies under instability conditions, coupling that must be understood in order to capture limit cycle dynamics.