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International Journal of Spray and Combustion Dynamics
Journal Prestige (SJR): 0.481

Citation Impact (citeScore): 1
Number of Followers: 15

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ISSN (Print) 1756-8277 - ISSN (Online) 1756-8285
Published by Sage Publications

[1174 journals]

The flame displacement speed: A key quantity for turbulent combustion and
combustion instability
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  Authors: Paul Palies
  Pages: 4 - 16
  Abstract: International Journal of Spray and Combustion Dynamics, Volume 14, Issue 1-2, Page 4-16, March–June 2022.
  Future combustion power and propulsion systems may operate in premixed regime enabling reduced fuel burn and reduced pollutant emissions. The turbulent premixed regime in those future combustion systems is likely to be in the corrugated regime where modeling the flame as a thin interface propagating into the fresh gas is made possible. The flame displacement speed is thus a key quantity for turbulent combustion in this regime. This quantity is also important for combustion instabilities. Indeed, the flame displacement speed [math] combined to the flow speed [math] determines the flame surface location by determining the flame surface speed [math]. The flame surface location has shown to play a major role on combustion instabilities. Research work have also demonstrated the role of the flame displacement speed on the flame response which is used for subsequent combustion instability prediction. In this context, the derivation of flame speed models and flame transfer function models based on this quantity are required. This paper presents the theoretical derivation of flame transfer function coefficients for swirling premixed flames in this context. The derivation is based on the definition of the flame speed for turbulent flame, its perturbed form for oscillating flow, and the kinematic flame-flow speed budget. The obtained results are compared to previous literature data and discussed. The effect of the flame angle, id est the effect of the swirl number on the flame response is also investigated. This works motivates detailed local measurements and simulations to evaluate flow-flame speed budget terms.
  Citation: International Journal of Spray and Combustion Dynamics
  PubDate: 2022-06-06T02:44:12Z
  DOI: 10.1177/17568277221081298
  Issue No: Vol. 14, No. 1-2 (2022)
Autoignition flame transfer matrix: Analytical model versus large eddy
simulations
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  Authors: Francesco Gant, Alexis Cuquel, Mirko R. Bothien
  Pages: 72 - 81
  Abstract: International Journal of Spray and Combustion Dynamics, Volume 14, Issue 1-2, Page 72-81, March–June 2022.
  Modern gas turbines need to fulfil increasingly stringent emission targets on the one hand and exhibit outstanding operational and fuel flexibility on the other. Ansaldo Energia GT26 and GT36 gas turbine models address these requirements by employing a combustion system in which two lean premixed combustors are arranged in series. Due to the high inlet temperatures from the first stage, the second combustor stage predominantly relies on autoignition for flame stabilization. In this paper, the response of autoignition flames to temperature, pressure and velocity excitations is investigated. The gas turbine combustor geometry is represented by a backward-facing step. Based on the conservation equations an analytical model is derived by solving the linearized Rankine-Hugoniot conditions. This is a commonly used analytical approach to describe the relation of thermodynamic quantities up- and downstream of a propagation stabilized flame. In particular, the linearized Rankine-Hugoniot jump conditions are derived taking into account the presence of a moving discontinuity as well as upstream entropy inhomogeneities. The unsteady heat release rate of the flame is modelled as a linear superposition of flame transfer functions, accounting for velocity, pressure, and entropy disturbances, respectively. This results in a 3[math]3 flame transfer matrix relating both primitive acoustic variables and the temperature fluctuations across the flame. The obtained analytical expression is compared to large eddy simulations with excellent agreement. A discussion about the contribution of the single terms to the modelling effort is provided, with a focus on autoignition flames.
  Citation: International Journal of Spray and Combustion Dynamics
  PubDate: 2022-06-06T02:47:08Z
  DOI: 10.1177/17568277221086261
  Issue No: Vol. 14, No. 1-2 (2022)
Large-eddy simulation and challenges for projection-based reduced-order
modeling of a gas turbine model combustor
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  Authors: Nicholas Arnold-Medabalimi, Cheng Huang, Karthik Duraisamy
  Pages: 153 - 175
  Abstract: International Journal of Spray and Combustion Dynamics, Volume 14, Issue 1-2, Page 153-175, March–June 2022.
  Computationally efficient modeling of gas turbine combustion is challenging due to the chaotic multi-scale physics and the complex non-linear interactions between acoustic, hydrodynamic, and chemical processes. A large-eddy simulation, referred to as the full order model (FOM), is performed for a gas turbine model combustor with turbulent combustion effects modeled using a flamelet-based method. Modal analysis reveals a high degree of correlation with averaged and instantaneous high-frequency particle image velocimetry fields. The dynamics of the precessing vortex core is quantitatively characterized using dynamic mode decomposition. The governing equations of the FOM are projected onto a low-dimensional linear manifold to construct a reduced-order model (ROM). A discretely-consistent least squares projection is used to guarantee global stability. The ROM provides an accurate reconstruction of the combustion dynamics within the training region, but faces a significant challenge in future state predictions. This limitation is mainly due to the increased projection error, which in turn is a direct consequence of the highly chaotic nature of the flow field, involving a wide range of dispersed coherent structures. This shortcoming is overcome using an adaptive basis method which yields accurate predictions of dynamics beyond the training region consistent with the FOM. Formal projection-based ROMs have not been applied to a problem of this scale and complexity, and achieving accurate and efficient ROMs is a grand challenge problem. A production-ready ROM method will significantly decrease the computational cost of the flame dynamics as well as the portability of this prediction to smaller-scale computers.
  Citation: International Journal of Spray and Combustion Dynamics
  PubDate: 2022-06-06T02:36:44Z
  DOI: 10.1177/17568277221100650
  Issue No: Vol. 14, No. 1-2 (2022)
Designing variable reflection coefficient for upstream and downstream
terminations to study their effect on flame thermoacoustics
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  Authors: Vertika Saxena, Viktor Kornilov, Ines Lopez Arteaga, LPH De Goey
  Abstract: International Journal of Spray and Combustion Dynamics, Ahead of Print.
  In this paper, the design, construction and results of experiments performed on a generic combustion system are presented. The setup is supplemented by various weakly frequency-dependent variable reflection coefficient (RC) devices as upstream and downstream acoustic terminations. The main objective of building such terminations is to provide a method to study burner/flame stability when it is placed between various acoustic configurations (RC: 0.1-0.9) and to determine the figure of merit of a burner based on the evaluation of its map of (in-)stability. Furthermore, burner design parameters such as the burner perforation pattern (holes diameter, pitch, perforation area, etc.) which will provide combustion stability for the widest range of burner's acoustic embedding conditions are identified. The experimental setup comprises of an upstream acoustic termination, a telescopic tube with adjustable length is placed after the upstream termination followed by the burner and the quartz tube. On the top of the quartz tube, the replaceable downstream terminations are installed. Nine downstream terminations are constructed by stacking plates of 0.25 mm thickness separated by spacers ranging from 0.1 to 1 mm thickness. Particularly, for the burners tested in this setup, the smallest hole diameter burner (with the largest perforation area) results in the largest stable region on the stability map in the parameter space. An increase in the flow velocity leads to an increase in the frequency of instability and makes a stable system tend to become unstable, while an increase in the equivalence ratio contributes to stabilizing system instability
  Citation: International Journal of Spray and Combustion Dynamics
  PubDate: 2022-07-02T07:52:11Z
  DOI: 10.1177/17568277221107983
Thermoacoustic stabilization of combustors with gradient-augmented
Bayesian optimization and adjoint models
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  Authors: Ushnish Sengupta, Matthew P. Juniper
  Abstract: International Journal of Spray and Combustion Dynamics, Ahead of Print.
  Bayesian optimization (BO) is a global optimization algorithm well-suited for multimodal functions that are costly to evaluate, e.g. quantities derived from computationally expensive simulations. Recent advances have made it possible to scale BO to high-dimensional functions and accelerate its convergence by incorporating derivative information. These developments have laid the groundwork for a productive interplay between BO and adjoint solvers, a tool to cheaply obtain gradients of objective functions w.r.t. tunable parameters in a simulated physical system. In thermoacoustics, adjoint-based optimization has previously been applied to Helmholtz solvers and low-order network models to find optimally stable combustor configurations. These studies have used conjugate gradient or quasi-Newton optimizers which can get stuck in local optima and may require many evaluations of the underlying model to find a good optimum. In this paper, we propose using gradient-augmented BO to optimize adjoint models. We consider two test cases from the thermoacoustics literature: optimizing design parameters in a 1D adjoint Helmholtz model of a Rijke tube and geometry optimization in a low-order network model of a longitudinal combustor. We show that compared to BFGS, a standard quasi-Newton method, our gradient-enhanced BO arrives at multiple, more optimal configurations using considerably fewer evaluations of the solver. This approach holds great promise for efficient thermoacoustic stabilization when designing using expensive 3D adjoint Helmholtz solvers.
  Citation: International Journal of Spray and Combustion Dynamics
  PubDate: 2022-06-24T06:17:17Z
  DOI: 10.1177/17568277221109118
Atomization characteristics of a bluff body-assisted sonic twin-fluid
atomizer
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  Authors: Raghav Sikka, Knut Vågsæther, Dag Bjerketvedt, Joachim Lundberg
  Abstract: International Journal of Spray and Combustion Dynamics, Ahead of Print.
  This study examines the gas dynamic effect and atomization behaviour of the sonic bluff body-assisted twin-fluid atomizer with three distinct geometry configurations based on cone distances (Lc) as 6.0 mm, 8.0 mm, and 10.0 mm. The atomization characteristics of these atomizers employing a 280 µm annular liquid sheet with a central bluff body (cone) are compared based on a range of air and liquid flow rates. The spray-bluff body impacted secondary atomization was characterized through volume-normalized droplet size distribution (DSD) & cumulative droplet distribution, excentricity plots, Sauter mean diameter (SMD), and relative span factor (Δ). When plotted for a given liquid flow rate, the DSD & cumulative droplet distribution becomes more uniform with the increase in the airflow rate independent of the cone distance (Lc). Excentricity plots exhibited high excentricity droplets at the spray centreline and a large fraction of nearly spherical droplets at off-centre spray locations. SMD and RSF (Δ) showed opposite trends when plotted against the air-to-liquid ratio (ALR) as SMD increases while RSF decreases with radial locations, respectively. When plotted for all radial locations, Sauter mean diameter (D32) and relative span factor (Δ) show a cluster formation. Larger SMD values correspond to lower RSF (Δ) values and vice-versa.
  Citation: International Journal of Spray and Combustion Dynamics
  PubDate: 2022-05-31T03:33:51Z
  DOI: 10.1177/17568277221104924
Proceedings of the Symposium on Thermoacoustics in Combustion
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  Authors: Mirko Bothien
  First page: 3
  Abstract: International Journal of Spray and Combustion Dynamics, Ahead of Print.
  
  Citation: International Journal of Spray and Combustion Dynamics
  PubDate: 2022-05-11T07:48:41Z
  DOI: 10.1177/17568277221099785
Nonlinear flame response modelling by a parsimonious set of ordinary
differential equations
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  Authors: Gregor Doehner, Matthias Haeringer, Camilo F. Silva
  First page: 17
  Abstract: International Journal of Spray and Combustion Dynamics, Ahead of Print.
  In this work we present a parsimonious set of ordinary differential equations (ODEs) that describes with satisfactory precision the linear and non-linear dynamics of a typical laminar premixed flame in time and frequency domain. The proposed model is characterized by two ODEs of second-order that can be interpreted as two coupled mass-spring-damper oscillators with a symmetric, nonlinear damping term. This non-linear term is identified as function of the rate of displacement following [math]. The model requires only four constants to be calibrated. This is achieved by carrying out an optimization procedure on one input and one output broadband signal obtained from high-fidelity numerical simulations (CFD). Note that the Transfer Function (FTF) or describing function (FDF) of the flame under investigation are not known a-priori, and therefore not used in the optimization procedure. Once the model is trained on CFD input and output time series, it is capable of recovering with quantitative accuracy the impulse response of the laminar flame under investigation and, hence, the corresponding frequency response (FTF). If fed with harmonic signals of different frequency and amplitude, the trained model is capable of retrieving with qualitative precision the flame describing function (FDF) of the studied flame. We show that the non-linear term [math] is essential for capturing the gain saturation for high amplitudes of the input signal. All results are validated against CFD data.
  Citation: International Journal of Spray and Combustion Dynamics
  PubDate: 2022-05-19T04:44:38Z
  DOI: 10.1177/17568277221094760
Iterative solvers for the thermoacoustic nonlinear eigenvalue problem and
their convergence properties
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  Authors: Georg A. Mensah, Philip E. Buschmann, Alessandro Orchini
  First page: 30
  Abstract: International Journal of Spray and Combustion Dynamics, Ahead of Print.
  The spectrum of the thermoacoustic operator is governed by a nonlinear eigenvalue problem. A few different strategies have been proposed by the thermoacoustic community to tackle it and identify the frequencies and growth rates of thermoacoustic eigenmodes. These strategies typically require the use of iterative algorithms, which need an initial guess and are not necessarily guaranteed to converge to an eigenvalue. A quantitative comparison between the convergence properties of these methods has however never been addressed. By using adjoint-based sensitivity, in this study we derive an explicit formula that can be used to quantify the behaviour of an iterative method in the vicinity of an eigenvalue. In particular, we employ Banach’s fixed-point theorem to demonstrate that there exist thermoacoustic eigenvalues that cannot be identified by some of the iterative methods proposed in the literature, in particular fixed-point iterations, regardless of the accuracy of the initial guess provided. We then introduce a family of iterative methods known as Householder’s methods, of which Newton’s method is a special case. The coefficients needed to use these methods are explicitly derived by means of high-order adjoint-based perturbation theory. We demonstrate how these methods are always guaranteed to converge to the closest eigenvalue, provided that the initial guess is accurate enough. We also show numerically how the basin of attraction of the eigenvalues varies with the order of the employed Householder’s method.
  Citation: International Journal of Spray and Combustion Dynamics
  PubDate: 2022-05-09T11:57:29Z
  DOI: 10.1177/17568277221084464
Analytical modelling of flame transfer functions for technically premixed
flames
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  Authors: Fernando Biagioli, Alessandro Innocenti, Ammar Lamraoui, Khawar J Syed
  First page: 42
  Abstract: International Journal of Spray and Combustion Dynamics, Ahead of Print.
  The linear response to harmonic acoustic excitation of the total heat release rate in technically premixed flames (Flame Transfer Function, FTF) is studied in case of an ideal swirl burner. The analysis is based on the linearization of the production rate for the mean reaction progress variable modelled with a turbulent flame speed closure. Three main components of the FTF are identified which are generated by: I) direct fluctuations in the fuel mixture fraction (formation enthalpy contribution), II) direct fluctuations in the turbulent flame speed and III) flame surface area fluctuations driven by velocity and turbulent flame speed fluctuations. The velocity fluctuation is separated into an irrotational acoustic displacement and a rotational convective component. The effect of the rotational velocity component on the FTF is modelled here in a semi-empirical way, related to swirl number fluctuations at the flame base due to the phase shift between convected tangential velocity fluctuations and acoustically propagating axial velocity fluctuations. It is finally shown that fuel mixture fraction fluctuations can be generated not only by air mass flow rate fluctuations but also by fuel flow rate fluctuations which depend upon the air side impedance at the fuel injection location. It is shown that this impedance changes with the geometry of the plenum placed upstream the burner affecting in this way also the FTF.
  Citation: International Journal of Spray and Combustion Dynamics
  PubDate: 2022-04-22T06:51:58Z
  DOI: 10.1177/17568277221094403
On the convective wave equation for the investigation of combustor
stability using FEM-methods
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  Authors: Gerrit Heilmann, Thomas Sattelmayer
  First page: 55
  Abstract: International Journal of Spray and Combustion Dynamics, Ahead of Print.
  Solving the Helmholtz equation with spatially resolved finite element method (FEM) approaches is a well-established and cost-efficient methodology to numerically predict thermoacoustic instabilities. With the implied zero Mach number assumption all interaction mechanisms between acoustics and the mean flow velocity including the advection of acoustic waves are neglected. Incorporating these mechanisms requires higher-order approaches that come at massively increased computational cost. A tradeoff might be the convective wave equation in frequency domain, which covers the advection of waves and comes at equivalent cost as the Helmholtz equation. However, with this equation only being valid for uniform mean flow velocities it is normally not applicable to combustion processes. The present paper strives for analyzing the introduced errors when applying the convective wave equation to thermoacoustic stability analyses. Therefore, an acoustically consistent, inhomogeneous convective wave equation is derived first. Similar to Lighthill’s analogy, terms describing the interaction between acoustics and non-uniform mean flows are considered as sources. For the use with FEM approaches, a complete framework of the equation in weak formulation is provided. This includes suitable impedance boundary conditions and a transfer matrix coupling procedure. In a modal stability analysis of an industrial gas turbine combustion chamber, the homogeneous wave equation in frequency domain is subsequently compared to the Helmholtz equation and the consistent Acoustic Perturbation Equations (APE). The impact of selected source terms on the solution is investigated. Finally, a methodology using the convective wave equation in frequency domain with vanishing source terms in arbitrary mean flow fields is presented.
  Citation: International Journal of Spray and Combustion Dynamics
  PubDate: 2022-03-24T04:45:27Z
  DOI: 10.1177/17568277221084470
Stability criteria of two-port networks, application to thermo-acoustic
systems
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  Authors: Mohammad Kojourimanesh, Viktor Kornilov, Ines Lopez Arteaga, Philip de Goey
  First page: 82
  Abstract: International Journal of Spray and Combustion Dynamics, Ahead of Print.
  System theory methods are developed and applied to introduce a new analysis methodology based on the stability criteria of active two-ports, to the problem of thermo-acoustic instability in a combustion appliance. The analogy between thermo-acoustics of combustion and small-signal operation of microwave amplifiers is utilized. Notions of unconditional and conditional stabilities of an (active) two-port, representing a burner with flame, are introduced and analyzed. Unconditional stability of two-port means the absence of autonomous oscillation at any embedding of the given two-port by any passive network at the system's upstream (source) and downstream (load) sides. It has been shown that for velocity-sensitive compact burners in the limit of zero Mach number, the criteria of unconditional stability cannot be fulfilled. The analysis is performed in the spirit of a known criterion in microwave network theory, the so-called Edwards-Sinsky's criterion. Therefore, two methods have been applied to elucidate the necessary and sufficient conditions of a linear active two-port system to be conditionally stable. The first method is a new algebraic technique to prove and derive the conditional and unconditional stability criteria, and the second method is based on certain properties of Mobius (bilinear) transformations for combinations of reflection coefficients and scattering matrix of (active) two-ports. The developed framework allows formulating design requirements for the stabilization of operation of a combustion appliance via purposeful modifications of either the burner properties or/and of its acoustic embeddings. The analytical derivations have been examined in a case study to show the power of the methodology in the thermo-acoustics system application.
  Citation: International Journal of Spray and Combustion Dynamics
  PubDate: 2022-04-12T08:01:09Z
  DOI: 10.1177/17568277221088465
Spray response on a model prefilmer under unsteady airflows of various
frequencies
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  Authors: Thomas Christou, Björn Stelzner, Nikolaos Zarzalis
  First page: 98
  Abstract: International Journal of Spray and Combustion Dynamics, Ahead of Print.
  An appealing concept for jet engine combustors is the Lean Premixed Prevaporized (LPP) combustor, which operates at high pressures. The low NOx emissions achieved by lean combustion are one of the targets for modern aircraft engines. However, these types of combustors can introduce thermoacoustic instabilities that can potentially damage the engine and reduce its lifespan. Since the potential instabilities on the fuel spray characteristics, i.e. the spray mass flux, can affect the flame stability, the need arises to investigate the spray response under an unsteady airflow.For this study, a model prefilmer was experimentally investigated to produce a two-dimensional droplet flow without swirl flow. An acoustic forcing in the range of 100–500 Hz was introduced into the airflow, characterized by a hot wire Constant Temperature Anemometry (CTA) setup. Droplet characteristics, namely the droplet diameter distribution and velocity, were determined using a Phase Doppler Anemometry (PDA) setup, while the acquired data were phase-averaged in one period of the airflow oscillation. The influence of the excitation frequency and the air-to-liquid ratio (ALR) on the spray was studied: the spray responded to the acoustic excitation and therefore critical performance parameters, such as the spray mass flux, oscillated indicating potential problems regarding the flame stability.
  Citation: International Journal of Spray and Combustion Dynamics
  PubDate: 2022-05-09T11:57:42Z
  DOI: 10.1177/17568277221092987
Response of spray number density and evaporation rate to velocity
oscillations
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  Authors: Sagar Kulkarni, Camilo F. Silva, Wolfgang Polifke
  First page: 107
  Abstract: International Journal of Spray and Combustion Dynamics, Ahead of Print.
  A theoretical investigation of the effect of gas velocity oscillations on droplet number density and evaporation rate is presented. Oscillations in gas velocity cause a number density wave, i.e. an inhomogeneous, unsteady variation of droplet concentration. The number density wave, as it propagates downstream at the mean flow speed, causes modulation of the local evaporation rate, creating a vapour wave with corresponding oscillations in equivalence ratio. The present work devises an analytical formulation of these processes. Firstly, the response of a population of droplets to oscillations in the gas velocity is modelled in terms of a number density wave. Secondly, the formulation is extended to incorporate droplet evaporation, such that an analytical expression for the evaporation rate modulation is obtained. Subsequently, the droplet 1D convection-diffusion transport equation with the calculated evaporation source term is solved using an appropriate Green’s function to determine the resulting equivalence ratio perturbations. The dynamic response of equivalence ratio fluctuations to velocity oscillations is finally characterized in terms of a frequency-dependent transfer function. The aforementioned analytical approach relies on a number of simplifying approximations, nevertheless it was validated with good agreement against 1D Euler-Lagrange CFD simulations.
  Citation: International Journal of Spray and Combustion Dynamics
  PubDate: 2022-03-31T03:20:35Z
  DOI: 10.1177/17568277221085957
Impact of shear-coaxial injector hydrodynamics on high-frequency
combustion instabilities in a representative cryogenic rocket engine
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  Authors: Wolfgang Armbruster, Justin Hardi, Michael Oschwald
  First page: 118
  Abstract: International Journal of Spray and Combustion Dynamics, Ahead of Print.
  The excitation mechanism of a thermoacoustic instability in a 42-element research rocket thrust chamber with representative operating conditions with respect to European cryogenic rocket engines is investigated in detail. From previous research it was known that the chamber 1T mode can be excited by persistent heat release rate oscillations which are modulated by the resonant modes of the liquid oxygen injectors. The excitation source of the longitudinal injector eigenmodes is investigated in this study. Fibre-optical probes measuring the OH* dynamics from the recess volume of two injectors showed additional frequency content which could neither be explained by the chamber acoustics, nor the acoustics of the injection system. Instead, the temporal evolution of these frequencies correlate with the oxidizer flow velocity. In this work we show that the additional flame modulation originates from a hydrodynamic effect in the injection system. Even though the exact process cannot be precisely identified, an effect designated orifice whistling at the injector inlet orifice seems to be a likely candidate. Combining the new results with previous publications about this combustor, it is now possible to explain past and present observations in terms of the hydrodynamic and thermoacoustic conditions which are necessary for the combustion instability to appear. The conditions, which lead to an injection-driven excitation of the 1T mode are matching frequencies of the 2L mode of the injectors and the chamber 1T mode as well as a Strouhal number between 0.2 and 0.4 based on the length and flow velocity of the injector inlet orifice.
  Citation: International Journal of Spray and Combustion Dynamics
  PubDate: 2022-04-27T08:06:09Z
  DOI: 10.1177/17568277221093848
Observation of reactive shear layer modulation associated with
high-frequency transverse thermoacoustic oscillations in a gas turbine
reheat combustor experiment
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  Authors: Jonathan McClure, Frederik M. Berger, Michael Bertsch, Bruno Schuermans, Thomas Sattelmayer
  First page: 131
  Abstract: International Journal of Spray and Combustion Dynamics, Ahead of Print.
  This paper presents the investigation of high-frequency thermoacoustic oscillations and associated flame dynamics in an experimental gas turbine reheat combustor at atmospheric pressure. Examination of dynamic pressure measurements reveals bursts of high-frequency periodic oscillations which appear randomly amidst stochastic fluctuations in the reheat combustor. Analysis of the flame dynamics during these bursts of periodic behaviour reveals that increased heat release in the reactive shear layers of the reheat flame is associated with greater thermoacoustic driving potential. This redistribution of heat release is likely due to the stochastic nature of auto-ignition kernel formation. To determine the underlying flame-acoustic coupling mechanism behind the driving potential, phase-resolved flame dynamics over the acoustic cycle are investigated which reveal the presence of an oscillatory heat release pattern associated with the first transverse eigenmode. An in-phase interaction between the acoustic field and these heat release oscillations in the shear layer regions indicates that this phenomenon likely constitutes a thermoacoustic driving mechanism. This is an important step towards the development of models for high-frequency thermoacoustic driving mechanisms relevant to reheat combustion systems, which will allow accurate prediction and mitigation of thermoacoustic instabilities in future designs.
  Citation: International Journal of Spray and Combustion Dynamics
  PubDate: 2022-03-31T03:23:36Z
  DOI: 10.1177/17568277221088192
Hybrid CFD/low-order modeling of thermoacoustic limit cycle oscillations
in can-annular configurations
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  Authors: Matthias Haeringer, Wolfgang Polifke
  First page: 143
  Abstract: International Journal of Spray and Combustion Dynamics, Ahead of Print.
  We propose a hybrid strategy for modeling non-linear thermoacoustic phenomena, e.g. limit-cycle (LC) oscillations, in can-annular combustion systems. The suggested model structure comprises a compressible CFD simulation limited to the burner/flame zone of one single can, coupled to a low-order model (LOM) representing the remaining combustor. In order to employ the suggested strategy for modeling non-linear phenomena like LC oscillations, the LOM must capture non-linear flame dynamics in the cans, which are not resolved by CFD. Instead of identifying such non-linear flame models in preliminary simulations, we aim at learning the non-linear dynamics “on-the-fly”, while simulating the self-excited system under consideration. Based on the observation of flame dynamics in the CFD domain, the parameters of the employed non-linear models are estimated during run time. The present study reveals that block-oriented models, which comprise a linear dynamic part followed by a static non-linear function, are well suited for this purpose.The proposed hybrid model is applied to a laminar can-annular combustor. Results agree well with the monolithic CFD simulation of the entire combustor, while the computational cost is drastically reduced. The employed flame models, whose parameters are identified during the simulation of the self-excited LC oscillation, represent well the relevant non-linear dynamics of the considered flame.
  Citation: International Journal of Spray and Combustion Dynamics
  PubDate: 2022-03-24T04:44:55Z
  DOI: 10.1177/17568277221085953
Comparison of the flame dynamics of a premixed dual fuel burner for
kerosene and natural gas
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  Authors: Jan Kaufmann, Manuel Vogel, Jannes Papenbrock, Thomas Sattelmayer
  First page: 176
  Abstract: International Journal of Spray and Combustion Dynamics, Ahead of Print.
  In this study, the flame dynamics of swirl stabilized lean premixed combustion is investigated for kerosene and natural gas operation. A natural gas swirl burner is retrofitted with a twin-fluid nozzle to allow performing all experiments with the identical burner hardware. The mixture preparation complexity is stepwise increased from perfectly premixed natural gas to technically premixed natural gas and lastly technically premixed kerosene combustion. Flame transfer functions (FTFs) for the three configurations are presented and compared with each other. This approach allows to experimentally decompose the FTF and isolate the contributions of equivalence ratio fluctuations and droplet dynamics. Furthermore, FTF data for a systematic variation of equivalence ratio and air mass flow in kerosene operation is presented and the impact of spray quality and convective delay time on the FTF is discussed. For all operation points, stationary flame images are provided and evaluated as basis for the FTF interpretation. Additionally, [math] emissions are measured in order to determine the degree of premixing in kerosene operation. Through a systematic FTF comparison, it was found that the frequency range in which droplets react to acoustic forcing can be read from the FTF phase. The spray quality was found to have a significant impact on the FTF whereas a change in the convective delay time does not affect the FTF.
  Citation: International Journal of Spray and Combustion Dynamics
  PubDate: 2022-04-12T08:01:28Z
  DOI: 10.1177/17568277221091405
Robust combustor design based on flame transfer function modification
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  Authors: Jakob G. R. von Saldern, Johann Moritz Reumschüssel, Jan Paul Beuth, Christian Oliver Paschereit, Kilian Oberleithner
  First page: 186
  Abstract: International Journal of Spray and Combustion Dynamics, Ahead of Print.
  Operation under stable conditions is an important prerequisite for gas turbine safety. While recent studies have focused primarily on acoustic design to avoid thermoacoustic instabilities, in the present study we shift the focus to improving stability margins by flame transfer function (FTF) modification. The flame transfer function of premixed flames is affected by various mechanisms such as variations in equivalence ratio, swirl fluctuations and shear layer instabilities. These mechanisms can be influenced by modifying parameters such as fuel distribution, injection location, swirl number or gas composition. Based on the Nyquist stability method we formulate criteria for how and at what frequencies the flame transfer function needs to be modified, in order to increase the stability margins of a thermoacoustic system. Gain and phase margin as well as the sensitivity function serve as measures of stability. The criteria are limited to single frequencies, which allows experimental FTF optimization with manageable effort. In the second part of this study it is shown that the Nyquist method can also be used as an efficient and compact way to determine whether the uncertainties of subsystems can affect the overall stability, without requiring eigenvalue calculations.
  Citation: International Journal of Spray and Combustion Dynamics
  PubDate: 2022-04-28T07:41:54Z
  DOI: 10.1177/17568277221088422
Erratum to “impact of burner plenum acoustics on the sound emission of a
turbulent lean premixed open flame”
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  Abstract: International Journal of Spray and Combustion Dynamics, Ahead of Print.
  
  Citation: International Journal of Spray and Combustion Dynamics
  PubDate: 2021-05-26T04:53:21Z
  DOI: 10.1177/17568277211008631