ORCID Profile
0000-0001-5923-2461
Current Organisation
University of Melbourne Melbourne School of Engineering
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Turbulent Flows | Interdisciplinary Engineering | Automotive Combustion and Fuel Engineering (incl. Alternative/Renewable Fuels) | Automotive Engineering
Energy Conservation and Efficiency in Transport | Expanding Knowledge in the Physical Sciences | Industrial Energy Conservation and Efficiency | Management of Greenhouse Gas Emissions from Transport Activities |
Publisher: Elsevier BV
Date: 05-2023
Publisher: Elsevier BV
Date: 02-2022
Publisher: ASME International
Date: 29-03-2021
DOI: 10.1115/1.4049910
Abstract: This paper reports on an optimization study of the CO turndown behavior of an axially staged combustor, in the context of industrial gas turbines (GTs). The aim of this work is to assess the optimally achievable CO turndown behavior limit given system and operating characteristics, without considering flow-induced behaviors such as mixing quality and flame spatial characteristics. To that end, chemical reactor network (CRN) modeling is used to investigate the impact of various system and operating conditions on the exhaust CO emissions of each combustion stage, as well as at the combustor exit. Different combustor residence time combinations are explored to determine their contribution to the exhaust CO emissions. The two-stage combustor modeled in this study consists of a primary (Py) and a secondary (Sy) combustion stage, followed by a discharge nozzle (DN), which distributes the exhaust to the turbines. The Py is modeled using a freely propagating flame (FPF), with the exhaust gas extracted downstream of the flame front at a specific location corresponding to a specified residence time (tr). These exhaust gases are then mixed and combusted with fresh gases in the Sy, modeled by a perfectly stirred reactor (PSR) operating within a set tr. These combined gases then flow into the DN, which is modeled by a plug flow reactor (PFR) that cools the gas to varying combustor exit temperatures within a constrained tr. Together, these form a simplified CRN model of a two-stage, dry-low emissions (DLEs) combustion system. Using this CRN model, the impact of the tr distribution between the Py, Sy, and DN is explored. A parametric study is conducted to determine how inlet pressure (Pin), inlet temperature (Tin), equivalence ratio (ϕ), and Py–Sy fuel split (FS), in idually impact indicative CO turndown behavior. Their coupling throughout engine load is then investigated using a model combustor, and its effect on CO turndown is explored. Thus, this aims to deduce the fundamental, chemically driven parameters considered to be most important for identifying the optimal CO turndown of GT combustors. In this work, a parametric study and a model combustor study are presented. The parametric study consists of changing a single parameter at a time, to observe the independent effect of this change and determine its contribution to CO turndown behavior. The model combustor study uses the same CRN, and varies the parameters simultaneously to mimic their change as an engine moves through its steady-state power curve. The latter study thus elucidates the difference in CO turndown behavior when all operating conditions are coupled, as they are in practical engines. The results of this study aim to demonstrate the parameters that are key for optimizing and improving CO turndown.
Publisher: Springer Science and Business Media LLC
Date: 28-05-2014
Publisher: Elsevier BV
Date: 2019
Publisher: Springer Science and Business Media LLC
Date: 22-11-2020
Publisher: Elsevier BV
Date: 08-2022
Publisher: Cambridge University Press (CUP)
Date: 12-07-2012
DOI: 10.1017/JFM.2012.264
Abstract: This paper presents an analysis of the energy transported by disturbances in gaseous combustion. It extends the previous work of Myers ( J. Fluid Mech. , vol. 226, 1991, 383–400) and so includes non-zero mean-flow quantities, large- litude disturbances, varying specific heats and chemical non-equilibrium. This extended form of Myers’ ‘disturbance energy’ then enables complete identification of the conditions under which the famous Rayleigh source term can be derived from the equations governing combusting gas motion. These are: small disturbances in an irrotational, homentropic, non-diffusive (in terms of species, momentum and energy) and stationary mean flow at chemical equilibrium. Under these assumptions, the Rayleigh source term becomes the sole source term in a conservation equation for the classical acoustic energy. It is also argued that the exact disturbance energy flux should become an acoustic energy flux in the far-field surrounding a (reacting or non-reacting) jet. In this case, the volume integral of the disturbance energy source terms are then directly related to the area-averaged far-field sound produced by the jet. This is demonstrated by closing the disturbance energy budget over a set of aeroacoustic, direct numerical simulations of a forced, low-Mach-number, laminar, premixed flame. These budgets show that several source terms are significant, including those involving the mean-flow and entropy fields. This demonstrates that the energetics of sound generation cannot be examined by considering the Rayleigh source term alone.
Publisher: Elsevier BV
Date: 2017
Publisher: Elsevier BV
Date: 2013
Publisher: Elsevier BV
Date: 06-2019
Publisher: Elsevier BV
Date: 2015
Publisher: Springer International Publishing
Date: 2020
Publisher: Elsevier BV
Date: 04-2021
Publisher: AIP Publishing
Date: 2023
DOI: 10.1063/5.0133045
Abstract: This study investigates the impact of the near-wall temperature gradient on hydrogen auto-ignition characteristics using one-dimensional (1D) fully resolved simulations. Ten cases are simulated, one featuring normal combustion and the other nine simulating auto-ignitive combustion with different initial pressures, equivalence ratios, and near-wall temperature gradients. The simulations show that the near-wall temperature gradient greatly affects the onset and intensity of the auto-ignition event. For cases with the initial conditions of 833.3 K and 15 bar, a small near-wall temperature gradient delays the timing of auto-ignition and places the auto-ignition kernel further away from the wall, facilitating deflagration-to-detonation transition of the auto-ignitive flame. This leads to a large increase in pressure oscillations within the domain and heat flux to the wall. When the initial conditions are changed to 900 K and 20 bar, the magnitude of the near-wall temperature gradient also affects the number of auto-ignition events, leading to a significant impact on the wall heat flux. The results suggest that an accurate modeling of the near-wall temperature gradient is necessary for the simulations of hydrogen end-gas auto-ignition. This requires special considerations in the near-wall region and a careful selection of the wall heat transfer model in Computational Fluid Dynamics (CFD) tools, such as Reynolds-Averaged Navier–Stokes (RANS) and Large-Eddy Simulation (LES).
Publisher: Elsevier BV
Date: 08-2021
Publisher: Elsevier BV
Date: 2021
Publisher: Elsevier BV
Date: 02-2012
Publisher: Cambridge University Press (CUP)
Date: 08-03-2021
Publisher: Elsevier BV
Date: 07-2016
Publisher: Elsevier BV
Date: 2017
Publisher: Elsevier BV
Date: 2017
Publisher: Elsevier BV
Date: 03-2020
Publisher: Elsevier BV
Date: 2015
Publisher: Elsevier BV
Date: 02-2020
Publisher: Cambridge University Press (CUP)
Date: 19-03-2018
DOI: 10.1017/JFM.2018.115
Abstract: This paper presents a numerical study of the sound generated by turbulent, premixed flames. Direct numerical simulations (DNS) of two round jet flames with equivalence ratios of 0.7 and 1.0 are first carried out. Single-step chemistry is employed to reduce the computational cost, and care is taken to resolve both the near and far fields and to avoid noise reflections at the outflow boundaries. Several significant features of these two flames are noted. These include the monopolar nature of the sound from both flames, the stoichiometric flame being significantly louder than the lean flame, the observed frequency of peak acoustic spectral litude being consistent with prior experimental studies and the importance of so-called ‘flame annihilation’ events as acoustic sources. A simple model that relates these observed annihilation events to the far-field sound is then proposed, demonstrating a surprisingly high degree of correlation with the far-field sound from the DNS. This model is consistent with earlier works that view a premixed turbulent flame as a distribution of acoustic sources, and provides a physical explanation for the well-known monopolar content of the sound radiated by premixed turbulent flames.
Publisher: Elsevier BV
Date: 10-2016
Publisher: Elsevier BV
Date: 09-2019
Publisher: Elsevier BV
Date: 07-2022
Publisher: Elsevier BV
Date: 2019
Publisher: American Institute of Aeronautics and Astronautics
Date: 21-05-2007
DOI: 10.2514/6.2007-3633
Publisher: American Society of Mechanical Engineers
Date: 21-09-2020
DOI: 10.1115/GT2020-14843
Abstract: The use of machine learning (ML) for modeling is on the rise. In the age of big data, this technique has shown great potential to describe complex physical phenomena in the form of models. More recently, ML has frequently been used for turbulence modeling while the use of this technique for combustion modeling is still emerging. Gene expression programming (GEP) is one class of ML that can be used as a tool for symbolic regression and thus improve existing algebraic models using high-fidelity data. Direct numerical simulation (DNS) is a powerful candidate for producing the required data for training GEP models and validation. This paper therefore presents a highly efficient DNS solver known as HiPSTAR, originally developed for simulating non-reacting flows in particular in the context of turbo-machinery. This solver has been extended to simulate reacting flows. DNSs of two turbulent premixed jet flames with different Karlovitz numbers are performed to produce the required data for training. GEP is then used to develop algebraic flame surface density models in the context of large-eddy simulation (LES). The result of this work introduces new models which show excellent performance in prediction of the flame surface density for premixed flames featuring different Karlovitz numbers.
Publisher: Elsevier BV
Date: 12-2021
Publisher: Elsevier BV
Date: 2015
Publisher: Elsevier BV
Date: 12-2018
Publisher: Cambridge University Press (CUP)
Date: 18-04-2011
DOI: 10.1017/JFM.2011.131
Abstract: This paper presents a numerical and theoretical investigation of the sound generated by premixed flame annihilation. Planar, axisymmetric and spherically symmetric flame annihilation events are considered. The compressible Navier–Stokes, energy and progress variable equations are first solved using simple chemistry simulations, resolving both the flame dynamics and the acoustics. These simulations show that the litude of the far-field sound produced by the annihilation events depends on the flame thickness, particularly for the axisymmetric and spherically symmetric flame annihilation events. The flame propagation velocity is also always observed to increase significantly prior to flame annihilation, which is in keeping with other reported experimental and numerical studies. A theory is then presented that relates the far-field sound to the flame annihilation event by using a previously reported and extended form of Lighthill's acoustic analogy. A comparison with the numerical results shows that this theory accurately represents the far-field sound produced by considering only the temporal heat release source term in Lighthill's acoustic analogy, as reported by others. Additional assumptions of an infinitely thin flame and constant flame speed are then invoked in an attempt to simplify the problem. In the planar annihilation, this theory results in good predictions of the overall pressure change. However, these assumptions lead to significant under-prediction of the litude of far-field sound produced for the axisymmetric and spherically symmetric annihilation events. Finally, dimensional reasoning supported by the simulations and theory is used to develop scalings of the far-field sound in terms of the flame parameters.
Publisher: American Society of Mechanical Engineers
Date: 21-09-2020
DOI: 10.1115/GT2020-15618
Abstract: This paper reports on an optimisation study of the CO turndown behaviour of an axially staged combustor, in the context of industrial gas turbines (GT). The aim of this work is to assess the optimally achievable CO turndown behaviour limit given system and operating characteristics, without considering flow-induced behaviours such as mixing quality and flame spatial characteristics. To that end, chemical reactor network modelling is used to investigate the impact of various system and operating conditions on the exhaust CO emissions of each combustion stage, as well as at the combustor exit. Different combustor residence time combinations are explored to determine their contribution to the exhaust CO emissions. The two-stage combustor modelled in this study consists of a primary (Py) and a secondary (Sy) combustion stage, followed by a discharge nozzle (DN), which distributes the exhaust to the turbines. The Py is modelled using a freely propagating flame (FPF), with the exhaust gas extracted downstream of the flame front at a specific location corresponding to a specified residence time (tr). These exhaust gases are then mixed and combusted with fresh gases in the Sy, modelled by a perfectly stirred reactor (PSR) operating within a set tr. These combined gases then flow into the DN, which is modelled by a plug flow reactor (PFR) that cools the gas to varying combustor exit temperatures within a constrained tr. Together, these form a simplified CRN model of a two-stage, dry-low emissions (DLE) combustion system. Using this CRN model, the impact of the tr distribution between the Py, Sy and DN is explored. A parametric study is conducted to determine how inlet pressure (Pin), inlet temperature (Tin), equivalence ratio (ϕ) and Py-Sy fuel split (FS), in idually impact indicative CO turndown behaviour. Their coupling throughout engine load is then investigated using a model combustor, and its effect on CO turndown is explored. Thus, this aims to deduce the fundamental, chemically-driven parameters considered to be most important for identifying the optimal CO turndown of GT combustors. In this work, a parametric study and a model combustor study are presented. The parametric study consists of changing a single parameter at a time, to observe the independent effect of this change and determine its contribution to CO turndown behaviour. The model combustor study uses the same CRN, and varies the parameters simultaneously to mimic their change as an engine moves through its steady-state power curve. The latter study thus elucidates the difference in CO turndown behaviour when all operating conditions are coupled, as they are in practical engines. The results of this study aim to demonstrate the parameters that are key for optimising and improving CO turndown.
Publisher: Springer Science and Business Media LLC
Date: 02-01-2021
Publisher: Elsevier BV
Date: 12-2019
Publisher: Springer Science and Business Media LLC
Date: 03-07-2018
Publisher: American Institute of Aeronautics and Astronautics (AIAA)
Date: 06-2020
DOI: 10.2514/1.J058480
Publisher: Springer Science and Business Media LLC
Date: 21-04-2015
Publisher: Elsevier BV
Date: 2015
Publisher: Cambridge University Press (CUP)
Date: 23-07-2015
DOI: 10.1017/JFM.2015.334
Abstract: A turbulent lifted slot-jet flame is studied using direct numerical simulation (DNS). A one-step chemistry model is employed with a mixture-fraction-dependent activation energy which can reproduce qualitatively the dependence of the laminar burning rate on the equivalence ratio that is typical of hydrocarbon fuels. The basic structure of the flame base is first examined and discussed in the context of earlier experimental studies of lifted flames. Several features previously observed in experiments are noted and clarified. Some other unobserved features are also noted. Comparison with previous DNS modelling of hydrogen flames reveals significant structural differences. The statistics of flow and relative edge-flame propagation velocity components conditioned on the leading edge locations are then examined. The results show that, on average, the streamwise flame propagation and streamwise flow balance, thus demonstrating that edge-flame propagation is the basic stabilisation mechanism. Fluctuations of the edge locations and net edge velocities are, however, significant. It is demonstrated that the edges tend to move in an essentially two-dimensional (2D) elliptical pattern (laterally outwards towards the oxidiser, then upstream, then inwards towards the fuel, then downstream again). It is proposed that this is due to the passage of large eddies, as outlined in Su et al. ( Combust. Flame , vol. 144 (3), 2006, pp. 494–512). However, the mechanism is not entirely 2D, and out-of-plane motion is needed to explain how flames escape the high-velocity inner region of the jet. Finally, the time-averaged structure is examined. A budget of terms in the transport equation for the product mass fraction is used to understand the stabilisation from a time-averaged perspective. The result of this analysis is found to be consistent with the instantaneous perspective. The budget reveals a fundamentally 2D structure, involving transport in both the streamwise and transverse directions, as opposed to possible mechanisms involving a dominance of either one direction of transport. It features upstream transport balanced by entrainment into richer conditions, while on the rich side, upstream turbulent transport and entrainment from leaner conditions balance the streamwise convection.
Location: Iran (Islamic Republic of)
Location: Australia
Start Date: 05-2018
End Date: 12-2021
Amount: $365,446.00
Funder: Australian Research Council
View Funded ActivityStart Date: 11-2016
End Date: 12-2019
Amount: $335,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2018
End Date: 12-2019
Amount: $956,700.00
Funder: Australian Research Council
View Funded Activity