Reheat flames response to entropy waves

Gant, Francesco; Bunkute, Birute; Bothien, Mirko R.

doi:10.1016/j.proci.2020.05.007

Cited by 8 publications

(10 citation statements)

References 11 publications

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“…The fact that temperature fluctuations can play such a large role is due to the exponential dependence of the mixture ignition delay time on temperature. 11 Consequently, the flame position is largely affected and so is the heat release rate fluctuation. 10 It has to be noted that this effect is very distinct for the BFS configuration studied here since the resulting flame is almost only autoignition stabilized.…”

Section: Discussionmentioning

confidence: 99%

“…where φ p and φ T are autoignition pressure and temperature sensitivity factors, 17,11 τ is the mean ignition delay time, σ is a measure of the flame thickness, p ′ (x fl ) is the acoustic pressure fluctuation at the flame location, and s ′ 1 is an entropic fluctuation:…”

Section: Analytic Flame Transfer Function Modelsmentioning

confidence: 99%

“…This frequency dependent effect is largely function of the autoignition delay time of the reactive mixture and, consequently, of the mean inlet temperature, pressure and of the fuel composition. 17,18,11 In general, variations of these parameters increasing the autoignition delay time, i.e. shifting the flame in a more downstream position, will result in larger gains.…”

Section: Flame Transfer Matrixmentioning

confidence: 99%

“…Chu 19 was the first to derive these jump conditions across a flame front in 1953. Additionally, analytical models for autoignition flame transfer functions (FTFs) to acoustic and entropic disturbances 17,11 are incorporated in the FTM modelling, resulting in a closed-form expression directly comparable to LES/SI results.…”

Section: Introductionmentioning

confidence: 99%

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Autoignition flame transfer matrix: Analytical model versus large eddy simulations

Gant¹,

Cuquel²,

Bothien

2022

International Journal of Spray and Combustion Dynamics

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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[Formula: see text]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.

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Section: Discussionmentioning

confidence: 99%

Section: Analytic Flame Transfer Function Modelsmentioning

confidence: 99%

Section: Flame Transfer Matrixmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Autoignition flame transfer matrix: Analytical model versus large eddy simulations

Gant¹,

Cuquel²,

Bothien

2022

International Journal of Spray and Combustion Dynamics

Self Cite

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“…LES allowed prediction of the spatiotemporal evolutions of the wave, while URANS overestimated the temperature level of the hot spots and the resultant noise [36]. Gant et al [37,38] developed an analytical model to predict the response of a flame to entropic waves, [38] and emphasized the role of turbulent mixing in practical configurations [37]. By conducting LES, Moreau et al [39] showed that the amplitude of entropy wave subsided and its shape dispersed during convection in a long path.…”

Section: Nomenclaturementioning

confidence: 99%

A comparative analysis of the evolution of compositional and entropy waves in turbulent channel flows

et al. 2022

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Indirect combustion noise, as an important source of noise in gas turbines, was traditionally attributed solely to entropy waves. In recent years, compositional waves were introduced as another contributor to indirect combustion noise. Nonetheless, unlike that of entropy waves, the annihilation of compositional waves by the mean flow has remained largely unexplored. Hence, the current numerical study analyses the spatiotemporal evolution of different components of compositional waves and compares them with the decay of entropy waves. A convecting wave, including a mixture of combustion products at elevated temperature, is introduced at the inlet of a simple channel. This allows simultaneous analysis of entropy and compositional waves. The passage of these along the channel is modeled using a large eddy simulation and the annihilation of the waves' components is examined in the frequency domain. It is shown that the turbulence level of the mean flow and convective heat transfer on the walls can both result in a considerable wave deterioration.However, the effects of heat losses from the channel walls are found to be stronger than that of turbulence intensity. Importantly, as the wave is convected, the chemical potential function remains coherent for most of the channel length and deterioration of the compositional wave majorly ensues from the mixture fraction gradient. The results indicate that, overall, the compositional sources feature 10% to 20% more dissipation in comparison with the entropic sources. Therefore, compositional waves are less likely to survive the flow and generate noise.

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Direct Numerical Simulation of hydrogen combustion at auto-ignitive conditions: Ignition, stability and turbulent reaction-front velocity

Gruber

Bothien

Ciani³

et al. 2021

Combustion and Flame

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Reheat flames response to entropy waves

Cited by 8 publications

References 11 publications

Autoignition flame transfer matrix: Analytical model versus large eddy simulations

Autoignition flame transfer matrix: Analytical model versus large eddy simulations

A comparative analysis of the evolution of compositional and entropy waves in turbulent channel flows

Direct Numerical Simulation of hydrogen combustion at auto-ignitive conditions: Ignition, stability and turbulent reaction-front velocity

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