On the reflection and transmission of circumferential waves through nozzles

Durán, I.; Morgans, Aimee S.

doi:10.1017/jfm.2015.247

Cited by 35 publications

(21 citation statements)

References 29 publications

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“…Many low order analytical models for entropy noise have been developed, e.g., [2, 12–15]. Analytical, experimental and numerical analyses have suggested that for typical gas turbine accelerations (from low subsonic flow to approximately sonic flow), entropy noise may greatly exceed the “direct combustion noise” generated by flame volume expansion.…”

Section: Introductionmentioning

confidence: 99%

Dispersion of Entropy Perturbations Transporting through an Industrial Gas Turbine Combustor

Xia

Durán

Morgans

et al. 2017

Flow Turbulence Combust

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In the context of combustion noise and combustion instabilities, the transport of entropy perturbations through highly simplified turbulent flows has received much recent attention. This work performs the first systematic study into the transport of entropy perturbations through a realistic gas turbine combustor flow-field, exhibiting large-scale hydrodynamic flow features in the form of swirl, separation, recirculation zones and vortex cores, these being ubiquitous in real combustor flows. The reacting flow-field is simulated using low Mach number large eddy simulations, with simulations validated by comparison to available experimental data. A generic artificial entropy source, impulsive in time and spatially localized at the flame-front location, is injected. The conservation equation describing entropy transport is simulated, superimposed on the underlying flow-field simulation. It is found that the transport of entropy perturbations is dominated by advection, with both thermal diffusion and viscous production being negligible. It is furthermore found that both the mean flow-field and the large-scale unsteady flow features contribute significantly to advective dispersion — neither can be neglected. The time-variation of entropy perturbation amplitude at combustor exit is well-modelled by a Gaussian profile, whose dispersion exceeds that corresponding to a fully-developed pipe mean flow profile roughly by a factor of three. Finally, despite the attenuation in entropy perturbation amplitude caused by advective dispersion, sufficient entropy perturbation strength is likely to remain at combustor exit for entropy noise to make a meaningful contribution at low frequencies.

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Section: Introductionmentioning

confidence: 99%

Dispersion of Entropy Perturbations Transporting through an Industrial Gas Turbine Combustor

Xia

Durán

Morgans

et al. 2017

Flow Turbulence Combust

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“…For non-compact choked nozzles with a supersonic diffuser [24] and for subcritical non-compact nozzles [25], the linear transfer functions have been calculated numerically and analytically for the upstream and downstream acoustic waves generated by an incident entropy disturbance. Duran & Morgans [26] studied numerically using high resolution 1-D and 2-D computations the propagation of circumferential waves (acoustic, entropy and vorticity waves) through an annular non-compact nozzle with isentropic mean flow throughout the divergent section of the nozzle (i.e. with no shocks).…”

Section: Introductionmentioning

confidence: 99%

Acoustic and Entropy Waves in Nozzles in Combustion Noise Framework

2017

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A low-order model is presented to study the propagation and interaction of acoustic and entropic perturbations through a convergent-divergent nozzle. The calculations deal with choked, unchoked, as well as compact and non-compact nozzles. In the choked case, a normal shock exists in the divergent section of the nozzle. To validate the models developed, cylindrical configurations corresponding to Entropy-WaveGenerator (EWG) and Hot-Acoustic-Testrig (HAT) of DLR are studied. For the EWG, an entropy wave is generated upstream of a nozzle by an electrical heating device, and for the HAT a speaker is used to generate pressure waves. In these two configurations and for the choked case, the supersonic region between the nozzle throat and the normal shock is assumed to be acoustically compact. The results of the low-order model are found to give excellent agreement with the experimental results of the EWG and HAT rigs. To give insight into the physics, the model is used to undertake a parametric study for a range of nozzle lengths and shock strengths. The low order model is finally used to calculate the direct to indirect (entropy and vorticity) combustion noise ratio for an idealised thin-annular combustor. For this model combustor the direct acoustic noise is found to dominate within the combustor while, the entropy indirect noise is found to be the main source of noise downstream of the choked nozzle. The indirect vorticity noise has a negligible contribution.

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“…Physically speaking, if the combustor's outlet is choked, these three types of perturbations interact, the reflected pressure perturbation will be excited by the vortical and entropic perturbations. The corresponding boundary condition can be found in Duran and Morgans [27]. As we are interested in the analysis of intrinsic thermoacoustic oscillation, we only consider the acoustic feedback mechanism.…”

Section: Comparison With Literature Resultsmentioning

confidence: 99%

Study an Acoustic-Intrinsic Thermoacoustic Feedback on Swirling Flame Combustors

Chen¹

2019

Proceedings of Global Power &Amp; Propulsion Society

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This paper investigates the intrinsic thermoacoustic feedback and its interaction with the cavity acoustic resonations in swirling flame combustors. The dynamics of acousticvortical-entropic perturbations due to the unsteady heat release rate in a swirling flame is given where the azimuthal and axial base flow velocities are present. The critical gain of the intrinsic thermoacoustic (ITA) oscillation is given meanwhile parametric analysis shows that the difference of the transit time between acoustic and vortical perturbations play an important role on the ITA critical gain. Applied to the verification of experimental results of a swirling flame combustor, the present work predicts correctly the thermoacoustic oscillations. Analysis on the interaction between the intrinsic thermoacoustic feedback and the traditional cavity acoustic resonation feedback shows that the thermoacoustic modes of the whole system are composed of both flame-induced modes and the cavity acoustic modes. The flame dynamics seems to be able to construct a virtual cavity feedback in the absence of acoustic feedbacks from the boundary conditions. The increase of the transit time difference between the acoustic and vortical perturbations before the flame front reduces the frequencies of flameinduced modes and worsens their stabilities. The cavity acoustic mode, on the other hand, forms a periodic orbit and approaches to the orbit's attractor.

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On the reflection and transmission of circumferential waves through nozzles

Cited by 35 publications

References 29 publications

Dispersion of Entropy Perturbations Transporting through an Industrial Gas Turbine Combustor

Dispersion of Entropy Perturbations Transporting through an Industrial Gas Turbine Combustor

Acoustic and Entropy Waves in Nozzles in Combustion Noise Framework

Study an Acoustic-Intrinsic Thermoacoustic Feedback on Swirling Flame Combustors

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