Separation of Hydrodynamic, Entropy, and Combustion Noise in a Gas Turbine Combustor

Muthukrishnan, M.; Strahle, Warren C.; Neale, D. H.

doi:10.2514/3.60895

Cited by 64 publications

(33 citation statements)

References 4 publications

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“…The problem was then termed entropy noise and correspondingly the density inhomogeneities or hot spots were called entropy waves [3,4]. It has been demonstrated that unsteady flames can generate entropy waves, which are advected downstream by the mean flow and may reach the exit nozzle of the combustor [3,5,6].…”

Section: Introductionmentioning

confidence: 99%

On the dissipation and dispersion of entropy waves in heat transferring channel flows

2017

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This paper investigates the hydrodynamic and heat transfer effects upon the dissipation and dispersion of entropy waves in non-reactive flows. These waves, as advected density inhomogeneities downstream of unsteady flames, may decay partially or totally before reaching the exit nozzle, where they are converted into sound. Attenuation of entropy waves dominates the significance of the subsequent acoustic noise generation.Yet, the extent of this decay process is currently a matter of contention and the pertinent mechanisms are still largely unexplored. To resolve this issue, a numerical study is carried out by compressible large eddy simulation (LES) of the wave advection in a channel subject to convective and adiabatic thermal boundary conditions. The dispersion, dissipation and spatial correlation of the wave are evaluated by post-processing of the numerical results. This includes application of the classical coherence function as well as development of nonlinear quantitative measures of wave dissipation and dispersion. The analyses reveal that the high frequency components of the entropy wave are always strongly damped. The survival of the low frequency components heavily depends upon the turbulence intensity and thermal boundary conditions of the channel. In general, high turbulence intensities and particularly heat transfer intensify the decay and destruction of the spatial coherence of entropy waves. In some cases, they can even result in the complete annihilation of the wave. The current work can therefore resolve the controversies arising over the previous studies of entropy waves with different thermal boundary conditions.

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Section: Introductionmentioning

confidence: 99%

On the dissipation and dispersion of entropy waves in heat transferring channel flows

2017

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“…Two mechanisms control combustion noise generation, related to the propagation of these two waves to the outlet: direct noise, generated when acoustic waves traverse the turbine stages, and indirect noise, a mechanism in which entropy waves generate noise when accelerated with the mean flow. This source can contribute significantly to the total noise (Candel 1972;Pickett 1975;Muthukrishnan et al 1978). Recent studies (Bake et al 2009;Howe 2010;Leyko et al 2009Leyko et al , 2008 have shown that the propagation of waves through non-uniform flows plays a major role in the generation and attenuation of combustion noise.…”

Section: Introductionmentioning

confidence: 99%

Solution of the quasi-one-dimensional linearized Euler equations using flow invariants and the Magnus expansion

2013

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The acoustic and entropy transfer functions of quasi-one-dimensional nozzles are studied analytically for both subsonic and choked flows with and without shock waves. The present analytical study extends both the compact nozzle solution obtained by Marble & Candel (1977) and the effective nozzle length proposed by Stow et al. (2002) and by Goh & Morgans (2011a) to non-zero frequencies for both modulus and phase through an asymptotic expansion of the linearized Euler equations. It also extends the piecewiselinear approximation of the velocity profile in the nozzle proposed by Moase et al. (2007) to any arbitrary profile or equivalently any nozzle geometry. The equations are written as a function of three variables, namely the dimensionless mass, total temperature and entropy fluctuations, yielding a first order linear system of differential equations with varying coefficients, which is solved using the Magnus expansion. The solution shows that both the modulus and the phase of the transfer functions of the nozzle have a strong dependence on the frequency. This holds for both choked flows and subsonic converging diverging nozzles. The method is used to compare two different nozzle geometries with the same inlet and outlet Mach numbers showing that, even if the compact solution predicts no differences between the transfer functions of the two nozzles, significant differences are found at non-zero frequencies. A parametric study is finally performed to calculate the indirect to direct noise ratio for a model combustor, showing that this ratio decreases at higher frequencies.

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“…Although the effects of noise or random excitations have been studied extensively in other elds (such as signal processing, economics and nance, and physics, to name a few 4 ), only a small amount of work has been done on the interactionsbetween noise and acoustic instabilities. Strahle,5,6 Muthukrishnan et al, 7 and Hedge and Strahle 8 studied combustion noise and possible interaction between noise and instabilitiesover a number of years.They concluded that the coupling between combustion noise and acoustic waves is not strong enough to drive large-amplitudeoscillations. 5¡ 8 Deur and Hessler 9 investigated external excitations as a possible explanation for large-amplitudeoscillationsin combustionchambers.As we will show, inclusion of noise will lead to external excitations that could theoretically produce large-amplitude forced oscillations as Deur and Hessler have suggested.However, there is a fundamental difference in the transient behavior of forced oscillationsand self-excited oscillations.…”

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confidence: 99%

Influence of random excitations on acoustic instabilities in combustion chambers

Burnley¹,

Culick²

2000

AIAA Journal

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Although ows in combustors contain considerable noise, arising from several kinds of sources, there is a sound basis for treating organized oscillations as distinct motions. That has been an essential assumption incorporated in virtually all treatments of combustion instabilities. However, certain characteristics of the organized or deterministic motions seem to have the nature of stochastic processes. For example, the amplitudes in limit cycles always exhibit a random character, and even the occurrence of instabilities seems occasionally to possess some statistical features. Analysis of nonlinear coherent motions in the presence of stochastic sources is, therefore, an important part of the theory. We report a few results for organized oscillations in the presence of noise. The most signi cant de ciency is that, because of the low level of current understanding, the stochastic sources of noise are modeled in ad hoc fashion and are not founded on a solid physical basis appropriate to combustion chambers.

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Separation of Hydrodynamic, Entropy, and Combustion Noise in a Gas Turbine Combustor

Cited by 64 publications

References 4 publications

On the dissipation and dispersion of entropy waves in heat transferring channel flows

On the dissipation and dispersion of entropy waves in heat transferring channel flows

Solution of the quasi-one-dimensional linearized Euler equations using flow invariants and the Magnus expansion

Influence of random excitations on acoustic instabilities in combustion chambers

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