The Entropy Wave Generator (EWG): A reference case on entropy noise

Bake, Friedrich; Richter, Christoph; Mühlbauer, Bernd; Kings, Nancy; Röhle, I.; Thiele, Frank; Noll, Berthold

doi:10.1016/j.jsv.2009.05.018

Cited by 155 publications

(171 citation statements)

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“…These resulted in improving the predictability of the acoustic conversion of entropy waves. For instance, the results of wellcontrolled experiments of Bake et al [19,20] in an entropy wave generator were initially in fair agreement with the classical prediction of Marble and Candel [12]. The causes of disagreement were explained and mostly resolved in the recent refinements of the original theory [15,11].…”

Section: Introductionmentioning

confidence: 92%

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: 92%

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

2017

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“…The nozzle analysed here is the one used for the Entropy Wave Generator (EWG) experiment. This experiment, performed by Bake et al (2009), studied the indirect noise generated by a convected entropy wave through a nozzle. The subsonic response of the nozzle is here studied as an example for several Mach number profiles as seen in figure 24 and in Table.…”

Section: Study Of Subsonic Nozzlesmentioning

confidence: 99%

“…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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“…We similarly define the thermo-acoustic Fant equation aŝ 23) whereL is the adjoint to L. Namely, the Fant equation is …”

Section: The Adjoint-equation Methodsmentioning

confidence: 99%

“…There is also a secondary 'indirect' combustion dipole source producing 'entropy noise' and is due to unevenly heated combustion products accelerating unevenly within the mean flow [11][12][13][14][15][16][17][18][19][20][21]. Although interest in this type of source has recently revived [22][23][24][25][26][27][28][29][30], understanding factors governing feedback on the direct monopole flame source (i.e. aerodynamics of the oscillating mean flow, structural vibrations, flame flashback, flame-vortex interactions, burn rate fluctuations produced by flame-area oscillation, saturation of nonlinear heat release rates, etc) are probably more important for the control of the system instabilities [31][32][33][34][35][36][37].…”

Section: Introductionmentioning

confidence: 99%