Amplification of aerodynamic noise by convected flow inhomogeneities

Morfey, C. L.

doi:10.1016/s0022-460x(73)80255-x

Cited by 182 publications

(111 citation statements)

References 8 publications

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“…The mechanism by which accelerated entropy waves generate acoustic waves (entropy noise) has been discussed in a number of papers, particularly in the context of nozzles and turbine blade rows (Morfey 1973;Ffowcs Williams & Howe 1975;Marble & Candel 1977;Stow et al 2002;Moase et al 2007;Huet & Giauque 2013).…”

Section: Indirect Noise Generationmentioning

confidence: 99%

Theory and application of reverberated direct and indirect noise

2017

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The generation of a temperature disturbance in a flow is accompanied by the production of acoustic waves (direct noise) and of an entropy perturbation. If this entropy perturbation is accelerated or decelerated (as is the case through a nozzle or flow restriction), additional acoustic waves are generated (indirect noise). Several studies have demonstrated this mechanism in controlled conditions by using entropy wave generators, in which entropy waves are generated and convected through a nozzle, leading to direct and indirect noise. An analytical analysis of the direct and indirect noise produced by the generation and acceleration of entropy waves in a reflective environment is presented. The effect of reverberation (repeated acoustic reflections) on low-frequency perturbations (characteristic of entropy wave generators) is determined analytically. These results are then implemented in a set of limit cases, showing the limit behaviours of such systems. The analytical model is applied to the case of the Cambridge entropy wave generator experiment, in which entropy waves are generated by an electric heater and accelerated through a subsonic orifice plate. Due to the clear time separation of direct and indirect noise in the experimental results, direct and indirect noise transfer functions can be extracted from the experimental data for the first time and compared directly with existing theoretical models. The backward-propagating indirect noise generated at an orifice plate is shown to be significantly higher than predicted by existing theoretical models for isentropic nozzles.

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Section: Indirect Noise Generationmentioning

confidence: 99%

Theory and application of reverberated direct and indirect noise

2017

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“…Indirect noise in a similar way to the direct combustion noise can propagate through the turbine and also can reflect back into the combustor. It is often called 'entropy noise' and was first investigated analytically at low Mach numbers by the early works of Marble & Candel [6] and Morfey [8] in the seventies. Combustion noise has been found to be important at low frequencies [9] and in the gas turbine geometry indirect noise dominates direct combustion noise at low frequencies [1,10,11].In a detailed review by Morgans and Duran [12], five stages of flow physics have been identified as being important for entropy noise in gas turbines.…”

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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“…Early analytical investigations deal with the development of the jet noise theory, extending the work of Lighthill [41] to nonuniform-density flows [22][23][24]. However these analytical solutions were limited to low-Mach-number flows and focused on the derivation of a formulation for the far field sound radiation into free space by inhomogeneities swept out of an orifice.…”

Section: Accounting For Entropy Convection In a Zero Mach Mean Flowmentioning

confidence: 99%

“…As shown by many authors [22][23][24][25], entropy fluctuations accelerated in a mean flow generate acoustic waves, which is the case when the combustor opens onto a high pressure distributor. Acoustic waves transmitted through the distributor produce indirect combustion noise, while acoustic waves travelling back to the flame may trigger low-frequency resonant modes called rumble [26,27].…”

Section: Introductionmentioning

confidence: 96%

Accounting for convective effects in zero-Mach-number thermoacoustic models

Motheau

Selle

Nicoud

2014

Journal of Sound and Vibration

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a b s t r a c tThis paper presents a methodology to account for some mean-flow effects on thermoacoustic instabilities when using the zero-Mach-number assumption. It is shown that when a computational domain is represented under the M¼ 0 assumption, a nonzero-Machnumber element can simply be taken into account by imposing a proper acoustic impedance at the boundaries so as to mimic the mean flow effects in the outer, not computed flow domain. A model that accounts for the coupling between acoustic and entropy waves is presented. It relies on a "delayed entropy coupled boundary condition" (DECBC) for the Helmholtz equation satisfied by the acoustic pressure. The model proves able to capture low-frequency entropic modes even without mean-flow terms in the fluctuating-pressure equation.

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Amplification of aerodynamic noise by convected flow inhomogeneities

Cited by 182 publications

References 8 publications

Theory and application of reverberated direct and indirect noise

Theory and application of reverberated direct and indirect noise

Acoustic and Entropy Waves in Nozzles in Combustion Noise Framework

Accounting for convective effects in zero-Mach-number thermoacoustic models

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