Indirect combustion noise: Experimental investigation of the vortex sound generation in accelerated swirling flows

Kings, Nancy; Enghardt, Lars; Bake, Friedrich

doi:10.2514/6.2013-2100

Cited by 7 publications

(9 citation statements)

References 14 publications

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“…We would like to note that just as entropy noise is generated when entropy waves are convected past a highly non-uniform flow, the convection of vorticity waves past such a flow also generates noise. This was demonstrated by Kings and Bake [81] and Kings et al [82] in a vorticity pulse experiment using a Vorticity Wave Generator test rig. Following this experiment, Kings et al [83] repeated their investigation successfully using broadband small scale vorticity waves as input.…”

Section: Part 2 Entropy Noise (Indirect Combustion Noise) 21 Introdmentioning

confidence: 74%

Combustion noise: modeling and prediction

et al. 2019

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This paper reviews both direct and indirect combustion noise. For convenience, they will simply be referred to as combustion noise and entropy noise. Combustion noise has been studied for well over half a century. However, because of the large number of parameters involved and the complexities inherent in the combustion processes, a widely accepted theory has yet to be developed. For this reason, this review focuses primarily on experimental measurements, semi-empirical relations and empirical but practical prediction methodologies. Important characteristic features and empirical correlations of combustion noise based on open flames and engine noise data are highlighted. Plausible generation of entropy noise by the passage of entropy waves through a nonuniform mean flow was first predicted theoretically circa 1970s. But it took forty years for its existence to be confirmed experimentally. Since then, there have been numerous publications on this subject. They are the primary materials of this review. The fundamental experiment and noise generation mechanism will be discussed first. Of great practical importance is whether there is significant generation of entropy waves inside an engine. This issue and new methods for modeling and predicting internally generated engine entropy noise are items that are examined at some length. Recent advances in computational methods especially in large eddy simulation lead us to envision an important role to be played by high-fidelity numerical simulation in future combustion and entropy noise research and prediction. A critical evaluation of a strategy for investigating and predicting the generation and propagation of these noise components from the combustor of an engine to its exhaust is included in this review.

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Section: Part 2 Entropy Noise (Indirect Combustion Noise) 21 Introdmentioning

confidence: 74%

Combustion noise: modeling and prediction

et al. 2019

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“…The source term is deduced from the solution of the linear vorticity equation, Eq. (17) and (18). In the following it is assumed that weak body forces are still present so that the complex amplitudes U v (x, ω) and V (x, ω) may slightly change in axial direction.…”

Section: Source Term For the Excitation Of Vorticity Wavesmentioning

confidence: 99%

Numerical Investigation of Indirect Noise Generation by Accelerated Vorticity

Ullrich

Bake

Kings

et al. 2015

21st AIAA/CEAS Aeroacoustics Conference

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Combustion noise of aero engines originates from unsteady combustion processes which in turn lead to vortical and temperature fluctuations. These so-called vorticity and entropy waves are convected from the combustor into the turbine where their acceleration results in an additional sound release, namely the indirect noise. In the present study the noise generation by accelerated vorticity waves is investigated in a convergent-divergent nozzle representing the simplest model of the flow through the turbine. A hybrid CFD/CAAapproach is applied which consists of RANS mean flow simulations followed by frequency domain simulations of linear acoustic and vortical fluctuations based on the linearized Navier-Stokes equations (LNSEs). Vorticity waves are excited by a body force term which is deduced from an analytical solution of the linearized vorticity equation. By this means, the indirect noise released by the accelerated vorticity waves is computed and compared with experimental measurements. The numerical simulation captures in general the coupling mechanisms relevant to indirect noise.

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“…Kings and Bake [9,10] ont développé un « Vorticity Wave Generator » (générateur d'ondes de vorticité). Dans ce montage un module d'injection tangentielle est placé en amont d'une tuyère amorcée dans un tuyau reliant un grand réservoir à l'entrée de la tuyère.…”

Section: Introductionunclassified

Main flow oriented vorticity noise experiments

et al. 2023

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Entropy inhomogeneities and vorticity spots induce so-called indirect combustion noise when passing through a choked nozzle; referred to as entropy noise and vorticity noise, respectively. We note that vorticity noise depends on the orientation of the vorticity; viz., oriented normal or parallel to the axial main flow. An experimental investigation of parallel component vorticity noise is presented. In the experiment a time- dependent swirling flow was induced by unsteady tangential injection in the pipe upstream of a choked convergent-divergent nozzle. As the resulting swirling flow passes through the nozzle, the axial stretching of the fluid caused an increase in rotation energy. The steady energy conservation in an isentropic flow implies a Mach number higher than unity at the throat and an associated reduction of density. Ergo, the critical mass-flow rate (for fixed reservoir pressure and temperature) decreases quadratically with increasing swirl intensity. The acoustic waves radiated downstream of the nozzle are a direct measure for this mass-flow modulation. Using a semi-empirical model, this sound production mechanism is demonstrated to indeed be quasi steady.

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Indirect combustion noise: Experimental investigation of the vortex sound generation in accelerated swirling flows

Cited by 7 publications

References 14 publications

Combustion noise: modeling and prediction

Combustion noise: modeling and prediction

Numerical Investigation of Indirect Noise Generation by Accelerated Vorticity

Main flow oriented vorticity noise experiments

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