Simple Pressure Source Model of Jet Noise

Scharton, Terry D.; White, Pritchard H.

doi:10.1121/1.1913103

Cited by 53 publications

(6 citation statements)

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“…The aeroacoustic far-field data are computed from the LES data by a Ffowcs Williams-Hawkings solver for the Ma = 0.9 jet as described in Gröschel et al (2008). The physical validity of the OID assumption (2.12) is verified by known results: the fast pressure term (sometimes referred to as 'shear noise') has been shown to dominate in free jets in terms of the hydrodynamic, turbulent pressures, and to correlate better with the far-field pressure than the quadratic slow pressure ('self-noise') (see Lee & Ribner 1972;Scharton & White 1972;Seiner 1974;Seiner & Reetoff 1974;Schaffar 1979;Juvé et al 1980;Schaffar & Hancy 1982;Panda et al 2005). It has furthermore been demonstrated in Cavalieri et al (2011a,b,c) that coherent flow structures generate noise by means of a wavepacket mechanism, while Rodriguez Alvarez et al (2011) show how these wavepackets can be modelled in the framework of linear stability theory.…”

Section: Acoustically Optimized Oid Of Jet Flowmentioning

confidence: 66%

On least-order flow representations for aerodynamics and aeroacoustics

et al. 2012

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We propose a generalization of proper orthogonal decomposition (POD) for optimal flow resolution of linearly related observables. This Galerkin expansion, termed 'observable inferred decomposition' (OID), addresses a need in aerodynamic and aeroacoustic applications by identifying the modes contributing most to these observables. Thus, OID constitutes a building block for physical understanding, leastbiased conditional sampling, state estimation and control design. From a continuum of OID versions, two variants are tailored for purposes of observer and control design, respectively. Firstly, the most probable flow state consistent with the observable is constructed by a 'least-residual' variant. This version constitutes a simple, easily generalizable reconstruction of the most probable hydrodynamic state to preprocess efficient observer design. Secondly, the 'least-energetic' variant identifies modes with the largest gain for the observable. This version is a building block for Lyapunov control design. The efficient dimension reduction of OID as compared to POD is demonstrated for several shear flows. In particular, three aerodynamic and aeroacoustic goal functionals are studied: (i) lift and drag fluctuation of a two-dimensional cylinder wake flow; (ii) aeroacoustic density fluctuations measured by a sensor array and emitted from a two-dimensional compressible mixing layer; † Email address for correspondence: michael.schlegel@tu-berlin.de

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Section: Acoustically Optimized Oid Of Jet Flowmentioning

confidence: 66%

On least-order flow representations for aerodynamics and aeroacoustics

et al. 2012

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“…In the second approach we study retarded-time causality correlations between a single farfield pressure signal and the source field. This is similar to experimental approaches used in the past, 2,3,4,5,6,7,8,9,10 except that correlations can here be effected between the observer and the entire source field; and, we can use the full Lighthill source term, rather than the approximations which are necessary in experiments.…”

Section: Introductionmentioning

confidence: 75%

Analysis of noise-controlled shear-layers

Eschricht¹,

Jordan

Wei

et al. 2007

13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference)

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Despite very similar flow-structures, the uncontrolled and controlled shear-layers of Wei & Freund 1 were found to generate radically different sound fields (a difference of up to 11dB). In this work we analyse these flows-with a view to better understanding what led to this sound reduction-using two approaches: (1) we analyse the inflow pressure fields in the κx − ω domain, where we find that the acoustically-matched components of the controlled flow have been reduced substantially, while the global structure remains very similar; and, (2) we use causality-correlations to study the kernel of the Lighthill solution: the spatiotemporal source-correlation fields are found to have been dramatically degenerated by virtue of very subtle changes in the controlled flow's evolution.

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“…We wish to understand the causal relationship which translates the physical mechanisms by which the flow dynamics ( a p i (t) p i (x)). In a first stage we assume a linear relationship between the fluctuating turbulent velocity and the acoustic far-field pressure: there is a considerable body of evidence to suggest that such an approximation is reasonable: the fast-pressure term (sometimes referred to as 'shear-noise') has been shown to dominate in free-jets in terms of the hydrodynamic, turbulent pressures, 26 and to correlate better with the far-field pressure than the quadratic slow-pressure ('selfnoise'); 18,21,24,22,23,19,1,20,29 Coiffet et al 6 have furthermore demonstrated that the coherent flow structures generate sound via a linear mechanism in the region upstream of the end of the potential core, and Guitton et al 30 have shown that such a mechanism exists as far downstream as 10D, and for Mach number ranging from 0.15 to 0.6: we therefore perform a linear mapping between the POD mode coefficients of the velocity field and those of the pressure field :…”

Section: Mumentioning

confidence: 99%

Identifying Noisy and Quiet Modes in a Jet

Jordan

Schlegel

Stalnov

et al. 2007

13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference)

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In the current jet noise study, an empirical modal decomposition is proposed which distills the noisy and quiet modes of the flow field. In particular, the POD of flows is generalised for an optimal resolution of the far-field noise as opposed to a least-order representation of the hydrodynamic fluctuation level. This decomposition technique, which we call 'most observable decomposition (MOD)', is based on a linear cause-effect relationship between the hydrodynamics (cause) and the far-field acoustics (observed effect). In the current study, this relationship is identified from a linear stochastic estimation between the flow field and the far-field pressure -taking into account the propagation time of sound. We employ MOD to turbulent jet noise at M a = 0.9, Re = 3600 using CFD/CAA data from RWTH Aachen. While more than 350 POD modes are necessary to capture only 50% of the flow fluctuation energy, a mere 24 MOD modes resolve 90% of the far-field acoustics. Evidently, far-field noise acts as filter which 'sees' only a low-dimensional subspace of the flow and 'ignores' silent subspaces which contain a large amount of fluctuation energy. The MOD methodology yields 'least-order' representations of any other observable as wellassuming a linear relationship between flow and observable.

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Simple Pressure Source Model of Jet Noise

Cited by 53 publications

References 0 publications

On least-order flow representations for aerodynamics and aeroacoustics

On least-order flow representations for aerodynamics and aeroacoustics

Analysis of noise-controlled shear-layers

Identifying Noisy and Quiet Modes in a Jet

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