An in situ method of wall acoustic impedance measurement in flow ducts

Dean, P. D.

doi:10.1016/s0022-460x(74)80357-3

Cited by 139 publications

(49 citation statements)

References 24 publications

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“…For example, through extensive experiments Melling (1973) determined the impedance of a liner by applying a semi-empirical method and realized that the linear or nonlinear behaviour of the excited flow in the liner depended mostly on the incident sound pressure level (SPL). The popular two-microphone method for impedance eduction, such as used by Dean (1974), was used because of its simplicity and reliability, even when a grazing flow was present. Solving an associated inverse problem is an indirect way to educe the impedance and has been studied by several, including Jones et al (2002), Taktak et al (2010), Enghardt et al (2012) and Piot, Primus & Simon (2012).…”

Section: Literature Reviewmentioning

confidence: 99%

“…In addition to the physical differences in the experimental setup and conditions it is important to mention that the impedance eduction methods are also different. The simulations use a two microphone method (Dean 1974) that connects pressure measurements taken on the liner facesheet and along the cavity end wall to estimate the local impedance that we showed to be useful when orifice effects are avoided (Zhang & Bodony 2012). Using the same data collected in Jones et al (2010), different hypotheses are available to link the mean flow and the pressure measurements taken within the GFIT to the estimated liner impedance.…”

Section: Surface Dragmentioning

confidence: 99%

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Numerical investigation of a honeycomb liner grazed by laminar and turbulent boundary layers

Zhang

Bodony

2016

J. Fluid Mech.

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Direct numerical simulations are used to study the interaction of a cavity-backed circular orifice with grazing laminar and turbulent boundary layers and incident sound waves. The flow conditions and geometry are representative of single degree-of-freedom acoustic liners applied in the inlet and exhaust ducts of aircraft engines and are the same as those from experiments conducted at NASA Langley. The simulations identify the fluid mechanics of how the sound field and state of the grazing boundary layer impact the in-orifice flow and suggest a simple flow analogy that enables scaling estimates. From the scaling estimates the simulations are then used to develop reduced-order models for the in-orifice flow and a time-domain impedance model is constructed. The liner is found to increase drag at all conditions studied by an amount that increases with the incident sound pressure amplitude.

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Section: Literature Reviewmentioning

confidence: 99%

Section: Surface Dragmentioning

confidence: 99%

Numerical investigation of a honeycomb liner grazed by laminar and turbulent boundary layers

Zhang

Bodony

2016

J. Fluid Mech.

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“…First developed by Dean [6], the in situ method relies on measurements performed with two microphones. The first, microphone μ 1 , is flush-mounted to the surface of the liner over which the flow is grazing (z = −25 mm, Fig.…”

Section: In Situ Microphone Methodsmentioning

confidence: 99%

Characterization of an acoustic liner by means of Laser Doppler Velocimetry in a subsonic flow

Minotti¹,

Simon²,

Gantié³

2008

Aerospace Science and Technology

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“…The most basic and commonly used direct methods to determine the acoustic impedance, are the two microphone technique and the insitu method [1,2]. This last methodology, specifically designed for acoustic liners, assumes that for a resonant cavity a unique relationship exists between the internal acoustic pressure and the acoustic particle velocity along the perforated plate.…”

Section: Introductionmentioning

confidence: 99%

Indirect acoustic impedance eduction in presence of flow based on an analytical two-port formulation

Santana

Roeck

Desmet

2014

Mechanical Systems and Signal Processing

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In order to assess the performance of advanced acoustic absorbing materials the acoustic impedance should be determined with high accuracy, especially, in presence of a grazing flow. This paper presents an analytical methodology for the grazing flow acoustic impedance eduction, based on a two-port representation of an acoustic system. This procedure is dedicated to the frequency range below the cut-on frequency of the transversal duct modes and its major appeal refers to a reduced number of microphones and the experimental rig simplicity. The methodology is verified by comparison with acoustic finite element simulations. Experiments are performed on two liner configurations and the educed impedance is compared with reference results obtained with a different approach at another test rig, and shows good agreement. A sensitivity analysis on the influence of the input parameters is carried out showing the influence of the rigid-/impedance wall transition effects, flow Mach number, number of microphones and microphone positioning accuracy.

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An in situ method of wall acoustic impedance measurement in flow ducts

Cited by 139 publications

References 24 publications

Numerical investigation of a honeycomb liner grazed by laminar and turbulent boundary layers

Numerical investigation of a honeycomb liner grazed by laminar and turbulent boundary layers

Characterization of an acoustic liner by means of Laser Doppler Velocimetry in a subsonic flow

Indirect acoustic impedance eduction in presence of flow based on an analytical two-port formulation

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