Aeroacoustic Response of a Slit-Shaped Diaphragm in a Pipe at Low Helmholtz Number, 2: Unsteady Results

Hofmans, Gcj Geert; Ranucci, M.; Ajello, G.; Aurégan, Yves; Hirschberg, Avraham

doi:10.1006/jsvi.2000.3458

Cited by 24 publications

(11 citation statements)

References 15 publications

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“…But the last term on the right-hand side of (12), which is related to the acoustic mass of the opening, is divergent in the strict formulation of two-dimensional potential flow. It is interesting to note that Hofmans et al 56 also encountered numerical problems when using (12) to calculate the pressure difference across the orifice. They therefore used an integral formulation.…”

Section: A Discrete Vortex Model Of the Vorticity Motion At The Openingmentioning

confidence: 98%

“…52 velocities by close vortices and the vortices unphysical passing through the solid wall due to time discretization, the time interval is set to be sufficiently small and a smooth technique is employed, in which the point vortices are assumed of a Rankine type. 55,56 The core diameter provides an order of magnitude of the effective shear layer thickness in the model. The core diameter of the new shed vortex is assigned as…”

Section: A Discrete Vortex Model Of the Vorticity Motion At The Openingmentioning

confidence: 99%

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Flow-excited acoustic resonance of a Helmholtz resonator: Discrete vortex model compared to experiments

Dai

Sun

2015

Physics of Fluids

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The acoustic resonance in a Helmholtz resonator excited by a low Mach number grazing flow is studied theoretically. The nonlinear numerical model is established by coupling the vortical motion at the cavity opening with the cavity acoustic mode through an explicit force balancing relation between the two sides of the opening. The vortical motion is modeled in the potential flow framework, in which the oscillating motion of the thin shear layer is described by an array of convected point vortices, and the unsteady vortex shedding is determined by the Kutta condition. The cavity acoustic mode is obtained from the one-dimensional acoustic propagation model, the time-domain equivalent of which is given by means of a broadband time-domain impedance model. The acoustic resistances due to radiation and viscous loss at the opening are also taken into account. The physical processes of the self-excited oscillations, at both resonance and off-resonance states, are simulated directly in the time domain. Results show that the shear layer exhibits a weak flapping motion at the off-resonance state, whereas it rolls up into large-scale vortex cores when resonances occur. Single and dual-vortex patterns are observed corresponding to the first and second hydrodynamic modes. The simulation also reveals different trajectories of the two vortices across the opening when the first and second hydrodynamic modes co-exist. The strong modulation of the shed vorticity by the acoustic feedback at the resonance state is demonstrated. The model overestimates the pressure pulsation amplitude by a factor 2, which is expected to be due to the turbulence of the flow which is not taken into account. The model neglects vortex shedding at the downstream and side edges of the cavity. This will also result in an overestimation of the pulsation amplitude.

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Section: A Discrete Vortex Model Of the Vorticity Motion At The Openingmentioning

confidence: 98%

Section: A Discrete Vortex Model Of the Vorticity Motion At The Openingmentioning

confidence: 99%

Flow-excited acoustic resonance of a Helmholtz resonator: Discrete vortex model compared to experiments

Dai

Sun

2015

Physics of Fluids

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“…In the latter case, the fluid compressibility inside the orifice does not play a significant role, and the four elements of the scattering matrix are no longer independent. [20][21][22] Benefiting from this circumstance, a new set of variables can be introduced, which facilitates the physical understanding of acoustic amplification and of pure tone generation.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

Whistling of an orifice in a reverberating duct at low Mach number

Lacombe

Moussou

Aurégan

2011

The Journal of the Acoustical Society of America

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An experimental investigation of the parameters controlling the whistling frequency and amplitude of an orifice in a confined turbulent flow is undertaken. A circular single hole orifice with sharp edges, a hole diameter equal to 0.015 m and a thickness equal to 0.005 m, is arranged in an air test rig with an inner diameter equal to 0.03 m. The Mach number ranges around 0.02 and the Reynolds number around 10(4). Variable reflecting boundary conditions are arranged upstream and downstream, and several flow velocities are tested. It is found that the Bode-Nyquist criterion accurately predicts the conditions of self-sustained oscillation and the value of the whistling frequency. Furthermore, it is found that the acoustic velocity in whistling regime varies from 1% to 15% of the steady flow velocity, and that it depends on the overall acoustic reflection of the surrounding pipe and on the Strouhal number.

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“…The unsteadiness caused by the #ow is expected to be important in that case because Sr"O(1). The response of the diaphragm at low Mach numbers for Sr"O(1) is discussed in a companion paper [11].…”

Section: Discussionmentioning

confidence: 99%

“…The third limit that is treated is Sr "nite such that M 1. In that case the unsteady numerical incompressible-#ow model presented in a companion paper [11] can be used.…”

Section: Defining the Approximationsmentioning

confidence: 99%

Aeroacoustic Response of a Slit-Shaped Diaphragm in a Pipe at Low Helmholtz Number, 1: Quasi-Steady Results

Hofmans

BOOT

Durrieu

et al. 2001

Journal of Sound and Vibration

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The aeroacoustic response of a diaphragm in a pipe is studied by means of an analytical model and experimental measurements. The study is restricted to quasi-two-dimensional diaphragms with a sharp-edged rectangular aperture at conditions for which the acoustic source region can be considered compact. The compactness of the source can be realized under two conditions: either a low Strouhal number and a jet Mach number of the order unity; or a low jet Mach number and a Strouhal number of order unity. In this paper, the focus is on the "rst case. The second case of low Mach number and Strouhal number of order unity is discussed in a companion paper. The results of a quasi-steady theory are compared with measurements of the re#ection and transmission coe$cients of a diaphragm. The theoretical model is based on Ronneberger's model for a step-wise expansion (D. Ronneberger 1967, Acustica 19, 222}235) and Bechert's description of an ori"ce used as an anechoic pipe termination (Bechert 1980 Journal of Sound and

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Aeroacoustic Response of a Slit-Shaped Diaphragm in a Pipe at Low Helmholtz Number, 2: Unsteady Results

Cited by 24 publications

References 15 publications

Flow-excited acoustic resonance of a Helmholtz resonator: Discrete vortex model compared to experiments

Flow-excited acoustic resonance of a Helmholtz resonator: Discrete vortex model compared to experiments

Whistling of an orifice in a reverberating duct at low Mach number

Aeroacoustic Response of a Slit-Shaped Diaphragm in a Pipe at Low Helmholtz Number, 1: Quasi-Steady Results

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