Error analysis of two-microphone measurements in ducts with flow

Åbom, Mats; Bodén, Hans

doi:10.1121/1.396322

Cited by 218 publications

(75 citation statements)

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“…For practical reasons the distance between the sound source and the muffler and the distance between the muffler and the termination should be small. A distance of five to 10 times the diameter of the tube is recommended (Abom and Bodén, 1988). In addition, the measurement point 1 (see Fig.…”

Section: Limitations and Validity Of Measurementsmentioning

confidence: 99%

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Muffler modeling by transfer matrix method and experimental verification

Gerges¹,

Jordan²,

Thieme³

et al. 2005

J. Braz. Soc. Mech. Sci. & Eng.

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Section: Limitations and Validity Of Measurementsmentioning

confidence: 99%

“…In order to avoid errors associated with this factor the transfer function method is best employed in the frequency band given by (see Gerges and Arenas, 2004;Chung andBlaser, 1980, andAbom andBodén, 1988)…”

Section: Limitations and Validity Of Measurementsmentioning

confidence: 99%

Muffler modeling by transfer matrix method and experimental verification

Gerges¹,

Jordan²,

Thieme³

et al. 2005

J. Braz. Soc. Mech. Sci. & Eng.

View full text Add to dashboard Cite

“…Therefore, it is necessary to post-process the solution to obtain the quantities needed for the evaluation of the scattering matrix: this could be done through a method called the plane wave decomposition method. Assuming that only plane waves propagate through the element, the Fourier coefficients of the acoustic pressure can be written as ( [31,35] and [36]),…”

Section: Scattering Matrixmentioning

confidence: 99%

Validation of a Discontinuous Galerkin Implementation of the Time-Domain Linearized Navier–Stokes Equations for Aeroacoustics

Arina¹

2016

Aerospace

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Abstract:The propagation of small perturbations in complex geometries can involve hydrodynamic-acoustic interactions, coupling acoustic waves and vortical modes. A propagation model, based on the linearized Navier-Stokes equations, is proposed. It includes the mechanism responsible for the generation of vorticity associated with the hydrodynamic modes. The linearized Navier-Stokes equations are discretized in space using a discontinuous Galerkin formulation for unstructured grids. Explicit time integration and non-reflecting boundary conditions are described. The linearized Navier-Stokes (LNS) model is applied to two test cases. The first one is the time-harmonic source line in an incompressible inviscid two-dimensional mean shear flow in an infinite domain. It is shown that the proposed model is able to capture the trailing vorticity field developing behind the mass source and to represent the redistribution of the vorticity. The second test case deals with the analysis of the acoustic propagation of an incoming perturbation inside a circular duct with a sudden area expansion in the presence of a mean flow and the evaluation of its scattering matrix. The computed coefficients of the scattering matrix are compared to experimental data for three different Mach numbers of the mean flow, M 0 = 0.08, 0.19 and 0.29. The good agreement with the experimental data shows that the proposed method is suitable for characterizing the acoustic behavior of this kind of network.

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“…A Nyquist-type criterion based on the spatial resolution of the sensor array is used to exclude aliased high frequencies. The cut-off frequency must be less than half the intrinsic frequency of the array, which corresponds to the wavelength being the separation between sensors [72]:…”

Section: Pressure Spectramentioning

confidence: 99%

A numerical approach for predicting flow-induced acoustics at near-stall conditions in an automotive turbocharger compressor

Garcia¹

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Airborne turbocharger noise is becoming a topic of major concern for automotive manufacturers. Particularly, a broadband noise named as whoosh is detected during some engine conditions (full load, tip-in and tip-out maneuvers). This thesis aims to contribute to the understanding of turbocharger compressor flow-induced acoustics by means of 3-dimensional CFD.A methodology to compare CFD and experimental spectra is developed so as to solve the issue of the different location of pressure probes. Pressure decomposition and different types of monitors are required by the model in order to provide meaningful spectra. A tip clearance sensitivity analysis is performed, concluding that tip clearance has an impact on compressor global variables but not on noise generation. CAD tip clearance profile is therefore safely used throughout the thesis. Most important set-up parameters such as grid spacing, solver type or time-step size are evaluated. The model is defined so that noise prediction accuracy is guaranteed in the whole hearing range. In any case, the time-step increment sensitivity analysis reflects that a significant save in computational effort could be made but retaining the right prediction of main spectra features.Finally, three operating conditions are studied at same compressor speed; from best efficiency point to a working point close to surge. All the points present backflows (flow moving from the passage outlet towards the inlet) near the shroud, although their thickness increase when reducing the mass flow. This recirculation zone increase the meridional velocity and improve incidence angle, thus extending the stability margin. Noise emission also is more intense as flow is reduced, particularly at low frequency range. At best efficiency point, a periodic flow separation is observed on the blades suction side. Stalled cells are transported towards the exducer producing a pulsating jet-wake structure that may increase the broadband noise slightly below the main blade passing frequency.In the two points with less mass flow, inducer and diffuser rotating stall can be noticed, causing the so-called whoosh noise. Actually, the point closest to surge presents an increase in the low frequency content found which masks whoosh noise. In this working point, a tornado-like structure is identified in the mixing region between the incoming and recirculating flows, increasing secondary flows and causing large pressure oscillations at the inducer. It is v considered that this phenomenon is responsible for the low frequency noise content rise.Keywords: CFD simulation; Aeroacoustics; Whoosh noise; Rotating stall; URANS; DES vi ResumenLos fabricantes del sector automotriz se están empezando a preocupar por el ruido aéreo generado por el turbogrupo. En particular, un ruido de banda ancha denominado whoosh es detectado en ciertas condiciones (a plena carga y en aceleraciones y desaceleraciones. Esta tesis pretende contribuir al entendimiento de la aeroacústica de los compresores de turbogrupos utilizando CFD tridimens...

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Error analysis of two-microphone measurements in ducts with flow

Cited by 218 publications

References 0 publications

Muffler modeling by transfer matrix method and experimental verification

Muffler modeling by transfer matrix method and experimental verification

Validation of a Discontinuous Galerkin Implementation of the Time-Domain Linearized Navier–Stokes Equations for Aeroacoustics

A numerical approach for predicting flow-induced acoustics at near-stall conditions in an automotive turbocharger compressor

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