On the multiple microphone method for measuring in-duct acoustic properties in the presence of mean flow

1998 ◽  
Vol 103 (3) ◽  
pp. 1520-1526 ◽  
Author(s):  
Seung-Ho Jang ◽  
Jeong-Guon Ih
Keyword(s):  
Acoustic Properties ◽  
Mean Flow

Experiments on the flow and acoustic properties of a moderate-Reynolds-number supersonic jet

1982 ◽  
Vol 116 ◽  
pp. 123-156 ◽  
Author(s):  
T. R. Troutt ◽  
D. K. Mclaughlin
Keyword(s):  
Reynolds Number ◽  
Large Scale ◽  
Near Field ◽  
Acoustic Properties ◽  
Generation Model ◽  
Initial Growth ◽  
Noise Generation ◽  
Mean Flow ◽  
Potential Core ◽  
Moderate Reynolds Number

An experimental investigation of the flow and acoustic properties of a moderate-Reynolds-number (Re = 70000), Mach number M = 2·1, axisymmetric jet has been performed. These measurements extended the experimental studies conducted previously in this laboratory to a higher-Reynolds-number regime where the flow and acoustic processes are considerably more complex. In fact, mean-flow and acoustic properties of this jet were determined to be closely comparable to published properties of high-Reynolds-number jets.The major results of the flow-field measurements demonstrate that the jet shear annulus is unstable over a broad frequency range. The initial growth rates and wavelengths of these instabilities as measured by a hot wire were found to be in reasonable agreement with linear stability theory predictions. Also, in agreement with subsonic-jet results, the potential core of the jet was found to be most responsive to excitation at frequencies near a Strouhal number of S = 0·3. The overall development of organized disturbances around S = 0·2 seems to agree in general with calculations performed using the instability theory originally developed by Morris and Tam.The acoustic near field was characterized in terms of sound-pressure level and directivity for both natural and excited (pure-tone) jets. In addition, propagation direction and azimuthal character of dominant spectral components were also measured. It was determined that the large-scale flow disturbances radiate noise in a directional pattern centred about 30° from the jet axis. The noise from these disturbances appears from simple ray tracing to be generated primarily near the region of the jet where the coherent fluctuations saturate in amplitude and begin to decay. It was also determined that the large-scale components of the near-field sound are made up predominately of axisymmetric (n = 0) and helical (n = ±1) modes. The dominant noise-generation mechanism appears to be a combination of Mach-wave generation and a process associated with the saturation and disintegration of the large-scale instability. Finally, the further development of a noise-generation model of the instability type appears to hold considerable promise.

scholarly journals 3D Acoustic Modelling of Dissipative Silencers with Nonhomogeneous Properties and Mean Flow

2014 ◽  
Vol 6 ◽  
pp. 537935 ◽  
Author(s):  
E. M. Sánchez-Orgaz ◽  
F. D. Denia ◽  
J. Martínez-Casas ◽  
L. Baeza
Keyword(s):  
Bulk Density ◽  
Acoustic Analysis ◽  
Sound Propagation ◽  
Transmission Loss ◽  
Acoustic Properties ◽  
Mean Flow ◽  
Absorbent Material ◽  
Outer Chamber ◽  
Nonhomogeneous Properties ◽  
Flow Effects

A finite element approach is proposed for the acoustic analysis of automotive silencers including a perforated duct with uniform axial mean flow and an outer chamber with heterogeneous absorbent material. This material can be characterized by means of its equivalent acoustic properties, considered coordinate-dependent via the introduction of a heterogeneous bulk density, and the corresponding material airflow resistivity variations. An approach has been implemented to solve the pressure wave equation for a nonmoving heterogeneous medium, associated with the problem of sound propagation in the outer chamber. On the other hand, the governing equation in the central duct has been solved in terms of the acoustic velocity potential considering the presence of a moving medium. The coupling between both regions and the corresponding acoustic fields has been carried out by means of a perforated duct and its acoustic impedance, adapted here to include absorbent material heterogeneities and mean flow effects simultaneously. It has been found that bulk density heterogeneities have a considerable influence on the silencer transmission loss.

scholarly journals Effective conditions for the reflection of an acoustic wave by low-porosity perforated plates

2014 ◽  
Vol 743 ◽  
pp. 448-480 ◽  
Author(s):  
S. Laurens ◽  
E. Piot ◽  
A. Bendali ◽  
M’B. Fares ◽  
S. Tordeux
Keyword(s):  
Characteristic Size ◽  
Acoustic Properties ◽  
Reflection And Transmission Coefficients ◽  
Periodic Pattern ◽  
Inviscid Fluid ◽  
Mean Flow ◽  
Rectangular Array ◽  
Reflection And Transmission ◽  
Elliptical Cross ◽  
Transmission Coefficients

AbstractThis paper describes an investigation of the acoustic properties of a rigid plate with a periodic pattern of holes, in a compressible, ideal, inviscid fluid in the absence of mean flow. Leppington & Levine (J. Fluid Mech., vol. 61, 1973, pp. 109–127) obtained an approximation of the reflection and transmission coefficients of a plane wave incident on an infinitely thin plate with a rectangular array of perforations, assuming that a characteristic size of the perforations is negligible relative to that of the unit cell of the grating, itself assumed to be negligible relative to the wavelength. One part of the present study is of methodological interest. It establishes that it is possible to extend their approach to thick plates with a skew grating of perforations, thus confirming recent results of Bendali et al. (SIAM J. Appl. Math., vol. 73 (1), 2013, pp. 438–459), but in a much simpler way without using complex matched asymptotic expansions of the full wave or to a grating of multipoles. As is well-known, effective compliances for the plate can then be derived from the corresponding approximations of the reflection and transmission coefficients. These compliances are expressed in terms of the Rayleigh conductivity of an isolated perforation. Consequently, in one other part of the present study, the methodology recently introduced by Laurens et al. (ESAIM, Math. Model. Numer. Anal., vol. 47 (6), 2013, pp. 1691–1712) to obtain sharp bounds for the Rayleigh conductivity has been extended to include the case for which the openings of the perforations on the upper and lower sides of the plate are elliptical in shape. This not only enables the determination of these bounds and of the associated reflection and transmission coefficients for actual plates with tilted perforations but also yields single expressions covering all usual cases of perforations: straight or tilted with a circular or an elliptical cross-section.

The influence of mean flow on the acoustic properties of a tube bank

1984 ◽  
Vol 396 (1811) ◽  
pp. 383-403 ◽  
Keyword(s):  
Dispersion Equation ◽  
Sound Propagation ◽  
Circular Cross Section ◽  
Cross Flow ◽  
Acoustic Properties ◽  
Mean Flow ◽  
Tube Bank ◽  
Conservation Of Energy ◽  
Trailing Edges ◽  
The Mean

The theory of sound propagation through a bank of rigid parallel tubes in the presence of a nominally steady, low Mach number cross flow is discussed. A detailed diffraction analysis is given for the idealized but mathematically tractable case of a bank of strips set at zero angle of attack to the mean flow. Various approximations for the dispersion equation governing the propagation of long waves are derived, including the influence of acoustically induced vortex shedding from the strip trailing edges and of hydrodynamic interactions between neighbouring strips. The sound is attenuated by a transfer of energy to the kinetic energy of the essentially incompressible field of the shed vorticity. It is shown how the principle of conservation of energy and a Kramers-Kronig dispersion relation can be combined to yield an alternative derivation of the dispersion equation. This procedure is applicable to a simplified model of propagation through a bank of rigid tubes of circular cross section, and an approximation to the dispersion equation is obtained in this case. The relevance of these results to bound resonances in tube bank cavities is discussed.

Frequency Domain Predictions of Acoustic Wave Propagation and Losses in a Swirl Burner With Linearized Navier-Stokes Equations

2015 ◽  
Author(s):  
Max Zahn ◽  
Moritz Schulze ◽  
Christoph Hirsch ◽  
Michael Betz ◽  
Thomas Sattelmayer
Keyword(s):  
Stokes Equations ◽  
Low Cost ◽  
Hybrid Approach ◽  
Computational Cost ◽  
Swirl Flow ◽  
Acoustic Energy ◽  
Acoustic Properties ◽  
Mean Flow ◽  
Swirl Burner ◽  
Acoustic Damping

A low-cost, high-quality hybrid CFD/CAA-methodology is used to predict the acoustic properties of a swirl burner including its complex swirl flow conditions. The numerically determined burner transfer matrix is validated against experimental data. The results demonstrate the capability of this low-cost hybrid approach to predict the acoustic characteristics of combustor components with high geometrical complexity. Most importantly it captures the effect of mean flow quantities on the fluctuating field. This causes the loss of acoustic energy and thus constitutes sources of acoustic damping. In this regard, reliable data can be obtained to characterize complex acoustic components at relatively low computational cost. Therefore, experimental efforts can be reduced which are generally required to provide data e.g. to set up low-order network models. The insight into the field of fluctuating quantities allows the analysis of linear acoustic damping phenomena. Essentially, in the context of isentropic conditions acoustic energy is lost due to the formation of vorticity disturbances. Source regions for vorticity disturbances are identified at flow separation edges and within the multiple shear layers of the complex swirl flow.

The acoustics of turbulence near sound-absorbent liners

1972 ◽  
Vol 51 (4) ◽  
pp. 737-749 ◽  
Author(s):  
John E. Ffowcs Williams
Keyword(s):  
Acoustic Properties ◽  
Plane Boundary ◽  
Fourth Power ◽  
Small Scale ◽  
Generation Process ◽  
Mean Flow ◽  
Acoustic Liners ◽  
Rigid Plane ◽  
Flow Effects ◽  
Scale Turbulence

Acoustic liners are often perforated screens backed by sound-absorbent material. Turbulence can interact with these screens to generate additional sound. The dynamics of the generation process is examined in this paper, where the liner is modelled as an infinite rigid plane boundary with a homogeneous array of circular orifices or rigid pistons. The acoustic properties of these boundaries are derived in the long wavelength limit. Small-scale turbulence is scattered by individual apertures into sound. Acoustically transparent surfaces support dipole scattering centres while more ‘opaque’ surfaces have monopoles at the apertures which convert turbulence into sound more effectively. It is shown that the process can be described once the response of an individual aperture in an infinite baffle is known. At low Mach numbers the screen can increase the sound radiated by adjacent turbulence by a factor equal to the inverse fourth power of the Mach number. Mean-flow effects are ignored but they are thought to increase the effects deduced in this preliminary study.

Acoustic Properties of Artifical Larnyx Speech

1988 ◽  
Vol 16 ◽  
pp. 31-39
Author(s):  
Bethann Moffet ◽  
Rebekah Pindzola
Keyword(s):  
Acoustic Properties
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