A Numerical Analysis for Perforated Muffler Components with Mean Flow

1999 ◽  
Vol 121 (2) ◽  
pp. 231-236 ◽  
Author(s):  
Chao-Nan Wang
Keyword(s):  
Wave Propagation ◽  
Performance Prediction ◽  
Present Method ◽  
Mean Flow ◽  
Acoustic Performance ◽  
Higher Order Modes ◽  
Element Approach ◽  
The Mean ◽  
Perforated Tube ◽  
Plane Wave Propagation

A boundary element approach for analyzing the perforated muffler components with mean flow is developed. Most of the research on perforated mufflers is based on the assumption of plane wave propagation. In the present method, the effects of mean flow, including the convection effect in governing equation and the change of acoustic impedance of perforated tube, are considered and the influences of higher order modes are also included. The acoustic performance prediction is performed on the perforated intruding tube mufflers and also on the plug muffler with and without mean flow. Comparisons of the influences of various porosity, the mean flow velocities, the tube thickness and the hole diameters are investigated. However, the results need to be verified by further experimental measurement.

A theoretical study of viscous effects in peristaltic pumping

1994 ◽  
Vol 279 ◽  
pp. 177-195 ◽  
Author(s):  
Alden M. Provost ◽  
W. H. Schwarz
Keyword(s):  
Wave Propagation ◽  
Pressure Gradient ◽  
Flow Rate ◽  
Mean Flow ◽  
Viscous Effects ◽  
Transverse Waves ◽  
Peristaltic Pumping ◽  
Mean Pressure ◽  
Flow Through ◽  
The Mean

Intuition and previous results suggest that a peristaltic wave tends to drive the mean flow in the direction of wave propagation. New theoretical results indicate that, when the viscosity of the transported fluid is shear-dependent, the direction of mean flow can oppose the direction of wave propagation even in the presence of a zero or favourable mean pressure gradient. The theory is based on an analysis of lubrication-type flow through an infinitely long, axisymmetric tube subjected to a periodic train of transverse waves. Sample calculations for a shear-thinning fluid illustrate that, for a given waveform, the sense of the mean flow can depend on the rheology of the fluid, and that the mean flow rate need not increase monotonically with wave speed and occlusion. We also show that, in the absence of a mean pressure gradient, positive mean flow is assured only for Newtonian fluids; any deviation from Newtonian behaviour allows one to find at least one non-trivial waveform for which the mean flow rate is zero or negative. Introduction of a class of waves dominated by long, straight sections facilitates the proof of this result and provides a simple tool for understanding viscous effects in peristaltic pumping.

scholarly journals Stratospheric Wave–Mean Flow Feedbacks and Sudden Stratospheric Warmings in a Simple Model Forced by Upward Wave Activity Flux

2014 ◽  
Vol 71 (11) ◽  
pp. 4055-4071 ◽  
Author(s):  
Jeremiah P. Sjoberg ◽  
Thomas Birner
Keyword(s):  
Wave Propagation ◽  
Inversion Layer ◽  
Wave Activity ◽  
Mean Flow ◽  
Stable States ◽  
Mass Model ◽  
Incoming Wave ◽  
Wave Forcing ◽  
The Mean ◽  
Wave Activity Flux

Abstract A classic result of studying stratospheric wave–mean flow interactions presented by Holton and Mass is that, for constant incoming wave forcing (at a notional tropopause), a vacillating stratospheric response may ensue. Simple models, such as the Holton–Mass model, typically prescribe the incoming wave forcing in terms of geopotential perturbation, which is not a proxy for upward wave activity flux. Here, the authors reformulate the Holton–Mass model such that incoming upward wave activity flux is prescribed. The Holton–Mass model contains a positive wave–mean flow feedback whereby wave forcing decelerates the mean flow, allowing enhanced wave propagation, which then further decelerates the mean flow, etc., until the mean flow no longer supports wave propagation. By specifying incoming wave activity flux, this feedback is constrained to the model interior. Bistability—where the zonal wind may exist at one of two distinct steady states for a given incoming wave forcing—is maintained in this reformulated model. The model is perturbed with transient pulses of upward wave activity flux to produce transitions between the two stable states. A minimum of integrated incoming wave activity flux necessary to force these sudden stratospheric warming–like transitions exists for pulses with time scales on the order of 10 days, arising from a wave time scale internal to the model at which forcing produces the strongest mean-flow response. The authors examine how the tropopause affects the internal feedback for this model setup and find that the tropopause inversion layer may potentially provide an important source of wave activity in the lower stratosphere.

Silencer for high-frequency turbocharger compressor noise via an acoustic straightener

2021 ◽  
Vol 263 (5) ◽  
pp. 1744-1755
Author(s):  
Pranav Sriganesh ◽  
Rick Dehner ◽  
Ahmet Selamet
Keyword(s):  
Wave Propagation ◽  
Plane Wave ◽  
High Frequency ◽  
Three Dimensional ◽  
Mean Flow ◽  
Analytical Treatment ◽  
Underlying Assumption ◽  
Wide Range ◽  
Plane Wave Propagation ◽  
Dimensional Wave

Decades of successful research and development on automotive silencers for engine breathing systems have brought about significant reductions in emitted engine noise. A majority of this research has pursued airborne noise at relatively low frequencies, which typically involve plane wave propagation. However, with the increasing demand for downsized turbocharged engines in passenger cars, high-frequency compressor noise has become a challenge in engine induction systems. Elevated frequencies promote multi-dimensional wave propagation rendering at times conventional silencer treatments ineffective due to the underlying assumption of one-dimensional wave propagation in their design. The present work focuses on developing a high-frequency silencer that targets tonal noise at the blade-pass frequency within the compressor inlet duct for a wide range of rotational speeds. The approach features a novel "acoustic straightener" that creates exclusive plane wave propagation near the silencing elements. An analytical treatment is combined with a three-dimensional acoustic finite element method to guide the early design process. The effects of mean flow and nonlinearities on acoustics are then captured by three-dimensional computational fluid dynamics simulations. The configuration developed by the current computational effort will set the stage for further refinement through future experiments.

ACOUSTIC ATTENUATION CHARACTERISTICS OF STRAIGHT-THROUGH PERFORATED TUBE SILENCERS AND RESONATORS

2008 ◽  
Vol 16 (03) ◽  
pp. 361-379 ◽  
Author(s):  
Z. L. JI
Keyword(s):  
Performance Prediction ◽  
Transmission Loss ◽  
Three Dimensional ◽  
Geometrical Parameters ◽  
Mean Flow ◽  
Acoustic Attenuation ◽  
One Dimensional ◽  
The One ◽  
Attenuation Characteristics ◽  
Perforated Tube

The one-dimensional analytical solutions are derived and three-dimensional substructure boundary element approaches are developed to predict and analyze the acoustic attenuation characteristics of straight-through perforated tube silencers and folded resonators without mean flow, as well as to examine the effect of nonplanar waves in the silencers and resonators on the acoustic attenuation performance. Comparisons of transmission loss predictions with the experimental results for prototype straight-through perforated tube silencers demonstrated that the three-dimensional approach is needed for accurate acoustic attenuation performance prediction at higher frequencies, while the simple one-dimensional theory is sufficient at lower frequencies. The BEM is then used to investigate the effects of geometrical parameters on the acoustic attenuation characteristics of straight-through perforated tube silencers and folded resonators in detail.

Wave propagation and transport in the middle atmosphere

1980 ◽  
Vol 296 (1418) ◽  
pp. 73-85 ◽  
Keyword(s):  
Wave Propagation ◽  
Middle Atmosphere ◽  
Transport Processes ◽  
Planetary Waves ◽  
Wave Radiation ◽  
Mean Flow ◽  
Flow Interaction ◽  
Wave Transport ◽  
Equatorial Wave ◽  
The Mean

The dynamics of wave propagation and wave transport are reviewed for vertically propagating, forced, planetary scale waves in the middle atmosphere. Such waves can be divided into two major classes: extratropical planetary waves and equatorial waves. The most important waves of the former class are quasi-stationary Rossby modes of zonal wave numbers 1 and 2 (1 or 2 waves around a latitude circle), which propagate vertically only during the w inter season when the m ean winds are westerly. These modes transport heat and ozone towards the poles, thus maintaining the mean temperature above its radiative equilibrium value in high latitudes and producing the high latitude ozone maximum . It is shown that these wave transport processes depend on wave transience and wave dam ping. The precise form of this dependency is illustrated for transport of a strongly stratified tracer by small amplitude planetary waves. The observed equatorial wave modes are of two types: an eastward propagating Kelvin m ode and a westward propagating mixed Rossby—gravity mode. These modes are therm ally damped in the stratosphere where they interact with the mean flow to produce eastward and westward accelerations, respectively. It is shown tha t in the absence of mechanical dissipation this wave—mean flow interaction is caused by the vertical divergence of a wave ‘radiation stress’. This wave—mean flow interaction process is responsible for producing the well known equatorial quasi-biennial oscillation.

Solution of the Parallel sheaR Layer Green's Function Using Conservation Equations

2009 ◽  
Vol 8 (6) ◽  
pp. 585-602 ◽  
Author(s):  
M. Z. Afsar
Keyword(s):  
Wave Propagation ◽  
Green’S Function ◽  
Green's Function ◽  
Acoustic Analogy ◽  
Mean Flow ◽  
Function Variable ◽  
Convective Derivative ◽  
The Mean ◽  
Parallel Shear Flow ◽  
Set Of Points

A parallel shear flow representation of a jet is a standard way to solve for the wave propagation terms in jet noise modeling using the acoustic analogy. In this paper we show by introducing a new primary Green's function variable, proportional to the convective derivative of the pressure-like Green's function, the wave propagation equations reduce to an exact conservation form that does not include any derivatives of the mean flow. We analyze this Green's function variable numerically and show its utility when the mean flow is defined by a CFD solution and known only at a discrete set of points.

Flow Induced Aerodynamic Noise Analysis of Perforated Tube Mufflers

2012 ◽  
Vol 29 (2) ◽  
pp. 225-231 ◽  
Author(s):  
C.-N. Wang ◽  
C.-C. Tse ◽  
S.-C. Chen
Keyword(s):  
Transmission Loss ◽  
Noise Analysis ◽  
Helmholtz Resonator ◽  
Aerodynamic Noise ◽  
Mean Flow ◽  
Flow Effect ◽  
Flow Induced Noise ◽  
The Mean ◽  
Cfd Method ◽  
Perforated Tube

AbstractDespite the analysis of muffler performance for many years, most works focus mainly on reducing inlet sound and fail to consider the flow effect. Most of their results correlate well with the experimental measurements. Subsequent works have considered the mean flow effect. Owing to Doppler's effect, transmission loss curve of the muffler will shift in its corresponding frequency. However, the correlation is worse than the experimental results since the flow induced noise does not include in the analysis. This work elucidates how flow induced noise affects muffler performance by analyzing a uniform flow that passes through perforated mufflers. The flow field is calculated with the CFD method, followed by evaluation of the aerodynamic noise based on the simulation results. Additionally, the procedure is simplified by computing and comparing only the total sound power induced by the flow in the muffler interior. Two muffler types, Helmholtz resonator and plug perforated tube muffler, are analyzed and discussed.

Numerical Mode Matching Approach for Acoustic Attenuation Predictions of Double-Chamber Perforated Tube Dissipative Silencers with Mean Flow

2014 ◽  
Vol 22 (02) ◽  
pp. 1450004 ◽  
Author(s):  
Z. Fang ◽  
Z. L. Ji
Keyword(s):  
High Frequency ◽  
Present Method ◽  
Transmission Loss ◽  
Mode Matching ◽  
Acoustic Behavior ◽  
Frequency Range ◽  
Mean Flow ◽  
High Frequencies ◽  
Perforated Tube ◽  
Double Chamber

The transfer matrix method (TMM) based on numerical mode matching (NMM) approach is developed to investigate the acoustic behavior of double-chamber perforated tube dissipative silencer with mean flow. The present method is verified by comparing the transmission loss (TL) predictions and experimental data. Then the effects of mean flow, perforated tube offset and lengths of perforations are studied computationally. As the Mach number increases, the TL of dissipative silencer is lowered at most frequencies. The perforated tube offset may change the acoustic behavior in the mid-high frequency range. Increasing the total length of perforations increases TL at the mid-high frequencies.

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