Acoustic Characteristics of an Expansion Chamber With Constant Mass Flow and Steady Temperature Gradient (Theory and Numerical Simulation)

1990 ◽  
Vol 112 (4) ◽  
pp. 460-467 ◽  
Author(s):  
Yang-Hann Kim ◽  
Jae Woong Choi ◽  
Byung Duk Lim
Keyword(s):  
Temperature Gradient ◽  
Transmission Loss ◽  
Matching Condition ◽  
Present Theory ◽  
Flow Speed ◽  
Gradient Theory ◽  
Mean Flow ◽  
Acoustic Wave Propagation ◽  
Expansion Chamber ◽  
Twisting Angle

The governing equation of acoustic wave propagation in a circular expansion chamber with mean flow and temperature gradient is solved. The circular chamber is divided into N segments and the flow speed and temperature are assumed to be constant in each segment. The solution is obtained in recursive form by applying the matching condition on the boundary of adjacent elements. The solution is verified by comparing it with the experimental results. The results demonstrate that the present theory can well predict the transmission loss of an expansion chamber which has offset, a twisting angle, mean flow, and temperature gradient.

General Solution of Acoustic Wave Equation for Circular Reversing Chamber with Temperature Gradient

1991 ◽  
Vol 113 (4) ◽  
pp. 543-550 ◽  
Author(s):  
Yang-Hann Kim ◽  
Jae Woong Choi
Keyword(s):  
Wave Equation ◽  
Temperature Gradient ◽  
General Solution ◽  
Acoustic Wave ◽  
Transmission Loss ◽  
Rigid Wall ◽  
Acoustic Wave Equation ◽  
Mean Flow ◽  
Helmholtz Resonators ◽  
Twisting Angle

A general solution for transmission loss in a circular reversing chamber with the effects of temperature gradient, offset, and twisting angle variations of inlet/outlet ports is obtained by using the mode matching technique. The assumptions included in the solution method are division of the reversing chamber into segments, continuity of pressure and velocity at the boundaries of adjacent elements, constant temperature along each segment, and rigid wall boundary condition. Furthermore, the general solution can reduce to the existing solution of acoustic wave equation for a reversing chamber when no mean flow of exhaust gas and temperature gradient are present. The numerical simulation results based upon the obtained governing equation have the same trough frequencies and shapes of transmission loss curves as the experimental results performed on various types of reversing chambers. From these simulations, it is determined that the diameter of the reversing chamber dictates that cutoff frequencies in the transmission loss curves, and its length controls the number of standing waves in the chamber. Reversing chambers exhibit the acoustic characteristics of simple expansion chambers when the ratios of length over diameter are small. Even for limiting cases, i.e., Helmholtz resonators and close ended pipes, simulations produce the predicted results derived by other existing theories for silencers.

scholarly journals An Efficient Scheme for Onboard Reduction of Moored χpod Data

2017 ◽  
Vol 34 (11) ◽  
pp. 2533-2546 ◽  
Author(s):  
Johannes Becherer ◽  
James N. Moum
Keyword(s):  
Heat Flux ◽  
Temperature Gradient ◽  
Fast Response ◽  
Flow Speed ◽  
Mean Flow ◽  
Temperature Variance ◽  
Efficient Scheme ◽  
Linear Accelerometer

AbstractA scheme for significantly reducing data sampled on turbulence devices (χpods) deployed on remote oceanographic moorings is proposed. Each χpod is equipped with a pitot-static tube, two fast-response thermistors, a three-axis linear accelerometer, and a compass. In preprocessing, voltage means, variances, and amplitude of the subrange (inertial-convective subrange of the turbulence) of the voltage spectrum representing the temperature gradient are computed. Postprocessing converts voltages to engineering units, in particular mean flow speed (and velocity), temperature, temperature gradient, and the rate of destruction of the temperature variance χ from which other turbulence quantities, such as heat flux, are derived. On 10-min averages, this scheme reduces the data by a factor of roughly 24 000 with a small (5%) low bias compared to complete estimates using inertial-convective subrange scaling of calibrated temperature gradient spectra.

scholarly journals An Investigation of Acoustic Attenuation Performance of Silencers with Mean Flow Based on Three-Dimensional Numerical Simulation

2016 ◽  
Vol 2016 ◽  
pp. 1-12 ◽  
Author(s):  
Wei Fan ◽  
Li-Xin Guo
Keyword(s):  
Flow Field ◽  
Flow Velocity ◽  
Cfd Simulation ◽  
Data Transfer ◽  
Transmission Loss ◽  
Three Dimensional ◽  
Mean Flow ◽  
Acoustic Attenuation ◽  
3D Fem ◽  
Expansion Chamber

Transmission loss (TL) is often used to evaluate the acoustic attenuation performance of a silencer. In this work, a three-dimensional (3D) finite element method (FEM) is employed to calculate the TL of some representative silencers, namely, circular expansion chamber silencer and straight-through perforated pipe silencer. In order to account for the effect of mean flow that exists inside the silencer, the 3D FEM is used in conjunction with the Computational Fluid Dynamics (CFD) simulation of the flow field. More concretely, the 3D mean flow field is computed by firstly using CFD, and then the obtained mean flow data are imported to an acoustic solution undertaken using FEM. The data transfer between the two steps is accomplished by mesh mapping. The results presented demonstrate good agreement between present TL predictions and previously published experimental and numerical works. Also, the details of the flow inside the silencers may be studied. Furthermore, the effect of mean flow velocity on acoustic attenuation performance of the silencers is investigated. It is concluded that for the studied silencers, in general, increasing flow velocity increases the TL and decreases the resonance peaks.

CFD Analysis of the Acoustic and Mean Flow Performance of Simple Expansion Chamber Mufflers

2004 ◽  
Author(s):  
J. M. Middelberg ◽  
T. J. Barber ◽  
S. S. Leong ◽  
K. P. Byrne ◽  
E. Leonardi
Keyword(s):  
Transmission Loss ◽  
Time History ◽  
Mean Flow ◽  
Inlet Pipe ◽  
Expansion Chamber ◽  
Acoustic Performance ◽  
Time Histories ◽  
History Of ◽  
Simple Expansion ◽  
The Mean

The acoustic and mean flow performance of different configurations of simple expansion chamber mufflers has been considered. The different configurations include extended inlet/outlet pipes and baffles inside the expansion section of the muffler. Both the acoustic and mean flow performance has been evaluated for each muffler. The acoustic CFD model of the muffler uses an axisymmetric grid with no mean flow and a single period sinusoid of suitable amplitude and duration imposed at the inlet boundary. The time history of the acoustic pressure and particle velocity are recorded at two points, one in the inlet pipe and the other in the outlet pipe. These time histories are Fourier transformed and the transmission loss of the muffler is calculated. The mean flow model of the muffler uses the same geometry, but has a finer mesh and has a suitable inlet velocity applied at the inlet boundary and the pressure drop across the muffler is found. The acoustic performance is compared with published experimental results.

scholarly journals 3D Global Weak-Form Mesh-Free Method for Acoustic Attenuation Analysis of Expansion Chambers

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Chun-Hui Fang ◽  
Cheng-Yang Liu ◽  
Zhi Fang
Keyword(s):  
Transmission Loss ◽  
Interpolation Method ◽  
Weak Form ◽  
Computational Accuracy ◽  
Acoustic Attenuation ◽  
Expansion Chamber ◽  
Acoustic Characteristics ◽  
Acoustic Modes ◽  
Mesh Free ◽  
Mesh Free Method

In order to avoid the dependence of mesh method on grids, a 3D global weak-form mesh-free method (MFM) is applied to study the three-dimensional acoustic characteristics of silencers. For the expansion chamber silencers, the 3D acoustic modes are extracted and the transmission loss results are computed by using the 3D global weak-form (MFM), which is based on the radial basis function point interpolation method (RPIM) for calculating the shape functions and Galerkin method for discretizing the system equation. The first 15 order 3D acoustic modes and TL results of a special expansion chamber silencer are presented to validate the computational accuracy of the proposed technique, and the relative errors are controlled within 0.5% by comparing with the 3D finite element method (FEF) calculations. Additionally, the effects of axial modes on the acoustic characteristics are investigated, and the pass through frequencies can be eliminated to enhance the acoustic attenuation performance by locating the side branch outlet on the nodal lines of axial modes.

Extended Stokes series: laminar flow through a loosely coiled pipe

1978 ◽  
Vol 86 (1) ◽  
pp. 129-145 ◽  
Author(s):  
Milton Van Dyke
Keyword(s):  
Laminar Flow ◽  
Flow Speed ◽  
Square Root ◽  
Mean Flow ◽  
Dean Number ◽  
Curvature Ratio ◽  
Wide Range ◽  
Square Root Singularity ◽  
Flow Through ◽  
The One

Dean's series for steady fully developed laminar flow through a toroidal pipe of small curvature ratio has been extended by computer to 24 terms. Analysis suggests that convergence is limited by a square-root singularity on the negative axis of the square of the Dean number. An Euler transformation and extraction of the leading and secondary singularities at infinity render the series accurate for all Dean numbers. For curvature ratios no greater than$\frac{1}{250} $, experimental measurements of the laminar friction factor agree with the theory over a wide range of Dean numbers. In particular, they confirm our conclusion that the friction in a loosely coiled pipe grows asymptotically as the one-quarter power of the Dean number based on mean flow speed. This contradicts a number of incomplete boundary-layer analyses in the literature, which predict a square-root variation.

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