scholarly journals Numerical Simulation of Acoustic Scattering by a Cylinder Based on the Enhanced Optimized Scheme

2021 ◽  
Vol 2101 (1) ◽  
pp. 012030
Author(s):  
Siqi Yuan ◽  
Ruixuan Ma ◽  
Conghai Wu ◽  
Shuhai Zhang
Keyword(s):  
Acoustic Waves ◽  
Acoustic Scattering ◽  
Numerical Results ◽  
Acoustic Energy ◽  
Two Dimensional ◽  
Benchmark Problem ◽  
Spatial Redistribution ◽  
Scattered Fields ◽  
The Waves ◽  
Scattering Of Acoustic Waves

Abstract The enhanced optimized scheme we developed in the early work is employed to simulate the scattering of acoustic waves from a two-dimensional cylinder by solving the Euler equations. The numerical results of a benchmark problem are found to be in excellent agreement with the exact solution. Our numerical results show that when acoustic waves propagate through a cylinder, the acoustic scattering results in a spatial redistribution of the acoustic energy as well as an alteration of the phase of the waves. The directivities of the scattered fields change significantly for the different length ratios of acoustic wavelength to the radius of the cylinder.

scholarly journals NUMERICAL INVESTIGATION OF THE ACOUSTIC DAMPING OF PLANE ACOUSTIC WAVES BY PERFORATED LINERS WITH BIAS FLOW

2012 ◽  
Vol 19 ◽  
pp. 6-17
Author(s):  
DAN ZHAO ◽  
ZHI YUAN ZHONG
Keyword(s):  
Frequency Domain ◽  
Real Time ◽  
Acoustic Waves ◽  
Method Of Lines ◽  
Single Layer ◽  
Numerical Results ◽  
Domain Model ◽  
Acoustic Energy ◽  
Acoustic Damping ◽  
Bias Flow

Perforated liners are extensively used in aero-engines and gas turbine combustors to suppress combustion instabilities. These liners, typically subjected to a low Mach number bias flow (a cooling flow through perforated holes), are fitted along the bounding walls of a combustor to convert acoustic energy into flow energy by generating vorticity at the rims of the perforated apertures. To investigate the acoustic damping of such liners with bias flow on plane acoustic waves, a time-domain numerical model is developed to compute acoustic wave propagation in a cylindrical duct with a single-layer liner attached. The damping mechanism of the liner is characterized in real-time by using a 'compliance', developed especially for this work. It is a rational function representation of the frequency-domain homogeneous compliance adapted from the Rayleigh conductivity of a single aperture with mean bias flow in the z-domain. The liner 'compliance' model is then incorporated into partial differential equations of the duct system, which are solved by using the method of lines. The numerical results are then evaluated by comparing with the numerical results of Eldredge and Dowling's frequency-domain model. Good agreement is observed. This confirms that the model and the approach developed are suitable for real-time characterizing the acoustic damping of perforated liners.

Experimental observation of resonant filtering in a two-dimensional phononic crystal waveguide

2005 ◽  
Vol 220 (9-10) ◽  
Author(s):  
Jerôme O. Vasseur ◽  
Pierre A. Deymier ◽  
Maxime Beaugeois ◽  
Yan Pennec ◽  
Bahram Djafari-Rouhani ◽  
...  
Keyword(s):  
Transmission Spectrum ◽  
Acoustic Waves ◽  
Theoretical Calculations ◽  
Phononic Crystal ◽  
Stop Band ◽  
Side Branch ◽  
Two Dimensional ◽  
Transmission Coefficients ◽  
The Waves ◽  
Model Structures

AbstractTransmission of acoustic waves through a two-dimensional composite material made of PVC cylinders surrounded by air is measured experimentally. The spectrum presents a very large absolute band gap in the audible frequency range. A waveguide created inside this phononic crystal by removing a row of cylinders can transmit very efficiently the waves falling inside the stop band. We show the existence of deaf modes in the band structure of the linear waveguide. Resonant filtering is also demonstrated experimentally by coupling the waveguide to a side branch resonator of variable length. Frequency filtering is observed in the form of narrow dips in the transmission spectrum of the waveguide. Most of these observations compare favorably with theoretical calculations of dispersion curves and transmission coefficients of model structures using the plane wave expansion and the finite difference time domain methods. Narrow dips similar to those of the guide with resonator are also observed in the transmission spectrum of a waveguide with a sharp bend.

MOTION OF A RIGID SPHERE IN AN ACOUSTIC WAVE FIELD

Geophysics ◽  
1945 ◽  
Vol 10 (1) ◽  
pp. 91-109 ◽  
Author(s):  
Alfred Wolf
Keyword(s):  
Acoustic Waves ◽  
Response Curve ◽  
Wave Length ◽  
Elastic Solid ◽  
Rigid Sphere ◽  
Resonance Effects ◽  
First Order ◽  
Solid Media ◽  
The Waves ◽  
Scattering Of Acoustic Waves

A rigid sphere in the field of plane acoustic waves in a fluid or in an elastic solid medium is subjected to harmonic forces in the direction of propagation of the waves, and proportional to their amplitude. The response curve is a function of the ratio of the circumference of the sphere to the wave length, and of the ratio of the mass of the sphere to the mass of the displaced medium. In an elastic solid, Poisson’s ratio must also be included among the variables. The response curve in fluids decreases continuously with decreasing wave length. In elastic solid media, the response curve has a maximum which is due to resonance effects. In general, the greater the mass of the sphere the smaller the response except in the neighborhood of resonance in elastic solid media. The scattering of acoustic waves by a rigid sphere is determined. The potential of scattered waves is developed in a series of spherical harmonics; it is shown that only the first order coefficients are affected by the motion of the sphere.

scholarly journals Boundary-layer receptivity for a parabolic leading edge. Part 2. The small-Strouhal-number limit

1997 ◽  
Vol 353 ◽  
pp. 205-220 ◽  
Author(s):  
P. W. HAMMERTON ◽  
E. J. KERSCHEN
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Acoustic Waves ◽  
Asymptotic Theory ◽  
Free Stream ◽  
Leading Edge ◽  
Numerical Results ◽  
Two Dimensional ◽  
Mean Flow ◽  
The Mean

In Hammerton & Kerschen (1996), the effect of the nose radius of a body on boundary-layer receptivity was analysed for the case of a symmetric mean flow past a two-dimensional body with a parabolic leading edge. A low-Mach-number two-dimensional flow was considered. The radius of curvature of the leading edge, rn, enters the theory through a Strouhal number, S=ωrn/U, where ω is the frequency of the unsteady free-stream disturbance and U is the mean flow speed. Numerical results revealed that the variation of receptivity for small S was very different for free-stream acoustic waves propagating parallel to the mean flow and those free-stream waves propagating at an angle to the mean flow. In this paper the small-S asymptotic theory is presented. For free-stream acoustic waves propagating parallel to the symmetric mean flow, the receptivity is found to vary linearly with S, giving a small increase in the amplitude of the receptivity coefficient for small S compared to the flat-plate value. In contrast, for oblique free-stream acoustic waves, the receptivity varies with S1/2, leading to a sharp decrease in the amplitude of the receptivity coefficient relative to the flat-plate value. Comparison of the asymptotic theory with numerical results obtained in the earlier paper confirms the asymptotic results but reveals that the numerical results diverge from the asymptotic result for unexpectedly small values of S.

scholarly journals Design of an acoustic energy distributor using thin resonant slits

2021 ◽  
Vol 477 (2247) ◽  
Author(s):  
Lucas Chesnel ◽  
Sergei A. Nazarov
Keyword(s):  
Asymptotic Analysis ◽  
Incident Wave ◽  
Acoustic Waves ◽  
Numerical Results ◽  
Acoustic Energy ◽  
Geometrical Parameters ◽  
Time Harmonic

We consider the propagation of time-harmonic acoustic waves in a device made of three unbounded channels connected by thin slits. The wavenumber is chosen such that only one mode can propagate. The main goal of this work is to present a device which can serve as an energy distributor. More precisely, the geometry is first designed so that for an incident wave coming from one channel, the energy is almost completely transmitted in the two other channels. Additionally, adjusting slightly two geometrical parameters, we can control the ratio of energy transmitted in the two channels. The approach is based on asymptotic analysis for thin slits around resonance lengths. We also provide numerical results to illustrate the theory.

scholarly journals Onset of Convection in Two-Dimensional Porous Cavities with Open and Conducting Boundaries

2021 ◽  
Vol 136 (3) ◽  
pp. 791-812
Author(s):  
Peder A. Tyvand ◽  
Jonas Kristiansen Nøland
Keyword(s):  
Critical Rayleigh Number ◽  
Numerical Results ◽  
Temperature Perturbation ◽  
Two Dimensional ◽  
Onset Of Convection ◽  
Order Problem ◽  
Fourth Order Problem ◽  
Thermally Conducting ◽  
Perturbation Pressure ◽  
Special Case

AbstractThe onset of thermal convection in two-dimensional porous cavities heated from below is studied theoretically. An open (constant-pressure) boundary is assumed, with zero perturbation temperature (thermally conducting). The resulting eigenvalue problem is a full fourth-order problem without degeneracies. Numerical results are presented for rectangular and elliptical cavities, with the circle as a special case. The analytical solution for an upright rectangle confirms the numerical results. Streamlines penetrating the open cavities are plotted, together with the isotherms for the associated closed thermal cells. Isobars forming pressure cells are depicted for the perturbation pressure. The critical Rayleigh number is calculated as a function of geometric parameters, including the tilt angle of the rectangle and ellipse. An improved physical scaling of the Darcy–Bénard problem is suggested. Its significance is indicated by the ratio of maximal vertical velocity to maximal temperature perturbation.

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