Standing acoustic waves in a low Mach number shear flow

AIAA Journal ◽  
1992 ◽  
Vol 30 (7) ◽  
pp. 1708-1715 ◽  
Author(s):  
Meng Wang ◽  
David R. Kassoy
Keyword(s):  
Mach Number ◽  
Shear Flow ◽  
Acoustic Waves ◽  
Low Mach Number

Self-generation of organized waves in an impinging turbulent jet at low Mach number

1982 ◽  
Vol 117 ◽  
pp. 425-441 ◽  
Author(s):  
Donald Rockwell ◽  
Andreas Schachenmann
Keyword(s):  
Mach Number ◽  
Phase Difference ◽  
Acoustic Waves ◽  
Near Field ◽  
Turbulent Jet ◽  
Maximum Pressure ◽  
Pressure Amplitude ◽  
Axisymmetric Cavity ◽  
Low Mach Number ◽  
Oscillation Frequencies

Self-generation of highly organized waves in a nominally turbulent jet at very low Mach number can arise from its impingement upon the downstream orifice of an axisymmetric cavity, having an impingement length much shorter than the corresponding acoustic wavelength. The oscillation frequencies are compatible with the resonant modes of a long pipe located upstream of the cavity and with jet-instability frequencies based on the column mode (0·3 [siml ] SD [siml ] 0·6), as well as the near-field shear layer mode (0·016 [siml ] Sθ0 [siml ] 0·03). Moreover, the frequency of the organized wave is constant from separation to impingement; consequently vortex pairing does not occur.Within the cavity, the pressure amplitude associated with the organized wave is directly related to the phase difference between the organized velocity fluctuations at separation and impingement. Maximum pressure amplitude occurs when this phase difference, measured along the cavity (i.e. jet) centre-line, is 2nπ. Streamwise amplitude and phase distributions of the organized wave cannot be explained from purely hydrodynamic considerations; however, they can be effectively modelled by superposing contributions from hydrodynamic and acoustic waves. This aspect has important consequences for externally excited jets as well.

A Semi-implicit Method for Resolution of Acoustic Waves in Low Mach Number Flows

2002 ◽  
Vol 181 (2) ◽  
pp. 545-563 ◽  
Author(s):  
Clifton Wall ◽  
Charles D. Pierce ◽  
Parviz Moin
Keyword(s):  
Mach Number ◽  
Acoustic Waves ◽  
Implicit Method ◽  
Low Mach Number

Acoustic destablilization of vortices

1979 ◽  
Vol 290 (1372) ◽  
pp. 353-371 ◽  
Keyword(s):  
Boundary Condition ◽  
Growth Rate ◽  
Mach Number ◽  
Acoustic Waves ◽  
Polar Angle ◽  
Inviscid Flow ◽  
Two Dimensional ◽  
Low Mach Number ◽  
The Stability ◽  
Good Agreement

A line vortex which has uniform vorticity 2Ω 0 in its core is subjected to a small two-dimensional disturbance whose dependence on polar angle is e imθ . The stability is examined according to the equations of compressible, inviscid flow in a homentropic medium. The boundary condition at infinity is that of outgoing acoustic waves, and it is found that this capacity to radiate leads to a slow instability by comparison with the corresponding incompressible vortex which is stable. Numerical eigenvalues are computed as functions of the mode number m and the Mach number M based on the circumferential speed of the vortex. These are compared with an asymptotic analysis for the m = 2 mode at low Mach number in which it is found that the growth rate is (π/ 32) M 4 Ω 0 in good agreement with the numerical results.

Numerical Prediction of Low Mach Number Jet Noise Ejected From Slit Nozzle

2011 ◽  
Author(s):  
Minoru Yamaguchi ◽  
Yusuke Iwata ◽  
Sadao Akishita ◽  
Yoshifumi Ogami
Keyword(s):  
Mach Number ◽  
Shear Flow ◽  
Green’S Function ◽  
Green's Function ◽  
Jet Noise ◽  
Frequency Range ◽  
Sound Emission ◽  
Low Mach Number ◽  
Number Flow ◽  
Low Mach Number Flow

Prediction of the low Mach number jet noise ejected from rectangular nozzle with high aspect ratio is described. Firstly measurement of the jet noise was conducted in semi-anechoic wind tunnel at the low Mach number flow condition. We were found that the sound power of the jet obeyed 6-th power of jet velocity. This means the jet noise is resulted not from quadrupole distribution in the shear flow of jet, but from dipole distribution on the surface of the exit of the nozzle. The model of vortex sound is applied as the sound generation mechanism at numerical simulation. The sound emission from the vortices in the shear flow is modified with the compact Green’s function representing the scattering effect from the surface of the exit of the nozzle in the lower frequency range. It is also modified with the non-compact Green’s function in the higher frequency range. Lastly calculated sound spectra are compared with measured spectra. The comparison will prove effectiveness of this modeling.

Transient acoustic processes in a low-Mach-number shear flow

1992 ◽  
Vol 238 ◽  
pp. 509-536 ◽  
Author(s):  
Meng Wang ◽  
D. R. Kassoy
Keyword(s):  
Mach Number ◽  
Shear Flow ◽  
Acoustic Waves ◽  
Layer Structure ◽  
Acoustic Streaming ◽  
Nonlinear Effects ◽  
Initial Boundary ◽  
Initial Boundary Value Problem ◽  
Mean Flow ◽  
Transverse Waves

A systematic perturbation procedure, based on a small mean flow Mach number and large duct Reynolds number, is employed to formulate and solve an initial-boundary-value problem for acoustic processes in a shear flow contained within a rigid-walled parallel duct. The results describe the general transient evolution of acoustic waves driven by a plane source located at a given duct cross-section. Forced bulk oscillations near the source and oblique wave generation are shown to result from refraction of the basic planar axial disturbance by the shear flow. Refraction also causes the axial waves to exhibit higher-order amplitude variations in the transverse direction. As the source frequency approaches certain critical values, specific refraction-induced oblique waves evolve into amplifying purely transverse waves. As a result, the magnitude of the refraction effect increases with time, and quasi-steady solutions do not exist. The analysis is extended to the thin acoustic boundary layer adjacent to the solid walls to examine the shear-layer structure induced by the variety of acoustic waves in the core flow. Nonlinear effects and acoustic streaming are shown to be negligibly small on the scale of a few axial wavelengths.

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