Aerodynamic noise emission from turbulent shear layers

1973 ◽  
Vol 59 (3) ◽  
pp. 451-479 ◽  
Author(s):  
S. P. Pao
Keyword(s):  
Wave Equation ◽  
Fourier Transformation ◽  
Shear Layers ◽  
Aerodynamic Noise ◽  
Wave Radiation ◽  
Turbulent Shear ◽  
Noise Emission ◽  
Round Jets ◽  
Spatial Dimensions ◽  
Supersonic Shear Layers

The Phillips (1960) convected wave equation is employed in this paper to study aerodynamic noise emission processes in subsonic and supersonic shear layers. The wave equation in three spatial dimensions is first reduced to an ordinary differential equation by Fourier transformation, then solved via the WKBJ method. Three typical solutions are required for discussions in this paper. The current results are different from the classical conclusions. The effects of refraction, convection, Mach-number dependence and temperature dependence of turbulent noise emission are analysed in the light of solutions to the Phillips equation. Owing to the inherent restrictions of the WKBJ transformation, the results of the present paper should be applied to wave radiation from shear layers whose thickness is no less than approximately one quarter of a wavelength. Such a condition is satisfied for turbulent round jets with an exit velocity greater than 0·6 times the ambient speed of sound.

Management of Turbulent Shear Layers in Separated Flow

1978 ◽  
Vol 15 (7) ◽  
pp. 385-386 ◽  
Author(s):  
W.W. Willmarth ◽  
R.F. Gasparovic ◽  
J.M. Maszatics ◽  
J.L. McNaughton ◽  
D.J. Thomas
Keyword(s):  
Separated Flow ◽  
Shear Layers ◽  
Turbulent Shear

Response above a plane-conducting earth to a pulsed vertical magnetic dipole at the surface

2000 ◽  
Vol 78 (9) ◽  
pp. 833-844 ◽  
Author(s):  
O M Abo-Seida ◽  
S T Bishay
Keyword(s):  
Wave Equation ◽  
Magnetic Dipole ◽  
Fourier Transformation ◽  
Laplace Transformation ◽  
Theoretical Study ◽  
Initial Boundary ◽  
Frequency Space ◽  
Hertz Vector ◽  
Vertical Magnetic Dipole ◽  
Pulsed Electromagnetic

A theoretical study of the pulsed electromagnetic radiation from a vertical magnetic dipole placed on a plane-conducting earth is presented. The application of a Laplace transformation in time and a Fourier transformation in the two orthogonal, horizontal, spatial components leads, under consideration of initial, boundary, and transition conditions, to an integral representation of the solution of the wave equation in frequency space. A modified Cagniard method is then used to derive closed-form expressions for the magnetic Hertz vector anywhere above the conducting earth. The method is used to perform numeric calculations of the magnetic Hertz vector, for different source-receiver distances, as well as different values of the earth's conductivity and permittivity. PACS Nos.: 41.20Jb, 42.25Bs, 42.25Gy, 44.05+e

Free Turbulent Shear Layers on Plug Nozzles

1977 ◽  
Vol 99 (2) ◽  
pp. 301-308
Author(s):  
C. J. Scott ◽  
D. R. Rask
Keyword(s):  
Turbulent Mixing ◽  
Schmidt Number ◽  
Error Function ◽  
Mixing Layer ◽  
Shear Layers ◽  
Turbulent Shear ◽  
Gas Chromatograph ◽  
Plug Nozzle ◽  
Turbulent Schmidt Number ◽  
Plug Nozzles

Two-dimensional, free, turbulent mixing between a uniform stream and a cavity flow is investigated experimentally in a plug nozzle, a geometry that generates idealized mixing layer conditions. Upstream viscous layer effects are minimized through the use of a sharp-expansion plug nozzle. Experimental velocity profiles exhibit close agreement with both similarity analyses and with error function predictions. Refrigerant-12 was injected into the cavity and concentration profiles were obtained using a gas chromatograph. Spreading factors for momentum and mass were determined. Two methods are presented to determine the average turbulent Schmidt number. The relation Sct = Sc is suggested by the data for Sc < 2.0.

A hybrid method applied to a 2.5D scalar wave equation

2008 ◽  
Vol 45 (12) ◽  
pp. 1517-1525
Author(s):  
P. F. Daley ◽  
E. S. Krebes ◽  
L. R. Lines
Keyword(s):  
Wave Equation ◽  
Finite Difference ◽  
Heterogeneous Medium ◽  
Integral Transform ◽  
P Wave ◽  
Acoustic Wave Equation ◽  
Seismic Modeling ◽  
Subsurface Structures ◽  
Spatial Dimensions ◽  
Finite Integral

The 3D acoustic wave equation for a heterogeneous medium is used for the seismic modeling of compressional (P-) wave propagation in complex subsurface structures. A combination of finite difference and finite integral transform methods is employed to obtain a “2.5D” solution to the 3D equation. Such 2.5D approaches are attractive because they result in computational run times that are substantially smaller than those for the 3D finite difference method. The acoustic parameters of the medium are assumed to be constant in one of the three Cartesian spatial dimensions. This assumption is made to reduce the complexity of the problem, but still retain the salient features of the approach. Simple models are used to address the computational issues that arise in the modeling. The conclusions drawn can also be applied to the more general fully inhomogeneous problem. Although similar studies have been carried out by others, the work presented here is new in the sense that (i) it applies to subsurface models that are both vertically and laterally heterogeneous, and (ii) the computational issues that need to be addressed for efficient computations, which are not trivial, are examined in detail, unlike previous works. We find that it is feasible to generate true-amplitude synthetic seismograms using the 2.5D approach, with computational run times, storage requirements, and other factors, being at reduced and acceptable levels.

Sign in / Sign up

Export Citation Format

Share Document