The mean acoustic field in layered media with rough interfaces

1995 ◽  
Vol 98 (1) ◽  
pp. 542-551 ◽  
Author(s):  
David H. Berman
Keyword(s):  
Acoustic Field ◽  
Layered Media ◽  
The Mean ◽  
Rough Interfaces

Electromagnetic Radiation Fields in Three-Layered Media With Rough Interfaces

2012 ◽  
Vol 50 (10) ◽  
pp. 4006-4013 ◽  
Author(s):  
Samira Tadros Bishay ◽  
Osama M. Abo-Seida ◽  
Hanan Shehata Shoeib
Keyword(s):  
Electromagnetic Radiation ◽  
Layered Media ◽  
Radiation Fields ◽  
Rough Interfaces

Radiation from SH‐wave line sources embedded in layered media having rough interfaces

1987 ◽  
Vol 81 (1) ◽  
pp. 37-43 ◽  
Author(s):  
Akhlesh Lakhtakia ◽  
Vijay K. Varadan ◽  
Vasundara V. Varadan
Keyword(s):  
Layered Media ◽  
Sh Wave ◽  
Rough Interfaces

scholarly journals A note on acoustic turbulence

2019 ◽  
Vol 874 ◽  
Author(s):  
Erik Lindborg
Keyword(s):  
Structure Function ◽  
Entropy Production ◽  
Acoustic Field ◽  
Three Dimensional ◽  
Weak Shock ◽  
Separation Distance ◽  
Ideal Gas ◽  
Order Structure ◽  
Specific Heats ◽  
The Mean

We consider a three-dimensional acoustic field of an ideal gas in which all entropy production is confined to weak shocks and show that similar scaling relations hold for such a field as for forced Burgers turbulence, where the shock amplitude scales as $(\unicode[STIX]{x1D716}d)^{1/3}$ and the $p$th-order structure function scales as $(\unicode[STIX]{x1D716}d)^{p/3}r/d$, $\unicode[STIX]{x1D716}$ being the mean energy dissipation per unit mass, $d$ the mean distance between the shocks and $r$ the separation distance. However, for the acoustic field, $\unicode[STIX]{x1D716}$ should be replaced by $\unicode[STIX]{x1D716}+\unicode[STIX]{x1D712}$, where $\unicode[STIX]{x1D712}$ is associated with entropy production due to heat conduction. In particular, the third-order longitudinal structure function scales as $\langle \unicode[STIX]{x1D6FF}u_{r}^{3}\rangle =-C(\unicode[STIX]{x1D716}+\unicode[STIX]{x1D712})r$, where $C$ takes the value $12/5(\unicode[STIX]{x1D6FE}+1)$ in the weak shock limit, $\unicode[STIX]{x1D6FE}=c_{p}/c_{v}$ being the ratio between the specific heats at constant pressure and constant volume.

Noise generation by high-frequency gusts interacting with an airfoil in transonic flow

2000 ◽  
Vol 411 ◽  
pp. 91-130 ◽  
Author(s):  
I. EVERS ◽  
N. PEAKE
Keyword(s):  
Steady Flow ◽  
Acoustic Field ◽  
Transonic Flow ◽  
High Frequency ◽  
Power Series Expansion ◽  
Outer Region ◽  
Leading Edge ◽  
Mean Flow ◽  
Flow Distortion ◽  
The Mean

The method of matched asymptotic expansions is used to describe the sound generated by the interaction between a short-wavelength gust (reduced frequency k, with k [Gt ] 1) and an airfoil with small but non-zero thickness, camber and angle of attack (which are all assumed to be of typical size O(δ), with δ [Lt ] 1) in transonic flow. The mean-flow Mach number is taken to differ from unity by O(δ2/3), so that the steady flow past the airfoil is determined using the transonic small-disturbance equation. The unsteady analysis is based on a linearization of the Euler equations about the mean flow. High-frequency incident vortical and entropic disturbances are considered, and analogous to the subsonic counterpart of this problem, asymptotic regions around the airfoil highlight the mechanisms that produce sound. Notably, the inner region round the leading edge is of size O(k−1), and describes the interaction between the mean-flow gradients and the incident gust and the resulting acoustic waves. We consider the preferred limit in which kδ2/3 = O(1), and calculate the first two terms in the phase of the far-field radiation, while for the directivity we determine the first term (δ = 0), together with all higher-order terms which are at most O(δ2/3) smaller – in fact, this involves no fewer than ten terms, due to the slowly-decaying form of the power series expansion of the steady flow about the leading edge. Particular to transonic flow is the locally subsonic or supersonic region that accounts for the transition between the acoustic field downstream of a source and the possible acoustic field upstream of the source. In the outer region the sound propagation has a geometric-acoustics form and the primary influence of the mean-flow distortion appears in our preferred limit as an O(1) phase term, which is particularly significant in view of the complicated interference between leading- and trailing-edge fields. It is argued that weak mean- flow shocks have an influence on the sound generation that is small relative to the effects of the leading-edge singularity.

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