Near Field Studies of Jet Noise

1957 ◽  
Vol 29 (6) ◽  
pp. 779-779
Author(s):  
Peter A. Franklen ◽  
Ira Dyer
Keyword(s):  
Near Field ◽  
Jet Noise ◽  
Field Studies

A proposed wavy shield for suppression of supersonic jet noise utilizing reflections

2021 ◽  
Vol 20 (1-2) ◽  
pp. 4-34
Author(s):  
Reda R Mankbadi ◽  
Saman Salehian
Keyword(s):  
Large Scale ◽  
Flat Surface ◽  
Near Field ◽  
Supersonic Jet ◽  
Jet Noise ◽  
Dominant Frequency ◽  
Wavy Surface ◽  
Initial Region ◽  
Reflected Waves ◽  
Free Jet

In this work we propose replacing the conventional flat-surface airframe that shields the engine by a wavy surface. The basic principle is to design a wavy pattern to reflect the incoming near-field flow and acoustic perturbations into waves of a particular dominant frequency. The reflected waves will then excite the corresponding frequency of the large-scale structure in the initial region of the jet’s shear layer. By designing the frequency of the reflected waves to be the harmonic of the fundamental frequency that corresponds to the radiated peak noise, the two frequency-modes interact nonlinearly. With the appropriate phase difference, the harmonic dampens the fundamental as it extracts energy from it to amplify. The outcome is a reduction in the peak noise. To evaluate this concept, we conducted Detached Eddy Simulations for a rectangular supersonic jet with and without the wavy shield and verified our numerical results with experimental data for a free jet, as well as, for a jet with an adjacent flat surface. Results show that the proposed wavy surface reduces the jet noise as compared to that of the corresponding flat surface by as much as 4 dB.

Validation of Jet Noise Simulations and Resulting Insights of Acoustic Near Field

AIAA Journal ◽  
2019 ◽  
Vol 57 (12) ◽  
pp. 5156-5167 ◽  
Author(s):  
W. C. P. van der Velden ◽  
D. Casalino ◽  
P. Gopalakrishnan ◽  
A. Jammalamadaka ◽  
Y. Li ◽  
...  
Keyword(s):  
Near Field ◽  
Jet Noise

Very Metal-Poor Stars and the Early Universe

2017 ◽  
Vol 13 (S334) ◽  
pp. 3-10
Author(s):  
John E. Norris
Keyword(s):  
Near Field ◽  
Field Studies ◽  
Far Field ◽  
Star Forming ◽  
Chemical Enrichment ◽  
Physical Conditions ◽  
The Galaxy ◽  
Formation And Evolution ◽  
The Universe ◽  
Insight Into

AbstractVery metal-poor stars ([Fe/H] < –2.0) inform our understanding of the formation and evolution of the Galaxy, and the physical conditions in the earliest star-forming environments of the Universe. They play an integral part in the paradigms of stellar populations, stellar archaeology, and near-field cosmology. We review the carbon-rich and carbon-normal sub-populations of the most iron-poor stars, providing insight into chemical enrichment at the earliest times in the Universe. We also discuss the role of very metal-poor stars in providing insight into the Galaxy’s halo, thick disk, and bulge, and the promise they hold for the future. A comparison between the abundances obtained for the nine most Fe-poor stars ([Fe/H] < –4.5) (all but one of which is C-rich) with abundances obtained from far-field cosmology suggests that the former are the most chemically primitive objects yet observed and probably older than the DLA- and sub-DLA systems for which data are currently available from far-field studies.

Near-field studies of surface plasmon generation: optical and terahertz studies

2008 ◽  
Author(s):  
H. W. Kihm ◽  
K. G. Lee ◽  
M. A. Seo ◽  
K. J. Ahn ◽  
A. J. L. Adam ◽  
...  
Keyword(s):  
Surface Plasmon ◽  
Near Field ◽  
Field Studies

Simultaneous Noise and Performance Measurements for High-Speed Jet Noise Reduction Technologies

2009 ◽  
Author(s):  
Dean Long ◽  
Steven Martens
Keyword(s):  
Noise Reduction ◽  
High Speed ◽  
Near Field ◽  
Jet Noise ◽  
Source Distribution ◽  
Test Facility ◽  
Wave Radiation ◽  
Far Field ◽  
Shock Cell ◽  
Field Noise

Model scale tests are conducted to assess the Noise/Performance trade for high speed jet noise reduction technologies. It is demonstrated that measuring the near field acoustic signature with a microphone array can be used to assess the far field noise using a procedure known as acoustic holography. The near field noise measurement is mathematically propagated producing an estimate of the noise level at the new location. Outward propagation produces an estimate of the far field noise. Propagation toward the jet axis produces the source distribution. Tests are conducted on convergent/divergent nozzles with three different area ratios, and several different chevron geometries. Noise is characterized by two independent processes: Shock cell noise radiating in the forward quadrant is produced when the nozzle is operated at non-ideally expanded conditions. Mach wave radiation propagates into the aft quadrant when the exhaust temperature is elevated. These results show good agreement with actual far field measurements from tests in the GE Cell 41 Acoustic Test Facility. Simultaneous performance measurement shows the change in thrust coefficient for different test conditions and configurations. Chevrons attached to the nozzle exit can reduce the noise by several dB at the expense of a minimal thrust loss.

scholarly journals Optical and terahertz near-field studies of surface plasmons in subwavelength metallic slits

2008 ◽  
Vol 10 (10) ◽  
pp. 105003 ◽  
Author(s):  
K J Ahn ◽  
K G Lee ◽  
H W Kihm ◽  
M A Seo ◽  
A J L Adam ◽  
...  
Keyword(s):  
Surface Plasmons ◽  
Near Field ◽  
Field Studies

Military jet noise source imaging using multisource statistically optimized near-field acoustical holography

2016 ◽  
Vol 139 (4) ◽  
pp. 1938-1950 ◽  
Author(s):  
Alan T. Wall ◽  
Kent L. Gee ◽  
Tracianne B. Neilsen ◽  
Richard L. McKinley ◽  
Michael M. James
Keyword(s):  
Noise Source ◽  
Near Field ◽  
Jet Noise ◽  
Source Imaging ◽  
Acoustical Holography

scholarly journals Secondary‐ion‐mass spectrometry and near‐field studies of Ti:LiNbO3optical waveguides

1995 ◽  
Vol 78 (9) ◽  
pp. 5345-5350 ◽  
Author(s):  
F. Caccavale ◽  
P. Chakraborty ◽  
A. Quaranta ◽  
I. Mansour ◽  
G. Gianello ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Secondary Ion Mass Spectrometry ◽  
Near Field ◽  
Field Studies ◽  
Ion Mass Spectrometry ◽  
Secondary Ion
Sign in / Sign up

Export Citation Format

Share Document