Near- and Far-Field Acoustic Measurements for Stepped Nozzles at Over- and Perfectly-Expanded Supersonic Jet Flow Conditions

2020 ◽  
Vol 142 (11) ◽  
Author(s):  
X. F. Wei ◽  
L. P. Chua ◽  
Z. B. Lu ◽  
H. D. Lim ◽  
R. Mariani ◽  
...  
Keyword(s):  
Near Field ◽  
Source Region ◽  
Supersonic Jet ◽  
Jet Flow ◽  
Far Field ◽  
Acoustic Measurements ◽  
Flow Conditions ◽  
Spectra Analysis ◽  
Highly Sensitive ◽  
Nozzle Configuration

Abstract Detailed near- and far-field acoustic measurements were conducted for two circular stepped nozzles with 30 deg and 60 deg design inclinations at over- and perfectly-expanded supersonic jet flow conditions and compared to those for a circular nonstepped nozzle. Far-field acoustic results show that stepped nozzles play an insignificant role in altering noise emissions at perfectly expanded condition. At an over-expanded condition, however, the longer stepped nozzle produces significant noise reductions at the sideline and upstream quadrants, while the shorter stepped nozzle does not. Noise spectra analysis and Schlieren visualizations show that noise reduction can be primarily attributed to mitigations in the broadband shock-associated noise (BSAN), due to the ability of the longer stepped nozzle in suppressing shock strengths at downstream region. Near-field acoustic measurements reveal that the source region, as well as the intensity of turbulent and shock noises, are highly sensitive to the stepped nozzle configuration. Furthermore, BSAN seems to be eliminated by the longer stepped nozzle in near-field region due to the shock structure modifications.

PREDICTION OF NOISE GENERATED BY A ROUND NOZZLE JET FLOW USING COMPUTATIONAL AEROACOUSTICS

2011 ◽  
Vol 19 (03) ◽  
pp. 291-316 ◽  
Author(s):  
ALI UZUN ◽  
M. YOUSUFF HUSSAINI
Keyword(s):  
Flow Field ◽  
Near Field ◽  
Internal Flow ◽  
Jet Flow ◽  
Computational Aeroacoustics ◽  
Far Field ◽  
Free Jet ◽  
Grid Points ◽  
Field Noise ◽  
Inflow Conditions

This paper demonstrates an application of computational aeroacoustics to the prediction of noise generated by a round nozzle jet flow. In this study, the nozzle internal flow and the free jet flow outside are computed simultaneously by a high-order accurate, multi-block, large-eddy simulation (LES) code with overset grid capability. To simulate the jet flow field and its radiated noise, we solve the governing equations on approximately 370 million grid points using high-fidelity numerical schemes developed for computational aeroacoustics. Projection of the near-field noise to the far-field is accomplished by coupling the LES data with the Ffowcs Williams–Hawkings method. The main emphasis of these simulations is to compute the jet flow in sufficient detail to accurately capture the physical processes that lead to noise generation. Two separate simulations are performed using turbulent and laminar inflow conditions at the jet nozzle inlet. Simulation results are compared with the corresponding experimental measurements. Results show that nozzle inflow conditions have an influence on the jet flow field and far-field noise.

Impact of Mechanical Chevrons on Supersonic Jet Flow and Noise

2009 ◽  
Author(s):  
K. Kailasanath ◽  
Junhui Liu ◽  
Ephraim Gutmark ◽  
David Munday ◽  
Steven Martens
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Near Field ◽  
Supersonic Jet ◽  
Initial Step ◽  
Nozzle Geometry ◽  
Jet Flows ◽  
Flow Conditions ◽  
Nozzle Geometries ◽  
The Impact

In this paper, we present observations on the impact of mechanical chevrons on modifying the flow field and noise emanated by supersonic jet flows. These observations are derived from both a monotonically integrated large-eddy simulation (MILES) approach to simulate the near fields of supersonic jet flows and laboratory experiments. The nozzle geometries used in this research are representative of practical engine nozzles. A finite-element flow solver using unstructured grids allows us to model the nozzle geometry accurately and the MILES approach directly computes the large-scale turbulent flow structures. The emphasis of the work is on “off-design” or non-ideally expanded flow conditions. LES for several total pressure ratios under non-ideally expanded flow conditions were simulated and compared to experimental data. The agreement between the predictions and the measurements on the flow field and near-field acoustics is good. After this initial step on validating the computational methodology, the impact of mechanical chevrons on modifying the flow field and hence the near-field acoustics is being investigated. This paper presents the results to date and further details will be presented at the meeting.

Near-Field Acoustic Radiations in a Two-Stream Supersonic Jet Flow

2017 ◽  
Author(s):  
Pinqing Kan ◽  
Christopher J. Ruscher ◽  
Jacques Lewalle ◽  
Mark N. Glauser ◽  
Sivaram P. Gogineni ◽  
...  
Keyword(s):  
Near Field ◽  
Supersonic Jet ◽  
Jet Flow

Near-Field and Far-Field Spectral Analysis of Supersonic Jet with and without Fluidic Injection

2014 ◽  
Author(s):  
Haukur E. Hafsteinsson ◽  
Lars-Erik Eriksson ◽  
Niklas Andersson ◽  
Daniel R. Cuppoletti ◽  
Ephraim J. Gutmark ◽  
...  
Keyword(s):  
Spectral Analysis ◽  
Near Field ◽  
Supersonic Jet ◽  
Far Field

scholarly journals Roughness effect on the efficiency of dimer antenna based biosensor

2012 ◽  
Vol 1 (2) ◽  
pp. 41 ◽  
Author(s):  
D. Barchiesi ◽  
S. Kessentini
Keyword(s):  
Surface Roughness ◽  
Near Field ◽  
Three Dimensional ◽  
Biological Molecules ◽  
Far Field ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
Roughness Effect ◽  
Highly Sensitive ◽  
Local Plasmon

The fabrication process of nanodevices is continually improved. However, most of the nanodevices, such as biosensors present rough surfaces with mean roughness of some nanometers even if the deposition rate of material is more controlled. The effect of roughness on performance of biosensors was fully addressed for plane biosensors and gratings, but rarely addressed for biosensors based on Local Plasmon Resonance. The purpose of this paper is to evaluate numerically the influence of nanometric roughness on the efficiency of a dimer nano-biosensor (two levels of roughness are considered). Therefore, we propose a general numerical method, that can be applied to any other nanometric shape, to take into account the roughness in a three dimensional model. The study focuses on both the far-field, which corresponds to the experimental detected data, and the near-field, responsible for exciting and then detecting biological molecules. The results suggest that the biosensor efficiency is highly sensitive to the surface roughness. The roughness can produce important shifts of the extinction efficiency peak and a decrease of its amplitude resulting from changes in the distribution of near-field and absorbed electric field intensities.

Instability Modal Behavior of the Acoustically Excited Impinging Plane Jet With a Small Cylinder

2004 ◽  
Vol 20 (2) ◽  
pp. 145-157 ◽  
Author(s):  
Fei-Bin Hsiao ◽  
I-Che Hsu ◽  
Cheng-Chiang Hsu
Keyword(s):  
Flow Field ◽  
Coherent Structures ◽  
Nozzle Exit ◽  
Near Field ◽  
Jet Flow ◽  
Core Region ◽  
Far Field ◽  
Potential Core ◽  
Modal Behavior ◽  
Small Cylinder

AbstractThe Instability modal behavior of coherent structures in a jet-small cylinder impinging flow field is extensively studied by hot-wire anemometry measurements. The free jet is employed with a small cylinder of 3 mm in diameter located in the potential core region at the impinging length of L/H = 1.5 for the near field impingement and L/H = 4 for the far field impingement. The jet exit velocity is operated at 10 m/sec with the Reynolds number of 1.03 × 104 based on the nozzle exit width H = 15mm. The impinging jet is locally excited at the nozzle exit with varicose mode (m =0) and sinuous mode (m = 1) disturbances at the fundamental frequency of the natural jet flow. Data indicate that the jet flow is greatly altered and significantly enhanced by strengthening the coherent structures of the flow due to resonance according to the feedback mechanism. Although the original natural jet preferably exhibits the varicose mode, the strong sinuous mode is dominant in the flow field owing to the presence of the small cylinder in the potential core region. In the near field impingement, the wake region behind the cylinder preserves the pure sinuous mode to where the jet vortices merge and then mildly fades out. Whereas in the jet shear layer, the sinuous mode exists in the initial portion and gradually transforms to the varicose mode. In the far field impingement, the alternate mode dominates in each frequency stage in pure impinging case and the modal behavior follows the selected mode with the introducing acoustic waves in the acoustic excitation cases.

Experimental Investigations of Sound From Flow Over Rough Surfaces

2009 ◽  
Author(s):  
Jason M. Anderson ◽  
Devin O. Stewart ◽  
William K. Blake
Keyword(s):  
Scaling Laws ◽  
Rough Surfaces ◽  
Near Field ◽  
Source Region ◽  
Directivity Pattern ◽  
Physical Models ◽  
Experimental Investigations ◽  
Far Field ◽  
Flow Speeds ◽  
Source Mechanisms

Turbulent boundary layer flows over rough surfaces are known to produce elevated far-field acoustic sound levels. The nature by which surface irregularities alter the near-field surface pressures and subsequently affect the sound generation to the scattering of high wavenumber convective pressures to low wavenumber acoustic pressures, which is typically interpreted as a dipole-like source. The focus of the current investigation is the experimental interrogation of both near- and far-field pressures due to the flow over roughened surfaces in order to identify the source mechanisms and to validate physical models of roughness sound. For rough surfaces composed of large geometrical elements (defined by large Reynolds numbers based on roughness height and friction velocity), such as hemispheres and cubes, the measured near-field surfaces pressures indicate that the local interstitial flows become important in determining the sound radiation characteristics. In order to describe the aeroacoustic source region, scaling laws are developed for surface pressures at locations around the roughness elements for various roughness configurations and flow speeds. Relationships between surface pressures amongst the rough surface elements and far-field pressures measured at several directional aspects were examined to identify roughness sound source mechanisms. Measurements of a dipole directivity pattern and dipole efficiency factors obtained when normalizing radiated sound by surface pressures offer support to the scattering theories for roughness sound. Using existing pressure scattering models as a basis, an empirical model for roughness sound is generated.

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