scholarly journals Effects of isotropic and anisotropic turbulent structures over spray atomization in the near field

2021 ◽  
pp. 103891
Author(s):  
Marco Crialesi-Esposito ◽  
L.A. Gonzalez-Montero ◽  
F.J. Salvador
Keyword(s):  
Near Field ◽  
Spray Atomization ◽  
Turbulent Structures

On the hydrodynamic and acoustic nature of pressure proper orthogonal decomposition modes in the near field of a compressible jet

2017 ◽  
Vol 836 ◽  
pp. 998-1008 ◽  
Author(s):  
Matteo Mancinelli ◽  
Tiziano Pagliaroli ◽  
Roberto Camussi ◽  
Thomas Castelain
Keyword(s):  
Proper Orthogonal Decomposition ◽  
Time Pressure ◽  
Near Field ◽  
Pressure Fluctuations ◽  
Orthogonal Decomposition ◽  
Spectral Energy ◽  
Far Field ◽  
Turbulent Structures ◽  
Proper Orthogonal ◽  
Compressible Jet

In this work an experimental investigation of the near-field pressure of a compressible jet is presented. The proper orthogonal decomposition (POD) of the pressure fluctuations measured by a linear array of microphones is performed in order to provide the streamwise evolution of the jet structure. The wavenumber–frequency spectrum of the space–time pressure fields re-constructed using each POD mode is computed in order to provide the physical interpretation of the mode in terms of hydrodynamic/acoustic nature. Specifically, non-radiating hydrodynamic, radiating acoustic and ‘hybrid’ hydro-acoustic modes are found based on the phase velocity associated with the spectral energy bumps in the wavenumber–frequency domain. Furthermore, the propagation direction in the far field of the radiating POD modes is detected through the cross-correlation with the measured far-field noise. Modes associated with noise emissions from large/fine scale turbulent structures radiating in the downstream/sideline direction in the far field are thus identified.

scholarly journals Towards Prediction and Control of Large Scale Turbulent Structure Supersonic Jet Noise

2009 ◽  
Author(s):  
Robert H. Schlinker ◽  
Ramons A. Reba ◽  
John C. Simonich ◽  
Tim Colonius ◽  
Kristjan Gudmundsson ◽  
...  
Keyword(s):  
Large Scale ◽  
Deterministic Model ◽  
Near Field ◽  
Supersonic Jet ◽  
Jet Noise ◽  
Shear Layers ◽  
Instability Wave ◽  
Turbulent Structures ◽  
Turbulence Structures ◽  
Scale Turbulence

In this paper, we report on progress towards developing physics-based models of sound generation by large-scale turbulent structures in supersonic jet shear layers generally accepted to be the source of aft-angle noise. Aside from obtaining better engineering prediction schemes, the development and optimization of long term jet noise reduction strategies based on controlling instability wave generated large-scale turbulence structures in the shear layer can be more successful if based on predictive flow-noise models, rather than on build and test approaches alone. Such models, if successful, may also provide a path by which laboratory scale demonstrations can be more reliably translated to engine scale. Results show that the noise radiated by large-scale structures in turbulent jet shear layers may be modeled using a RANS based PSE method and projected to the far-field using a Kirchhoff surface approach. A key enabler in this procedure is the development of near-field microphone arrays capable of providing the pressure statistics needed to validate the instability wave models. Our framework provides, for the first time, a deterministic model that will allow understanding and predicting noise radiated by large-scale turbulence.

On the Development of Incompressible Round and Equilateral Triangular Jets Due to Reynolds Number Variation

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
Seyed Sobhan Aleyasin ◽  
Nima Fathi ◽  
Mark Francis Tachie ◽  
Peter Vorobieff ◽  
Mikhail Koupriyanov
Keyword(s):  
Reynolds Number ◽  
Near Field ◽  
Reynolds Stresses ◽  
Turbulent Structures ◽  
Potential Core ◽  
Round Jets ◽  
Flat Side ◽  
Reynolds Number Effects ◽  
Velocity Decay ◽  
Number Variation

The aim of this study is to examine the effects of Reynolds number (Re = 6000–20,000) on mean and turbulent quantities as well as turbulent structures in the near and intermediate regions of equilateral triangular and round sharp contraction jets. The results show shorter potential core length, faster growth of turbulence intensity, and faster diffusion of turbulent structures to the centerline of the triangular jets, implying enhanced mixing in the near field of these jets. On the other hand, the velocity decay and jet spread rates are higher in the round jets. The obtained data in the round jets show that the jet at Re = 6000 has the most effective mixing, while an increase in Reynolds number reduces the mixing performance. In the triangular jets, however, no Reynolds number effects were observed on the measured quantities including the length of the potential core, the decay and spread rates, the axis-switching locations, and the value of the Reynolds number. In addition, the asymptotic values of the relative turbulence intensities on the jet centerline are almost independent of the Reynolds number and geometry. The ratios of transverse and spanwise Reynolds stresses are unity except close to the jet exit where the flow pattern in the major plane of the triangular jet deflects toward the flat side. Proper orthogonal decomposition (POD) analysis revealed that turbulent structures in minor and major planes have identical fractional kinetic energy. The integral length scales increased linearly with the streamwise distance with identical slope for all the test cases.

Near Field Aeroacoustic Experimental Investigation in Low Speed Axial Fans

2008 ◽  
Author(s):  
Stefano Bianchi ◽  
Alessandro Corsini ◽  
Franco Rispoli ◽  
Anthony G. Sheard
Keyword(s):  
Flow Field ◽  
Incidence Angle ◽  
Near Field ◽  
Anechoic Chamber ◽  
Tip Clearance ◽  
Axial Fan ◽  
Present Program ◽  
Turbulent Structures ◽  
Experimental Database ◽  
Low Speed

This paper describes a technique for the investigation of noise sources correlated to tip clearance flows in a low-speed axial fan. A detailed experimental acoustic study is carried out examining the chord-wise evolution of a rotor flow field in the proximity of the blade tip in a low-solidity impeller. The experiment is performed by keeping the rotor “frozen” inside an anechoic chamber. The Mach number, Reynolds number, and blade incidence angle are set in the static frame of reference, reproducing the flow field in the rotating frame. The ‘frozen’ fan rotor is mounted in an anechoic chamber. The near-field pressure perturbations are measured using a chord-traversed microphone. Near-field pressure data is then compared with theoretical predictions, experimental data, and numerical simulations. In this way the validity of the developed experimental scheme is assessed. The purpose of the present program of work is to identify the change in near-field noise as a result of the chord-wise turbulent structures that are located close to the blade surface at the tip. The objective is to study the evolution of turbulent flow structure paths along the chord, and thus to provide insights into their acoustic significance. The present program of work is facilitated by the existence of a detailed pre-existing experimental database on the fan studied.

scholarly journals Effect of fluid injection on turbulence and noise reduction of a supersonic jet

2019 ◽  
Vol 377 (2159) ◽  
pp. 20190082 ◽  
Author(s):  
Chitrarth Prasad ◽  
Philip Morris
Keyword(s):  
Noise Reduction ◽  
High Performance ◽  
Large Scale ◽  
Near Field ◽  
Supersonic Jet ◽  
Acoustic Mode ◽  
Turbulent Structures ◽  
Direct Cross ◽  
Cross Correlations ◽  
Convection Speed

Supersonic jets, such as the ones used in high-performance military aircraft, have both downstream and upstream noise components due to the large-scale turbulent structures and the presence of shock cells in the jet plume. The fluid insert technology is a noise reduction method that has been shown to effectively reduce both these noise components. This paper analyses the unsteady flow changes associated with different fluid insert configurations with a goal of helping to understand the detailed noise reduction mechanisms. Using direct cross-correlations of the near-field data with the far-field microphone signals, it is found that even the use of a single injector as a fluid insert helps break up the large-scale structures of the flow. However, a more azimuthally distributed blowing is required to reduce the upstream broadband shock-associated noise (BBSAN). Addition of upstream injectors at each azimuthal location further enhances the BBSAN reduction. Decomposition of the jet flow-field into hydrodynamic and acoustic modes shows that fluid insert nozzles reduce the amplitude and convection speed of the coherent acoustic mode in the plane of highest noise reduction. This article is part of the theme issue ‘Frontiers of aeroacoustics research: theory, computation and experiment’.

Near-field scanning optical microscopy

1986 ◽  
Vol 44 ◽  
pp. 642-643
Author(s):  
E. Betzig ◽  
A. Harootunian ◽  
M. Isaacson ◽  
A. Lewis
Keyword(s):  
Near Field ◽  
Optical Microscope ◽  
Visible Radiation ◽  
Field Methods ◽  
Optical Elements ◽  
Optical Region ◽  
Order Of Magnitude ◽  
Nondestructive Imaging ◽  
Scanning Optical Microscopy ◽  
Near Field Scanning

In general, conventional methods of optical imaging are limited in spatial resolution by either the wavelength of the radiation used or by the aberrations of the optical elements. This is true whether one uses a scanning probe or a fixed beam method. The reason for the wavelength limit of resolution is due to the far field methods of producing or detecting the radiation. If one resorts to restricting our probes to the near field optical region, then the possibility exists of obtaining spatial resolutions more than an order of magnitude smaller than the optical wavelength of the radiation used. In this paper, we will describe the principles underlying such "near field" imaging and present some preliminary results from a near field scanning optical microscope (NS0M) that uses visible radiation and is capable of resolutions comparable to an SEM. The advantage of such a technique is the possibility of completely nondestructive imaging in air at spatial resolutions of about 50nm.

Principles of Planar Near-Field Antenna Measurements

2007 ◽  
Author(s):  
Stuart Gregson ◽  
John McCormick ◽  
Clive Parini
Keyword(s):  
Near Field ◽  
Antenna Measurements
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