Near-Field and Acoustic Far-Field Response of a High-Speed Jet to Excitation

AIAA Journal ◽  
2015 ◽  
Vol 53 (7) ◽  
pp. 1894-1909 ◽  
Author(s):  
M. Crawley ◽  
A. Sinha ◽  
M. Samimy
Keyword(s):  
High Speed ◽  
Near Field ◽  
Far Field ◽  
Field Response

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.

On the Connection Between Near-Field and Far-Field Solutions of High-Speed Jet Noise

2008 ◽  
Author(s):  
Foluso Ladeinde ◽  
Xiaodan Cai ◽  
Ken Alabi ◽  
Ramons Reba ◽  
Robert Schlinker ◽  
...  
Keyword(s):  
High Speed ◽  
Near Field ◽  
Jet Noise ◽  
Far Field

HELICOPTER NOISE PREDICTIONS USING KIRCHHOFF METHODS

1996 ◽  
Vol 04 (03) ◽  
pp. 321-339 ◽  
Author(s):  
ROGER C. STRAWN ◽  
RUPAK BISWAS ◽  
ANASTASIOS S. LYRINTZIS
Keyword(s):  
Experimental Data ◽  
Finite Difference ◽  
High Speed ◽  
Impulsive Noise ◽  
Near Field ◽  
Rotor Blades ◽  
Far Field ◽  
Computationally Efficient ◽  
Efficient Manner ◽  
Helicopter Noise

This paper presents two methods for predicting the noise from helicopter rotors in forward flight. Aerodynamic and acoustic solutions in the near field are computed with a finite-difference solver for the Euler equations. Two different Kirchhoff acoustics methods are then used to propagate the acoustic signals to the far field in a computationally-efficient manner. One of the methods uses a Kirchhoff surface that rotates with the rotor blades. The other uses a nonrotating Kirchhoff surface. Results from both methods are compared to experimental data for both high-speed impulsive noise and blade-vortex interaction noise. Agreement between experimental data and computational results is excellent for both cases. The rotating and nonrotating Kirchhoff methods are also compared for accuracy and efficiency. Both offer high accuracy with reasonable computer resource requirements. The Kirchhoff integrations efficiently extend the near-field finite-difference results to predict the far field helicopter noise.

An Innovative Package EMC Solution Using a Highly Cost-Effective Sputtered Conformal Shield

2016 ◽  
Vol 2016 (DPC) ◽  
pp. 002152-002181 ◽  
Author(s):  
Nozad Karim ◽  
Rong Zhou ◽  
Jun Fan
Keyword(s):  
High Speed ◽  
Metal Layer ◽  
Near Field ◽  
Cost Effective ◽  
Circuit Board ◽  
System Level ◽  
Normal Operation ◽  
Far Field ◽  
Wide Range ◽  
The Cost

High-speed digital and wireless devices radiate undesired electromagnetic noises that affect the normal operation of other devices causing electromagnetic interference (EMI) problems. Printed circuit board (PCB) and system-level shielding may alleviate inter-system EMI between the PCB board and the outside environment, but does not prevent intra-system EMI within the shielding enclosure. Package and System in Package (SiP) level shielding is often used to minimize intra-system EMI issues. An external metal lid is traditionally employed to prevent noise emission from a device, but the cost and size of this technique makes it unattractive for modern electronics. Conformal shielding is gaining momentum due to its size and height advantages. However, high cost and complexity of the sprayed coating shield prevents it from being used for a wide range of low cost commercial applications. In this paper, an innovative shielding technology with sputtered metal conformal shield is investigated using a specially designed test vehicle. By sputtering a conductive material onto a package, a very thin (typically a few μm) metal layer is constructed on the top and around four sides of the package. This thin sputtered metal layer adds virtually zero penalty to the package size. The cost and complexity of the sputtering process is significantly lower compared to a spraying process. Several types of shielded and unshielded modules were built and extensively tested for both far-field and near-field shielding effectiveness (SE) in a semi-anechoic chamber. The performance of the sputtered conformal shield is compared to that of an unshielded module and the sprayed shield. The measured results show that the sputtered shield performs equally well to a sprayed shield, in far field test, with most measurements better than 40 dB of SE. In near field testing, sputtered shields mostly outperform the sprayed shield, especially when compared in the entire scanned region. A well-designed sputtered conformal shield can, therefore, be a very cost-effective EMI solution for a wide range of packages, such as SiP. Also in the paper, a full wave 3D HFSS model is presented and simulated results for both far and near field are compared with measured data.

Near-field to far-field prediction for high-speed board using an empirical approach

2010 ◽  
Author(s):  
Manish Oswal ◽  
Kye-Yak See ◽  
Weishan Soh ◽  
Weng Yew Chang ◽  
Lin Biao Wang ◽  
...  
Keyword(s):  
High Speed ◽  
Near Field ◽  
Empirical Approach ◽  
Far Field

Controlled‐source audiofrequency magnetotelluric responses of three‐dimensional bodies

Geophysics ◽  
1991 ◽  
Vol 56 (2) ◽  
pp. 255-264 ◽  
Author(s):  
N. B. Boschetto ◽  
G. W. Hohmann
Keyword(s):  
Plane Wave ◽  
Electric Field ◽  
Near Field ◽  
Three Dimensional ◽  
Sole Source ◽  
Far Field ◽  
Field Zone ◽  
Wave Source ◽  
Controlled Source ◽  
Field Response

Modeling the controlled‐source audiofrequency magnetotelluric (CSAMT) responses of simple three‐dimensional (3-D) structures due to a grounded electric bipole confirms that the CSAMT technique accurately simulates plane‐wave results in the far‐field zone of the transmitter. However, at receiver sites located above large conductive or resistive bodies, the presence of the inhomogeneity extends or reduces, respectively, the frequency range of the far‐field zone. Measurements made on the surface beyond a large 3-D body display a small but spatially extensive effect due to decay of the artificial primary field. Situating a 3-D inhomogeneity beneath the source permits an evaluation of “source overprint” effects. When such a body is resistive, a slight shift in the near‐field response to higher frequencies occurs. When a body below the transmitter is conductive, it is possible to make far‐field measurements closer to the transmitter or lower in frequency. However, as the size of the conductor and its secondary‐field response increases, large transition‐zone responses distort the data. For both a plane‐wave source and a finite source, current channeling into a 3-D conductor from conductive overburden enhances the response of a target. The modeled response of a dike‐like conductor shows no better results for either the broadside or collinear configuration. The location and extent of such a body are better defined when measuring the electric field perpendicular to the strike of the prism, but resistivity estimates are better when using the electric field parallel to the strike of the prism, irrespective of transmitter orientation. Models designed from data collected at Marionoak, Tasmania, yield results which indicate that the thin, vertical graphitic unit intersected by drilling is detectable by the CSAMT method, but probably is not the sole source of the large anomaly seen in the CSAMT data.

Analysis of the near-field and far-field sound pressure generated by high-speed trains pantograph system

2020 ◽  
Vol 169 ◽  
pp. 107506
Author(s):  
Yue-ying Zhao ◽  
Zhi-gang Yang ◽  
Qi-liang Li ◽  
Chao Xia
Keyword(s):  
High Speed ◽  
Sound Pressure ◽  
Near Field ◽  
Far Field ◽  
High Speed Trains ◽  
Field Sound

Simultaneous Noise and Performance Measurements for High Speed Jet Noise Reduction Technologies: Part II—Near Field Array Calibration

2011 ◽  
Author(s):  
Dean Long ◽  
Steve Martens
Keyword(s):  
Noise Reduction ◽  
High Speed ◽  
Near Field ◽  
Jet Noise ◽  
Source Distribution ◽  
Wave Radiation ◽  
Far Field ◽  
Performance Measurements ◽  
Shock Cell ◽  
Field Noise

Part I of this paper describes a methodology for assessing the far field jet noise from high speed exhaust nozzles using a microphone array in the near field of the exhaust plume. 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. Part II described here provides a direct validation of this process using a generic CD nozzle in a facility where both the near field and the far field are measured simultaneously. Comparison of these data sets show good agreement over the typical operating range for this type of nozzle. The far field 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. Subsequent tests in an acoustically treated nozzle thrust stand demonstrate the value of the near field array allowing immediate feedback on the noise/performance tradeoff for high speed jet noise reduction technologies.

Correlations and Wavelet Based Analysis of Near-Field and Far-Field Pressure of a Controlled High-Speed Jet

2011 ◽  
Author(s):  
Kerwin Low ◽  
Zachary Berger ◽  
Jacques Lewalle ◽  
Basman El-Hadidi ◽  
Mark Glauser
Keyword(s):  
High Speed ◽  
Near Field ◽  
Far Field
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