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  • 1995-1999  (10)
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Year
  • 1
    Electronic Resource
    Electronic Resource
    A New Rational Approach to Jet Noise Reduction (1998)
    Springer
    Theoretical and computational fluid dynamics 10 (1998), S. 373-383 
    Details
    ISSN: 1432-2250
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract: This paper offers a new rational approach to jet noise suppression methodology. The tools required to implement such an approach are discussed. These involve the use of global velocimetry to measure those Lighthill turbulent stress tensor terms thought most important to noise generation. The framework of the dynamic systems model as it applies to the development of a noise suppression model is discussed, as well as the latest results on the development of an actuator for control input. The dynamic systems model offers a unique opportunity to study the influence of a concept noise reduction scheme on noise reduction through appropriate algorithms that relate turbulent jet processes to noise.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001620050070
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    Paper (German National Licenses)
    Fulltext
  • 2
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    A New Rational Approach to Jet Noise Reduction (1998)
    Springer
    Details
    Publication Date: 1998-01-01
    Print ISSN: 0935-4964
    Electronic ISSN: 1432-2250
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Springer
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    PAPER CURRENT
  • 3
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    Application Focused Schlieren to Nozzle Ejector Flowfields (1999)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The motivation of the testing was to reduce noise generated by eddy Mach wave emission via enhanced mixing in the jet plume. This was to be accomplished through the use of an ejector shroud, which would bring in cooler ambient fluid to mix with the hotter jet flow. In addition, the contour of the mixer, with its chutes and lobes, would accentuate the merging of the outer and inner flows. The objective of the focused schlieren work was to characterize the mixing performance inside of the ejector. Using flow visualization allowed this to be accomplished in a non-intrusive manner.
    Keywords: Aircraft Propulsion and Power
    Type: First NASA/Industry High Speed Research Program Nozzle Symposium; 15-1 - 15-14; NASA/CP-1999-209423
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Prediction, Measurement, and Suppression of High Temperature Supersonic Jet Noise (1999)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The photograph in figure 1 displays a water cooled round convergent-divergent supersonic nozzle operating slightly overexpanded near 2460 F. The nozzle is designed to produce shock free flow near this temperature at Mach 2. The exit diameter of this nozzle is 3.5 inches. This nozzle is used in the present study to establish properties of the sound field associated with high temperature supersonic jets operating fully pressure balanced (i.e. shock free) and to evaluate capability of the compressible Rayleigh model to account for principle physical features of the observed sound emission. The experiment is conducted statically (i.e. M(sub f) = 0.) in the NASA/LaRC Jet Noise Laboratory. Both aerodynamic and acoustic measurements are obtained in this study along with numerical plume simulation and theoretical prediction of jet noise. Detailed results from this study are reported previously by Seiner, Ponton, Jansen, and Lagen.
    Keywords: Acoustics
    Type: First NASA/Industry High Speed Research Program Nozzle Symposium; 27-1 - 27-34; NASA/CP-1999-209423
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    Near Field Pressure Fluctuations in the Exit Plane of a Choked Axisymmetric Nozzle (1997)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Nearfield pressure data are presented for an unheated jet issuing from an underexpanded sonic nozzle for two exit lip thicknesses of 0.200 and 0.625 nozzle diameters. Fluctuating measurements were obtained on the nozzle exit surface as well as in the acoustic nearfield. Narrowband spectra are presented for numerous operating conditions expressed in terms of the fully expanded Mach number based on nozzle pressure ratio.
    Keywords: Acoustics
    Type: NASA-TM-113137 , NAS 1.15:113137
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 6
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    Mixing Enhancement by Tabs in Round Supersonic Jets (1998)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The objective of this study was to analyze jet plume mass flow entrainment rates associated with the introduction of counter-rotating streamwise vorticity by prism shaped devices (tabs) located at the lip of the nozzle. We have examined the resulting mixing process through coordinated experimental tests and numerical simulations of the supersonic flow from a model axisymmetric nozzle. In the numerical simulations, the total induced vorticity was held constant while varying the distribution of counter-rotating vorticity around the nozzle lip training edge. In the experiment, the number of tabs applied was varied while holding the total projected area constant. Evaluations were also conducted on initial vortex strength. The results of this work show that the initial growth rate of the jet shear layer is increasingly enhanced as more tabs are added, but that the lowest tab count results in the largest entrained mass flow. The numerical simulations confirm these results.
    Keywords: Fluid Mechanics and Heat Transfer
    Type: NASA/CR-1998-207690 , NAS 1.26:207690 , AIAA Paper 98-2326 , Aeroacoustics Conference; Jun 02, 1998 - Jun 04, 1998; Toulouse; France
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 7
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    Shock-free supersonic elliptic nozzles and method of forming same (1996)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: A method of forming a shock-free supersonic elliptic nozzle, in which the nozzle to be designed is divided into three sections, a circular-to-elliptic section which begins at a circular nozzle inlet, an elliptic subsonic section downstream from the circular-to-elliptic section and a supersonic section downstream from the elliptic subsonic section. The maximum and minimum radii for each axial point in the circular-to-elliptic section and the elliptic subsonic section are then separately determined, the maximum and minimum radii being the radii for the widest part of an elliptic cross-section and the narrowest part of the elliptic cross-section, respectively. The maximum and minimum radii for each axial point in the supersonic section are determined based on the Method of Characteristics, Then, each of the three sections are based on the maximum and minimum radii for each axial point in the section. The resulting nozzle is acoustically superior.
    Keywords: Aircraft Propulsion and Power
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 8
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    Screws, Propellers and Fans Based on a Mobius Strip (1998)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A Mobius strip concept is intended for improving the working efficiency of propellers and screws. Applications involve cooling, boat propellers, mixing in appliance, blenders, and helicopters. Several Mobius shaped screws for the average size kitchen mixers have been made and tested. The tests have shown that the mixer with the Mobius shaped screw pair is most efficient, and saves more than 30% of the electric power by comparison with the standard. The created video film about these tests illustrates efficiency of Mobius shaped screws.
    Keywords: Engineering (General)
    Type: AIAA/CEAS-98-2260 , 4th Aeronautics Conference; Jun 02, 1998 - Jun 04, 1998; Toulouse; France
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 9
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    Jet Nozzle Having Centerbody for Enhanced Exit Area Mixing (1999)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: A nozzle arrangement includes a nozzle and a centerbody. The longitudinal axis of the centerbody is coaxially aligned with the nozzle. The centerbody has a free end portion shaped to create vortices in exhaust exiting the exit area. The vortices enhance mixing action in the exhaust and reduce exhaust noise while augmenting thrust.
    Keywords: Aircraft Propulsion and Power
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 10
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    Acoustic Study of B Helical Mode for Choked Axisymmetric Nozzle (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: An acoustic near-field study was performed for an axisymmetric conical convergent nozzle operating at a pressure ratio corresponding to a fully expanded Mach number of 1.3. The acoustic measurements were performed in the nozzle exit plane using multiple sensors arranged around the periphery of the nozzle. The acquired data were simultaneously digitized. The acoustic spatial characteristics, describing the large-scale structure associated with the preferred shear layer instability mode, were determined for the dominant B screech mode. The nozzle was fitted with a lip thickening device to determine the effect of this geometric variable on the spatial structure of the jet. For the thin-lipped configuration, the flapping structure of the B screech mode was found to precess in a time- dependent manner about the jet axis. Increasing of the nozzle exit lip thickness altered the spatial characteristics of this mode from a flapping to a time-dependent flapping or spinning. Using the autobicoherence spectrum, frequency dependencies were found to exist in the acoustic data of the thick-lipped configuration. These dependencies may be related to the nonlinearity of the jet and/or the time-dependent nature of the B mode spatial structure.
    Keywords: Acoustics
    Type: NASA-TM-111777 , NAS 1.15:111777 , AIAA Journal; 33; 3; 413-420
    Format: text
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    NASA TECHNICAL REPORTS
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