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  • 1
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    Control of Combustion-Instabilities Through Various Passive Devices (2005)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Results of a computational study on the effectiveness of various passive devices for the control of combustion instabilities are presented. An axi-symmetric combustion chamber is considered. The passive control devices investigated are, baffles, Helmholtz resonators and quarter-waves. The results show that a Helmholtz resonator with a smooth orifice achieves the best control results, while a baffle is the least effective for the frequency tested. At high sound pressure levels, the Helmholtz resonator is less effective. It is also found that for a quarter wave, the smoothness of the orifice has the opposite effect than the Helmholtz resonator, i.e. results in less control.
    Keywords: Acoustics
    Type: 11th AIAA/CEAS Aeroacoustic Conference; May 23, 2005 - May 25, 2005; Monterey, CA; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Impact of Air Injection on Jet Noise (2007)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The objective of this viewgraph presentation is to review the program to determine impact of core fluidic chevrons on noise produced by dual stream jets (i.e., broadband shock noise - supersonic, and mixing noise - subsonic and supersonic). The presentation reviews the sources of jet noise. It shows designs of Generation II Fluidic Chevrons. The injection impacts shock structure and stream disturbances through enhanced mixing. This may impact constructive interference between acoustic sources. The high fan pressures may inhibit mixing produced by core injectors. A fan stream injection may be required for better noise reduction. In future the modification of Gen II nozzles to allow for some azimuthal control: will allow for higher mass flow rates and will allow for shallower injection angles A Flow field study is scheduled for spring, 2008 The conclusions are that injection can reduce well-defined shock noise and injection reduces mixing noise near peak jet noise angle
    Keywords: Acoustics
    Type: Fall Acoustics Technical Working Group; Dec 04, 2007 - Dec 05, 2007; Cleveland, OH; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Collaboration with Williams International to Demonstrate the Characteristics of a Foam-Metal-Liner Installed Over-the-Rotor of a Turbofan Engine (2008)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A Williams International FJ44-3A 3000-lb thrust class turbofan engine was used as a demonstrator for foam-metal liner installed in close proximity to the fan. Two foam metal liner designs were tested and compared to the hardwall. Traditional Single-Degree-of-Freedom liner designs were also evaluated to provide a comparison. Normalized information on farfield acoustics is presented in this paper. The results show that up to 5 dB PWL overall attenuation was achieved in the forward quadrant. In general, the foam-metal liners performed better when the fan tip speed was below sonic.
    Keywords: Acoustics
    Type: E-16781 , Acoustics Technical Working Group Meeting; Sep 23, 2008 - Sep 24, 2008; Williamsburg, VA; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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