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  • 1
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    On the use of a Prandtl-Glauert-Lorentz transformation for acoustic scattering by rigid bodies with a uniform flow (2019)
    Elsevier
    Details
    Publication Date: 2019-03-01
    Print ISSN: 0022-460X
    Electronic ISSN: 1095-8568
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Elsevier
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    PAPER CURRENT
  • 2
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    The use of staggered scheme and an absorbing buffer zone for computational aeroacoustics (1995)
    In:  Other Sources
    Details
    Publication Date: 2013-08-29
    Description: Various problems from those proposed for the Computational Aeroacoustics (CAA) workshop were studied using second and fourth order staggered spatial discretizations in conjunction with fourth order Runge-Kutta time integration. In addition, an absorbing buffer zone was used at the outflow boundaries. Promising results were obtained and provide a basis for application of these techniques to a wider variety of problems.
    Keywords: ACOUSTICS
    Type: NASA. Langley Research Center, ICASE(LaRC Workshop on Benchmark Problems in Computational Aeroacoustics (CAA) p 233-244 (SEE N95-30133 10-71); NASA. Langley Resear
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    In-Duct and Far-Field Experimental Measrements from the ANCF for the Purpose of Improved Broadband Liner Optimization (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A process for the design and evaluation of novel broadband acoustic liner concepts with limited fan source information is being evaluated. A pair of advanced broad-bandwidth liners were designed and manufactured for the NASA Glenn Research Center's Advanced Noise Control Fan (ANCF): (i) a constant impedance liner and (ii) a variable impedance liner. The insertion loss of both liners was measured in-duct utilizing the ANCF's Configurable Fan Artificial Noise System in a clean configuration with no-flow. Additionally, the acoustic characteristics of the Variable Impedance Liner were measured in the standard ANCF configuration with and without flow. The experimental setup, in-duct mode power levels, and far-field directivity are presented herein.
    Keywords: Aircraft Propulsion and Power; Acoustics
    Type: GRC-E-DAA-TN15030 , AIAA/CEAS Aeroacoustics Conference; Jun 16, 2014 - Jun 20, 2014; Atlanta, GA; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Improved Broadband Liner Optimization Applied to the Advanced Noise Control Fan (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The broadband component of fan noise has grown in relevance with the utilization of increased bypass ratio and advanced fan designs. Thus, while the attenuation of fan tones remains paramount, the ability to simultaneously reduce broadband fan noise levels has become more desirable. This paper describes improvements to a previously established broadband acoustic liner optimization process using the Advanced Noise Control Fan rig as a demonstrator. Specifically, in-duct attenuation predictions with a statistical source model are used to obtain optimum impedance spectra over the conditions of interest. The predicted optimum impedance information is then used with acoustic liner modeling tools to design liners aimed at producing impedance spectra that most closely match the predicted optimum values. Design selection is based on an acceptance criterion that provides the ability to apply increased weighting to specific frequencies and/or operating conditions. Constant-depth, double-degree of freedom and variable-depth, multi-degree of freedom designs are carried through design, fabrication, and testing to validate the efficacy of the design process. Results illustrate the value of the design process in concurrently evaluating the relative costs/benefits of these liner designs. This study also provides an application for demonstrating the integrated use of duct acoustic propagation/radiation and liner modeling tools in the design and evaluation of novel broadband liner concepts for complex engine configurations.
    Keywords: Acoustics
    Type: NF1676L-17755 , AIAA/CEAS Aeroacoustics Conference; Jun 16, 2014 - Jun 20, 2014; Atlanta, GA; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    Acoustic Scattering Predictions for Complex Sources and Aircraft Configurations (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: No abstract available
    Keywords: Acoustics
    Type: NF1676L-21341 , 2015 Spring Acoustics Technical Working Group Meeting; Apr 21, 2015 - Apr 22, 2015; Hampton, VA; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 6
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    Modeling of Broadband Liners Applied to the Advanced Noise Control Fan (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The broadband component of fan noise has grown in relevance with an increase in bypass ratio and incorporation of advanced fan designs. Therefore, while the attenuation of fan tones remains a major factor in engine nacelle acoustic liner design, the simultaneous reduction of broadband fan noise levels has received increased interest. As such, a previous investigation focused on improvements to an established broadband acoustic liner optimization process using the Advanced Noise Control Fan (ANCF) rig as a demonstrator. Constant-depth, double-degree of freedom and variable-depth, multi-degree of freedom liner designs were carried through design, fabrication, and testing. This paper addresses a number of areas for further research identified in the initial assessment of the ANCF study. Specifically, incident source specification and uncertainty in some aspects of the predicted liner impedances are addressed. This information is incorporated in updated predictions of the liner performance and comparisons with measurement are greatly improved. Results illustrate the value of the design process in concurrently evaluating the relative costs/benefits of various liner designs. This study also provides further confidence in the integrated use of duct acoustic propagation/radiation and liner modeling tools in the design and evaluation of novel broadband liner concepts for complex engine configurations.
    Keywords: Acoustics; Aircraft Propulsion and Power
    Type: NF1676L-20210 , AIAA/CEAS Aeroacoustics Conference; Jun 22, 2015 - Jun 26, 2015; Dallas, TX; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 7
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    Communal Sensor Network for Adaptive Noise Reduction in Aircraft Engine Nacelles (2011)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Emergent behavior, a subject of much research in biology, sociology, and economics, is a foundational element of Complex Systems Science and is apropos in the design of sensor network systems. To demonstrate engineering for emergent behavior, a novel approach in the design of a sensor/actuator network is presented maintaining optimal noise attenuation as an adaptation to changing acoustic conditions. Rather than use the conventional approach where sensors are managed by a central controller, this new paradigm uses a biomimetic model where sensor/actuators cooperate as a community of autonomous organisms, sharing with neighbors to control impedance based on local information. From the combination of all individual actions, an optimal attenuation emerges for the global system.
    Keywords: Acoustics
    Type: NF1676L-12746 , IEEE Sensors 2011 Conference; Oct 28, 2011 - Oct 31, 2011; Limerick; Ireland
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 8
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    Broadband Liner Optimization for the Source Diagnostic Test Fan (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The broadband component of fan noise has grown in relevance with the utilization of increased bypass ratio and advanced fan designs. Thus, while the attenuation of fan tones remains paramount, the ability to simultaneously reduce broadband fan noise levels has become more appealing. This paper describes a broadband acoustic liner optimization study for the scale model Source Diagnostic Test fan. Specifically, in-duct attenuation predictions with a statistical fan source model are used to obtain optimum impedance spectra over a number of flow conditions for three liner locations in the bypass duct. The predicted optimum impedance information is then used with acoustic liner modeling tools to design liners aimed at producing impedance spectra that most closely match the predicted optimum values. Design selection is based on an acceptance criterion that provides the ability to apply increased weighting to specific frequencies and/or operating conditions. Typical tonal liner designs targeting single frequencies at one operating condition are first produced to provide baseline performance information. These are followed by multiple broadband design approaches culminating in a broadband liner targeting the full range of frequencies and operating conditions. The broadband liner is found to satisfy the optimum impedance objectives much better than the tonal liner designs. In addition, the broadband liner is found to provide better attenuation than the tonal designs over the full range of frequencies and operating conditions considered. Thus, the current study successfully establishes a process for the initial design and evaluation of novel broadband liner concepts for complex engine configurations.
    Keywords: Acoustics
    Type: NF1676L-13790 , 18th AIAA/CEAS Aeroacoustics Conference; Jun 04, 2012 - Jun 06, 2012; Colorado Springs, CO; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 9
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    Assessment of Radiated Fan Noise Prediction Capabilities Using Static Engine Test Data (2011)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This paper describes further assessment of the CDUCT-LaRC code via comparison with static engine test data. In an effort to improve confidence in the use of CDUCT-LaRC for liner optimization studies addressing realistic three-dimensional geometries, inlet radiated fan noise predictions were performed at 54% and 87% engine speed settings. Predictions were then compared with far-field measurements to assess the approach and implementation. The particular configurations were chosen to exercise the three-dimensional capability of CDUCT-LaRC and it s applicability to realistic configurations and conditions. At the 54% engine speed setting, the predictions capture the general directivity and acoustic treatment effects quite well. Comparisons of the predicted and measured directivity at the 87% power setting were more problematic. This was likely due in part to the difficulties in source specification and possibly the nonlinear nature of buzz-saw tones at this engine operating condition. Overall, the approach captured the basic trends and provided a conservative estimate of liner effects from which relative performance metrics could be inferred.
    Keywords: Acoustics
    Type: NF1676L-11679 , 17th AIAA/CEAS Aeroacoustics Conference; Jun 06, 2011 - Jun 08, 2011; Portland, OR; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 10
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    Acoustic Directivity and Insertion Loss Measurements of Advanced Liners Installed the Inlet of the DGEN Aeropropulsion Research Turbofan (2019)
    In:  CASI
    Details
    Publication Date: 2019-07-20
    Description: The NASA Glenn Research Centers DGEN Aeropropulsion Research Turbofan (DART) is based on the Price Induction DGEN380a small, ~500-lbf thrust class, high-bypass, geared-turbofan engine with a separate flow nozzle. The general characteristics of the DART make it an ideal candidate for utilization as a test bed for engine aeroacoustic research in a relevant performance environment. The DART was used to document the efficacy of acoustic liners installed in the inlet of the DGEN380. An advanced multi-degree-of-freedom liner (MDOF) was designed and tested, along with a traditional single-degree-of- freedom liner (SDOF), and those results compared to a hard-wall baseline inlet. Farfield acoustic data were acquired from an external array, evaluated, and reported here-in terms of overall, broadband, and tonal components of the insertion loss.
    Keywords: Acoustics
    Type: NASA/TM-2019-220161 , E-19677
    Format: application/pdf
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