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  • 1
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    Blade-Mounted Flap Control for BVI Noise Reduction Proof-of-Concept Test (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: This report describes a wind tunnel test of the McDonnell Douglas Helicopter Systems (MDHS) Active Flap Model Rotor at the NASA Langley 14- by 22-Foot Subsonic Tunnel. The test demonstrated that BVI noise reductions and vibration reductions were possible with the use of an active flap. Aerodynamic results supported the acoustic data trends, showing a reduction in the strength of the tip vortex with the deflection of the flap. Acoustic results showed that the flap deployment, depending on the peak deflection angle and azimuthal shift in its deployment schedule, can produce BVI noise reductions as much as 6 dB on the advancing and retreating sides. The noise reduction was accompanied by an increase in low frequency harmonic noise and high frequency broadband noise. A brief assessment of the effect of the flap on vibration showed that significant reductions were possible. The greatest vibration reductions (as much as 76%) were found in the four per rev pitching moment at the hub. Performance improvement cam results were inconclusive, as the improvements were predicted to be smaller than the resolution of the rotor balance.
    Keywords: Acoustics
    Type: NASA-CR-195078 , NAS 1.26:195078 , L6BCK-FR-94001
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Acoustic Characteristics of a Model Isolated Tiltrotor in DNW (1999)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: An aeroacoustic wind tunnel test was conducted using a scaled isolated tiltrotor model. Acoustic data were acquired using an in-flow microphone wing traversed beneath the model to map the directivity of the near-field acoustic radiation of the rotor for a parametric variation of rotor angle-of-attack, tunnel speed, and rotor thrust. Acoustic metric data were examined to show trends of impulsive noise for the parametric variations. BVISPL maximum noise levels were found to increase with alpha for constant mu and C(sub T), although the maximum BVI levels were found at much higher a than for a typical helicopter. BVISPL levels were found to increase with mu for constant alpha and C(sub T. BVISPL was found to decrease with increasing CT for constant a and m, although BVISPL increased with thrust for a constant wake geometry. Metric data were also scaled for M(sub up) to evaluate how well simple power law scaling could be used to correct metric data for M(sub up) effects.
    Keywords: Aircraft Design, Testing and Performance
    Type: American Helicopter Society 55th Annual Forum; May 25, 1999 - May 27, 1999; Montreal; Canada
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Acoustic Characteristics of a Model Isolated Tiltrotor in DNW (1999)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: An aeroacoustic wind tunnel test was conducted using a scaled isolated tiltrotor model. Acoustic data were acquired using an in-flow microphone wing traversed beneath the model to map the directivity of the near-field acoustic radiation of the rotor for a parametric variation of rotor angle-of-attack, tunnel speed, and rotor thrust. Acoustic metric data were examined to show trends of impulsive noise for the parametric variations. BVISPL maximum noise levels were found to increase with mu for constant alpha and C(sub T), although the maximum BVI levels were found at much higher cc than for a typical helicopter. BVISPL levels were found to increase with mu for constant alpha and C(sub T). BVISPL was found to decrease with increasing C(sub T) for constant alpha and mu, although BVISPL increased with thrust for a constant wake geometry. Metric data were also scaled for M,i, to evaluate how well simple power law scaling could be used to correct metric data for M(sub tip) effects.
    Keywords: Acoustics
    Type: 55th; May 25, 1999 - May 27, 1999; Montreal, Quebec; Canada
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Prediction of blade-vortex interaction noise using airloads generated by a finite-difference technique (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The present numerical finite-difference scheme for helicopter blade-load prediction during realistic, self-generated three-dimensional blade-vortex interactions (BVI) derives the velocity field through a nonlinear superposition of the rotor flow-field yielded by the full potential rotor flow solver RFS2 for BVI, on the one hand, over the rotational vortex flow field computed with the Biot-Savart law. Despite the accurate prediction of the acoustic waveforms, peak amplitudes are found to have been persistently underpredicted. The inclusion of BVI noise source in the acoustic analysis significantly improved the perceived noise level-corrected tone prediction.
    Keywords: ACOUSTICS
    Type: AHS, Annual Forum; May 21, 1990 - May 23, 1990; Washington, DC; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 5
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    A User's Manual for ROTTILT Solver: Tiltrotor Fountain Flow Field Prediction (1999)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: A CFD solver has been developed to provide the time averaged details of the fountain flow typical for tiltrotor aircraft in hover. This Navier-Stokes solver, designated as ROTTILT, assumes the 3-D fountain flowfield to be steady and incompressible. The theoretical background is described in this manual. In order to enable the rotor trim solution in the presence of tiltrotor aircraft components such as wing, nacelle, and fuselage, the solver is coupled with a set of trim routines which are highly efficient in CPU and suitable for CFD analysis. The Cartesian grid technique utilized provides the user with a unique capability for insertion or elimination of any components of the bodies considered for a given tiltrotor aircraft configuration. The flowfield associated with either a semi or full-span configuration can be computed through user options in the ROTTILT input file. Full details associated with the numerical solution implemented in ROTTILT and assumptions are presented. A description of input surface mesh topology is provided in the appendices along with a listing of all preprocessor programs. Input variable definitions and default values are provided for the V22 aircraft. Limited predicted results using the coupled ROTTILT/WOPWOP program for the V22 in hover are made and compared with measurement. To visualize the V22 aircraft and predictions, a preprocessor graphics program GNU-PLOT3D was used. This program is described and example graphic results presented.
    Keywords: Acoustics
    Type: NASA/CR-1999-208973 , NAS 1.26:208973 , L9KVJC-FR-98001
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 6
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    Blade vortex interaction noise reduction techniques for a rotorcraft (1998)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: An active control device for reducing blade-vortex interactions (BVI) noise generated by a rotorcraft, such as a helicopter, comprises a trailing edge flap located near the tip of each of the rotorcraft's rotor blades. The flap may be actuated in any conventional way, and is scheduled to be actuated to a deflected position during rotation of the rotor blade through predetermined regions of the rotor azimuth, and is further scheduled to be actuated to a retracted position through the remaining regions of the rotor azimuth. Through the careful azimuth-dependent deployment and retraction of the flap over the rotor disk, blade tip vortices which are the primary source for BVI noise are (a) made weaker and (b) pushed farther away from the rotor disk (that is, larger blade-vortex separation distances are achieved).
    Keywords: Aircraft Design, Testing and Performance
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 7
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    Blade vortex interaction noise reduction techniques for a rotorcraft (1996)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: An active control device for reducing blade-vortex interactions (BVI) noise generated by a rotorcraft, such as a helicopter, comprises a trailing edge flap located near the tip of each of the rotorcraft's rotor blades. The flap may be actuated in any conventional way, and is scheduled to be actuated to a deflected position during rotation of the rotor blade through predetermined regions of the rotor azimuth, and is further scheduled to be actuated to a retracted position through the remaining regions of the rotor azimuth. Through the careful azimuth-dependent deployment and retraction of the flap over the rotor disk, blade tip vortices which are the primary source for BVI noise are (a) made weaker and (b) pushed farther away from the rotor disk (that is, larger blade-vortex separation distances are achieved).
    Keywords: Aircraft Design, Testing and Performance
    Format: application/pdf
    Location Call Number Expected Availability
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    NASA TECHNICAL REPORTS
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