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  • 1
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    The HART II test – measurement of helicopter rotor wakes (2004)
    Elsevier
    Details
    Publication Date: 2004-06-01
    Print ISSN: 1270-9638
    Electronic ISSN: 1626-3219
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Elsevier
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    PAPER CURRENT
  • 2
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    Sensitivity of acoustic predictions to variation of input parameters (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Rotor noise prediction codes predict the thickness and loading noise produced by a helicopter rotor, given the blade motion, rotor operating conditions, and fluctuating force distribution over the blade surface. However, the criticality of these various inputs, and their respective effects on the predicted acoustic field, have never been fully addressed. This paper examines the importance of these inputs, and the sensitivity of the acoustic predicitions to a variation of each parameter. The effects of collective and cyclic pitch, as well as coning and cyclic flapping, are presented. Blade loading inputs are examined to determine the necessary spatial and temporal resolution, as well as the importance of the chordwise distribution. The acoustic predictions show regions in the acoustic field where significant errors occur when simplified blade motions or blade loadings are used. An assessment of the variation in the predicted acoustic field is balanced by a consideration of Central Processing Unit (CPU) time necessary for the various approximations.
    Keywords: AERODYNAMICS
    Type: American Helicopter Society, Journal (ISSN 0002-8711); 39; 3; p. 43-52
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Sensitivity of acoustic predictions to variation of input parameters (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The noise prediction code WOPWOP predicts the thickness and loading noise produced by a helicopter rotor, given the blade motion, rotor operating conditions, and fluctuating force distribution over the blade surface. However, the criticality of these various inputs, and their respective effects on the predicted acoustic field, have never been fully addressed. This paper examines the importance of these inputs, and the sensitivity of the acoustic predictions to a variation of each parameter. The effects of collective and cyclic pitch, as well as coning and flapping, are presented. Blade loading inputs are examined to determine the necessary spatial and temporal resolution, as well as the importance of the cordwise distribution. The acoustic predictions show regions in the acoustic field where significant errors occur when simplified blade motions or blade loadings are used. An assessment of the variation in the predicted acoustic field is balanced by a consideration of CPU time necessary for the various approximations.
    Keywords: ACOUSTICS
    Type: In: AHS and Royal Aeronautical Society, Technical Specialists' Meeting on Rotorcraft Acoustics(Fluid Dynamics, Philadelphia, PA, Oct. 15-17, 1991, Proceedings (A93-29401 10-71); 11 p.
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Preliminary Work for Modeling the Propellers of an Aircraft as a Noise Source in an Acoustic Boundary Element Analysis (1998)
    In:  Other Sources
    Details
    Publication Date: 2011-08-23
    Description: An algorithm for generating appropriate velocity boundary conditions for an acoustic boundary element analysis from the kinematics of an operating propeller is presented. It constitutes the initial phase of Integrating sophisticated rotorcraft models into a conventional boundary element analysis. Currently, the pressure field is computed by a linear approximation. An initial validation of the developed process was performed by comparing numerical results to test data for the external acoustic pressure on the surface of a tilt-rotor aircraft for one flight condition.
    Keywords: Acoustics
    Type: Noise Control Engineering; Volume 46; No. 3; 132-136
    Format: text
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    NASA TECHNICAL REPORTS
  • 5
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    Synergistic Airframe-Propulsion Interactions and Integrations: A White Paper Prepared by the 1996-1997 Langley Aeronautics Technical Committee (1998)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: This white paper addresses the subject of Synergistic Airframe-Propulsion interactions and integrations (SnAPII). The benefits of SnAPII have not been as extensively explored. This is due primarily to the separateness of design process for airframes and propulsion systems, with only unfavorable interactions addressed. The question 'How to design these two systems in such a way that the airframe needs the propulsion and the propulsion needs the airframe?' is the fundamental issue addressed in this paper. Successful solutions to this issue depend on appropriate technology ideas. This paper first details some ten technologies that have yet to make it to commercial products (with limited exceptions) and that could be utilized in a synergistic manner. Then these technologies, either alone or in combination, are applied to both a conventional twin-engine transonic transport and to an unconventional transport, the Blended Wing Body. Lastly, combinations of these technologies are applied to configuration concepts to assess the possibilities of success relative to five of the ten NASA aeronautics goals. These assessments are subjective, but they point the way in which the applied technologies could work together for some break-through benefits.
    Keywords: Aeronautics (General)
    Type: NASA/TM-1998-207644 , NAS 1.15:207644 , L-17723
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 6
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    Aircraft noise prediction program theoretical manual: Rotorcraft System Noise Prediction System (ROTONET), part 4 (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: This document describes the theoretical methods used in the rotorcraft noise prediction system (ROTONET), which is a part of the NASA Aircraft Noise Prediction Program (ANOPP). The ANOPP code consists of an executive, database manager, and prediction modules for jet engine, propeller, and rotor noise. The ROTONET subsystem contains modules for the prediction of rotor airloads and performance with momentum theory and prescribed wake aerodynamics, rotor tone noise with compact chordwise and full-surface solutions to the Ffowcs-Williams-Hawkings equations, semiempirical airfoil broadband noise, and turbulence ingestion broadband noise. Flight dynamics, atmosphere propagation, and noise metric calculations are covered in NASA TM-83199, Parts 1, 2, and 3.
    Keywords: ACOUSTICS
    Type: NASA-TM-83199-PT-4 , L-16700-PT-4 , NAS 1.15:83199-PT-4
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 7
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    A Comparison of Measured and Predicted XV-15 Tiltrotor Surface Acoustic Pressures (1997)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Predicted XV-15 exterior surface acoustic pressures are compared with previously published experimental data. Surface acoustic pressure transducers were concentrated near the tip-path-plane of the rotor in airplane mode. The comparison emphasized cruise conditions which are of interest for tiltrotor interior noise - level flight for speeds ranging from 72 m/s to 113 m/s. The predictions were produced by components of the NASA Langley Tiltrotor Aeroacoustic Code (TRAC) system of computer codes. Comparisons between measurements and predictions were made in both the time and frequency domains, as well as overall sound pressure levels. In general, the predictions replicated the measured data well. Discrepancies between measurements and predictions were noted. Some of the discrepancies were due to poor correlation of the measured data with the rotor tach signal. In other cases limitations of the predictive methodology have been indicated.
    Keywords: Acoustics
    Type: AHS Technical Specialists'' Meeting for Rotorcraft Acoustics and Aerodynamics; Oct 28, 1997 - Oct 30, 1997; Williamsburg, VA; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 8
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    A Study of the Effects of Blade Shape on Rotor Noise (1997)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A new rotor noise prediction system called the Tiltrotor Aeroacoustic Code (TRAC) has been developed under the Short Haul (Civil Tiltrotor) program between NASA, the Army, and the U.S. helicopter industry. This system couples the comprehensive rotorcraft code CAMRAD.Mod1 with either the high resolution sectional loads code HIRES or the full potential CFD code FPRBVI to predict unsteady blade loads, which are then input to the noise prediction program WOPWOP. In this paper, HIRES will be used to predict the blade-vortex interaction (BVI) noise trends associated with blade shape. The baseline shape selected was a 17% scale model of a contemporary design 4 bladed rotor. Measurements for this rotor were acquired in the Duits-Nederslandse Windtunnel (DNW). The code is used to predict noise for the base configuration and the results are compared to the measured data. This provides a firm foundation for investigating the BVI noise trends associated with blade shape. The shapes selected for study are based on variation of sweep and taper which reflect plausible "passive" design concepts. Comparisons of power required, integrated noise, and aerodynamics are made and important trends are noted.
    Keywords: Acoustics
    Type: AHS Technical Specialists'' Meeting for Rotorcraft Acoustics and Aerodynamics; Oct 28, 1997 - Oct 30, 1997; Williamsburg, VA; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 9
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    Tiltrotor Aeroacoustic Code (TRAC) Prediction Assessment and Initial Comparisons with Tram Test Data (1999)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A prediction sensitivity assessment to inputs and blade modeling is presented for the TiltRotor Aeroacoustic Code (TRAC). For this study, the non-CFD prediction system option in TRAC is used. Here, the comprehensive rotorcraft code, CAMRAD.Mod1, coupled with the high-resolution sectional loads code HIRES, predicts unsteady blade loads to be used in the noise prediction code WOPWOP. The sensitivity of the predicted blade motions, blade airloads, wake geometry, and acoustics is examined with respect to rotor rpm, blade twist and chord, and to blade dynamic modeling. To accomplish this assessment, an interim input-deck for the TRAM test model and an input-deck for a reference test model are utilized in both rigid and elastic modes. Both of these test models are regarded as near scale models of the V-22 proprotor (tiltrotor). With basic TRAC sensitivities established, initial TRAC predictions are compared to results of an extensive test of an isolated model proprotor. The test was that of the TiltRotor Aeroacoustic Model (TRAM) conducted in the Duits-Nederlandse Windtunnel (DNW). Predictions are compared to measured noise for the proprotor operating over an extensive range of conditions. The variation of predictions demonstrates the great care that must be taken in defining the blade motion. However, even with this variability, the predictions using the different blade modeling successfully capture (bracket) the levels and trends of the noise for conditions ranging from descent to ascent.
    Keywords: Aircraft Propulsion and Power
    Type: 25th European Rotorcraft Forum; Sep 14, 1999 - Sep 16, 1999; Rome; Italy
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 10
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    HART-II: Prediction of Blade-Vortex Interaction Loading (2003)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: During the HART-I data analysis, the need for comprehensive wake data was found including vortex creation and aging, and its re-development after blade-vortex interaction. In October 2001, US Army AFDD, NASA Langley, German DLR, French ONERA and Dutch DNW performed the HART-II test as an international joint effort. The main objective was to focus on rotor wake measurement using a PIV technique along with the comprehensive data of blade deflections, airloads, and acoustics. Three prediction teams made preliminary correlation efforts with HART-II data: a joint US team of US Army AFDD and NASA Langley, German DLR, and French ONERA. The predicted results showed significant improvements over the HART-I predicted results, computed about several years ago, which indicated that there has been better understanding of complicated wake modeling in the comprehensive rotorcraft analysis. All three teams demonstrated satisfactory prediction capabilities, in general, though there were slight deviations of prediction accuracies for various disciplines.
    Keywords: Aircraft Design, Testing and Performance
    Type: 29th European Rotorcraft Forum; Sep 16, 2003 - Sep 18, 2003; Friedrichshafen; Germany
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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