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Author: Qidou Zhou
Publisher:
ISBN:
Category :
Languages : en
Pages : 199
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Author: Qidou Zhou
Publisher:
ISBN:
Category :
Languages : en
Pages : 199
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Author: Thomas F. Brooks
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
ISBN: 9781722910808
Category :
Languages : en
Pages : 192
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The rotor broadband noise mechanisms considered are the following: (1) lift fluctuation due to turbulence ingestion; (2) boundary layer/trailing edge interaction; (3) tip vortex formation; and (4) turbulent vortex shedding from blunt trailing edge. Predictions show good agreement with available experimental data. The study shows that inflow turbulence is the most important broadband noise source for typical helicopters' main rotors at low- and mid-frequencies. Due to the size difference, isolated helicopter tail rotor broadband noise is not important compared to the much louder main rotor broadband noise. However, the inflow turbulence noise from a tail rotor can be very significant because it is operating in a highly turbulent environment, ingesting wakes from upstream components of the helicopter. The study indicates that the main rotor turbulent wake is the most important source of tail rotor broadband noise. The harmonic noise due to ingestion of main rotor tip vortices is studied. Chou, Shau-Tak Rudy Unspecified Center AERODYNAMIC NOISE; AIRCRAFT NOISE; BROADBAND; HELICOPTER TAIL ROTORS; HELICOPTERS; NOISE GENERATORS; ROTARY WINGS; ROTOR AERODYNAMICS; BLUNT TRAILING EDGES; HARMONIC OSCILLATION; NOISE PREDICTION (AIRCRAFT); TURBULENT WAKES; VORTEX SHEDDING; VORTICES...
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 282
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Author: Albert R. George
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ISBN:
Category : Rotors
Languages : en
Pages : 104
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Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
ISBN: 9781723511417
Category :
Languages : en
Pages : 276
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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. Weir, Donald S. and Jumper, Stephen J. and Burley, Casey L. and Golub, Robert A. Langley Research Center NASA-TM-83199-PT-4, L-16700-PT-4, NAS 1.15:83199-PT-4 RTOP 532-06-37-01...
Author: Damaris Zachos
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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The capability to predict aircraft noise is important in the development of acoustically aware aircraft. The first principles noise prediction model developed in this work evaluates medium weight-class aircraft models and a conceptual electric vertical takeoff and landing (eVTOL) design. This work contains four significant system improvements over the previous version of the noise prediction system: the incorporation of a dual compact thickness noise model, a standardized command file generation system for PSUHeloSim, an improved trim matrix solution for the HeloSim model, and the capability to "calibrate" broadband noise predictions. These enhancements, along with the definition of new helicopter models developed in this work will be described. Multiple helicopters were used to validate the noise prediction system. The Sikorsky S-76D and Bell 205 from Phase III of a joint NASA/FAA/ARMY flight test were simulated together with the Bell 407 and Bell 206 models from Phase II test by the same participants. The simulated noise from medium-weight class aircraft, such as the S-76D and Bell 205 was compared with the noise predictions for the lighter weight class aircraft, i.e., the Bell 407 and Bell 206. In particular, the S-76D was compared against the Bell 407 because both aircraft have four-bladed main rotors. The Bell 205 was compared with the Bell 206 because both aircraft have two-bladed main rotors. It was determined that the directionality of the thickness and broadband noise was similar between aircraft of different weight-classes. Loading noise magnitude and directivity changed between light and medium weight-class aircraft. A novel eVTOL concept based on the proposed Jaunt Journey aircraft was modeled in the noise prediction system for multiple steady-flight conditions. Comparisons were made with a baseline propeller to evaluate the effectiveness of a low-noise electric propeller design. The novel eVTOL rotor indicated low thickness and loading noise and significant reduction in broadband noise. A full model of the eVTOL aircraft was used to determine the noise of each of the propellers, main rotor, and full aircraft. The predicted noise of the novel eVTOL indicated lower total noise than a comparable conventional aircraft design.
Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
ISBN: 9781721026104
Category :
Languages : en
Pages : 86
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The problem of broadband noise generated by turbulence impinging on a downstream blade row is examined from a theoretical viewpoint. Equations are derived for sound power spectra in terms of 3 dimensional wavenumber spectra of the turbulence. Particular attention is given to issues of turbulence inhomogeneity associated with the near field of the rotor and variations through boundary layers. Lean and sweep of the rotor or stator cascade are also handled rigorously with a full derivation of the relevant geometry and definitions of lean and sweep angles. Use of the general theory is illustrated by 2 simple theoretical spectra for homogeneous turbulence. Limited comparisons are made with data from model fans designed by Pratt & Whitney, Allison, and Boeing. Parametric studies for stator noise are presented showing trends with Mach number, vane count, turbulence scale and intensity, lean, and sweep. Two conventions are presented to define lean and sweep. In the "cascade system" lean is a rotation out of its plane and sweep is a rotation of the airfoil in its plane. In the "duct system" lean is the leading edge angle viewing the fan from the front (along the fan axis) and sweep is the angle viewing the fan from the side (, perpendicular to the axis). It is shown that the governing parameter is sweep in the plane of the airfoil (which reduces the chordwise component of Mach number). Lean (out of the plane of the airfoil) has little effect. Rotor noise predictions are compared with duct turbulence/rotor interaction noise data from Boeing and variations, including blade tip sweep and turbulence axial and transverse scales are explored.Hanson, Donald B.Glenn Research CenterINTERACTIONAL AERODYNAMICS; ROTORS; STATORS; CASCADE FLOW; TURBOFAN ENGINES; HOMOGENEOUS TURBULENCE; NOISE PREDICTION; ENGINE NOISE; POWER SPECTRA; LEADING EDGES; DUCTS; BROADBAND; BLADE TIPS; AIRFOILS; BOUNDARY LAYERS; MACH NUMBER; SWEEP ANGLE
Author: Jason D.M. Botha
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Robert W. Paterson
Publisher:
ISBN:
Category : Rotors (Helicopters)
Languages : en
Pages : 136
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