Download or read book Broadband Rotor Noise Analysis written by Albert R. George and published by . This book was released on 1984 with total page 98 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Broadband Rotor Noise Analyses written by Albert R. George and published by . This book was released on 1984 with total page 104 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Broadband Rotor Noise Analyses written by Albert R. George and published by . This book was released on 1984 with total page 104 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Analyses of Broadband Noise Mechanisms of Rotors written by Albert R. George and published by . This book was released on 1983 with total page 52 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Rotor Broadband Noise Prediction with Comparison to Model Data written by Thomas F. Brooks and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book A Study of Rotor Broadband Noise Mechanisms and Helicopter Tail Rotor Noise written by and published by . This book was released on 1990 with total page 192 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Further Analysis of Broadband Noise Measurements for a Rotating Blade Operating with and Without Its Shed Wake Blown Downstream written by James Scheiman and published by . This book was released on 1974 with total page 68 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book A model for rotor broadband noise prediction written by Qidou Zhou and published by . This book was released on 2004 with total page 199 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Broadband Noise of Fans With Unsteady Coupling Theory to Account for Rotor and Stator Reflection Transmission Effects written by National Aeronautics and Space Adm Nasa and published by Independently Published. This book was released on 2018-09-23 with total page 98 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report examines the effects on broadband noise generation of unsteady coupling between a rotor and stator in the fan stage of a turbofan engine. Whereas previous acoustic analyses treated the blade rows as isolated cascades, the present work accounts for reflection and transmission effects at both blade rows by tracking the mode and frequency scattering of pressure and vortical waves. The fan stage is modeled in rectilinear geometry to take advantage of a previously existing unsteady cascade theory for 3D perturbation waves and thereby use a realistic 3D turbulence spectrum. In the analysis, it was found that the set of participating modes divides itself naturally into "independent mode subsets" that couple only among themselves and not to the other such subsets. This principle is the basis for the analysis and considerably reduces computational effort. It also provides a simple, accurate scheme for modal averaging for further efficiency. Computed results for a coupled fan stage are compared with calculations for isolated blade rows. It is found that coupling increases downstream noise by 2 to 4 dB. Upstream noise is lower for isolated cascades and is further reduced by including coupling effects. In comparison with test data, the increase in the upstream/downstream differential indicates that broadband noise from turbulent inflow at the stator dominates downstream noise but is not a significant contributor to upstream noise.Hanson, Donald B.Glenn Research CenterTURBOFAN ENGINES; ENGINE NOISE; ROTOR STATOR INTERACTIONS; NOISE MEASUREMENT; TURBULENT FLOW; SIGNAL ANALYZERS; ACOUSTIC COUPLING; SOUND TRANSMISSION; WAVE REFLECTION; BROADBAND
Download or read book Broadband Noise of Fans written by Donald B. Hanson and published by BiblioGov. This book was released on 2013-08 with total page 100 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report examines the effects on broadband noise generation of unsteady coupling between a rotor and stator in the fan stage of a turbofan engine. Whereas previous acoustic analyses treated the blade rows as isolated cascades, the present work accounts for reflection and transmission effects at both blade rows by tracking the mode and frequency scattering of pressure and vortical waves. The fan stage is modeled in rectilinear geometry to take advantage of a previously existing unsteady cascade theory for 3D perturbation waves and thereby use a realistic 3D turbulence spectrum. In the analysis, it was found that the set of participating modes divides itself naturally into "independent mode subsets" that couple only among themselves and not to the other such subsets. This principle is the basis for the analysis and considerably reduces computational effort. It also provides a simple, accurate scheme for modal averaging for further efficiency. Computed results for a coupled fan stage are compared with calculations for isolated blade rows. It is found that coupling increases downstream noise by 2 to 4 dB. Upstream noise is lower for isolated cascades and is further reduced by including coupling effects. In comparison with test data, the increase in the upstream/downstream differential indicates that broadband noise from turbulent inflow at the stator dominates downstream noise but is not a significant contributor to upstream noise.
Download or read book Evaluation of the Annoyance Due to Helicopter Rotor Noise written by Harry Sternfeld and published by . This book was released on 1978 with total page 84 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Research on Helicopter Rotor Noise written by A. R. George and published by . This book was released on 1978 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt: Research was conducted on aspect of noise generation by helicopters. A general review of helicopter noise was prepared and published as one part of the work. Methods were developed for the analysis of high frequency broadband noise from rotors. Physical and analytical approximations were devised which allow practical calculation of noise from various loading mechanisms. Atmospheric turbulence noise was investigated including some effects of inflow distribution. A method for predicting trailing edge noise for rotors was developed. The results show that trailing edge noise can be quite important at high frequencies when the small scale components of ingested turbulence are weak compared to those of the blade boundary layer turbulence. In the area of high speed noise from high Mach number advancing blades the research was primarily concentrated on the radiated sound from the Lighthill stress associated with the occurrence of unsteady shock formation and disappearance on advancing transonic rotor blades. A simplified model of an impulsively started and stopped shock was used as the known near field in order to find the far field radiation.
Download or read book NASA Reference Publication written by and published by . This book was released on 1977 with total page 800 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Predictions of Rotor Broadband Noise written by Jason D.M. Botha and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Time Varying Rotor Noise Computations and Analysis of Electric Vertical Take Off and Landing Aircraft written by Ze Feng Gan and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis makes contributions to two important aspects of computing the time-varying rotor noise of electrical vertical take-off and landing (eVTOL) aircraft for urban air mobility (UAM) applications: the time variation of rotor broadband noise, and noise due continuously-varying rotor angular speed. The noise prediction software PSU-WOPWOP was updated to compute the broadband noise spectrum as a function of observer time within a rotor period. Time-varying broadband noise spectra and directivity computations for helicopter main rotors in forward flight show significant modulation with the blade passage frequency, due to convective amplification and retarded-time effects. Qualitative agreement between noise predictions and flight test data was obtained. The noise prediction software PSU-WOPWOP was also updated to compute the discrete frequency noise of rotors with continuously-varying rotational speed, which may require accepting input kinematics and aerodynamic loading data at unevenly-spaced source time intervals. Order of magnitude analysis and numerical simulations demonstrated that thickness noise modulations caused by variable rotor speed are primarily due to the time variation of instantaneous rotor speed, rather than angular acceleration, for typical rotor speed variations expected for manned eVTOL aircraft.
Download or read book Theory for Broadband Noise of Rotor and Stator Cascades with Inhomogeneous Inflow Turbulence Including Effects of Lean and Sweep written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-06-11 with total page 86 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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
Download or read book Evaluation of the Annoyance Due to Helicopter Rotor Noise written by and published by . This book was released on 1978 with total page 84 pages. Available in PDF, EPUB and Kindle. Book excerpt:
