Download or read book Noise of a Model Helicopter Rotor Due to Ingestion of Turbulence written by Robert W. Paterson and published by . This book was released on 1979 with total page 136 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Noise of a Model Helicopter Rotor Due to Ingestion of Turbulence written by Robert William Paterson and published by . This book was released on 1979 with total page 162 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Helicopter Rotor Noise Due to Ingestion of Atmospheric Turbulence written by John C. Simonich and published by . This book was released on 1986 with total page 156 pages. Available in PDF, EPUB and Kindle. Book excerpt: A theoretical study was conducted to develop an analytical prediction method for helicopter main rotor noise due to the ingestion of atmospheric turbulence. This study incorporates an atmospheric turbulence model, a rotor mean flow contraction model and a rapid distortion turbulence model which together determine the statistics of the non-isotropic turbulence at the rotor plane. Inputs to the combined mean inflow and turbulence models are controlled by atmospheric wind characteristics and helicopter operating conditions. A generalized acoustic source model was used to predict the far field noise generated by the non-isotropic flow incident on the rotor. Absolute levels for acoustic spectra and directivity patterns were calculated for full scale helicopters, without the use of empirical or adjustable constants. Comparisons between isotropic and non-isotropic turbulence at the rotor face demonstrated pronounced differences in acoustic spectra. Turning and contraction of the flow for hover and low speed vertical ascent cases result in a 3 dB increase in the acoustic spectrum energy and a 10 dB increase in tone levels. Compared to trailing edge noise, turbulence ingestion noise is the dominant noise mechanism below approximately 30 rotor harmonics, while above 100 harmonics, trailing edge noise levels exceed turbulence ingestion noise by 25 dB.
Download or read book Helicopter Rotor Noise Due to Ingestion of Atmospheric Turbulence written by and published by . This book was released on 1986 with total page 190 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Experimental Assessment of Helicopter Rotor Turbulence Ingestion Noise in Hover written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-07-06 with total page 68 pages. Available in PDF, EPUB and Kindle. Book excerpt: An experiment was conducted to assess the accuracy of a theory for non-isotropic turbulence ingestion. In order to generate non-isotropic turbulence in a controlled environment, a scale model rotor in a closed chamber was used so that the turbulence generated by the rotor was reingested by the recirculating flow. Simultaneous measurements of turbulence inflow properties and far field acoustics were acquired. Measurements confirmed that the inflow turbulence was highly non-isotropic. The measured aerodynamic properties were used as inputs for the noise prediction procedure. The general agreement between the non-isotropic noise prediction procedure and the experiment was good, although the procedure generally overpredicts the quasi-tonal low to mid range frequencies and underpredicts the higher broadband signals. The predicted sound power level as a function of polar angle was in close agreement with measurements, except near the rotor plane, which is not modeled by the present analysis. It is determined that the most sensitive parameter influencing the predicted noise was the turbulence intensity. Simonich, J. C. and Schlinker, R. H. and Amiet, R. K. Unspecified Center...
Download or read book Noise of a Model Helicopter Rotor Due to Ingestion of Turbulence written by Robert William Paterson and published by . This book was released on 1979 with total page 136 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Experimental Assessment of Helicopter Rotor Turbulence Ingestion Noise in Hover written by John Charles Simonich and published by . This book was released on 1989 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Experimental Assessment of Helicopter Rotor Turbulence Ingestion Noise in Hover written by and published by . This book was released on 1989 with total page 72 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 A Study of Rotor Broadband Noise Mechanisms and Helicopter Tail Rotor Noise written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-07-17 with total page 192 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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...
Download or read book Proposed Investigation of the Effects of Tip Vortex Interaction and Turbulence Ingestion on Helicopter Rotor Noise written by United Aircraft Corporation. Research Laboratories and published by . This book was released on 1974 with total page 52 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Measurements of Atmospheric Turbulence Effects on Tail Rotor Acoustics written by National Aeronautics and Space Adm Nasa and published by . This book was released on 2018-11-09 with total page 84 pages. Available in PDF, EPUB and Kindle. Book excerpt: Results from an outdoor hover test of a full-scale Lynx tail rotor are presented. The investigation was designed to further the understanding of the acoustics of an isolated tail rotor hovering out-of-ground effect in atmospheric turbulence, without the effects of the main rotor wake or other helicopter components. Measurements include simultaneous rotor performance, noise, inflow, and far-field atmospheric turbulence. Results with grid-generated inflow turbulence are also presented. The effects of atmospheric turbulence ingestion on rotor noise are quantified. In contradiction to current theories, increasing rotor inflow and rotor thrust were found to increase turbulence ingestion noise. This is the final report of Task 13A--Helicopter Tail Rotor Noise, of the NASA/United Kingdom Defense Research Agency cooperative Aeronautics Research Program. Hagen, Martin J. and Yamauchi, Gloria K. and Signor, David B. and Mosher, Marianne Ames Research Center...
Download or read book Noise Produced by Turbulent Flow Into a Rotor written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-07-09 with total page 38 pages. Available in PDF, EPUB and Kindle. Book excerpt: A users manual for a computer program for the calculation of noise produced by turbulent flow into a helicopter rotor is presented. These inputs to the program are obtained from the atmospheric turbulence model and mean flow distortion calculation, described in another volume of this set of reports. Descriptions of the various program modules and subroutines, their function, programming structure, and the required input and output variables are included. This routine is incorporated as one module of NASA's ROTONET helicopter noise prediction program. Amiet, R. K. and Egolf, C. G. and Simonich, J. C. Unspecified Center NAS1-17763; RTOP 505-63-51...
Download or read book Measurements of Atmospheric Turbulence Effects on Tail Rotor Acoustics written by and published by . This book was released on 1994 with total page 86 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Effects of Free Stream Turbulence on Model Helicopter Rotor Noise written by Krishnaswamy Sundararajan Aravamudan and published by . This book was released on 1977 with total page 228 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Helicopter Rotor Broadband Noise Due to Rotor turbulence Interaction and a Nonlinear Turbulence Distortion Theory written by Morgan Williams and published by . This book was released on 1984 with total page 244 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Experimental and Theoretical Studies on Model Helicopter Rotor Noise written by Krishnaswamy Sundararajan Aravamudan and published by . This book was released on 1978 with total page 158 pages. Available in PDF, EPUB and Kindle. Book excerpt: A simplified Mach number scaling law is obtained for rotational and broadband noise components of a model helicopter rotor. The broadband noise sources are further classified into low frequency and high frequency components. The scaling laws are based on the geometric and performance parameters of the rotor and characteristics of the flow field. The existing theory of Lowson and Ollerhead is used deriving the conventional sixth power law for the rotational noise of geometrically similar blades operating in similar flow environ. The knowledge of unsteady aerodynamics was exploited to yield analytical formulation for the low frequency broadband radiation. The ambiguous state of the art regarding the origin and nature of high frequency broadband noise does not permit such a straightforward scaling law for this frequency regime. Vortices are assumed to be shed at unknown Strouhal frequency and the scaling law is derived by simply integrating the blade sectional velocity over the span. The MIT 5 x 7-1/2 foot anechoic wind tunnel was used to perform experiments at controlled flow environ. Turbulence was generated at the inlet of the tunnel and simultaneous measurements of acoustic and turbulence signals were made. The experimentally obtained results are compared with the computed intensities and spectra of rotational noise, low frequency broadband noise and high frequency broadband noise from model rotors.
