Download or read book An Experimental Study of Helicopter Rotor Impulsive Noise written by William E. Bausch and published by . This book was released on 1971 with total page 244 pages. Available in PDF, EPUB and Kindle. Book excerpt: Results of a study of helicopter rotor impulsive noise (RIN) are presented. Rotor noise, together with rotor blade dynamic and pressure data, was measured during hover and cruise of a CH-53A helicopter for use in a correlation study of calculated and measured noise. In addition, the rotor rotational noise analysis described in U.S. Army Aviation Materiel Laboratories (USAAVLABS) technical Report 70-1B was modified to reduce computation time and to include blade flapping and coning motions. The inclusion of these motions, however, is shown to have little effect on the predicted noise. Correlation of calculated and measured noise harmonic amplitudes is generally within 5 dB through the third harmonic at distances less than 1000 feet in front of the helicopter. Waveform correlation of calculated and measured time histories of acoustic pressure is good. RIN is identified as being primarily a rotational noise phenomenon, ordered at the blade passage frequency and its harmonics, rather than amplitude modulated broadband noise. Hover RIN is shown to be due to vortex interference (blade/wake interaction RIN), while cruise RIN is shown to be due to the combination of acoustic effects of a high subsonic tip Mach number on wave propagation and blade drag, and is referred to as advancing blade RIN.
Download or read book Helicopter Impulsive Noise Theoretical and Experimental Status written by F. H. Schmitz and published by . This book was released on 1983 with total page 110 pages. Available in PDF, EPUB and Kindle. Book excerpt: The theoretical and experimental status of helicopter impulsive noise is reviewed. The two major source mechanisms of helicopter impulsive noise are addressed: high-speed impulsive noise and blade-vortex interaction impulsive noise. A thorough physical explanation of both generating mechanisms is presented together with model and full-scale measurements of the phenomena. Current theoretical prediction methods are compared with experimental findings of isolated rotor tests. The noise generating mechanisms of high speed impulsive noise are fairly well understood - theory and experiment compare nicely over Mach number ranges typical of today's helicopters. For the case of blade-vortex interaction noise, understanding of noise generating mechanisms and theoretical comparison with experiment are less satisfactory. Several methods for improving theory-experiment are suggested.
Download or read book Reduction of High speed Impulsive Noise by Blade Planform Modification of a Model Helicopter Rotor written by David Alan Conner and published by . This book was released on 1982 with total page 68 pages. Available in PDF, EPUB and Kindle. Book excerpt: An experiment has been performed to investigate the reduction of high-speed impulsive noise for the UH-1H helicopter by using an advanced main rotor system. The advanced rotor system had a tapered blade planform compared with the rectangular planform of the standard rotor system. Models of both the advanced main rotor system and the UH-1H standard main rotor system were tested at 1/4 scale in the Langley 4- by 7-Meter Tunnel. In-plane acoustic measurements of the high-speed impulsive noise demonstrated that the advanced rotor system on the UH-1H helicopter reduced the high-speed impulsive noise by up to 20 dB, with a reduction in overall sound pressure level of up to 6 dB. (Author).
Download or read book Investigation of Blade Impulsive Noise on a Scaled Fully Articulated Rotor System written by James Scheiman and published by . This book was released on 1977 with total page 52 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Comparison of Measured and Calculated Helicopter Rotor Impulsive Noise written by and published by . This book was released on 1978 with total page 36 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Investigation of Helicopter Rotor Blade wake Interactive Impulsive Noise written by and published by . This book was released on 1987 with total page 172 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Comparison of Measured and Calculated Helicopter Rotor Impulsive Noise wind Tunnel Test Data and Prediction Analysis Techniques written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-07-26 with total page 30 pages. Available in PDF, EPUB and Kindle. Book excerpt: The thickness noise theory is discussed. Two full-scale rotors were tested in a wind tunnel with several tips involving changes in chord, thickness, and sweep. Impulsive noise data reduction procedures used are described. The calculated and measured impulsive noise peak pressures as a function of advancing tip Mach number are compared, showing good correlation for all rotors considered. Johnson, W. and Lee, A. Ames Research Center NASA-TM-78473, A-7355 NAS2-9399; RTOP 505-10-21
Download or read book Model Helicopter Rotor High speed Impulsive Noise Measured Acoustics and Blade Pressures written by and published by . This book was released on 1983 with total page 40 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book An Experimental and Theoretical Study of Helicopter Rotor Noise written by Ying-Chieh Albert Lee and published by . This book was released on 1975 with total page 350 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Correlation of Helicopter Impulsive Noise from Blade vortex Interaction with Rotor Mean Inflow written by Andrew B. Connor and published by . This book was released on 1987 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Subjective assessment of simulated helicopter blade slap noise written by Ben William Lawton and published by . This book was released on 1976 with total page 60 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book New Computational Methods for the Prediction and Analysis of Helicopter Noise written by Roger C. Strawn and published by . This book was released on 1996 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: "This paper describes several new methods to predict and analyze rotorcraft noise. These methods are: 1) a combined computational fluid dynamics and Kirchhoff scheme for far-field noise predictions, 2) parallel computer implementation of the Kirchhoff integrations, 3) audio and visual rendering of the computed acoustic predictions over large far-field regions, and 4) acoustic tracebacks to the Kirchhoff surface to pinpoint the sources of the rotor noise. The paper describes each method and presents sample results for three test cases. The first case consists of in-plane high-speed impulsive noise and the other two cases show idealized parallel and oblique blade-vortex interactions. The computed results show good agreement with available experimental data but convey much more information about the far-field noise propagation. When taken together, these new analysis methods exploit the power of new computer technologies and offer the potential to significantly improve our prediction and understanding of rotorcraft noise."
Download or read book Preliminary Study of a Model Rotor in Descent written by and published by . This book was released on 2000 with total page 44 pages. Available in PDF, EPUB and Kindle. Book excerpt: Within a program designed to develop experimental techniques for measuring the trajectory and structure of vortices trailing from the tips of rotor blades, the present preliminary study focuses on a method for quantifying the trajectory of the trailing vortex during descent flight conditions. This study also presents rotor loads and blade surface pressures for a range of tip-path plane angles and Mach numbers. Blade pressures near the leading edge and along the outer radius are compared with data obtained on the same model rotor, but in open jet facilities. A triangulation procedure based on two directable laser-light sheets, each containing an embedded reference, proved effective in defining the spatial coordinates of the trailing vortex. When interrogating a cross section of the flow that contains several trailing vortices, the greatest clarity was found to result when the flow is uniformly seeded. Surface pressure responses during blade-vortex interactions appeared equally sensitive near the leading edge and along the outer portion of the blade, but diminished rapidly as the distance along the blade chord increased. The pressure response was virtually independent of whether the tip-path plane angle was obtained through shaft tilt or cyclic pitch. Although the shape and frequency of the pressure perturbations on the advancing blade during blade-vortex interaction are similar to those obtained in open-jet facilities, the angle of the tip-path plane may need to be lower than the range covered in this study.
Download or read book The Development of Experimental Techniques for the Study of Helicopter Rotor Noise written by and published by . This book was released on 1974 with total page 178 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Helicopter Model Rotor blade Vortex Interaction Impulsive Noise Scalability and Parametric Variations written by and published by . This book was released on 1984 with total page 36 pages. Available in PDF, EPUB and Kindle. Book excerpt: Acoustic data taken in the anechoic Deutsch-NIederlaendischer Windkanal (DNW) have documented the blade-vortex interaction (BVI) impulsive noise radiated from 1/7-scale model main rotor of the AH-1 series helicopter. Average model-scale data were compared with averaged full-scale, in-flight acoustic data under similar nondimensional test conditions. At low advance ratios (mu = 0.164-0.194), the data scale remarkably well in level and waveform shape, and also duplicate the directivity pattern of BVI impulsive noise. At moderate advance ratios (mu = 0.224-0.270), the scaling deteriorates, suggesting that the model-scale rotor is not adequately simulating the full-scale BVI noise; presently, no proved explanation of this discrepancy exists. Carefully performed parametric variations over a complete matrix of testing conditions have shown that all of the four governing nondimensional parameters -- tip Mach number at hover, advance ratio, local inflow ratio, and thrust coefficient -- are highly sensitive to BVI noise radiation. Keywords: Helicopter noise; Blade vortex interaction; Measured acoustics.
Download or read book Subjective Field Study of Response to Impulsive Helicopter Noise written by Clemans A. Powell and published by . This book was released on 1981 with total page 48 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Should Helicopter Noise be Measured Differently from Other Aircraft Noise written by John A. Molino and published by . This book was released on 1982 with total page 96 pages. Available in PDF, EPUB and Kindle. Book excerpt:
