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.

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 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 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 Research on Helicopter Rotor Noise written by A. R. George and published by . This book was released on 1975 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt: During the period of this contract, research was carried out on three main aspects of helicopter rotor noise. These were the prediction of broadband noise due to random loadings, high speed blade noise, and noise due to the acceleration of solid bodies. The noise due to the acceleration of solid bodies was investigated experimentally and compared to calculations based on Farassat's results. The final results show excellent agreement between theory and experiment and a paper has been submitted to the Journal of Sound and Vibration reporting this work.

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 Noise Part 1 Review and theoretical study written by John W. Leverton and published by . This book was released on 1968 with total page 66 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1990 with total page 996 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Helicopter Rotor Noise Investigation During Ice Accretion written by Baofeng Cheng and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: An investigation of helicopter rotor noise during ice accretion is conducted using experimental, theoretical, and numerical methods. This research is the acoustic part of a joint helicopter rotor icing physics, modeling, and detection project at The Pennsylvania State University Vertical Lift Research Center of Excellence (VLRCOE). The current research aims to provide acoustic insight and understanding of the rotor icing physics and investigate the feasibility of detecting rotor icing through noise measurements, especially at the early stage of ice accretion. All helicopter main rotor noise source mechanisms and their change during ice accretion are discussed. Changes of the thickness noise, steady loading noise, and especially the turbulent boundary layer trailing edge (TBL-TE) noise due to ice accretion are identified and studied.The change of the discrete frequency noise (thickness noise and steady loading noise) due to ice accretion is calculated by using PSU-WOPWOP, an advanced rotorcraft acoustic prediction code. The change is noticeable, but too small to be used in icing detection. The small thickness noise change is due to the small volume of the accreted ice compared to that of the entire blade, although a large iced airfoil shape is used. For the loading noise calculation, two simplified methods are used to generate the loading on the rotor blades, which is the input for the loading noise calculation: 1) compact loading from blade element momentum theory, icing effects are considered by increasing the drag coefficient; and 2) pressure loading from the 2-D CFD simulation, icing effects are considered by using the iced airfoil shape.Comprehensive rotor broadband noise measurements are carried out on rotor blades with different roughness sizes and rotation speeds in two facilities: the Adverse Environment Rotor Test Stand (AERTS) facility at The Pennsylvania State University, and The University of Maryland Acoustic Chamber (UMAC). In both facilities the measured high-frequency broadband noise increases significantly with increasing surface roughness heights, which indicates that it is feasible to quantify helicopter rotor ice-induced surface roughness through acoustic measurements. Comprehensive broadband noise measurements based on different accreted ice roughness at AERTS are then used to form the data base from which a correlation between the ice-induced surface roughness and the broadband noise level is developed. Two parameters, the arithmetic average roughness height, R_a, and the averaged roughness height, based on the integrated ice thickness at the blade tip, are introduced to describe the ice-induced surface roughness at the early stage of the ice accretion. The ice roughness measurements are correlated to the measured broadband noise level. Strong correlations (absolute mean deviations of 9.3% and 11.2% for correlation using R_a and the averaged roughness height respectively) between the ice roughness and the broadband noise level are obtained, which can be used as a tool to determine the accreted ice roughness in the AERTS facility through acoustic measurement. It might be possible to use a similar approach to develop an early ice accretion detection tool for helicopters, as well as to quantify the ice-induced roughness at the early stage of rotor ice accretion. Rotor broadband noise source identification is conducted and the broadband noise related to ice accretion is argued to be turbulent boundary layer trailing edge (TBL-TE) noise. Theory suggests TBL-TE noise scales with Mach number to the fifth power, which is also observed in the experimental data. The trailing edge noise theories developed by Ffowcs Williams and Hall, and Howe both identify two important parameters: boundary layer thickness and turbulence intensity. Numerical studies of 2-D airfoils with different ice-induced surface roughness heights are conducted to investigate the extent that surface roughness impacts the boundary layer thickness and turbulence intensity (and ultimately the TBL-TE noise). The results show that boundary layer thickness and turbulence intensity at the trailing edge increase with the increased roughness height. Using Howes trailing edge noise model, the increased sound pressure level (SPL) of the trailing edge noise due to the increased displacement thickness and normalized integrated turbulence intensity are 6.2 dB and 1.6 dB for large and small accreted ice roughness heights, respectively. The estimated increased SPL values agree well with the experimental results, which are 5.8 dB and 2.6 dB for large and small roughness height, respectively.Finally a detailed broadband noise spectral scaling for all measured broadband noise in both AERTS and UMAC facilities is conducted. The magnitude and the frequency spectrum of the measured broadband noise are scaled on characteristic velocity and length. The peak of the laminar boundary layer vortex shedding (LBL-VS) noise coalesces well on the Strouhal scaling in those cases. For the measured broadband noise from a rotor with relatively large roughness heights, no contribution of the LBL-VS noise is observed. The velocity scaling shows that the TBL-TE noise, which is the dominant source mechanism, scales with Mach number to the fifth power based on the absolute frequency. The length scaling shows that the TBL-TE noise scales well on the absolute roughness height based on Howes TE noise theory.

Download or read book Experimental and Theoretical Analysis of Helicopter Rotor Hub Vibratory Forces written by NORMAN D. HAM and published by . This book was released on 1959 with total page 80 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Helicopter Theory written by Wayne Johnson and published by Courier Corporation. This book was released on 2012-03-07 with total page 1122 pages. Available in PDF, EPUB and Kindle. Book excerpt: Monumental engineering text covers vertical flight, forward flight, performance, mathematics of rotating systems, rotary wing dynamics and aerodynamics, aeroelasticity, stability and control, stall, noise, and more. 189 illustrations. 1980 edition.

Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 610 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 Technical Abstract Bulletin written by and published by . This book was released on with total page 1048 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Helicopter Noise Blade Slap Part 2 Experimental Results written by John W. Leverton and published by . This book was released on 1972 with total page 84 pages. Available in PDF, EPUB and Kindle. Book excerpt:

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.