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  • 1
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    Predictions of Low-Frequency and Impulsive Sound Radiation From Horizontal-Axis Wind Turbines (1982)
    American Society of Mechanical Engineers
    Details
    Publication Date: 1982-05-01
    Description: This paper develops theoretical models to predict the radiation of low-frequency and impulsive sound from horizontal-axis wind turbines due to three sources: (i) steady blade loads, (ii) unsteady blade loads due to operation in a ground shear, (iii) unsteady loads felt by the blades as they cross the tower wake. These models are then used to predict the acoustic output of MOD-I, the large wind turbine operated near Boone, N. C. Predicted acoustic time signals are compared to those actually measured near MOD-I; good agreement is obtained.
    Print ISSN: 0199-6231
    Electronic ISSN: 1528-8986
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Published by American Society of Mechanical Engineers
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    PAPER CURRENT
  • 2
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    A theoretical analysis of the effect of thrust-related turbulence distortion on helicopter rotor low-frequency broadband noise (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The purpose of the analysis is to determine if inflow turbulence distortion may be a cause of experimentally observed changes in sound pressure levels when the rotor mean loading is varied. The effect of helicopter rotor mean aerodynamics on inflow turbulence is studied within the framework of the turbulence rapid distortion theory developed by Pearson (1959) and Deissler (1961). The distorted inflow turbulence is related to the resultant noise by conventional broadband noise theory. A comparison of the distortion model with experimental data shows that the theoretical model is unable to totally explain observed increases in model rotor sound pressures with increased rotor mean thrust. Comparison of full scale rotor data with the theoretical model shows that a shear-type distortion may explain decreasing sound pressure levels with increasing thrust.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Prediction of low frequency and impulsive sound radiation from horizontal axis wind turbines (1981)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Theoretical models to predict the radiation of low frequency and impulsive sound from horizontal axis wind turbines due to three sources: (1) steady blade loads; (2) unsteady blade loads due to operation in a ground shear; (3) unsteady loads felt by the blades as they cross the tower wake. These models are then used to predict the acoustic output of MOD-1, the large wind turbine operated near Boone, N.C. Predicted acoustic time signals are compared to those actually measured near MOD-1 and good agreement is obtained.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA. Lewis Research Center Wind Turbine Dyn.; p 401-409
    Format: application/pdf
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  • 4
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    Numerical solutions of transonic flows by parametric differentiation and integral equation techniques (1980)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The paper discusses results of an exploratory study of the advantages obtained by combining integral equation methods with the method of parametric differentiation in the treatment of transonic flow problems. In the proposed method, the nonlinear unsteady transonic flow equation for small perturbations is transformed into a linear equation by the use of the method of parametric differentiation. The linear equation is split into a pair of weakly coupled partial differential equations by writing the transformed perturbation potential as the sum of a steady component and an unsteady component. The solution of the steady equation as an integral equation is based on Ogana's treatment (1978). As a test case, the formulation is applied to predict the steady transonic flow over a nonlifting parabolic-arc airfoil.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA Journal; 18; Dec. 198
    Format: text
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  • 5
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    Wind tunnel investigations of model rotor noise at low tip speeds (1978)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Experimental and related analytical results on model rotor rotational and broadband noise obtained in the anechoic wind tunnel and rotor facility are summarized. Factors studied include various noise sources, effects of helicopter performance parameters on noise generated by a model main rotor, appropriate scaling laws for the various types of main rotor noise, and the effects of intensity and size scales of injected turbulence on the intensity and spectra of broadband noise.
    Keywords: ACOUSTICS
    Type: NASA. Langley Res. Center Helicopter Acoustics; p 221-261
    Format: application/pdf
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  • 6
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    Application of quasi-linearization techniques to the analysis of aerodynamic-noise fields (1972)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The method of parametric differentiation was used as a means of obtaining solutions which describe aerodynamically generated sound fields, and which are valid over an increased range of a specific parameter. Details of applying the method to the problem of calculating the sound field of two rectilinear vortices rotating about an axis between them in a compressible medium are discussed. Pressure distribution in the far field are obtained. Parametric differentiation was also applied to the calculation of aerodynamic sound generated by a rotating cylinder in a viscous, compressible medium. The formulation of this problem in parametric space is given, and a procedure for obtaining a solution is outlined.
    Keywords: PHYSICS, GENERAL
    Type: NASA-CR-112084 , AEEP-4074-105-72U
    Format: application/pdf
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  • 7
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    Farfield viscous effects in nonlinear noise propagation (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Discussion of the method of parametric differentiation in application to predictions of farfield noise propagation in both lossless and dissipative media. It is shown that, in the lossless medium, the governing equation, transformed to parameter space, reduces to a wave equation in the farfield. In the dissipative medium, the system of nonlinear partial differential equations, transformed to parameter space, reduces to a linear partial differential equation of the propagating type which contains a third-order derivative as well as the wave operator.
    Keywords: AERODYNAMICS
    Format: text
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  • 8
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    Modeling of unsteady small disturbance transonic flow using parametric differentiation, pseudospectral analysis and finite-differencing (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A procedure for solving the nonlinear unsteady small disturbance transonic equation is formulated. This procedure is a synthesis of a pseudospectral method, parametric differentiation, and finite differencing. It is equally applicable to lifting and nonlifting airfoils. The procedure is particularly well suited to aeroelastic stability studies that may require a set of affine solutions.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 84-0875
    Format: text
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  • 9
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    Anechoic wind tunnel study of turbulence effects on wind turbine broadband noise (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This paper describes recent results obtained at MIT on the experimental and theoretical modelling of aerodynamic broadband noise generated by a downwind rotor horizontal axis wind turbine. The aerodynamic broadband noise generated by the wind turbine rotor is attributed to the interaction of ingested turbulence with the rotor blades. The turbulence was generated in the MIT anechoic wind tunnel facility with the aid of biplanar grids of various sizes. The spectra and the intensity of the aerodynamic broadband noise have been studied as a function of parameters which characterize the turbulence and of wind turbine performance parameters. Specifically, the longitudinal integral scale of turbulence, the size scale of turbulence, the number of turbine blades, and free stream velocity were varied. Simultaneous measurements of acoustic and turbulence signals were made. The sound pressure level was found to vary directly with the integral scale of the ingested turbulence but not with its intensity level. A theoretical model based on unsteady aerodynamics is proposed.
    Keywords: ACOUSTICS
    Type: DOE/NASA Workshop on Horizontal Axis Wind Turbine Technology; May 08, 1984 - May 10, 1984; Cleveland, OH; United States|DASCON Engineering, Collected Papers on Wind Turbine Technology; p 229-236
    Format: application/pdf
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  • 10
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    Calculation of unsteady small disturbance transonic flow at arbitrary reduced frequency using an extended integral equation method. (1983)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A novel analytical-numerical method for calculating unsteady small disturbance transonic flow over airfoils has been developed. The method uses an extended integral equation technique, based on both the velocity potential and the acceleration potential, to predict unsteady aerodynamic loading on airfoils oscillating in subcritical transonic free stream conditions. The formulation is an extension of the work of Sivaneri and Harris (1980) for steady, non-lifting flows and utilizes the linear theory of Landahl (1961) for decoupling of steady and unsteady components. The analytical-numerical procedure involves several intnegrating schemes and applies to general frequencies of oscillations. The technique is illustrated by computing the transonic flow about parabolic arc airfoils. Specific unsteady results for reduced frequencies based on semi-chord of 0.01, 0.1, 0.3, 0.4 and 0.6 are given. Comparison of results with those obtained by an ADI finite difference scheme is made.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 83-0884 , Structures, Structural Dynamics and Materials Conference; May 02, 1983 - May 04, 1983; Lake Tahoe, NV
    Format: text
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