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  • 1
    Electronic Resource
    Electronic Resource
    Stability of high-speed compressible rotating Couette flow (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 393-404 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this study, the linear stability of high-speed, rotating Couette flow to two- and three-dimensional disturbances in finite-gap spacings, including the full effects of compressibility and viscosity, is considered. Particularly, the combined effects of Mach number, Reynolds number, radial heating, and gap spacing are investigated. For a stationary outer cylinder, the primary instability is an axisymmetric mode independent of the Mach number. Increasing Mach numbers have a destabilizing effect for wide gaps, and a stabilizing effect for narrow gaps. For a sufficiently fast, counter-rotating outer cylinder, the primary instability becomes a three-dimensional traveling wave. Compressibility has a stabilizing effect on these modes regardless of the gap width; also, heating at the outer cylinder stabilizes the flow. Bicritical points for the primary instability corresponding to the crossover of the azimuthal wave numbers are determined for cylinders counter-rotating with equal angular speed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858887
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    Paper (German National Licenses)
    Fulltext
  • 2
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    Stability of high‐speed compressible rotating Couette flow (1993)
    American Institute of Physics
    Details
    Publication Date: 1993-02-01
    Print ISSN: 0899-8213
    Topics: Physics
    Published by American Institute of Physics
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    PAPER CURRENT
  • 3
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    Rotorcraft noise prediction (1982)
    In:  CASI
    Details
    Publication Date: 2006-04-17
    Description: The purpose of this presentation is to give a general strategy for rotorcraft noise prediction. This strategy is expressed through a modular software system design rather than theoretical analysis of the aerocoustic phenomena. The crucial design choices in a software system design are the module interface definitions. An interface is the data that are passed from one module to another. A module takes data from one (input) interface and transforms it, through a prediction method, to another (output) interface. In system design, the method is less important than the interface. The two types of methods available may be braodly classified as empirical or analytical, although no method is purely one or the other. These two general approaches will be compared as they apply to rotorcraft noise prediction.
    Keywords: ACOUSTICS
    Type: Rotorcraft Noise; p 291-308
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Effects of wall admittance changes on duct transmission and radiation of sound. (1973)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: This paper is concerned with the effect of changes in duct wall acoustic properties on the transmission of sound through ducts. Two special problems are considered. The first problem is that of a rectangular infinite-length duct with airflow and a single change in duct wall acoustic admittance. The second problem is that of an axisymmetric field in a finite circular duct without airflow and with an arbitrary number of duct wall acoustic admittance changes. Results for the first problem show the effect of wall admittance change and flow on the acoustic power transmission within the duct. Results for the second problem show the interactive effects of multiple duct liner sections on power radiated from a finite duct.
    Keywords: PHYSICS, GENERAL
    Format: text
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    NASA TECHNICAL REPORTS
  • 5
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    Nonlinear acoustic theory for thin porous sheets (1968)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Nonlinear method for predicting acoustic properties of thin porous sheets
    Keywords: PHYSICS, GENERAL
    Type: PROGR. OF NASA RES. RELATING TO NOISE ALLEVIATION OF LARGE SUBSONIC JET AIRCRAFT 1968; P 17-27
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 6
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    Multiple eigenvalues of sound-absorbing circular and annular ducts (1974)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: Eigenvalue equations of the form D(lambda) = 0 are studied for acoustic modes in circular and annular ducts without flow. The ducts have locally reacting walls with arbitrary wall admittance. It is shown that circular ducts may have double eigenvalues, or wall admittances where both D(lambda) and D prime (lambda) are zero. These double eigenvalues are formed by the coalescence of the lowest-order eigenfunction with some higher-order eigenfunction. The eigenfunctions, or acoustic modes, associated with the double eigenvalues are found to be orthogonal to themselves so that the standard expansion formula for the acoustic field, which is obtained from a separation-of-variables analysis, is invalid. An alternate expansion formula for the acoustic field is derived. This alternate formula shows that the coalesced acoustic mode is linearly amplified by the transmission distance and exponentially attenuated at the expected rate. The expansion formula also reveals a new eigenfunction, or acoustic mode, which is exponentially attenuated at the same rate as the coalesced eigenfunction.
    Keywords: PHYSICS, GENERAL
    Type: Acoustical Society of America; vol. 55
    Format: text
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    NASA TECHNICAL REPORTS
  • 7
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    Generalized radiation impedances and reflection coefficients of circular and annular ducts (1973)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: Morse's equation for the radiation impedance of a vibrating rigid piston is extended to give the generalized radiation impedances of all modes in circular and annular ducts which have arbitrary wall admittance and which terminate in an infinite baffle. The extended equation is reduced to a single infinite integral which is a function of the mode radiation directivity factors. An infinite matrix equation is derived which relates the generalized mode reflection coefficients to the radiation impedances. Results are presented which show that the duct-wall admittance is a significant parameter in the effect of duct-determination reflections and that mode-coupling reflection effects may be more important than direct-mode reflection effects.
    Keywords: PHYSICS, GENERAL
    Type: Acoustical Society of America; vol. 54
    Format: text
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    NASA TECHNICAL REPORTS
  • 8
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    NASA progress in aircraft noise prediction (1981)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Some of the essential features of aircraft noise prediction are described and the basis for evaluating its capability and future potential is discussed. A takeoff noise optimizing procedure is described which calculates a minimum noise takeoff procedure subject to multiple site noise constraints.
    Keywords: AIR TRANSPORTATION AND SAFETY
    Type: The 1980 Aircraft Safety and Operating Probl., Pt. 2; p 721-757
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 9
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    The acoustic field of a point source in a uniform boundary layer over an impedance plane (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The acoustic field of a point source in a boundary layer above an impedance plane is investigated anatytically using Obukhov quasi-potential functions, extending the normal-mode theory of Chunchuzov (1984) to account for the effects of finite ground-plane impedance and source height. The solution is found to be asymptotic to the surface-wave term studies by Wenzel (1974) in the limit of vanishing wind speed, suggesting that normal-mode theory can be used to model the effects of an atmospheric boundary layer on infrasonic sound radiation. Model predictions are derived for noise-generation data obtained by Willshire (1985) at the Medicine Bow wind-turbine facility. Long-range downwind propagation is found to behave as a cylindrical wave, with attention proportional to the wind speed, the boundary-layer displacement thickness, the real part of the ground admittance, and the square of the frequency.
    Keywords: ACOUSTICS
    Type: AIAA PAPER 86-1923
    Format: text
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    NASA TECHNICAL REPORTS
  • 10
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    Aircraft Noise Prediction Program theoretical manual: Propeller aerodynamics and noise (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The prediction sequence used in the aircraft noise prediction program (ANOPP) is described. The elements of the sequence are called program modules. The first group of modules analyzes the propeller geometry, the aerodynamics, including both potential and boundary-layer flow, the propeller performance, and the surface loading distribution. This group of modules is based entirely on aerodynamic strip theory. The next group of modules deals with the first group. Predictions of periodic thickness and loading noise are determined with time-domain methods. Broadband noise is predicted by a semiempirical method. Near-field predictions of fuselage surface pressrues include the effects of boundary layer refraction and scattering. Far-field predictions include atmospheric and ground effects.
    Keywords: ACOUSTICS
    Type: NASA-TM-83199-PT-3 , L-15937 , NAS 1.15:83199-PT-3
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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