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  • 1
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    Tensile strength of simple liquids predicted by a model of molecular interactions (1985)
    Institute of Physics
    Details
    Publication Date: 1985-04-14
    Print ISSN: 0022-3727
    Electronic ISSN: 1361-6463
    Topics: Physics
    Published by Institute of Physics
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    PAPER CURRENT
  • 2
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    The effect of a row of Helmholtz resonators on the turbulence in a boundary layer (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Detailed acoustic measurements were made of the resonator's response as the free stream speed was varied from 30 mph to 155 mph. The average sound pressure level (SPL) and peak frequency response clearly show the existence of strong tuning between the boundary layer and the resonator for the Helmholtz (f sub 0) mode as well as for the first standing wave (f sub 1) mode. The narrow speed range for tuning and the gap between the strong tuning for the Helmholtz mode and the first standing wave mode is evident. The frequency at which the peak SPL response occurred at each speed is given. The peak response for the Helmholtz mode occurred at a free stream velocity of 26 m/s (at which RE sub theta = 6,560) with a resonant frequency of 570 Hz and a sound pressure level of 141 dB. The peak response for the first standing wave occurs at the maximum wind tunnel speed of 70 m/s (at which Re sub theta = 14,900) Hz with a resonant frequency of 1,890 Hz and a sound pressure level of 154 dB. At resonance the microphones do not maintain a constant SPL, but rather the latter fluctuates in a seemingly random fashion. The values presented here are time averaged rms values. Of interest was the occurrence of phase locking between adjacent resonators witha phase lag of 180 deg. This report covers the period from 5 May to 30 September on the subject project.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-179832 , NAS 1.26:179832
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Study of nonequilibrium two-phase flow of a gas-particle mixture Technical note no. 2 (1966)
    In:  CASI
    Details
    Publication Date: 2019-05-29
    Description: Two-phase nonequilibrium flow of particle suspensions in gaseous medium
    Keywords: FLUID MECHANICS
    Type: NASA-CR-74767 , AS-66-5
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Excitation of a Helmholtz resonator by a turbulent boundary layer (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: A turbulent boundary layer on the fuselage of a glider is used to excite a Helmholtz resonator whose openings are comparable in size to the turbulent eddies in the boundary layer. The resonator was excited at both the Helmholtz frequency and a standing wave frequency. The level of the resonator response and the response frequency are the major results. A shift in the response frequency, compared to acoustic excitation, indicates an interaction of turbulent and acoustic motions and a modification of the orifice end correction. A strong excitation phenomenon occurs when the resonator and boundary layer are tuned, in which case turbulent eddies of about the orifice diameter in size flow past the orifice and impose a frequency equal to one of the resonant frequencies of the resonator.
    Keywords: ACOUSTICS
    Type: Acoustical Society of America; vol. 58
    Format: text
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    NASA TECHNICAL REPORTS
  • 5
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    Low-frequency pressure fluctuations in axisymmetric turbulent boundary layers (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Measurements were made of wall pressure fluctuations under a turbulent boundary layer on the fuselage of a sailplane. Experiments with the sailplane offered a noise-free flow with a low free-stream turbulence level. In this environment the wall-pressure spectrum of a turbulent boundary layer with natural transition was found to drop off at low frequencies. Correlations between several wall-mounted microphones revealed that the large-scale motions contribute about 35% to the mean square pressure. Velocity fluctuations at several positions within and outside the boundary layer were measured and correlated with the wall pressure. It seems that the irrotational motions in the turbulent region are primarily responsible for the large-scale wall-pressure fluctuations. A time-lagged conditional correlation of the pressure was introduced to gain further insight into the pressure-producing motions.
    Keywords: AERODYNAMICS
    Type: Journal of Fluid Mechanics; 97; Mar. 25
    Format: text
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    NASA TECHNICAL REPORTS
  • 6
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    A theoretical and flight test study of pressure fluctuations under a turbulent boundary layer. Part 2: Flight test study (1967)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The study of pressure fluctuations under a turbulent boundary layer was undertaken with the objective of extending previous work to lower frequencies. Wind tunnel and flight test measurements are invalid at low frequencies because of extraneous acoustic noises and free stream turbulence. A glider was instrumented and used as a test bed to carry microphones into a smooth flow free of acoustic noise. Hodgson had previously measured the spectrum of boundary layer noise on a glider wing. These tests showed a drop off at low frequencies that could not be reproduced in any other facility. The measurements were made on the forward fuselage of a glider where the boundary layer could develop naturally and have some length in a zero pressure gradient before the measurements were made. Two different sets of measurements were made.
    Keywords: FLUID MECHANICS
    Type: NASA-CR-140448
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 7
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    Excitation of a Helmholtz resonator by a turbulent boundary layer (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A turbulent boundary layer on the fuselage of a glider was used to excite a Helmholtz resonator. The resonator orifice was flush with the surface and smaller than the boundary layer thickness. Resonator frequencies were chosen so they would tune with different portions of the boundary layer wall pressure spectrum. The resonators were excited at both the Helmholtz frequency and a standing wave frequency. The results show a shift in the Helmholtz frequency when the boundary layer is present. This shift indicates the degree to which the turbulence interacts with the acoustic motion in the orifice and modifies the end correction. Four of the nine resonators tested were 'strongly' excited and radiated considerable acoustic sound. This phenomenon occurs when turbulent eddies about the size of the orifice are convected past the orifice with the proper velocity to impose a frequency that matches a resonant frequency of the resonator. Turbulent eddies which are either smaller or larger than the orifice will not produce strong excitation.
    Keywords: AERODYNAMICS
    Type: Acoustical Society of America, Meeting; Apr 07, 1975 - Apr 11, 1975; Austin, TX
    Format: text
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    NASA TECHNICAL REPORTS
  • 8
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    Wall pressure spectra calculations for equilibrium boundary layers (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Calculation of the flow direction wave-number spectrum of pressure fluctuations on the wall under a turbulent boundary layer. Particular attention is paid to finding the spectral density of the wall pressure fluctuations as a function of the streamwise wave number. For this purpose a five-dimensional integration is employed in which the equilibrium boundary layers are assumed to have velocity profiles given by the law of the wall plus Cole's wake function.
    Keywords: FLUID MECHANICS
    Type: Journal of Fluid Mechanics; 65; Aug. 28
    Format: text
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    NASA TECHNICAL REPORTS
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