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  • 11
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    The computation of complex jet and nozzle flows (1980)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: APL JANNAF 12th Plume Technol. Meeting, Vol. 1; p 57-84
    Format: text
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  • 12
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    The 'preferred mode' of the axisymmetric jet (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Detailed distributions of different time-average and phase-average flow properties for an axisymmetric free jet under controlled perturbation at the jet preferred mode are explored. The data are compared with the corresponding unexcited jet data. It is found that the effect of the perturbation is to increase jet spread and mean velocity decay, as well as to increase the peak values of the time-average fluctuation intensities and Reynolds stress in the axisymmetric mixing layer.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics; 110; Sept
    Format: text
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  • 13
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    Turbulence suppression in free shear flows by controlled excitation (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Turbulence suppression in the near field of a free shear flow under controlled excitation is investigated in four circular jets, a plane jet, and a plane mixing layer. The suppression is a consequence of an excitation-induced modification of the shear layer structure and occurs at the excitation frequency corresponding to the maximally unstable disturbance frequency of the initial free shear layer. The most pronounced suppression occurs when the shear layer is excited at a frequency 40% higher than the natural roll-up frequency. Excitation at a Strouhal number of about 0.017 produces a rapid roll-up and early breakdown of the shear layer, and thus inhibits the formation of the energetic large-scale vortices which otherwise survive farther downstream, grow to larger sizes, and undergo successive pairings in the corresponding unexcited flow.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics; 103; Feb. 198
    Format: text
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  • 14
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    Vortex pairing in a circular jet under controlled excitation. I - General jet response. II - Coherent structure dynamics (1980)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Hot-wire and flow visualization studies were performed in three air jets subjected to pure-tone excitation. The instability, vortex roll-up, and transition to the controlled excitation were investigated. The conditions most favorable to vortex parting were determined as a function of the excitation Strouhal number, the Reynolds number, and the initial shear-layer state; it was shown that the rolled-up vortex rings undergo pairing under 'the shear layer mode', and the 'jet-column mode' when the Strouhal numbers based on the initial shear-layer momentum thickness are 0.012 and 0.85, respectively. Coherent ring-like vortical structures could be educed to the end of the potential core; however, the paired vortex becomes weaker with increasing downstream distances. The transverse transport of 'u' momentum by the coherent structures was much larger during the pairing process than in regions where a single vortex is studied.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics; 101; Dec. 11
    Format: text
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  • 15
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    The dominant coherent structure of the circular jet organized by controlled perturbation (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The dominant large-scale coherent structure of a circular jet has been organized through controlled perturbation at the jet Strouhal number of 0.3, induced acoustically in two air jets through cavity resonance. Selected phases of the coherent structure were studied for three Reynolds numbers (25,000; 55,000; and 110,000), and two limiting initial conditions; laminar and fully turbulent initial boundary layers. Distributions of phase-average structure properties, i.e., longitudinal and lateral velocities, coherent vorticity and Reynolds stress, phase-random turbulence intensities and Reynolds stress, and streamline and pseudo-streamfunction patterns are obtained. The phase-random turbulence intensity is greatest at the structure center where the coherent vorticity is also the maximum. Some properties of the structure show mild but systematic dependence on Reynolds number.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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  • 16
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    The 'whistler-nozzle' phenomenon (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The whistler nozzle is a simple device which can induce jet self-excitations of controllable amplitudes and frequencies and appears highly promising for many applications involving turbulent transport, combustion and aerodynamic noise. The characteristics of this curious phenomenon are documented for different values of the controlling parameters and attempts to explain the phenomenon. It is shown that the whistler excitation results from the coupling of two independent resonance mechanisms: shear-layer tone resulting from the impingement of the pipe-exit shear layer on the collar lip, and organ-pipe resonance of the pipe-nozzle. The crucial role of the shear-layer tone in driving the organ-pipe resonance is proven by reproducing the event in pipe-ring and pipe-hole configurations in the absence of the collar. It is also shown that this phenomenon is the strongest when the self-excitation frequency matches the preferred mode of the jet. Previously announced in STAR as N83-20706
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 134; Sept
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  • 17
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    Heat pipes for wing leading edges of hypersonic vehicles (1990)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: Wing leading edge heat pipes were conceptually designed for three types of vehicle: an entry research vehicle, aero-space plane, and advanced shuttle. A full scale, internally instrumented sodium/Hastelloy X heat pipe was successfully designed and fabricated for the advanced shuttle application. The 69.4 inch long heat pipe reduces peak leading edge temperatures from 3500 F to 1800 F. It is internally instrumented with thermocouples and pressure transducers to measure sodium vapor qualities. Large thermal gradients and consequently large thermal stresses, which have the potential of limiting heat pipe life, were predicted to occur during startup. A test stand and test plan were developed for subsequent testing of this heat pipe. Heat pipe manufacturing technology was advanced during this program, including the development of an innovative technique for wick installation.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-181922 , NAS 1.26:181922
    Format: application/pdf
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  • 18
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    The coupling between scales in shear flows (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The relationship between large and small-scale motions in turbulent shear flows is studied using short-time correlation measurements. Boundary layers, plane and axisymmetric mixing layers, plane wakes, and the far fields of plane and circular jets are examined. The coupling is found to be significant in all flows. Phase reversal across the shear region is found to occur in the boundary layers and the mixing layers only. This is interpreted to mean that in these layers the streamwise extent of the large structure over which the small-scale activity reaches a peak moves from one transverse end of the large structure over which its ensemble-averaged u-fluctuation is positive to another where it is negative. In the far field of jets and wakes, the small-scale peak activity remains confined to that half of the streamwise extent of the large structure where its ensemble-averaged u-fluctuation is positive.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids (ISSN 0031-9171); 27; 2221-222
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  • 19
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    The self-excited axisymmetric jet (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The results of a number of investigations suggest that large-scale coherent structures and their interactions play key roles in the transport of heat, mass, and momentum, and in the generation of aerodynamic noise. Investigations related to the study of a large-scale coherent structure in the circular jet are considered, taking into account the advantages of inducing controlled perturbation through self-sustained excitation with the whistler nozzle. The primary objective of the present study was to document the jet response to self-excitation and the sensitivity of this response to the initial condition and the Reynolds number R(D). It was also felt that the results would find use in the control of mixing and aerodynamic noise in a jet.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics; 115; Feb. 198
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  • 20
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    Natural large-scale structures in the axisymmetric mixing layer (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The present study is concerned with the optimization of conditional sampling techniques for eduction of naturally occurring large-scale structures in an axisymmetric mixing layer, and a comparison of the natural structure with that induced by means of controlled excitation. Questions regarding the sensitivity of the educed structure to the excitation amplitude are also explored. Aspects regarding the eduction with the high-speed-side reference signal are considered, taking into account structure identification, the smearing effect and a comparison with the structure under excitation, the effects of the threshold level, and the effect of a trigger-level window. Attention is given to structure characteristics and their dependence on Reynolds number and initial condition.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 138; 325-351
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